ASHRAE-D-21513-20100324

Heat Gain from Electrical and Control Equipment in Industrial Plants

ASHRAE Research Project 1104-TRP

PHASE I – PART A: PART B:

CLASSIFICATION TEST PLAN

Warren N. White, Ph.D. Department of Mechanical and Nuclear Engineering and Anil Pahwa, Ph.D. Department of Electrical and Computer Engineering

Kansas State University June 10, 2001

ASHRAE

TRP – 1104 Heat Gains from Electrical and Control Equipment in Industrial Plants

Table of Contents Page List of Figures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix List of Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

x

Introduction and Executive Summary . . . . . . . . . . . . . . . . . . . . . . .

1

Heat Loss and Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . 2 Assessment Results

. . . . . . . . . . . . . . . . . . . . . . . . . . . .

2

Conclusions and Recommendations . . . . . . . . . . . . . . . . . . . . 10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Phase I Results

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

The Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 First Category . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Review of Environmental Heat Gains . . . . . . . . . . . 15 Standards . . . . . . . . . .

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Equipment Heat Loss . . . .

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Liquid Immersed Units . . . . . . . . . . . 16 Dry Type Units . . . . . . . . . . . . . . . 18 Ambient Temperature Influence . . . . . . . . . . 19 Measurement Uncertainty . . . . . . . . . . . . . 21 Manufacturers . . . . . . . . . . . . . . . . . . . 21 Information Deficiencies . . . . . . . . . . . . . 21 Test Plan. . . . . . . . . . . . . . . . . . . . . . . 21

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TRP – 1104 Heat Gains from Electrical and Control Equipment in Industrial Plants References . . . . . . . . . . . . . . . . . . . . . 22 Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Review of Environmental Heat Gains . . . . . . . . . . . 23 Standards . . . . . . . . . . . . . . . . . . . . . . 23 Equipment Heat Losses . . . . . . . . . . . . . . 23 Measurement Uncertainty . . . . . . . . . . . . . 23 Manufacturers . . . . . . . . . . . . . . . . . . . 24 Information Deficiencies . . . . . . . . . . . . . . 24 Test Plan. . . . . . . . . . . . . . . . . . . . . . . 24 References . . . . . . . . . . . . . . . . . . . . . 25

Second Category . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Cables and Cable Trays

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Review of Environmental Heat Gains . . . . . . . . . . . 27 Standards . . . . . . . . . . .

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Equipment Heat Losses. . . . . . . . . . . . . . . 27 Heat Loss in Cable Trays . . . . . . . . . . . . . 28 Measurement Uncertainty . . . . . . . . . . . . . 31 Manufacturers . . . . . . . . . . . . . . . . . . . 31 Information Deficiencies . . . . . . . . . . . . . 31 Test Plan. . . . . . . . . . . . . . . . . . . . . . . 32 References . . . . . . . . . . . . . . . . . . . . . 32 Adjustable Speed Drives . . . . . . . . . . . . . . . . . . . . . . 33

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TRP – 1104 Heat Gains from Electrical and Control Equipment in Industrial Plants Review of Environmental Heat Gains . . . . . . . . . . . 33 Standards . . . . . . . . . . .

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Equipment Heat Losses . . . . . . . . . . . . . . . 33 Measurement Uncertainty . . . . . . . . . . . . . 34 Manufacturers . . . . . . . . . . . . . . . . . . . 34 Information Deficiencies . . . . . . . . . . . . . 34 Test Plan. . . . . . . . . . . . . . . . . . . . . . . 34 References . . . . . . . . . . . . . . . . . . . . . 36 Battery Chargers . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Review of Environmental Heat Gains . . . . . . . . . . . 37 Standards . . . . . . . . . . . .

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Equipment Heat Losses . . . . . . . . . . . . . . 37 Manufacturers . . . . . . . . . . . . . . . . . . . 38 Measurement Uncertainty . . . . . . . . . . . . . 38 Information Deficiencies . . . . . . . . . . . . . 38 Test Plan. . . . . . . . . . . . . . . . . . . . . . . 38 References . . . . . . . . . . . . . . . . . . . . . 39 Inverters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Review of Environmental Heat Gains . . . . . . . . . . . 40 Standards . . . . . . . . . . .

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Equipment Heat Losses . . . . . . . . . . . . . . 40 Manufacturers . . . . . . . . . . . . . . . . . . . 40 Measurement Uncertainty . . . . . . . . . . . . . 40

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TRP – 1104 Heat Gains from Electrical and Control Equipment in Industrial Plants Information Deficiencies . . . . . . . . . . . . . 41 Test Plan. . . . . . . . . . . . . . . . . . . . . . . 41 References . . . . . . . . . . . . . . . . . . . . . 42 Circuit Breakers . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Review of Environmental Heat Gains . . . . . . . . . . . 43 Standards . . . . . . . . . . .

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Equipment Heat Losses . . . . . . . . . . . . . . 43 Manufacturers . . . . . . . . . . . . . . . . . . . 44 Measurement Uncertainty . . . . . . . . . . . . . 44 Information Deficiencies . . . . . . . . . . . . . 44 Test Plan. . . . . . . . . . . . . . . . . . . . . . . 44 References . . . . . . . . . . . . . . . . . . . . . 50 Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Review of Environmental Heat Gains . . . . . . . . . . . 51 Standards . . . . . . . . . . .

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Equipment Heat Losses . . . . . . . . . . . . . . 51 Measurement Uncertainty . . . . . . . . . . . . . 53 Manufacturers . . . . . . . . . . . . . . . . . . . 53 Information Deficiencies . . . . . . . . . . . . . 53 Test Plan. . . . . . . . . . . . . . . . . . . . . . . 53 References . . . . . . . . . . . . . . . . . . . . . 55 Composite Equipment . . . . . . . . . . . . . . . . . . . . . . . 56 Motor Control Centers . . . . . . . . . . . . . . . . . . . . . . . 58

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TRP – 1104 Heat Gains from Electrical and Control Equipment in Industrial Plants Review of Environmental Heat Gains . . . . . . . . . . . 58 Standards . . . . . . . . . . .

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Equipment Heat Losses . . . . . . . . . . . . . . 58 Measurement Uncertainty . . . . . . . . . . . . . 59 Manufacturers . . . . . . . . . . . . . . . . . . . 59 Information Deficiencies . . . . . . . . . . . . . 59 Test Plan. . . . . . . . . . . . . . . . . . . . . . . 59 Low Voltage Circuit Breakers. . . . . . . . 59 Disconnect Switches. . . . . . . . . . . . . 59 Motor Starters . . . . . . . . . . . . . . . . 59 Bus Bars

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Space Heaters . . . . . . . . . . . . . . . . 61 Auxiliary Compartments. . . . . . . . . . . 61 Adjustable Speed Drives. . . . . . . . . . . 61 Enclosure . . . . . . . . . . . . . . . . . . 61 References . . . . . . . . . . . . . . . . . . . . . 61 Medium Voltage and DC Switchgear . . . . . . . . . . . . . . . 63 Review of Environmental Heat Gains . . . . . . . . . . . 63 Standards . . . . . . . . . . .

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Equipment Heat Losses . . . . . . . . . . . . . . 63 Measurement Uncertainty . . . . . . . . . . . . . 63 Manufacturers . . . . . . . . . . . . . . . . . . . 64 Information Deficiencies . . . . . . . . . . . . . 64

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TRP – 1104 Heat Gains from Electrical and Control Equipment in Industrial Plants Test Plan. . . . . . . . . . . . . . . . . . . . . . . 64 Medium Voltage and DC Breakers . . . . . 64 Bus Bars

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Control Power Transformers . . . . . . . . 64 Potential Transformers . . . . . . . . . . . 64 Current Transformers . . . . . . . . . . . . 64 Auxiliary Compartments. . . . . . . . . . . 64 Space Heaters . . . . . . . . . . . . . . . . 64 Enclosure . . . . . . . . . . . . . . . . . . 65 References . . . . . . . . . . . . . . . . . . . . . 65 Panelboards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Review of Environmental Heat Gains . . . . . . . . . . . 66 Standards . . . . . . . . . . .

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Equipment Heat Losses . . . . . . . . . . . . . . 66 Measurement Uncertainty . . . . . . . . . . . . . 66 Manufacturers . . . . . . . . . . . . . . . . . . . 66 Information Deficiencies . . . . . . . . . . . . . 66 Test Plan. . . . . . . . . . . . . . . . . . . . . . . 66 Low Voltage Circuit Breakers. . . . . . . . 66 Bus Bars

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Enclosure . . . . . . . . . . . . . . . . . . 66 References . . . . . . . . . . . . . . . . . . . . . 67 Unit Substation . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

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TRP – 1104 Heat Gains from Electrical and Control Equipment in Industrial Plants Review of Environmental Heat Gains . . . . . . . . . . . 68 Standards . . . . . . . . . . .

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Equipment Heat Losses . . . . . . . . . . . . . . 68 Measurement Uncertainty . . . . . . . . . . . . . 68 Manufacturers . . . . . . . . . . . . . . . . . . . 68 Information Deficiencies . . . . . . . . . . . . . 68 Test Plan. . . . . . . . . . . . . . . . . . . . . . . 68 Low Voltage Circuit Breakers. . . . . . . . 68 Bus Bars

. . . . . . . . . . . . . . . . . . 68

Auxiliary Compartments. . . . . . . . . . . 68 Space Heaters . . . . . . . . . . . . . . . . 69 Unit Substation Transformers . . . . . . . . 69 Enclosure . . . . . . . . . . . . . . . . . . 69 References . . . . . . . . . . . . . . . . . . . . . 69 Third Category . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 Transfer Switches . . . . . . . . . . . . . . . . . . . . . . . . . . 70 Review of Environmental Heat Gains . . . . . . . . . . . 70 Standards . . . . . . . . . . .

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Equipment Heat Losses . . . . . . . . . . . . . . 70 Measurement Uncertainty . . . . . . . . . . . . . 70 Manufacturers . . . . . . . . . . . . . . . . . . . 70 Information Deficiencies . . . . . . . . . . . . . 71 Test Plan. . . . . . . . . . . . . . . . . . . . . . . 71

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TRP – 1104 Heat Gains from Electrical and Control Equipment in Industrial Plants References . . . . . . . . . . . . . . . . . . . . . 71

Summary of Phase II Information . . . . . . . . . . . . . . . . . . . . . 72 Uncertainty of Test Results . . . . . . . . . . . . . . . . . . . . . . . . . 73 Phase II Budget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Letter of Contact Example . . . . . . . . . . . . . . . . . . . . . . . . . 79 Equipment Donation from General Electric. . . . . . . . . . . . . . . . . 82 E-Mail - Western Resources Concerning Med. Voltage Breakers . . . . . 83 E-Mail on Two Matched 15 kV ABB Med. Voltage Breakers - TVA . . . 84 E-Mail Regarding Battery Chargers from TVA . . . . . . . . . . . . . . 87

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List of Figures FIGURES Figure 1: ASD Test Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

35

Figure 2: Apparatus for Testing Losses in Circuit Breakers . . . . . . . . . . . . . . .

46

Figure 3: Apparatus for Testing Losses in Reactors . . . . . . . . . . . . . . . . . . .

54

Figure 4: Apparatus for Testing Motor Starters . . . . . . . . . . . . . . . . . . . . .

60

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List of Tables TABLES Table 1: Equipment to be Investigated . . . . . . . . . . . . . . . . . . . . . . . . . .

3

Table 2: Equipment Categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

Table 3: Equipment Table Summary . . . . . . . . . . . . . . . . . . . . . . . . . .

7

Table 3a: Equipment Table Summary (continued) . . . . . . . . . . . . . . . . . . . .

8

Table 4: Limits for Temperature Rises . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Table 5: Influence of 20 oC Change in Ambient Temperature on Load Loses . . . . . . 20 Table 6: Components of Composite Equipment . . . . . . . . . . . . . . . . . . . . . 56 Table 7: Electric Power Equipment to be Tested . . . . . . . . . . . . . . . . . . . . . 75 Table 8: Budget for Testing for ASHRAE TRP 1104. . . . . . . . . . . . . . . . . . . 76 Table 9: Phase II Time Schedule for Completion of Work . . . . . . . . . . . . . . . . 77 Table 10: Summary of Equipment Testing

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TRP – 1104 Heat Gains from Electrical and Control Equipment in Industrial Plants

Introduction and Executive Summary In order to size the required equipment, the HVAC design engineer must be able to estimate with certainty the amount of energy added from various heat sources and lost through various heat sinks located in a room. Heat could be added from several sources such as the presence of many people in a classroom or office, solar radiation through windows, and incandescent room lighting. A sink could consist of outside doors and windows in winter or a basement floor or wall that remains at an essentially constant temperature throughout the year. By closely estimating the heat gain or loss, the HVAC equipment will not be undersized with insufficient capacity or oversized with costly unutilized excess capability. Building and industrial plants make use of electrical power for many uses such as lighting, driving motorized devices, HVAC, and energy transmission and distribution throughout the structure. All of this electrical equipment contributes to the total heat load. Estimating the total amount of rejected heat is a necessary part of sizing the heating and refrigeration equipment required for the building. The primary source of information available to the design engineer for estimating the electrical equipment rejected heat is the paper by Rubin (1979). In this well used document, the rejected heat values for transformers, power distribution equipment, motors, switchgear, and power cables, to name a few, were presented in tables for a range of equipment sizes common to indoor equipment. The data presented by Rubin was obtained from the paper presented by Hickok (1978) and from other, unspecified manufacturers. Hickok, who worked for GE at the publication time of his paper, states, “The data are on General Electric products …” At no point in either Hickok’s paper or in Rubin’s paper is there a discussion of measurement procedure or measurement uncertainty. Rubin’s motivation for publishing the data was to aid the HVAC design engineer. Hickok’s motivation in his paper was to aid the factory engineer in identifying plant locations where efficiency could be improved. Hickok’s motivation is easy to appreciate since the energy price shocks provided by two oil embargoes made increasing efficiency of existing plants, buildings, and factories the first choice in reducing the costs of production. McDonald and Hickok (1985) later co-authored an update of Hickok’s 1978 paper with much of the same data. The information provided by these papers is dated. Since the oil embargoes of the 1970’s, many electrical equipment manufacturers have taken pains to increase the efficiency of their products. At the same time, advances in power electronics and computer control have made much of the technology reflected in the 1970 equipment obsolete. Another change that has occurred since Rubin published his work is that the manufacturing standards that apply to the various items of power equipment have been re-issued and updated several times. These standards could provide details for measuring the power loss in the equipment where, perhaps, originally none existed. Also, the standards might specify a maximum level of uncertainty for performing the measurements and any data reported by a manufacturer claiming to follow the standard could be deemed reliable. Thus, there is a need to update the 20 years old information presented by Rubin. A recent addition to the published information regarding motor heat gains is contained in Chapter 11 of the 1997 ASHRAE Fundamentals Handbook which provides a table of “Heat

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Gains from Typical Electric Motors” for fractional horsepower AC motors up to 250 horsepower three phase motors. The purpose of this work is to provide a means of estimating the rejected heat of specific electrical equipment by a means similar to Rubin, but which accounts for updated data, current testing standards, level of use, and more than one power equipment manufacturer. To accomplish this goal, the work is divided into phases consisting of an assessment of the availability of reliable data and a testing phase for providing a reference for those data deemed uncertain. Phase I of this project consists of an assessment part and a test planning part. The assessment part (Part A) requires a review of the heat loss measurement procedures included in the manufacturing standards for each type of power equipment included in this study along with a survey of the measurement procedures used by manufacturers when the standards do not cover this type of measurement. Based on the results of this assessment, a testing program is planned (Part B of Phase I) to verify loss information supplied by manufacturers. Phase II consists of the execution of the data gathering and testing program. This document describes the assessment and test - planning phase of the investigation. The organization of the material to be presented includes a summary of the Phase I conclusions and the recommendations concerning the Phase II work. Also included, is a description of the method or strategy used in the assessment. The results of the assessment will then be presented followed by a recommendation for those types of equipment to be included in the testing phase. The remainder of the report contains an examination of each type of equipment, the manufacturing standards relevant to the assessment, and a discussion supporting the conclusions reached in the assessment.

Heat Loss and Heat Transfer The equipment rate of heat losses to be determined in this work represent constant values from steady operation. The device rejecting heat is assumed to have reached thermal equilibrium with the surroundings and no thermal transient process is taking place. Thus, all heat loss occurring in a device is additional heat added to the surroundings. The manner in which the heat transfer takes place is not of a concern. Heat convection to the surroundings and conduction to surrounding structures is not hard to appreciate as viable transfer mechanisms. Any thermal radiation is assumed to be absorbed by the surrounding structures (perhaps after several absorptions and re-emissions) and the eventual manifestation of the radiant energy is an increase in room temperature in the absence of any environmental control.

Assessment Results The scope of the equipment specified in ASHRAE TRP – 1104 is listed in Table 1. The equipment review is divided into three categories. The first category consists of equipment for which either well defined methods for loss determination are specified in the manufacturing standards . The third category includes equipment for which there is no standard either requiring or describing any heat loss tests and for which no heat loss data could be found. The second

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category includes all equipment satisfying neither of the first and third category descriptions. Items in the second category represent a wide range of different conditions. The best description for this category is that information is available on equipment heat losses however the measurement quality is unknown. The manufacturing standards covering rate of heat loss Equipment

Size Range

Electric Motors Medium Voltage Switchgear (breakers, heaters, and auxiliary compartments) Unit Substation Components (including breakers, heaters, bus losses, and auxiliary compartments) Transformers

10 – 4000 hp (reg. and high efficiency) 5 kV, 7.2 kV, and 13.8 kV with 1200, 2000, and 3000 amp breakers 800, 1600, 2000, 3200, and 4000 amp frame sizes 300 – 2500 kVA and 120/208/600 V units below 300 kVA Standard Sizes Standard Sizes for 120, 125, and 600 V 0.6, 5, and 15 kV of widths 12” – 30” 100 to 600 amp 20, 30, 50, 75, and 100 kV - single phase 150 kV – three phase 125 VDC for 100 to 1500 amp 0.6 kV for 150, 260, 400, 600, 800, an 1000 amp Standard NEMA sizes

Reactors Panelboards Cable and Cable Trays Battery Chargers Inverters DC Switchgear Manual Transfer Switches

Motor Control Centers (starters, breakers, auxiliary relay compartments, bus losses, and space heaters) Variable (adjustable) Speed Drives 25 to 500 hp – three phase Table 1: Equipment to be Investigated Category 1

Category 2

Category 3

Transformers Motors

Cable and Cable Trays Adjustable Speed Drives Battery Chargers Inverters Reactors Circuit Breakers Substation Components (heaters, bus losses, and auxiliary compartments) Panelboards Motor Control Centers Medium Voltage and DC Switchgear

Transfer Switches

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TRP – 1104 Heat Gains from Electrical and Control Equipment in Industrial Plants

measurement of the second category equipment are in some cases excellent and in other cases poor or nonexistent. In the case where the standards for equipment in the second category provide good information regarding heat loss measurements, the following of the standards by the manufacturing community is not commonplace. Table 3 is a summary of the results of the equipment under consideration including relevant standard numbers and overall results from the manufacturer surveys regarding losses. The details of the survey are included in the body of the report. The justification for the equipment classification is contained in the report sections to follow the Executive summary where the each device is discussed. The discussion in the sections to follow will support and expand the information shown in Table 3. The organization of Table 3 reflects the equipment classification, the results of finding and examining the relevant manufacturing standards, the results of the manufacturer survey, and finally the number of manufacturers reporting data through either their web pages, catalogs, or though their responses to the survey. The columns of Table 3 are arranged in the same order in which the equipment items are covered in the text of this report. The first category equipment is contained in the two equipment columns toward the left of the table. The third category equipment item is contained in the rightmost column of the table. The three columns of the second category equipment labeled as Composite Devices consist of those devices which are made up of several different pieces of equipment, some of which are contained in the other columns of the table. The devices that fall into this distinction will be treated in a different way when the heat losses are discussed in the report. The leftmost column of the table contains subject headings regarding the standards search, the manufacturers survey, the deficiencies of the available data, the category the equipment item is placed into, and finally the details of the test plan. The lower part of the table contains space where additional manufacturing standard information is provided. For each equipment piece, the relevant standard describing the power loss or efficiency determination is listed. In some cases, there is more than one standard and in others cases there are no standards that address power loss. Where possible, the article number which addresses rate of heat loss and/or efficiency is listed. In some cases, such as NEMA MG 1, the loss testing procedures are spread over many articles. Whether the standard is commonly used by manufacturers or not is also indicated in the table. The next few lines of the table summarize the results of the manufacturer survey. The approximate number of manufacturers is listed in the table. The source of manufacturer names for a given equipment item was the NEMA web site which has a search engine for such purposes. The word approximate is used since the names of manufacturers obtained from NEMA for a specific equipment piece would consist of only NEMA members and this may exclude some foreign manufacturers. Any list of manufacturers for a particular equipment item would include both OEMs and equipment service companies. The immediate task once a group of names is obtained from NEMA is to eliminate all companies that are not OEMs. If a company did not have extensive information on their web site and if they did not respond to the survey, then the type of company might not be easy to determined. Also shown for some of the equipment categories together with the number of NEMA listed manufacturers is the number of

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OEMs of this particular equipment type and size found (number following slash). The number of manufacturers contacted in the survey is listed. This number might be smaller than the approximation number of manufacturers for the reasons just cited. The number of manufacturers who responded to the survey is also listed. Not all manufacturers who responded to the survey supplied data. Some responded that they were not an OEM or did not make products in the range under question. Finally, the number of manufacturers reporting heat gains is listed. This is the number of different manufacturers providing information through either a web site and/or a response to the manufacturer survey. The source of the data is next listed in the table which, in many circumstances, is the web site and/or catalog. The assessed quality of the data next follows in the table. Usually the data was classified as good or uncertain. When no data are available, the quality is listed as N/A. Deficiencies in the data are next listed in the table. All of the five situations that apply are checked with an “X” in the table. If a standard detailing how heat loss and/or efficiency is available but not used by industry then the line titled “Standard but not used” receives a check. If the significant standard applying to the manufacture and testing of the device does not address heat loss or efficiency, then the box on the line of “Standard not germane to heat loss” is checked. If the available loss data is measured in a way consistent with a standard, then the box titled “Data available and consistent” is marked. If the opposite is true then the box corresponding to “Data available but not consistent” is marked. If no data is available, then the “Data not available” cell is marked. In the section of the table titled “Recommended Testing,” the action to be taken with each device is listed. First the source of the data to be used in completing or building the loss tables is listed. For the Category I equipment, this is listed as “Manufacturers” while for Category II equipment, this is listed as “Man. and test” for Manufacturer and Test meaning that the data is coming from both sources. For Category III equipment, this is listed as “Test.” The purposes of the test are listed in the next line. The number of different sizes of each device to be tested is provided on the next line of the table. On the line of the table designating the number of test sizes, there are some notes for the equipment classified as “Composite Devices.” The composite devices or equipment are Category II items which can be characterized as consisting of a collection of many different components. Some of these different components are already listed in the table and no additional tests for these devices are needed. Some of the components of the composite devices are found in more than one composite device. If the composite device component is not already listed in the TRP 1104 Work Statement then some testing will need to be done but the testing of the component is mentioned in the table only once. In order to provide some estimation of the variation of the power losses of identical pieces of equipment, it would be beneficial to test more than one device of a given size and manufacturer. In order to best utilize the financial resources and the generosity of manufacturers, it is recommended that we test one device of a given size and manufacturer and then estimate the repeatability of the measurement through a knowledge of the manufacturer’s quality control. The use of one device for testing is especially viable when there exists manufacturer data to which a comparison can be made. In those cases where there is not a large amount of data, it is recommended that at least two identical items be tested. The number of identical items to be tested is listed on the next line of the table. The source of the equipment for the testing is specified as either loan or donation. There is money in the original project budget for building the test apparatus for measuring heat losses, however there are not

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sufficient financial resources for purchasing all the equipment to be tested. In order to appreciate how the losses of the same size equipment might vary from manufacturer to manufacturer, the number of different manufacturers from which to obtain equipment is listed on the next line of the table. In all cases where testing is warranted, it is recommended that equipment be obtained from at least 2 different manufacturers. The lower portion of Table 3 contains additional standard information that did not fit in the upper area of the table.

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TRP – 1104 Heat Gains from Electrical and Control Equipment in Industrial Plants First C ategory

Equipm ent T ype:

S econd C ategory

Transform ers

M otors

C ables & C able Trays

Adjustable Battery Speed D rives C hargers

Inverters

R eactors

C ircuit Breakers

MCC Com ponents

See Below Yes See Below Yes

See Below Yes See Below Yes

IEEE 835 Yes Intro pp. 1-45 N /A

IEEE 995 N EM A PE-5 Yes Yes Sect. 5/ 1987 8.8 No No

N one N one N /A N /A

IEEE C 57.16 Yes 7.1, 11.4 No

IEEE C 37.09 No 5.14 / 1999 Yes

None N/A N/A N/A

R eview T ype R eview Subcategory R elevant Standards Standard/D ate Is Standard Specific to H eat G ains? H eat G ain Article N o. U sed by Industry? M anufacturers Approxim ate N um ber N um ber C ontacted N um ber of R eplied # R eporting Values for Heat G ains H ow is data reported? W eb, C atalog, Q uality of data

30 20 5 2 See Below G ood

27 0 N /A N /A W eb, C at. G ood

36 0 0 0 Form ula G ood

21 21 5 7 W eb, C at. U ncertain

4 4 1 3 W eb U ncertain

18/4 8 0 3

33/5 0 0 1

W eb W eb U ncertain U ncertain

17/5 26 17 28 4 2 2 2 W eb, Cat. W eb, C at. U ncertain Uncertain

D eficiencies in Data Standard but not used Standards not germ ane to heat loss D ata availible and consistent D ata availible but not consistent D ata not available

X

X

X X

X

X

X

X X

X

X X

X

X

X

M an. and test Verify

M an. and test Verify See N ote 1 N /A Purchase, D onation, and Loan 2 of each item

R ecom m ended T esting

D ata Source Purpose of T est

M anufacturers

M anufacturers C alculation

N um ber of T est Sizes N um ber of T ypes within each size

Equipm ent Source # of different M an. Equipm ent to test

Add. Stand./Section/D ate

IEEE C 57.12.90 IEEE 115

IEEE 835

4.1-4.6/1995 8.0, 9.4 / 1999 IEEE C 57.12.91 IEEE 112 5,6 / 1996 8.0, 9.4 / 1995 IEEE 113 NEM A TP 2-19981985 NEM A M G -1 4.0 / 1998 N ote N ote N ote N ote

1: 2: 3: 4:

M an. and test M an. and test Verify Verify

M an. and test M an. and test Verify Verify

2 >2

3 > 2

2 > 2

3 >1

Loan or D onation

Loan or Donation

Loan or Donation

Purchase

2 > 1 Purchase, Donation, and Loan

3

3

3

2

2

IEEE 995

N EM A PE-5, 1985

IEEE C 57.16

1994 Sect. 5/ 1987 8.8 / 1996

1996

LV CB, ASD, and enclosures tested elsewhere - D issconnect switches - test with m otor starters, m otor starters - 2 sizes, Bus bars - calculation, space heaters - 2 sizes, Auxiliary com partm ents M V and D C C B, bus bars, auxiliary com partm ents, space heaters, and enclosures tested elsewhere - Potential, control power, and current transform ers - get m anufacturer data LV CB, bus bars, and enclosures investigated elsewhere LV CB, Bus bars, auxiliary com partm ents, space heaters, unit substation transform ers, and enclosurers tested elsewhere

TA B LE 3: EQ U IPM EN T SU M M A R Y

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Equipment

Accuracy

Data Source

Transformers

Sufficient Published Data

Motors

Sufficient Published Data

Cables and Cable Trays Bus Bars

Sufficient Calculations Sufficient Calculations

Reactors

Fair

Published Data /Measurements Motor Starters Fair Published Data /Measurements Space Heaters Sufficient Published Data /Measurements Low Voltage Fair/ Not Published Data Circuit Breakers Certain /Measurements Medium Fair/ Not Published Data Voltage Circuit Certain /Measurements Breakers Adjustable Fair/ Not Published Data Speed Drives Certain /Measurements Battery Fair/ Not Published Data Chargers Certain /Measurements Inverters Not Published Data Certain Auxiliary Not Published Data Compartments Certain Manual Not Not Available Transfer Available Switches

No. No. of of Man. Sizes

Testing Total Add. Total tests Man. No. Req. to Test

Add. Funds Req.

2/5

3

6

2

12

20K

2/5

2

2

2

8

2

2

4

1/5

3

3

3

12

17K

1/5

3

3

3

12

430K

2

1 Size 2 each

3

6

41K

Wait

3 2

3

410K 6

320K

TABLE 3a: EQUIPMENT SUMMARY (continued) Table 3a lists different equipment categories, an assessment of the accuracy of the study results, the source of the equipment heat loss data, the number of different manufacturers from which test equipment will be obtained, the number of test sizes, the total number of items to be tested with the TRP – 1104 budget, the additional manufacturers necessary to test to change the accuracy designation, the total number of tests required to have a “Sufficient” accuracy designation, and the additional funds required to accomplish this. In the “Number of Phase I - Report – Rev. 4.2

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Manufacturers” column, the table entry of “i / j’ denotes “i” manufacturers out of a total of “j” manufacturers found in this work. The assessment of accuracy is divided into three designations being “Sufficient,” “Fair”, and “Not Certain.” The designation of “sufficient” is applied to that equipment for which the results will be a realistic representation of the heat losses of this particular device and size. The next level of accuracy designation is “Fair” which is used in those situations where the subset of the different manufacturer products to be tested is deemed too small to warrant a “Sufficient” designation. In the case of reactors and combination motor starters, only 40% of the manufacturers found in this study can be tested using the equipment obtained through purchases and donations. The last designation of accuracy is “Not Certain” which is used for those situations where the only information available is manufacturer published data having neither documented test methods nor uncertainty. The “Not Certain” designation is used for auxiliary compartments and inverters since manufacturer loss data is available, however no test articles are available. The accuracy of some equipment items in Table 3a have been classified as “Fair/Not Certain” which has been applied in those situations where the sample of equipment to test is too small to draw conclusions. The “Fair/Not Certain” designation has been applied to low and medium voltage circuit breakers, adjustable speed drives, and battery chargers. The seventh column of Table 3a lists the number of additional manufacturers required. This figure refers to the number of other company manufactured equipment items that need to be tested in order to change the accuracy designation from “Fair” to “Sufficient.” The criterion for making this accuracy transition is to test 75% or more of the manufacturers, found in this study, of a particular equipment item and size. The last column of the table presents the expense of additional equipment to purchase so as to change the accuracy designation from that listed to “Sufficient.” For reactors and combination motor starters, this additional equipment expense is totaled together. Based on Table 3a, there are several testing options available each with an additional expense for equipment purchase. These testing options are: 1) No additional expense – Accuracy per column of Table 3a. 2) 20K – Accuracy of transformers to combination motor starters in Table 3a is “Sufficient.” 3) 37K – Accuracy of transformers to low voltage breakers in Table 3a is “Sufficient.” The 37K include to 20K from the second testing option. 4) 1240K – Accuracy of transformers to inverters in Table 3a is “Sufficient.” This figure includes the 37K from the third testing option. The total budget for TRP – 1104 is $138K. The second option listed above would bring the total project budget up to $158K. The third testing option would bring the total project budget up to $175K. Note that the increase in expense for testing is exclusively for equipment purchase. Funding for equipment purchase does not incur university overhead. Also, purchases by Kansas State University are not subject to sales tax. Thus, every additional dollar for equipment purchase goes exclusively to that purpose.

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Conclusions and Recommendations From the foregoing, it is evident that not all of the equipment listed in the TRP – 1104 work statement will be able to be tested. Even so, advantage still exists in continuing with the Phase II investigation. An examination of Table 3a shows that 50% of the items listed have received an accuracy designation of either “Sufficient” or “Fair.” Thus, the project as budgeted provides approximately half of the information desired. If additional funds were available for equipment purchase, the priority for using these funds would be: •

Purchase additional reactors and combination motor starters to change the accuracy designation for these two equipment items from “Fair” to “Sufficient.” While the selected reactor test items completely bracket the available equipment, only small to medium size combination motor starters are to be tested. The limiting factor for testing the NEMA 4 and NEMA 5 starters is expense.

•

Purchase additional low voltage breakers. Owing to expense, only small to medium frame sizes are being tested in this work.

If $20K or $37K were available for equipment purchase, this would allow the additional testing of the reactors and the combination motor starters and possibly low voltage circuit breakers. The priority established in the above list is dictated by what additional testes are possible given a limited amount of additional funds. The purchase of adjustable speed drives, battery chargers, and inverters for testing purposes is very expensive owing to the great expense of these power electronic devices. As stated earlier, there is advantage in continuing with the Phase II investigation. The benefits of the Phase II work can be summarized as: •

This is the first update to the tables originally presented by Rubin in the late 70’s. The Phase II information will consist of test data and recently collected information from manufacturers.

•

In addition to the updated loss information, methods of predicting losses for fractions of full load capacity and variations of room temperature will also be provided in the Phase II work.

•

The tests and test methods will be documented so that the test procedures can be repeated and/or applied to new equipment.

•

A design guide for using the accumulated heat loss information will be a product of the Phase II efforts. A significant feature of the results to be presented is that Phase II marks the start of being able to attach significance to the quality of estimated heat loads.

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In addition to the above recommendations, several conclusions are drawn on the basis of the Phase I work. These conclusions are: •

The Phase II work should continue since this allows the opportunity to begin the updating of Rubin’s work. As stated earlier, calibrated heat loss information for approximately half of the items listed in Table 3a can be developed in Phase II. In addition to the tested data, manufacturer published data has been gathered – even for some equipment devices for which testing will involve significant additional expense.

•

There is a significant need for the information to be developed in this study.

•

The scope of this project is very larger.

•

Serious consideration should be given to updating and refining the heat loss information through continued testing and future projects.

•

The current study goes a long way in providing the necessary information and establishing a firm foundation for any future work and investigations in this area.

•

So that no testing opportunity is lost, recruitment of equipment will continue throughout the testing portion of Phase II.

References American Society of Heating, Refrigeration, and Air-Conditioning Engineers, 1997 ASHRAE Fundamentals Handbook, Chapter 28, “Nonresidential Cooling and Heating Load Calculations,” ASHRAE, 1997. Hickok, Herbert N., “Electrical Energy Losses in Power Systems,” IEEE Transactions on Industry Applications, vol IA-14, no. 5, Sep-Oct 1978, pp. 373-387. McDonald, William J. and Hickok, Herbert N., “Electrical Energy Losses in Power Systems,” IEEE Transactions on Industry Applications, vol. IA-21, no. 3, May – June 1985, pp. 803-819. Rubin, I. M., “Heat Losses from Electrical Equipment in Generating Stations,” IEEE Transactions on Power Apparatus and Systems, vol. PAS-98, no. 4, July-Aug. 1979, pp. 11491152.

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Phase I –Results The Method The method or strategy behind the assessment is described here. This is important information since this documents the approach taken and future inquiries along these lines can make use of this strategy and/or improve the strategy through modification. Without this information, any future inquiry would have to start from scratch as this study did. The strategy consists of a sequential process through which the conclusions regarding a specific type of equipment were reached. The specific types of equipment are listed in Table 1. The steps of the assessment process consist of: 1) One very important source of information is equipment manufacturers. Manufacturers of a particular equipment item were located through a search of the National Electrical Manufacturers Association web site located at the URL (http://www.nema.org/standards/) which has a manufacturers and product search capability. This search provided the starting point for any contact with equipment manufacturers. Together with the manufacturer name, recording the web site address together with e-mail address provides a means for making contacts and the location of information relevant to specific equipment. 2) In parallel to the effort of identifying equipment manufacturers, the manufacturing standards for the equipment under study relevant to heat loss were identified. The identification process began by creating a list of manufacturing standards relevant to the type of equipment. This was first attempted by searching manufacturer web sites for the specific standards that were followed in the equipment production. An improved method of accumulating this information was through the Global Engineering Documents web site (http://global.ihs.com) by clicking on the link to Document Search. This gives one the capability of searching for standard documents having a particular phrase or word in the title. The advantage offered by this search is the ability to receive titles of standards that are applicable to the product of interest from many standard organizations. Also, by doing a search on a partial standard number, for example C57, many standard titles from ANSI and IEEE related to transformers could be found. The list of relevant standards were refined by excluding those standards that did not address equipment heat loss or efficiency. In addition to the standards specified in the TRP-1104 work statement, standards from ANSI, NEMA, and UL were included in the review. 3) The relevant standards for each product were acquired. The number of standards to be examined is so large that the purchase of these documents was not an option. Standards were acquired through Inter-Library Loan at the Hale Library at Kansas State University. A problem of searching other libraries for the standards is that many libraries do not list individual standards by number in their holdings, they only list that they have e.g. NEMA or ANSI standards.

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4) Each of the acquired standards were reviewed to determine if the standard requires power loss measurements to be made and if so how are the measurements to be performed and what are the uncertainty levels of the test procedures. The process of reviewing standards is best summarized as the determination of the heat gain measurement requirements, measurement methods, measurement uncertainty, and measurement reporting. Based upon the results of the standard review, the specific equipment item was placed into one of two broad classes. One class consisted of those devices for which clear power loss measurement information was present while the other class consisted of those devices for which no power loss information was presented in the standard. While the standards helped in the eventual classification of the equipment, they were not used exclusively in the final equipment classification required by the TRP-1104 work statement. An example where no heat loss standards were found is the transfer switch. In contrast to the transfer switch example just cited, the availability of a document requiring and describing the measurement of heat loss does not necessarily mean that manufacturers will use the standard. Heat loss information was found for battery chargers in the standard NEMA PE 5 covering utility type battery chargers; however, no manufacturer was found that claimed to follow this relevant standard that specifies how battery charger efficiency is to be determined. 5) Contact though e-mail was made to the companies included on the NEMA obtained manufacturer lists to inquire about dissipated heat from their products. The motivation behind this step was to acquire information useful to the eventual classification of the equipment. Since a contact was being made with equipment manufacturers, information not only relevant to the classification was sought but also information useful to other parts of the study. For each type of power equipment involved in the survey, a contact letter was written which explained the nature of the project and requested information relevant to this study. The requested information consists of the name and number of the standards followed in determining the loss numbers or the procedures used to determine the losses in the case where no loss determination procedures are specified in the standards. Also, the manufacturer is requested to supply loss numbers for their products or to specify the web pages and/or public company documents where loss figures are presented. In doing this company contact, the web address of that part of the company’s web site which best corresponds to the product of interest was noted. The home web page address of the companies contained on the product manufacturer lists can also be found on the NEMA web site at the address (http://www.nema.org/membership/members.html). Also the e-mail address to which the letter of contact is sent was recorded. In this fashion, we are able to put together an e-mail distribution list for the various products so that if we need to seek additional information at some time in the future, this can be quickly done. An example of the contact letter is included in the Appendix. This step was not done for every piece of equipment under study, e.g. cables, since it was not expected that power losses would vary from manufacturer to manufacturer and excellent cable loss models are available.

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6) Each of the equipment types is documented regarding applicable standards, loss measurement methods, and results of the manufacturer survey. From the accumulated data, the equipment is classified into one of three categories as specifies by the TRP-1104 work statement. The overall results of the assessment are summarized in the Introduction and Executive Summary section. The justification behind the classification is presented in each of the equipment sections of the report to follow. The manufacturer lists are not included in this document. The first category consisted of those products for which the standards require specific tests for loss determination. Included in this first category are devices that have very well documented information regarding the power loss mechanisms and test procedures from which loss information can be accumulated and reported. This first category includes transformers and motors. The second category included those devices where there was some information that could be used to help in the loss determination but verification of the information was needed. The devices in this category are reactors, DC and medium voltage switchgear, circuit breakers, panelboards, motor control centers, inverters, battery chargers, adjustable speed drives, plus cables and cable trays. The remainder of the power equipment constitutes the third category that includes transfer switches. The third category is characterized by the situation where there is both an absence of loss data and the standards do not require the rate of heat losses to be measured. 7) From the assessment determined in the previous steps, a test plan is devised to provide the information necessary to complete this study for each of the equipment items listed in the ASHRAE TRP 1104 work statement. In case of the first category equipment, the information will be gathered from manufacturer web sites and through personal contacts. For the equipment in the second and third categories, the test plan involves experimental procedures for building and/or verifying the information necessary to complete this study. Both the steps of the test plan and the necessary experimental apparatus are described for each of the required equipment items.

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First Category The first category consists of transformers and motors. Each of the first category equipment types will be examined here.

Transformers Of all the equipment studied in this work, the state of the art for transformer losses is among the best defined. According to the insulating medium, transformers are divided into two categories which are liquid immersed units and dry-type units. The testing and manufacturing standards are written according to this insulating distinction. The sizes of the transformers covered in this study range up to 2.5 MVA. Specifically, the types of transformers under consideration are unit sub-station transformers from 0.3 to 2.5 MVA plus power and lighting transformers 300 KVA and below.

Review of Environmental Heat Gains Standards The method of testing to determine the total power losses for both dry and liquid immersed core and coils are specified in IEEE Std. C57.12.90 for liquid immersed windings and IEEE Std. C57.12.91 for dry type windings. Also relevant to the loss determination are IEEE Std. C57.12.00 and Std. C57.12.01 since these documents specify what is to be measured and also specify measurement uncertainty and IEEE Std. C57.12.80 which defines many terms used in the other cited documents. Two other useful documents related to losses are NEMA TP 1 and NEMA TP 2 for distribution transformers. NEMA TP 1 defines a “Class 1” efficiency for distribution transformers which is presented in the form of a table. The table lists the minimum efficiency necessary for “Class 1” designation for both single and three phase units as a function of rated KVA. There is a table for dry type units and another table for liquid immersed units. For dry type units, the table in the standard makes a distinction between low voltage and medium voltage transformers. The “Class 1” efficiency essentially defines an upper limit for rejected heat. NEMA TP 1 and NEMA TP 2 observe the test codes presented in IEEE Std. C57.12.90 and C57.12.91. Dry type power and lighting transformers are covered in NEMA ST 20 which observes IEEE Std. C57.12.01 and C57.12.91. Equipment Heat Losses As stated earlier, it is assumed that the device under discussion is operating in a “steady state” capacity. Thus, it is assumed that the transformer has been operated in the current condition for a sufficient period of time that all thermal transients have decayed to the point that they can no longer be detected. Under these conditions, any energy loss is in the form of heat that travels to the local environment. The manner in which the heat transfer takes place is not of a concern. Heat convection to the surroundings and conduction to surrounding structures is not hard to Phase I - Report – Rev. 4.2

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appreciate as viable transfer mechanisms. Any thermal radiation is assumed to be absorbed by the surrounding structures (perhaps after several absorptions and re-emissions) and the eventual manifestation of the radiant energy is an increase in room temperature in the absence of any environmental control. The definitions of total losses as defined by the standards are slightly different for liquid – immersed units and for dry type units. Each of these two cases will be treated separately. Not included in the loss figure is any power required for cooling fans, oil pumps, or any other ancillary equipment. For units of 2.5 MVA or less, this is not an issue since the primary cooling means is free convection, however, forced air cooling is an option available on some larger unit substation transformers. The power consumed by the fan must be included in any loss figures. The rating and efficiency of the fan motor determines the environmental heat gain created by a forced air fan. The fan heat loss is small compared to that of the transformer. Units having a forced air cooling option will have different capacities and heat losses for each cooling mode, i.e. self cooled or forced air. It should be noted that for both dry and liquid immersed type windings, both IEEE Std. C57.12.00 and C57.12.01 state that transformers conforming to those standards are suitable for operation at rated KVA so long as the ambient temperature does not exceed 40 oC and the average ambient temperature does not exceed 30 oC in a 24 hour period. To be presented in the following text is a discussion of no load and load losses for both dry and liquid immersed windings. The influence of the ambient temperature on losses will also be discussed. It will be shown that the variable to which the losses are the most sensitive is the load current while the ambient temperature does not play a significant role in determining the total losses. Before discussing the different transformer types, the measurement of the winding resistance will be covered first since this is common to both transformer insulation types. The winding resistance is measured after the unit has remained de-energized for a specific time (three to eight hours for liquid immersed units and 24 to 72 hours for dry type units) in a draft free area. The use of the time span is to assure that the unit is in thermal equilibrium with the environment and, thus, the winding temperature is known. Once the base resistance value is measured, the winding resistance is used as a means of measuring the average winding temperature. The variation of resistance with temperature is determined by T + Tk Rs = Rm s Tm + Tk where Rm is the measured cold resistance at temperature Tm in oC, Rs is the resistance corresponding to some other average winding temperature Ts in oC, and Tk is 234.5 oC for copper windings or 225 oC for aluminum windings.

Liquid Immersed Units: The total losses are defined as the sum of the load losses and the no load losses. The load losses are determined at rated frequency and current then corrected to the reference temperature. To conduct the load test, one winding is short circuited while the other winding is excited to the point where rated current flows in the windings. The losses occurring in this situation are the load losses. Since the transformer is excited at a reduced voltage, the no

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load losses are small and the measured losses attributable only to load losses. The no load losses are determined at rated frequency and voltage and are reported at the no load loss standard reference temperature. The standard reference temperature for load losses of liquid immersed transformers is 85o C. The standard reference temperature for no load losses is 20o C. In general, transformer losses vary with core and coil temperature. The use of the reference temperature is to express these measurements on a basis that allows comparison with other units. The following discussion illustrates how transformer losses are reported using the reference temperatures. The no load losses occur when the unit is excited at rated voltage and frequency in the absence of any load current. No load losses are made up of core losses (hysteresis, eddy-current, and magneto-striction), dielectric or insulation losses, and winding I2R created by the no load excitation current and the circulating current which might be present in parallel windings. The transformer core contributes the greatest portion of the no load losses. The no load losses are essentially a constant value, however, the losses are a very mild function of core temperature which influences core steel resistivity, hysteresis losses, and stress caused by magnetostriction (the 120 Hz. hum one hears from an energized unit). Also, how the losses vary with core temperature is determined by core design and by the way an individual unit is constructed, i.e. matched units may have different loss variations with core temperature change. The constraints under which the no load loss measurements are made is that rated sinusoidal voltage is applied to a unit where the average insulating liquid temperature is within ± 10oC of the 20oC reference temperature and the difference between the top and bottom liquid temperature does not exceed 5oC. Should the test conditions differ from those presented by the standards, a correction is applied to the measured data through the calculation of

P(Tr ) = P(Tm )[1 + (Tm − Tr )K T ] where P(Tm) is the no load losses at the measurement temperature Tm in oC, P(Tr) is the no load losses at the reference temperature Tr (20oC), KT is an empirically derived constant having units of oC-1. A suggested value for KT in the absence of other information is 0.00065 (o C)-1 as stated in IEEE Std. C57.12.90. Given the no load loss value at the reference temperature, the no load loss value at some temperature can be determined from this last result by turning the last equation around to produce

P(Tm ) =

P(Tr ) 1 + (Tm − Tr )K T

where P(Tm) is now the no load losses at some other temperature Tm. Notice that the losses decrease as the temperature Tm increases. To illustrate how insensitive the no load loss is to core temperature variation, evaluate the expression just presented with the suggested constant and a temperature difference of 65 oC (i.e. 85 oC – 20 oC), the decrease in no load losses is a factor of 4%. Also consider that the 85oC number used in this calculation is the standard load loss winding reference temperature, not the core temperature. Under load, the winding is the hottest part of the transformer. The core and insulating liquid would be at lower temperatures. Thus, the actual difference between the no load losses at the no load reference temperature and the no Phase I - Report – Rev. 4.2

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load losses under load conditions will be smaller than 4%. The change in no load losses is then on the same order as the loss measurement uncertainty (to be presented in a later section). From this brief argument, it is seen that the omission of the temperature correction provides a slightly conservative figure for the no load losses should the transformer core temperature increase. To account fo the increase in core temperature, one suggestion is to evaluate the loss at the temperature value of 55oC for Tm, a figure close to the average of the 20oC and the 85oC reference temperatures. This would compensate for some of the reduction in loss with core temperature increase. It should also be appreciated that little change would occur in overall heat load if the no load losses at the reference temperature of 20oC were used. Also, the inference that the no load losses are an even weaker function of ambient temperature than with core temperature is a valid conclusion. The recommendation of this work is to treat the no load loss as a constant. Load losses are measured when rated current flows in both the excited and the unexcited windings. The load losses include winding I2R and eddy-current losses, stray magnetic field losses in the transformer structures or tank, and losses associated with circulating currents in parallel connected windings or strands. The load losses are broken into two parts being the stray losses (caused by eddy currents induced in transformer structures such as core clamps, shields, and tank surfaces) and the winding I2R losses. The load losses are determined by wattmeter measurements. Once the load losses are determined, the unit is de-energized and the winding resistance is measured. The winding resistance determines the average winding measurement temperature, Tm. By calculating the I2R loss and subtracting this from the load losses, the stray losses are determined. The stay loss decreases with temperature (resistivity increases with temperature that, in turn, limits the induced currents causing stray loss) while the I2R loss increases with winding temperature. Variation of load losses with winding temperature for a transformer is described by  T +T   T + Tm    + Pr (Tm ) k P(T) = Ps (Tm ) K  TK + Tm   TK + T  where P(T) is the power loss at the desired temperature T specified in o C, Ps(Tm ) is the stray loss at the measured temperature Tm specified in o C, Pr(Tm) is the winding I2R loss at the measurement temperature, and TK is the same as defined previously. Note that this calculation applies to both liquid immersed and dry type units as well with the exception that the standard reference temperature for liquid immersed load losses differs from that for dry type load losses. In performing the load tests, IEEE Std. C57.12.90 states that no ambient temperature correction need be applied to the data provided the ambient temperature is within the range of 10 to 40 oC.

Dry Type Units: The total losses of a transformer are the sum of the no load losses at room temperature (25 oC ) and the load losses at the standard reference temperature. The standard reference temperature for load losses is the highest rated winding temperature rise plus 20 oC. A temperature rise is defined as a measured temperature less the ambient temperature. The highest rated temperature rise is determined by the insulation class and is shown in Table 4. The information for Table 4 is taken from IEEE Std. C57.12.01. The highest average winding temperature rise under full load is a transformer nameplate item. The highest average

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temperature rise is dependent on the type of winding insulation and can range from 75o C to 150o C. Any loss figure or efficiency reported for a unit would incorporate this temperature value. Highest Average Winding Temperature Rise (oC) 130 75 150 90 180 115 200 130 220 150 Table 4: Limits for Temperature Rises (assuming 40oC maximum ambient temperature and 30 oC average ambient temperature) Insulation System Temperature Class (oC)

The standards do not specify the necessity for temperature correction of the no load losses for dry type windings. IEEE Std. C57.12.91 does acknowledge that the no load losses are a function of core temperature. The recommendation for this work is to treat the no load losses as constant. Ambient Temperature Influence When the ambient conditions differ from those assumed by the standards (30 oC), IEEE Std. C57.12.91 specifies a correction for the average winding temperature for dry type windings. The standards are concerned with determining the average winding temperature which would occur when the ambient temperature differs from the expected 30oC. If the ambient temperature differs from this figure, then C57.12.91 supplies a formula for correcting the measured average winding temperature occurring at the current ambient temperature to the average winding temperature which would occur if the ambient were 30oC. The concern of this work is just the opposite in that the average winding temperature occurring at an ambient temperature other than 30oC is of interest given that the reference temperature rise occurs at an ambient of 30oC. The recommendation is to take this correction and use it in reverse. The reversed temperature correction takes the form n

 T + Tk + Ta  Tcr = Tr  r   Tr + Tk + Tra  where Tr is the load loss reference temperature rise, Tcr is the corrected average winding temperature rise, Tk is as defined previously, Tra is the standard ambient temperature (30oC), and Ta is the new ambient temperature. The suggested value for the exponent n is 0.8 for ventilated, self cooled units, 1.0 for ventilated units with forced air, and 0.7 for sealed units. This expression applies to dry type units. However, since liquid immersed units are also sealed this expression can be used for those units. For liquid immersed units, IEEE Std. C57.12.90 does not specify a temperature correction, however it does state that an appropriate temperature correction can be used.

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influence of the environment on transformer load losses can be determined. It will be seen that the change in losses produced by this calculation will be small and the recommendation in this work is to ignore the influence of ambient temperature on load losses. The correction of load losses based on ambient temperature variations requires the knowledge of both portions of the load loss, namely the I2R loss and the stray loss. The I2R loss can be determined from the winding resistance at the load loss reference temperature and the rated current. The winding resistance is not a nameplate item and must obtained from the manufacturer. As an example of this calculation, consider two separate evaluations of the last expression, one to provide the largest possible factor for temperature rise increase and another to provide the smallest possible factor given a 20oC increase in the ambient temperature. The calculations are summarized in Table 5.

o

Reference Rise - C Tk - oC Ta - oC Tra - oC n Tcr - oC Standard Reference Temperature - oC Tm = Tcr + standard rise

 TK + Tm   TK + Tr

  

Largest 55 225 50 30 0.7 57.5 85

Smallest 150 234.5 50 30 0.7 155 180

107

205

1.07

1.06

Notes

factor for I2R loss

0.93 0.94 factor for stray loss  Tk + Tr     TK + Tm  Table 5: Influence of 20 oC Change in Ambient Temperature on Load Losses The information in Table 5 shows the factor of how the losses will change with an increase of 20 o C in the ambient temperature. Should the ambient temperature fall by 20 oC, the numbers in the last two lines of Table 5 are swapped. Depending on the size of the stray loss relative to the I2R loss, the new load losses are within ± 7% of the losses at the standard reference temperature. To put this in perspective, consider that the ambient temperature is changed by 67% and found that the load losses changed by less the 7%. Now consider if the winding current were to increase from 100% to 110%. A 10% change in current will produce at least a 21% increase in load loss (the “at least” stems from the possibility that the winding resistance could increase). Also, consider the case where the I2R loss is the same size as the stray loss. From the numbers in Table 5, it is seen that the load losses would be unchanged. If the I2R loses were three times larger than the stray loss, the increase in load losses for a 20 oC increase in ambient temperature would be 3%, the same as the loss measurement uncertainty. Phase I - Report – Rev. 4.2

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If the changes in losses with ambient temperature were ignored, then the overall uncertainty of the load loss figure at the reference temperature would be slightly larger then ± 7%. Measurement Uncertainty Any manufacturer citing that they follow the standards specified previously would be providing believable data. In making any table related to transformer losses, it will be necessary to ascertain that the manufacturer follows these standards before using that information. For all of the sizes of transformers included in this study, the standards require the manufacturer to either test a representative sample of a specific transformer size or to make direct measurements on the unit in order to determine the loss values. Units tested in accordance with IEEE Std. C57.12.90 or C57.12.91 (observed by NEMA TP1, TP2 and ST20) to determine losses must have a measurement uncertainty of ± 3% or less. Losses presented by manufacturers were interpreted as being the average of a test batch. The uncertainty of the average losses of a test batch would be smaller than ± 3% and the specific value would depend upon the number of units in the test batch being averaged. It is then seen that the ± 3% is an upper limit for loss uncertainty. Manufacturers A table of manufacturers was assembled using the method described earlier in this report. Of the thirty manufacturer names obtained from the NEMA web site, twenty manufacturers were sent email requests for loss data and testing methods. Five manufacturers replied. Of the five, three manufacturers reported loss data. The three manufacturers who supplied the loss data are well known within the power and utility industry. Information Deficiencies All of the manufacturers examined in this work state that they follow IEEE Std. C57.12.90 and C57.12.91. The information supplied by these manufacturers is believable since it is known how the tests were made and the uncertainty of the results. Owing to the clear standards used by industry and the availability of good loss data, transformers are placed in Category I. The only information deficiency regarding transformer losses is the construction of the heat gain tables to present the results of this work Test Plan In order to complete the loss tables required in this work, the following tasks will be accomplished: 1) The loss data will be separated into that for dry type and liquid immersed units.

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2) For each transformer size required by the TRP 1104 work statement, the average and standard deviation of the manufacturer data for both no load and full load losses will be reported. 3) Additional contacts with larger (having significant market share/reputation) manufacturers of transformers will be made through a telephone survey to acquire more data points for the loss tables. If any new information is obtained, this new data will be included with the other information. The reporting of load and no load data allows for diversity since the loss at some fractional current load level, say x, can be determined by P(x) = PNL + PL x2 where P(x) is the power loss at a given per unit current load - x, PNL is the no load loss, and PL is the full load loss. This expression provides an interpolation of the power loss as a function of load current. These tasks are to be completed in Phase II of this project. No additional resources or equipment will be needed for the execution of the steps just listed.

References IEEE Std. C57.12.00 – 1999 General Requirements for Liquid – Immersed Distribution, Power, and Regulating Transformers. IEEE Std. C57.12.01 – 1998 Standard General Requirements for Dry-Type Distribution and Power Transformers Including Those with Solid Cast and/or Resin-Encapsulated Windings. IEEE Std.C57.12.80 – 1978 (R1992) Terminology for Power and Distribution Transformers. IEEE Std. C57.12.90 - 1999 Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers. IEEE Std. C57.12.91 - 1995 Test Code for Dry-Type Distribution and Power Transformers. NEMA ST 20 – 1992 (R1997) Dry-Type Transformers for General Applications. NEMA TP 1 – 1996 Guide for Determining Energy Efficiency for Distribution Transformers. NEMA TP 2 – 1998 Test Method for Measuring the Energy Consumption of Distribution Transformers.

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Motors Since the size range under consideration as specified by the TRP-1104 work statement is from 10 horsepower to 4000 horsepower, the devices examined in this work include polyphase induction motors, polyphase synchronous motors, and DC motors.

Review of Environmental Heat Gains Standards The significant standards for motors regarding heat loss consist of NEMA MG 1 together with IEEE Std. 112 for induction motors, IEEE Std. 115 for synchronous motors, and IEEE Std. 113 for DC motors. It should be noted that IEEE Std. 113 has been withdrawn and has not been superseded. The various frame assignments for integral hp, AC induction motors is contained in NEMA MG 1.

Equipment Heat Losses The determination of the efficiency, definition of losses, measurement methods for polyphase induction motors is covered in Sections 5 and 6 of IEEE Std. 112. Efficiency determination for synchronous motors is covered in Section 4 of IEEE Std. 115. IEEE Std. 113 describes the determination of efficiency of DC machines. For synchronous, induction, and DC machinery, NEMA MG 1 states that the procedures specified in IEEE Std. 115, 112, and 113, respectively are to be followed. The losses for a motor are determined by first selecting a representative sample of a given size motor. The losses which can be divided into quantities such as winding I2R loss, friction and windage, core loss, stray field or eddy loss, etc. are added together and used in an efficiency calculation. The nominal efficiency is determined from the mean of the sample efficiencies. Heat loss values in BTU’s/hr. are not available, however, the nominal efficiency can be observed on manufacturer web pages or catalogs. All of the efficiency measurements are at steady state therefore, any heat loss must go to the environment. Warming the equipment and thermal transients are not considered. The ambient temperature does have an effect on the heat loss of all three types of motors considered. Specifically, there are two types of losses that are affected by ambient temperature. These are I2R losses and stray-load losses. The value of the winding resistance increases linearly as the ambient temperature increases, in the same manner as with transformers. This increase in resistance changes the I2R losses. The stray-load losses have an inverse relationship with ambient temperature. So as the ambient temperature increases, the stray-load loss will decrease. Chapter 28 of the ASHRAE FUNDAMENTALS Handbook contains a table of heat gains from typical electric motors. The motors under consideration in the ASHRAE Handbook are both single and polyphase AC motors.

Measurement Uncertainty For power measurements associated with the determination of the efficiency of an induction motors using Test Method B specified by the standard (IEEE Std. 112), the uncertainty of the instruments is specified by the standards to be no greater than ±0.2 % of full scale. For all other general measurements the instrument uncertainty is to be no greater than ±0.5 % of full scale.

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IEEE Std. 115 for synchronous machines does not specify instrument uncertainty values other than to state that instruments of high accuracy are to be used in the testing. Since the overall efficiency is calculated from the sum of several different types of losses, the overall uncertainty depends on the combination of the uncertainties of each individual test. There are five to six different types of tests for different types of losses depending on the type of motor being tested (synchronous, induction, or DC). Since many variables go into this, an overall uncertainty is hard to quantify at this time.

Manufacturers In compiling the information related to electrical machinery, no manufacturers were contacted owing to the easy availability of information regarding motor efficiencies. A list of manufacturers has been compiled for use in Phase II. This list is not presented here.

Information Deficiencies There are two primary deficiencies in the information related to power losses of electric motors. These are: 1) What is the size of the contribution of the I2R and stray-load losses to the overall heat loss of the motor? 2) What is the overall uncertainty of the efficiency numbers found on manufacturers web sites and catalogs? In order to determine the influence of the ambient temperature on the power losses, the portion of the losses attributable to I2R heating needs to be estimated. Also, while the uncertainty of the instruments used in the test procedures specified by the standards are themselves specified in the same documents, the overall uncertainty of the efficiency figures is not immediately obvious. The determination of efficiency is a process involving many steps and separate tests. The results of these tests are combined together in the efficiency calculation. The overall uncertainty is a function of the uncertainty of the individual tests. Given the tests and the instrument uncertainty, no overall uncertainty estimate has so far been found.

Test Plan The test plan for DC, induction, and synchronous motors consists of several steps. These steps are: 1) Tables of heat loss information are to be built from the data acquired regarding motor efficiency. This may require phone calls to the manufacturers in addition to the data found on their web sites and catalogs. A significant item to extract from the manufacturer contacts is an estimate of the portion of the total power losses contributed by I2R and stray losses.

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2) An estimate of the efficiency uncertainty cap is to be determined through calculations. This will be accomplished by determining the uncertainty of individual tests that contribute to the overall efficiency reported by the manufacturers. The uncertainties of individual tests are then to be combined into an overall uncertainty. 3) Once the contribution of I2R and stray losses to the overall efficiency can be estimated, this information is then used to provide an estimate of the influence of the ambient temperature on the power losses. 4) In order to address diversity in power losses based upon equipment loading, two approaches are to be tried. The first is based on the overall efficiency where reduced loads entail proportionally reduced heat losses. The second approach is to attempt to segregate the losses into those that remain constant with load such as friction and windage and those that vary with load such as I2R. Which approach is feasible will be determined in this step of the test plan.

References IEEE Std. 112 – 1996, Test Procedure for Polyphase Induction Motors and Generators. IEEE Std. 113 – 1985, Guide: Test Procedures for Direct-Current Machines. IEEE Std. 115 – 1995, Part I – Acceptance and Performance Testing, Part II – Test Procedures and Parameter Determination for Dynamic Analysis. NEMA MG 1 – 1998, Motors and Generators.

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Second Category The equipment falling into the second category is reviewed in the following sections with an explanation regarding the information found from investigating the standards and conducting manufacturer surveys. Also presented are the test plans for each of the second category equipment. All those devices classified as Category II (or second category) can be determined from entries in Table 3.

Measurements Equipment placed in this category has been designated as those devices for which loss information is known, however the quality of the loss numbers is uncertain. To remedy this lack of certainty, measurements of environmental heat gains are necessary. The tests are necessary to draw a conclusion as to the trend between the published data and the measured data. The test procedure to be used with each type of equipment is, in certain cases, unique and, in other cases, similar to that required for other equipment types. If the procedure to test one item is the same as that specified for another item, then the test setup or apparatus will not be presented again.

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Cables and Cable Trays Characteristics of electrical cables have been studied by different investigators for well over one hundred years. The bibliography presented by Anders, 1997 adequately demonstrates this point. Various standards governing cables are available and the literature on cables is well documented as seen in IEEE Std. 835, IEEE Standard Power Cable, Ampacity Tables and NEMA WC-51, Ampacities of Cables in Open-Top Cable Trays. The most valuable reference, however, is a recently published book by Anders, 1997 (see references at the end of the section). This book provides details on construction of cables, losses in cables, and methods to compute capacity of cables under different conditions. The range of consideration of cable trays is from 12 to 30 inch widths in increments of 6 inches. Also, the AC voltage level of the cables in the tray is either 600 V, 5 kV, or 15 kV.

Review of Environmental Heat Gains Standards IEEE and NEMA standards available for cables address constructional details, ampacity issues, losses, and issues related to testing of physical characteristics of cables. The most significant standard is IEEE Std 835-1994, IEEE Standard Power Cable Ampacity Tables. Also significant to cable trays is NEMA WC-51-1986, Ampacities of Cables in Open-top Cable Trays. The book by Anders is the most comprehensive on the subjects and it includes all the issues discussed in the IEEE and NEMA standards. The original approach to developing cable ampacities was presented in the pioneering paper by Neher and McGrath, 1957.

Equipment Heat Losses Cable heat losses are caused by I2R losses in the conductor. These heat losses depend upon the cable material, e.g. copper or aluminum, the current level, and the current type, either AC or DC. The limiting factor for the cable heat loss is the temperature rise of the conductor, since too high a temperature rise will damage the electrical insulation. The ampacity of the cable, the maximum ability to safely conduct electric current, is the subject of the cited standards and references. Losses take place in different parts of the cable. The most significant are the resistive losses in the main conductor. These losses however are influenced by the skin effect and proximity effect. Expressions to account for these effects are available in the literature and can be very easily included in any loss calculations. Other significant losses take place in the sheath of the cable. The sheath is usually made of solid lead or aluminum, or concentric copper or aluminum. Sheath losses consist of two parts, one is due to eddy currents and the other due to circulating currents. Circulating currents are induced in the sheath due to magnetic interaction of main conductors with the sheath. Circulating current in sheaths exist only if sheaths of two or more cables are bonded together at least at two locations. Eddy current losses are much smaller than circulating current losses and are generally neglected. The power cables also have dielectric losses in the insulating material and they are dependent upon the electric field across the dielectric. These losses are significant only at transmission voltages (above 69 kV).

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In power plants, power cables are routed in cable trays, which come in 12 to 30 inch widths in 6 inch increments. In special situations, such as nuclear plants, cables are routed through conduits, mainly for safety. Trays and conduits will have some eddy current losses, but they are extremely small and, thus, are neglected. Hence, if sheaths are not connected, the bulk of the cable losses are the resistive losses in the main conductors. Thus, if the number of cables and their physical arrangement in the trays are known, total losses per foot of that specific cable tray can be computed. Rubin, 1979 assumed typical cable arrangements in trays of different sizes to obtain a rough approximation of losses. However, he has neither specified the cable sizes and arrangement of cables in the trays nor the method used to calculate the values. Thus, it is impossible to duplicate his results just so that his assumptions could be identified. Moreover, his results are not of much use since different cable sizes and arrangement could be used in a specific tray size. To follow is a discussion and some calculations to demonstrate that there is essentially an upper limit to the amount of heat that can be produced by a full cable tray of a given width. Based upon this discussion, a test plan is presented which accounts for tray width, cable size, number of cables, insulation and sheath type, loading, and ambient temperature.

Heat Loss in Cable Trays The National Electrical Code specifies the maximum number of conductors and their ampacities in cable trays, from which the maximum possible heat loss can be calculated. It is recognized that trays will rarely be filled with the maximum number of conductors and that these conductors will rarely be operated at maximum current, so substantial discount factors will need to be used. The following looks only at the maximum possible heat loss that meets the NEC as an illustration of the calculation. Conductors may be either copper or aluminum. Only copper will be used in the following discussion. Copper wire maintains its integrity to very high temperatures, but its insulation is only specified to temperatures such as 60, 75, and 90 oC. A given insulation may be put on a conductor in different thicknesses, which makes a difference in how many conductors fit in a tray. The sizes of conductor plus insulation are given in NEC Table 5. (The Table appears after Article 830 and before Appendix A of the NEC). Many of the insulation types cover only a few wire sizes. There are four families of insulation that cover a range of conductor size from 1 gauge or smaller to 1000 kcmil or larger. The first includes types RH, RHH, RHW, and RHW-2. The second includes types TW, THW, THHW, and THW-2. The third includes THHN, THWN, and THWN-2. And the fourth includes XHHW, XHHW-2, and XHH. Once the conductor size and insulation type is selected, this table can be used to find the diameter of the cable (conductor plus insulation). The next step is to find out how many cables can be placed in a cable tray. This is prescribed in Article 318, Cable Trays. There are four main combinations: multi-conductor cables versus single conductor cables, and 2000 volts or less versus greater than 2000 volts. Then there are

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other constraints based on wire size. It also makes a difference if the cable tray is covered or not. And there is a separate calculation for the case where the cables are spaced apart at least one diameter as opposed to the case where they can touch each other. All of the rules were developed with heating effects in mind, so any combination should not result in vastly different losses. Consider a 6 inch uncovered tray with single conductor cables of 1/0 copper and THHW insulation, rated at 600 V. Table 5 gives the diameter of this cable as 0.532 in and the area as 0.2223 in2. Article 318-10(a)(4) states “Where any of the single conductor cables are Nos. 1/0 through 4/0, the sum of the diameters of all single conductor tables shall not exceed the cable tray width.” The ratio 6/0.532 = 11.3 so the maximum number of cables is 11. Article 318-11(b)(2) contains the statement “Where installed according to the requirements of Section 318-10, the ampacities for No. 1/0 through 500 kcmil single conductor cables in uncovered cable trays shall not exceed 65 percent of the allowable ampacities in Tables 310-17 and 317-19.” Table 310-17 is for insulation ratings up to 90 oC while Table 310-19 covers the range 150 oC through 250 oC. Type THHW is listed in the second column of Table 310-17. The allowable ampacity is given as 230 A for a single cable in free air at 30 oC. This figure is multiplied by 0.65 to get the allowable ampacity for each cable in the tray, which is (0.65)(230) = 150 A. The worst case heating loss is when all 11 cables are carrying 150 A. The dc resistance of 1/0 copper is 0.09827 ohms per 1000 ft at 20 oC. The power loss to the environment under these conditions would be Ω P = (11 conductors)(0.09827 )(150)2 = 24,300 W/kft = 24.3 W/ft. kft One problem with this computation is that resistance increases with temperature. If the conductors started at 20 oC, they would not remain at that temperature for long. The temperature coefficient of annealed copper is 0.00393 ohm/ohm/degree C at 20 oC. If the temperature of the copper increased to 50 oC, the power loss would increase by 24.3(0.00393)(50-20) = 2.86 W/ft. It is obvious that conductor temperature is an important parameter in determining the heat losses to the surrounding space. In general, the resistance R2 of a conductor at temperature T2 in terms of the resistance R1 at temperature T1 is given by R2 = R1( 1 +α (T2 - T1)) where α is positive number specifying the fractional change in electrical resistance per change in conductor temperature. This calculation is similar to the one carried out for transformer winding electrical resistance. A second problem with this computation is that skin effect is ignored. This was done solely for the purpose of this discussion. In general, the resistance with alternating currents is always

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higher than with direct currents. The effect is negligible for small diameters, but should be considered for larger diameters. A third problem with this calculation is that interactions with surrounding materials are ignored. How the cable is installed must be accounted for in finding the overall heat gain. The lack of consideration of the surrounding materials was done simply to demonstrate the influence of these materials on the heat gains for the purposes of the current discussion. If the cable is resting on an aluminum surface, the magnetic fields will induce eddy currents in the aluminum. If the material is steel, there will be both eddy current and hysteresis losses. The National Electrical Code attempts to deal with all these effects in Table 9, “Alternating-Current Resistance and Reactance for 600 –Volt Cables, 3-Phase, 60 Hz, 75 oC, -Three Single Conductors in Conduit”. This Table lists resistance values of 0.12 Ω /kft for PVC conduit, 0.13Ω /kft for aluminum conduit, and 0.12 w/kft for steel conduit. PVC is non-conducting so the listed values are just the resistance of the copper. The dc resistance of 1/0 copper at 75 oC is 0.1195 Ω /kft, so skin effect does not affect the tabulated value, given to two significant digits, up to this size. For larger sizes, skin effect does make a difference in the table. At 1000 kcmil, the tabulated ac resistance is 19% higher than the dc resistance of the same cable. For AC conductors, it would be good practice to use Table 9, rather the dc resistance. However, if the conductor temperature is known to be less than 75 oC, the values given in Table 9 can be reduced by using the equation shown above. Using the 75 oC AC resistance for 1/0 cable, the loss would be P = (11)(0.12)(150)2 = 29,7000 W/kft = 29.7 W/ft. What happens if another option is chosen? Suppose Article 318-11(b)(3) is used. This article states: “Where single conductors are installed in a single layer in uncovered cable trays, with a maintained space of not less than one cable diameter between individual conductors, the ampacity of Nos. 1/0 and larger cables shall not exceed the allowable ampacities in Tables 31017 and 310-19.” This reduces the allowable number of cables in a 6 inch tray from 11 to 6, but increases the allowable ampacity from 65% of 230 A to the full 230 A. The maximum power loss in the tray is now P = (6)(0.12)(230)2 = 38,000 W/kft = 38 W/ft. Consider a new example, using 750 kcmil copper wire and THHW insulation, in a 6 inch tray. From Table 5, the diameter is 1.218 in and the area is 1.1652 in 2. If the tray contains conductors, all of the same size, then Article 318-10(a)(2) applies which states: “Where are all of the cables from 250 kcmil, the sum of the cross-sectional areas of all single conductor cables shall not exceed the maximum allowable cable fill area in Column 1 of Table 318-10, for the appropriate cable tray width." Table 318-10 specifies a maximum cable area of 6.5 in2 for a 6 inch tray. The ratio 6/1.1652 = 5.58, so the maximum number of cables is 5. Article 318-11(b)(1) specifies that the ampacity of this size cable can not exceed 75% of the number shown in Table 310-17, which is 785 A. The result is (0.75)(785) = 589 A. Table 9 gives an ac resistance of 0.019 Ω/kft. The power loss is

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Measurement Uncertainty Calculations similar to the above could be performed for several wire sizes, a “thick” and a “thin” insulation, multi-conductor cables and single conductor cables, and different tray widths, to find a typical maximum power loss per foot. Based on the above examples, this number is probably in the range of 30 to 35 W/ft for 6 inch tray. Not all trays will have the maximum number of cables, and not all cables will be carrying a maximum current. If the voltage drop is used as a determining criterion rather than maximum ampacity, one would expect to see the wire size increase, with a resulting drop in losses of at lease a factor or two. If efficiency is used instead of voltage drop, the losses might decrease by a factor of ten. By efficiency, we mean using the optimum wire size to minimize the sum of capital and operating costs. For example, suppose a building is designed with 100 ft of tray that dissipates 30 W/ ft continuously. The total dissipation is 3 kW, which results in (3)(8760) = 26,280 kWh / year. This is multiplied by the cost of kWh to get an annual payment. If this energy is being extracted by air conditioning, this represents an additional cost. An appropriate interest rate and time period can be used to find a present worth of energy loss. If the incremental cost of a larger wire diameter is less than the present worth of electricity saved, then the obvious choice is to install a larger wire. In these days of relatively cheap copper and relatively expensive electricity, the economic optimum could easily be several wire sizes larger than the minimum specified by the NEC. In such a case, the NEC may not even be a good starting place for determining losses. It would not be unrealistic for the actual losses to be in the range of 1 to 3 W /ft, rather than the 30 W/ft calculated above. Uncertainty related to the loss calculations themselves is small, i.e. if all of the many factors cited above were known then the heat losses produced by the calculations would be close to the actual conductor power losses.

Manufacturers No manufacturers were contacted during Part A of Phase I concerning cable power losses owing to the quality of the loss models. Likewise, no manufacturer list was created.

Information Deficiencies Of concern here is the loss produced by a single conductor and the power dissipated by an array of conductors in a cable tray. In order to construct tables for use by HVAC engineers, both situations must be considered. The ability to calculate the cable tray power losses is readily available. Calculations are necessary to produce these tables. At the present time, these tables do not exist.

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Test Plan The test plan for cables and cable trays is divided into the following steps: 1) Construct tables for single conductor power loss which include factors of conductor material, size, insulation and sheathing, and ambient temperature. These losses will depend on the load current and the tables are to be constructed with that fact well represented. Should any of the factors mentioned above be found not to be a significant influence on the results, it will then be removed from consideration. 2) As illustrated by the discussion, it was seen that the maximum losses produced by a given size cable tray was not heavily dependent upon the conductor size. The test plan for cable trays consists of randomly choosing the many cited factors for a given tray width. By repeating this calculation many times, each time selecting a new batch of factors, the intent is to arrive at a statistical mean loss for the given cable tray width. It should be appreciated that the test plan to be used here consists exclusively of a numerical calculation. The mathematical loss models for cables are of sufficient quality that the needed results can be obtained through the evaluation of these models. These tasks are to be completed in Phase II of this project. No additional resources or equipment will be needed for the execution of the steps just listed.

References G.J. Anders, Rating of Electric Power Cables, IEEE Press, New York, 1997. IEEE Std. 835-1994 IEEE Standard Power Cable, Ampacity Tables. Mark W. Earley (Editor), Joseph V. Sheehan (Editor), John M. Caloggero, National Electrical Code Handbook 1999 (National Electrical Code Handbook, Natl. Fire Protection Assn.; ISBN: 0877654379, 8th Ed, 1999. Neher, J.H. and M.H. McGrath, “The Calculation of the Temperature Rise and Load Capability of Cable Systems,” Transactions of the American Institute of Electrical Engineers, Vol. 76, 1957. NEMA WC-51-1986 Ampacities of Cables in Open-Top Cable Trays.

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Adjustable Speed Drives The standard NEMA ICS 7 – 1993 defines a “drive” as a combination of the power converter, motor, motor mounted auxiliary devices (encoders, tachometers, thermal switches and detectors, air blowers, heaters, and vibration sensors). A drive system is an interconnected combination of equipment that provides a means of adjusting the speed of a mechanical load coupled to a motor. The concern of this work are three phase adjustable speed drives in sizes ranging from 25 to 500 hp in 50 hp increments.

Review of Environmental Heat Gains Standards There are many standards which treat adjustable speed drives yet only one treats the determination of losses. This standard is the withdrawn ANSI/IEEE Std. 995 - 1987 titled “IEEE Recommended Practice for Efficiency Determination of Alternating-Current Adjustable-Speed Drives.” Most of the other standards are issued by NEMA and UL and cover construction and manufacturing details. Testing is done primarily to verify ratings and to assure safety considerations. A useful discussion of adjustable speed drives is found in Chapter 40 of the ASHRAE Heating, Ventilating, and Air Conditioning SYSTEMS AND EQUIPMENT Handbook. However, no loss information is presented.

Equipment Heat Losses It is quite common to find power loss figures for adjustable speed drives listed on manufacturer web sites. This common situation occurs despite the lack of clear, widely used standard covering equipment heat loss. Despite the absence of a standard, data on heat losses is plentiful. No information was discovered from which the quality of the data can be inferred nor has any published presentation of manufacturer power loss measurement methods for adjustable speed drives been located. In examining the reported rate of heat losses, it has been found that for a given horsepower rating, the loss figures from different manufacturers vary widely. The conclusion regarding the reason for the difference in loss figures is one of technology, not all adjustable speed drives work on the same principles. Some technologies are more efficient than others. A comparison of data from one manufacturer with another is not straight forward since different manufacturers use different techniques for design of variable frequency drives. Some examples are: different manufacturers use either silicon controlled rectifiers (SCR), insulated gate bipolar transistor (IGBT), or metal-oxide semiconductor field-effect transistor (MOSFET) for the electronics circuits in the drives. These drives are either pulse width modulated (PWM) or pulse amplitude modulated (PAM) and their internal operating frequency varies from 2 kHz to 15 kHz. Moreover, these drives are designed sometimes for constant torque operation while others are designed for variable torque operation. Thus, it is expected that the losses reported by different manufacturers will span a wide range and that is indeed reflected by the data found in this study.

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Measurement Uncertainty No uncertainty numbers are available with the loss figures available from manufacturer web sites and catalogs. It is desirable to have a confidence interval to attach to the loss figures presented by manufacturers.

Manufacturers A list of adjustable speed drive manufacturers was compiled and these manufacturers were contacted through e-mail concerning losses and loss test methods. The results of this survey were used in completing Table 3. We were able to identify 21 manufacturers associated with adjustable speed drives trough the NEMA web site. All of these identified manufacturers were contacted through e-mail concerning equipment heat losses and/or efficiencies. Of the 21 contacted, five manufacturers replied. Of those not replying, loss data were found on two web sites bringing to seven the total number of manufacturers having available loss data.

Information Deficiencies Owing to the good quantity of uncertain power loss data, adjustable speed drives are placed in the second category. There is a sizable amount of data available on adjustable speed drive heat losses, however, the quality of this data has not been ascertained. Since so many manufacturers supply loss information for adjustable speed drives, supplying this information appears to be a competitive issue. Assuming that this is a competitive issue, then the loss numbers are concluded to be on the low side or the efficiency was determined at the most favorable load level. Before a table of losses can be completed, some quantification of the loss figure uncertainty and validity must be made. This is a Phase II activity.

Test Plan The test plan is divided into the following steps: 1) The construction of the test apparatus shown in Figure 1 is the first step of the test plan. A thermally insulated box will be constructed. Inlet and outlet power lines will be available as well as cooling air for maintaining the environmental temperature. The temperature of the environmental air in addition to the inlet and outlet air will be measured by means of thermocouples. The air flow rate is measured by means of a turbine flow meter. The data acquisition will be accomplished by a laptop computer. The fan speed will be controlled by the computer to maintain the interior temperature at a desired level. The AC motor can be loaded by a DC generator tied to a resistor bank or to an eddy current brake (not shown in the figure). This allows testing at different power levels. The output power of the AC motor is determined through the measurement of shaft torque (through moment arm and scale) and shaft speed. By knowing the efficiency of the motor and the motor output power, the load level of the ASD can be determined. The rejected heat is determined by D C p ∆T Q=m

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D the mass flow rate of the air, Cp is the specific heat of air at where Q is the heat gain, m an average inlet and outlet temperature, and ∆T is the temperature difference between the ambient air and the heated air. The calorimeter was chosen to measure the dissipated heat over other methods since it is simple and accurate. Rejected heat could be determined by measuring the input and output power. This is not as easy as it sounds. The variable frequency supply is accomplished though electronic switching of the power, a process rich in noise and voltage spikes. Even if it were possible to separately measure the voltage and current (and then compute the power), the measuring instruments must have a flat frequency response over a very wide band of frequencies since the frequency content of the current and voltage signals would be so different. Also, computing a difference in input and output power is a process that can introduce its own significant error. Exhaust Air Flowmeter

Thermocouple 50 HP AC Motor

Insulated Box

Adjustable Speed Drive

AC Supply

DC Generator

Fan Variable DC Supply

Resistor Bank Ambient Air

Thermocouples

Figure 1: ASD Test Apparatus 2) Once the test apparatus is constructed, the device will be calibrated so that the uncertainty of any test results will be known. The goal of the calibration process will be to achieve a measurement uncertainty of ±10%. The calibration process will consist of introducing a known heat source into the calorimeter and recording the output. A resistive bank whose current, voltage, and power dissipation can be measured externally through other instruments of known uncertainty would provide the necessary information for calibrating the test device. 3) Given the range of ASDs to be covered by ASHRAE TRP 1104, only two sizes of drives can be tested with the given apparatus, these are 25 and 50 hp. The intent is to vary the load and the environmental temperature to determine the power loss.

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4) For the two sizes tested, the goal is to draw conclusions concerning the quality of the published loss information, specifically the correctness of the published heat loss figure and the variation of heat loss with room temperature and load. In addition, there are a number of other concerns to be addressed. These are: A) Is the published information higher or lower than the measured data? B) Is it possible to infer the quality of the published information for the equipment sizes not tested? C) How can diversity be determined for those devices not tested? D) Will tests at higher power levels be necessary? 5) Based on the test results and the data available from manufacturers, tables will be constructed showing the loss information and confidence intervals. In order to assemble the test apparatus, several pieces of equipment need to be purchased. These are: 1) 50 hp, three phase induction motor 2) Laptop computer 3) Data acquisition equipment 4) Shop time 5) Load cell, turbine flow meter, and speed transducer 6) DC power supply, amp, and fan 7) Insulating board, TC wire, miscellaneous equipment TOTAL

$ 500 $2000 $1000 $ 500 $1000 $1000 $ 500 $6500

The items listed here are covered by the project budget. Additional resources necessary for the tests are the adjustable speed drive units themselves. Owing to the price of adjustable speed drives, purchasing these devices for measurement purposes is expensive. It is necessary to rely on equipment donations and/or loans in order to accomplish this task.

References American Society of Heating, Refrigeration, and Air-Conditioning Engineers, 2000 ASHRAE Heating, Ventilating, and Air-Conditioning Systems and Equipment Handbook, Chapter 40, “Motors, Motor Controls, and Variable-Speed Drives,” ASHRAE, 2000. ANSI/IEEE Std. 995 – 1987, IEEE Recommended Practice for Efficiency Determination of Alternating-Current Adjustable-Speed Drives. NEMA ICS 7 – 1993, Industrial Control and Adjustable Speed Drives.

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Battery Chargers A battery charger is classified as a converter since it converts AC power to DC power. Battery chargers can be used to replenish power supplies of mobile units such as fork lifts or backup emergency devices such as IC engine starters for generators. The range of battery charger sizes to be studied in this work is 100 to 600 amp in 100 amp increments.

Review of Environmental Heat Gains Standards In searching for standards for battery chargers, four have been found. There are three UL standards and one NEMA standard. The three UL documents, UL 458, Power Converters/Inverters and Power Converter/Inverter Systems for Land Vehicles and Marine Crafts, UL 508C Power Conversion Equipment, and UL 1564 Industrial Battery Chargers are written for chargers for mobile vehicles. The NEMA standard, NEMA PE 5, Utility Type Battery Chargers is not aimed at a specific application. The NEMA document is the only one specifying a test for the measurement of efficiency. The efficiency is determined by measuring the total power supplied to the charger through the AC connection with a wattmeter and by determining the charger output power by measurements of the output voltage and current. The efficiency is then the ratio of the DC volt-amp output divided by the input watts and the fraction is expressed in per cent. The power not delivered to the load is lost to the surrounding space. The input power includes the power delivered to accessories such as panel lights and fans which also adds entirely to the environmental heat gain. NEMA PE 5 also states in the documentation section, “Instruction manuals and test reports shall be made available for all chargers.” The tests performed on battery chargers are divided into two classes designated as “design tests” and “production tests.” The efficiency test is part of the design test sequence. Design tests consist of measurements made on the device to assure its performance with the NEMA PE 5 standard and to determine the device performance characteristics. Design tests are usually performed when design changes occur or for new products. Design tests are not performed on each production unit. While the NEMA PE 5 standard appears to provide exactly the information needed by this study, no manufacturer of battery chargers was found to use the standard.

Equipment Heat Losses Information on battery charger heat loss was found on some manufacturer web sites. These losses are presented in the form of BTU/hr values and efficiencies. Some manufacturers have presented curves of charger efficiency as a function of load current. In examining these battery charger efficiency curves, the efficiency of the device generally appears to peak near 50% of load. Generally, the efficiency curves are concave downward with the greatest difference between the minimum and maximum efficiency less than 10 %. In examining the tables of published efficiency, it appears that the peak value is reported as opposed to an average value.

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No information has been found on the way these losses are measured. Based on this information, the conclusion drawn as to the quality of the loss data is that the heat losses at rated load will be greater than reported, whereas the heat losses at a fractional load will probably be closer. However, no conclusion can be drawn as to the validity of the data since no information on testing procedure has been found.

Manufacturers Only three manufacturers of chargers have been found A list of battery charger manufacturers was created and these manufacturers were contacted by e-mail and by telephone to ask about heat loss and test methods. The results of the survey were used in completing Table 3. Information from all three manufacturers is available. One manufacturer has data for the complete range of equipment specified in the work statement, while the other two manufacturers present power loss numbers for only part of the range.

Measurement Uncertainty No measurement uncertainty for charger heat loss or efficiency is specified by the standards. No manufacturer has provided any information regarding the uncertainty of their published loss numbers. One battery charger manufacturer used the efficiency value of 85% for calculating the power loss numbers for all of its products, another used 92%. No conclusions can be drawn as to the correctness of the loss measurements.

Information Deficiencies Since loss information has been found, battery chargers are placed in Category II. In addition to the tables to be produced by this study, other information deficiencies consist of insufficient data at certain current levels and a complete lack of power loss measurement uncertainty. The information needed to complete this work is to ascertain the quality of the loss information. Only one manufacturer supplies the data for the entire range required by ASHRAE TRP 1104. It is necessary to test equipment from the other manufacturers to determine brackets on the losses of a unit of a particular size. Battery chargers come in different voltage levels, such as 12, 24, or 48 volts for smaller current ratings and 24 or 48 volts for the higher current ratings. The voltage levels need to be reflected in the tabulated data to be produced by this study if the different voltage levels are significant to the power losses.

Test Plan In order to acquire the information necessary to complete this study, a test plan will be initiated. This test plan consists of using a modified version of the apparatus shown in Figure 1 to provide the measurement data. The test plan consists of: 1) The test setup of Figure 1 is to be modified for the battery charger. The battery charger is placed in the insulated box. The output of the battery charger is delivered to either a resistive load, a DC motor and eddy-current brake, or the DC motor driving the AC induction machine as a generator connected to a resistive load. The

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TRP – 1104 Heat Gains from Electrical and Control Equipment in Industrial Plants charger output voltage and current will be measured. The voltage measurement will be made with the data acquisition equipment which is part of the test setup shown in Figure 1. A transducer will be necessary to measure the DC current. The measurement of output voltage and current is necessary to determining the load with which the battery charger is being operated. The laboratory kVA constraints discussed in the section on adjustable speed drives do not limit out ability to make tests anywhere in the range of battery charger ratings. As stated earlier, the device of Figure 1 will be calibrated so that the uncertainty is no larger than ±10%. Since the test setup will be slightly changed for these measurements, the calibration procedure will again be performed to check the validity of the measurements performed in the evaluation. In order to test the complete range of battery chargers, chargers of 100 A, 400 A, and 600 A capacity will be tested. Testing one of these devices from two different manufacturers will provide the information necessary for this study.

2) The price of battery chargers is large compared to the total project budget. It is necessary to rely on equipment donations and/or loans in order to conduct these tests. 3) The goal of the testing will be to verify published heat loss values. One manufacturer supplies curves of battery charger efficiency as a function of load. If these curves could be verified, then an extremely good collection of data will be had on which to base diversity information. 4) The final step of the test plan is to use the measured information to construct the tables necessary for the HVAC design engineer. The resource necessary to construct the test apparatus is a DC current transducer, which will require $500 to purchase. In order to conduct the tests themselves, battery chargers need to be obtained. If these items could be loaned or donated, then the tests can be accomplished. The steps described in this test plan are to be completed during Phase II.

References NEMA PE 5 – 1996, Utility Type Battery Chargers. UL 458 – 1993, Power Converters/Inverters and Power Converter/Inverter Systems for Land Vehicles and Marine Crafts. UL 508C – 1996, Power Conversion Equipment. UL 1564- 1993, Industrial Battery Chargers.

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Inverters An inverter is a device used for converting DC power to variable or constant frequency AC power for applications such as motor speed control or an uninterruptible power supply. This process of power inversion could be carried out with a DC motor and AC generator. The devices under consideration accomplish the inversion with solid state electronics. The range of inverters under consideration consists of single phase units of ratings 20, 30, 50, 75, and 100 kVA and a three phase unit of 150 kVA.

Review of Environmental Heat Gains Standards No standards were found which treat inverter efficiency or heat dissipation. The only standard found in the database searches addressing inverter manufacturing and testing was UL 458 titled “Standard for Power Converters/Inverters and Power Converter/Inverter Systems for Land Vehicles and Marine Crafts.” Of the testing covered by this standard, no procedures or requirements are specified which treat power loss or efficiency.

Equipment Heat Losses Information on inverter heat loss was found on some manufacturer web sites. These losses are presented in the form of efficiencies. One company faxed a data sheet that contained heat loss in BTU’s/hr. No information has been found on the way that the efficiency or BTU’s/hr were measured. Likewise, no uncertainty information is presented with the power loss values or efficiencies.

Manufacturers A list of manufacturers of inverters was created and these manufacturers were surveyed through e-mail contacts and by examination of company web sites. The results of this survey were used in completing Table 3. One manufacturer has data for the complete range of equipment, while two other manufacturers only have partial data. From the NEMA web page 18 manufacturers of inverters were identified. After some visits were made to web sites, 10 manufacturers were eliminated owing to the size of the manufactured inverters, the company only manufactures products related to inverters, or the company is no longer an inverter manufacturer. Of the remaining eight companies, e-mail contacts were made and no manufacturers responded. Loss information has been found on two web sites and another manufacturer faxed a sheet containing losses after a phone contact was made.

Measurement Uncertainty Given the data presented by some of the manufacturers, no conclusion can be reached as to the uncertainty of the measured test data since neither the test method is known nor is the uncertainty of the instruments used in conducting the test provided.

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Information Deficiency Since efficiency values have been found for inverters, the task remains to verify this information. Owing to this fact, this equipment is placed in Category II. That which is not known is the uncertainty of the loss numbers, how uniform the loss information is for different manufacturers of the same size of equipment, how the ambient temperature influences the rejected heat, and how the power losses vary with load.

Test Plan In order to determine the information required in this study, testing of inverters must be performed. The testing of the inverters is broken into the following steps: 1) The inverters will also be placed into an insulated box as indicated in Figure 1. The uncertainty goal of this test apparatus, as stated previously, is ±10%. The major difference between the test apparatus for inverters and adjustable speed drives is the power source. For adjustable speed drives, the power source was a three phase supply. A DC power source, which is available in the laboratory, is necessary to run the inverter. The same power limitation applies to the inverter test apparatus, thus it will only be possible to test single phase inverters of 20 and 30 kVA sizes. The output of the inverter will be delivered to a resistive load. The load of the inverter will be determined through computing the time average of the power delivered to the resistance bank. The testing of a 20 and a 30 kVA units at different input voltage levels will supply the information necessary for this study. Owing to the price of inverters, the purchase of these devices is expensive. It is necessary to rely on equipment donations and/or loans in order to conduct these tests. 2) The questions to be answered by the tests are: A) How well do the measured results agree with the published data? B) Does uniformity exist in similar size inverter losses from different manufacturers? C) What role does the input voltage levels play in the determination of power losses? D) Can any conclusions be drawn concerning the loss information from inverter sizes not tested? E) What is the influence of load level (diversity) and ambient temperature on heat loss values? F) Are measurements at higher power levels necessary? 3) The final step of the test process is to arrange the loss information is tables for the purposes of this project. This table will present the loss data together with uncertainty information. No additional resources will be necessary to construct the test apparatus. Ideally, in order to conduct the tests, at least two matched inverters of the 20 and 30 kVA sizes are necessary. Also

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ideally, having inverters from at least three different manufacturers will provide answers regarding uniformity of losses. The test plan describes activities to be performed during Phase II of this project.

Reference UL 458 – 1993, Standard for Power Converters/Inverters and Power Converter/Inverter Systems for Land Vehicles and Marine Crafts.

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Circuit Breakers The circuit breakers in this study consist of both low and medium voltage AC devices and DC breakers. The actuator of the breaker does not contribute a significant portion of the overall device rate of heat loss. The power loss of the circuit breaker comes from I2R ohmic heating. The ranges of devices under consideration consist of DC breakers from 100 to 1500 amp, low voltage breakers up to 4000 amp, and medium voltage breakers from 1200 to 3000 amp.

Review of Environmental Heat Gains Standards There is only one standard which comes close to treating breaker power loss and this standard is IEEE Std. C37.09, Test Procedure for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis. According to IEEE Std. C37.09, the DC resistance is measured by passing 100 amps through the breaker and then determining the voltage drop. The motivation for testing the DC resistance is simply to determine the continuity of the conducting path. These are over a hundred standards in the IEEE/ANSI C37 series and C37.09 is the only standard which provides a test procedure for the breaker DC resistance. No breaker standard reviewed in this work was found to address circuit breaker heat loss.

Equipment Heat Losses The circuit breaker dissipates heat through I2R losses. The DC resistance provides only part of the picture for AC devices since skin effect tends to increase the resistance value. Also, conductor temperature plays a roll in determining resistance. The influence of a conducting enclosure around the breaker can increase the losses of AC breakers through stray loss created by eddy-currents in the enclosure material. Proximity effect of the individual breaker poles, mounted close to one another, can also increase the heat loss of the breaker compared to a single pole. The environmental temperature could also play a roll in influencing the conductor temperature and the breaker resistance. All of the items mentioned here have some influence on the total breaker heat loss. The thermal performance of the breaker is of concern to the electrical design engineer. Overheating, especially in those breakers that are thermally activated is to be avoided. This overheating, caused by excessive current, alters the shape (through thermal expansion) of the latch holding the breaker in the “on” or energized position. Once the latch changes shape, the spring pressing against the breaker switch all the while it is energized is free to move the breaker to the “off” position, thus, tripping the breaker. Should overheating, caused by other factors such as the environment, take place in the absence of excessive current then nuisance tripping of the breaker occurs. This information provides an upper limit for the breaker conductor temperature and, as a result, the power loss. No information has been found in this work that accounts for all of the various influencing conditions cited above. A discussion on how the breaker heat losses can be modeled is now presented. Increases in conductor resistance above the DC value caused by skin effect might Phase I - Report – Rev. 4.2

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possibly be estimated through analytical or empirical corrections. Likewise, the DC resistance could be measured at room temperature using a current much smaller than the device rating which could be several thousand amps. In this case, at the rated current, the breaker conductor temperature approaches the maximum temperature rise specified by the standards. If the DC resistance was measured at reduced current and at room temperature, then the temperature rise caused by the rated AC current increases the electrical resistance above the measured DC value corrected for skin effect. By using a resistance corrected for both skin effect and temperature, the I2R calculation at rated current might provide a useful estimate of the overall device losses. The study of the increase in breaker heat losses with an enclosure might provide another empirical means to estimate the enclosure influence. Likewise, the determination of the sensitivity of the heat losses to ambient temperature, with and without an enclosure, might provide a way to model the power loss should this be a significant factor. This brief discussion highlights a strategy that might provide a means of predicting the breaker heat loss.

Manufacturers A list of circuit breaker manufacturers was assembled and the manufacturers were contacted by e-mail concerning breaker losses and loss test methods. This information was used in completing Table 3. From one manufacturer, a catalog containing the DC power loss values was obtained while from another a spreadsheet providing loss as a function of load current for breakers of several frame sizes was obtained. The purpose of the DC power loss values, provided by one manufacturer, is to provide information useful to field maintenance and testing of breakers. The DC power loss of an AC breaker is measured by passing a DC current through the breaker equal in value to the rated RMS current. No information on the measurement uncertainty of the manufacturer supplied data was found.

Measurement Uncertainty The standard C37.09 does not address instrument uncertainty in the measurement of the DC resistance. If the DC resistance is to provide a possible means to model the heat losses, the quality of the resistance value must be known. As stated earlier, no breaker manufacturer measurement uncertainty information has been found.

Information Deficiencies Starting with the DC power loss value, the DC resistance can be found. The uncertainty of the DC resistance must be determined. If the heat loss is to be based upon the DC ohms to which empirical factors are applied, then the quality of the base resistance value must be known. The influence of AC skin effect, load created conductor temperature increase, enclosures, and ambient temperature has to be determined in order to adequately account for all the contributing factors of breaker heat loss. None of this information on influences is currently available.

Test Plan The goal of the test plan is to provide a means of predicting the heat loss of a circuit breaker which accounts for the various factors mentioned. To achieve this end, the plan has as a first

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sub-goal to determine the uncertainty of the power loss information that is publicly available. The second sub-goal is to quantify the influence of all of the other factors. Based upon the measured data, a decision on whether the breaker power losses can be approached through empirical factors or not has to be made. If empirical factors can be used then the treatment of breaker losses would be a fast and simple calculation since once the breaker DC resistance is corrected for skin effect, temperature, enclosure, and ambient temperature then the heat loss of the breaker can be estimated given the load current. If the empirical approach is not practical, then tables of loss information must be developed. The initial approach is to study the loss influence factors for several breakers in order to build a body of information for determining the empirical factors or to construct tables to satisfy the needs of this study. Several breakers will have to be tested to assemble this information and to provide a basis of deciding how to model the breaker losses. This activity would be conducted during Phase II of this work. Before the steps of the test plan are enumerated, a discussion of the measurement of breaker power loss will be presented. This discussion will lead to the construction of an additional test apparatus. The philosophy of breaker usage is that if the breaker performs its desired task, and if the dc resistance is below some specified value, then whatever the losses happen to be are just accepted as part of the cost of doing business. One reason for this situation is that circuit breaker (CB) power losses are difficult to measure. One obvious way to measure the losses would be to place wattmeters on both the line side and the load side of the breaker and simply subtract the two readings. Since the readings would be so close, subtractive cancellation would render the result useless. To illustrate this point, consider the example of the three-pole, 300 A, 480 V CB operated at the rated voltage and current supplying a unity power factor load. The power is 3 (300 )(480) = 250,000 W. Based on the tests of a CB removed from service, the power loss is probably no more than 100 W. This is one part in 2500, virtually impossible to measure. If it is assumed that dielectric losses are independent of ohmic losses, then it becomes possible to test a CB on the bench with a modest amount of test equipment. A wattmeter could be used to measure the loss at rated voltage and no current to determine the dielectric losses. To determine the load losses, rated current could be passed through the breaker at low voltage and these power losses could be measured by a wattmeter. The sum of the two wattmeter readings would be the CB power loss. The dielectric loss can usually be neglected without significant error (a reasonable assumption for medium voltage levels and below). As a confirmation of small dielectric losses, a modern wattmeter could not measure a loss (less than 0.1 W) when the middle pole of a 300 A CB was energized at rated voltage and the outer poles were grounded. This brief test demonstrates that only the load losses need to be measured. In order to test CB load losses, a source is needed that will deliver hundreds of amperes at a fraction of a volt. Unfortunately, such sources are not readily available from equipment manufacturers. After a source is located, there is still a problem with test leads. Even heavy cables will have significant voltage drops at these current levels. Connections need to be bolted. Even the best plug and socket will probably dissipate a similar amount of power as each pole of

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the CB would dissipate. The desired qualities of the breaker test apparatus include that it is inexpensive, easy to use, constructed of readily available components, low uncertainty (say ± 5% ), and portable. One method of driving rated current through a CB and measuring the power is shown in Figure 2. The power source is a single-phase autotransformer, rated at 120VAC and 8 A. (larger ratings would obviously work but are not essential). Next is a modern single-phase wattmeter. A wide variety is commercially available. The recommendation is to use a wattmeter that provides a visual and a digital readout (data acquisition system compatible) of watts, power factor or VA, volts, and amps. The wattmeter should have a convenient means of excitation and must be compatible with the autotranformer. The capacitor limits the current to the very low impedance to be tested and allows the use of the full range of the variable autotransformer without damage to the instruments. A capacitance of 150 µF will allow 5A to flow at a voltage of about 90 VAC. An inductive reactor could also be used in series, but a motor run capacitor is more efficient. The power loss in the capacitor and leads is measured by moving the lead from one terminal of the load (high current) side of the current transformer to the opposite terminal (thus forming a short) and applying power. On the prototype of this apparatus, a figure of 7.5 W at 5 A was measured in a preliminary test. Variable Autotransformer C1 120 VAC

Current Transformer

150 µF 5:400 Turns Ratio

Wattmeter

Breaker Load

Figure 2: Apparatus for Testing Losses in Circuit Breakers

High currents are obtained with a current transformer (CT) operated backwards from the normal application. Usually a conductor carrying a large current is passed through the CT opening and the low current winding are used to measure a proportional output current. For example, a 400:5 CT would produce an output of 5 A when 400 A passed through the opening. It is unusual to operate a CT in this reverse mode, so a word of explanation is in order. Any 60 Hz, iron core transformer will act like an ideal transformer under no load conditions, provided the voltage is not excessive. In the no load configuration, the unexcited winding is left as an open circuit and the current in this winding is zero while the voltage is proportional to the excitation voltage through the turns ratio. If the unexcited winding is short - circuited, the winding voltage is zero and the winding current is inversely proportional to excited winding current through the turns

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ratio. If the excitation voltage is too high, the corresponding magnetic flux causes the iron to saturate. There will be a large magnetizing current and the output tends to decrease from the expected value without saturation. A CT is just like any other transformer in that it can be operated in either direction (5 A in or 5A out) as long as the iron does not saturate. As the load resistance increases from zero, the output (and input) voltages rises. When the voltage gets to the voltage rating of the transformer, there will be saturation of the magnetic path. Therefore a CT can supply rated current to a resistive load (such as the resistance of one pole of a circuit breaker) if the resistance is not too large. Neither the voltage rating nor the VA rating of a CT is published. The only number published is something called the burden, specifying the maximum load for which the CT maintains its rated accuracy. The CT is still useful for loads beyond the specified burden. The actual rating would have to be determined experimentally. For example, a GE JCW – O 400:5 CT goes into saturation at about 22 V on the 5A winding. It would be called a 100 VA transformer. This is generally consistent with its weight of about five pounds. The rated voltage on the high current side would be 100/400 = 0.25 V. The maximum impedance would be 0.25/400 = 625 µΩ. By way of reference, a 30-inch length of 2 gauge welding cable with heavy copper lugs soldered at each end has a resistance of about 500 µΩ. Two such cables in parallel would have a resistance of about 250 µΩ, so a resistance of up to 625 – 250 = 375 µΩ could be measured with this circuit. A larger resistance could be measured by putting two or three CTs in parallel, or by using lower resistance test leads. Actual measurement of the power loss in a CB at room temperature requires a two step process. First, the test leads are inserted through the opening of the CT, and the terminations are securely bolted together creating a short circuit. There is now a shorted turn through the CT. Power measurements are made at several convenient current levels. The wattmeter would measure the losses in the capacitor, the CT, the low current leads, and the high current leads. Second, the test lead termination is unbolted and the CB now takes the place of the short circuit. Power measurements are repeated at the same current levels. The difference in the wattmeter readings, with and without the breaker, is the power loss in one pole or phase of the CB. For example, circuit losses for a 400:5 CT with two test leads were measured at 48 W for rated current. When a 400 A CB was inserted, the measured losses increased to about 78 W. Each pole of this particular CB is dissipating78 – 48 = 30 W when rated current is flowing. The total loss (maximum) in three-phase operation would be 3(30) = 90 W. Normally, a CB is operated at no more than about 80% of its rated current, so the actual loss would be less than the maximum. Likewise a used CB was tested where pitting, wear, and oxidation of the breaker contacts could have taken place. New breakers may have lower losses than the particular device that was used to test the prototype apparatus. It is not difficult to measure power and the true rms voltage and current on the low current side of the CT to within 1%. The current in the high current side can be measured to within 1% with a second CT operated in the conventional fashion. It is probably not realistic to expect the actual power losses in a given CB to be known to this level of uncertainty, for a number of reasons. Two are obvious since they apply to most types of electrical equipment. The first is that the ohmic loss varies as the square of the current, and the actual current is usually not known. The second is that ohmic loss increases with temperature and the actual conductor temperature is

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usually not known. But reasonable estimates can be made for load diversity and for ambient temperature. A good engineer might get within 5% or 10% with these estimates. If this is true, there is little need to measure power to an uncertainty of less than 1%. Metering class CTs (0.1% uncertainty) are not needed for this work. A less expensive relay class CT will be adequate. Another, hard to control factor is the variability of the contact resistance. There are three contact surfaces involved in this testing, two at the terminals of the CT, and one at the pole inside the breaker. The history of the surfaces (dust, grease, corrosion, pitting) can make a substantial difference in measured power loss. Values may change when a CB is opened and reclosed. For example, the 400 A CB mentioned above and used with the prototype apparatus tests had measured resistances of 140, 140, and 200 µΩ of its three phases, using 20 A DC. The measured power loss of the same phases was 27.1 and 31.4 W, respectively. Both methods indicate that the third pole has higher losses, presumably due to surface conditions. If the CB could be disassembled and all surfaces polished, the readings would probably be closer. Calculated loses at the 400 amp AC current using the DC resistance measured at 20 A DC were 22.4, 22.4, and 31.8 W. The AC resistance is always higher than the DC resistance and the percentage difference between AC and DC resistance increases as the circuit breaker rating increases. The measured and calculated powers look plausible for the first two poles. For the third pole it appears that 20 A was not enough to thoroughly wet the surfaces. A higher DC current would yield a lower resistance, giving a calculated loss closer to 25 W than 31.8 W. A demonstration of the influence of an enclosure where hysteresis and eddy current losses in the metals located near the current carrying conductors was performed. Laying a CB on a steel sheet increased the measured power losses by 2% above the value obtained by mounting the CB on wood or some other non-conducting surface. The influence of the enclosure created stray loss on the overall breaker power loss needs to be examined for AC devices. Since the breaker transfers heat to the surroundings via free convection, it is unclear at this time if the enclosure alters or hinders the free convective air flow (especially when the enclosure is ventilated) and, thus, the breaker electrical resistance and associated power losses. There are several steps in the test plan. This idea will have to be examined. The steps of the test plan are: 1) The apparatus of Figure 2 needs to be constructed. The intended limit on the test currents is 2000 amp. Required for this testing will be two CTs of the 400:5 turns ratio size and two CTs of the 1000/2000:5 rating. The second two CTs provide 2000 amp test capability. Two CTs are required for either test setup where one CT supplies the load and the other CT is used to measure the load current. The wattmeter needs to be purchased as well as large diameter cable and copper lugs for attaching leads to the breaker. The same laptop computer used with the apparatus of Figure 1 will be used with the test setup of Figure 2. The apparatus of Figure 2 and the laptop computer provide a portable testing device. It would be possible to visit a manufacturer or equipment distributor and measure breaker AC resistance. A variable

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TRP – 1104 Heat Gains from Electrical and Control Equipment in Industrial Plants autotransformer is already available. An estimate of the equipment expenses is provided at the end of this section. The goal of the apparatus and experiment design is to predict the device losses with an uncertainty no larger than ±10%. This uncertainty will be obtained through proper calibration.

2) In order to provide control of the ambient temperature, the breaker will be placed in the insulated box of Figure 1. The insulated box provides some redundancy to the power loss measurements. The redundancy is beneficial since it provides confirmation of the other test results. 3) The testing will investigate the following questions: A) What is the uncertainty of the power loss values provided by manufacturers? B) How do the losses vary with load current? C) By what factor does the AC resistance increase over the DC resistance? Does this factor depend upon rating of the breaker? D) By what factor does the AC resistance increase when the breaker is placed in an enclosure? E) What is the influence of ambient temperature on the breaker losses (with and without an enclosure)? 4) Based on the results of the testing program, a decision will be made regarding the modeling of the circuit breaker power loses. The test data is to be organized into a form suitable for use by HVAC engineers. In order to complete these tests, several equipment items need to be purchased. These are: 1) 2) 3)

Current Transformers Wattmeter Shipping, conductors, lugs TOTAL

$ 400 $ 600 $ 200 $1200

The equipment items to be purchased fit within the project budget. In order to perform these tests, DC circuit breakers and both low and medium voltage circuit breakers must be obtained. Since data are available for low voltage AC breakers, only the 800 and 2000 amp frames need to be tested. It was learned that all the breakers within a frame are the same breaker with the exception that the breaker is set to trip at different current levels. This is easily appreciated since all the breakers within a frame have the same price. Thus, it is only necessary to purchase one breaker per frame with the current rating being the same as the frame size. This one breaker will then provide heat loss information for any breaker in the frame. The plan is to purchase two breakers, 800 and 2000 amp, from two different manufacturers in order to perform the tests. Breakers having ratings greater than 2000 amp cannot be tested with the apparatus of Figure 2. Low voltage AC breakers can also be used as DC breakers at voltage levels of 125 or 250 volts. The low voltage AC breakers then serve a dual purpose. Medium voltage AC circuit breakers have a current rating of 1200, 2000, and 3000 amps for voltage levels of 5, 10, and 15 kV. The plan is to test the 5 and 15 kV breakers having ratings of 1200

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and 2000 amps. Owing to the price of the medium voltage breakers, the purchase of these devices is expensive. A loan of two identical 15 kV medium voltage breakers from ABB (through TVA) has been secured. Western Resources has agreed to allow us into one of their generation facilities to test a 15 kV medium voltage breaker. The Appendix contains a copy of the communications regarding this equipment. Other than the test equipment listed for purchase and the test pieces, no other resources are necessary. All TRP 1104 listed equipment that will be purchased in order to perform the Phase II tests is listed in a later section. The activity described in the test plan is to be performed during Phase II of this project.

Reference IEEE Std. C37.09 – 1999. Test Procedure for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis.

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Reactors Series reactors are used in situations involving limiting current on feeder lines under fault conditions and in motor starting, among other applications. Reactors of interest in this study are of the air or gapped core, dry-type and are cooled exclusively by natural convection. Another, more common name for a reactor is an inductor. By construction, the reactor appears similar to a transformer, with the exception that there is only one winding, no secondary. Given the similarity of reactors to transformers, it is not surprising that the same standards committee within IEEE that produced the transformer standards has produced the standard for series reactors. The concern of this work is the power loss of standard size series and load reactors. The series reactor is usually found in both DC and AC applications where the reactor is connected in series with the power line for filtering and/or current limiting purposes. During normal operation, there is only a resistive voltage drop across the reactor for DC applications or a small voltage drop in AC applications. Should a fault occur on the line, the line current would tend to increase rapidly, however, since the current in an inductor cannot change instantaneously, the increase in line current caused by the fault is limited by the inductor. The limiting of the fault current is only temporary, but this provides sufficient time for any fault remediation device, such as a breaker, to operate. The limiting of the fault current protects the surrounding equipment. Another application of series reactors consists of using the reactor to filter voltage spikes and/or fast voltage rise times for electric motor, DC bus capacitors, and rectifier protection and prevention of voltage spike produced nuisance tripping. Rectifiers are used on both the input (DC) and output (AC) sides of an inverter. The same core steel used in transformer cores is used in reactors. The main distinction between transformer cores and reactor cores is that reactor cores have sizable air gaps in the magnetic circuit. The air gaps reduce the winding inductance and prevent saturation. Saturation of the magnetic path is undesirable since saturation could greatly reduce the inductance during high voltage spikes which is exactly when the reactor is most needed to counteract or filter the voltage harmonics or disturbances.

Review of Environmental Heat Gains Standards The definitive standards for reactors begin with ANSI C57.16-1958 that covered both dry-type and oil filled reactors. This standard was withdrawn (although it is reported to be still used by the industry) when IEEE Std. C57.16-1996 was issued. C57.16-1996 is titled Standard Requirements, Terminology and Test Code for Dry-Type Air Core Series-Connected Reactors. Even though a clear standard exists for loss determination, a visit to reactor manufacturer web sites have demonstrated that the standard followed by manufacturers is not C57.16 but rather UL 506 – 2000, Specialty Transformers. UL 506 does not call for the determination of heat losses.

Equipment Heat Losses Reactor heat losses are divided into those produced through load current created I2R heating and conductor skin effect (including conductor eddy losses), those produced by current circulating in

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parallel windings, and finally eddy losses induced in metallic parts via stray magnetic fields. It should be noted that stray field induced losses in surrounding equipment or apparatus is an application issue and not part of the reported reactor losses. The winding AC resistance of the reactor is obtained by dividing the sum total of the losses by the square of the rated current. According to C57.16, the loss figure of any individual reactor is not to exceed the average unit power losses by more than 6%. While the application of this standard is clear for single phase units, for three units the average loss of a particular phase is used for the basis of comparison for the losses of the same phase of a given unit. Since gapped core reactors do not saturate, the loss test can be determined at any current level and then corrected for rated current. A significant result of this situation is that the losses of the reactor can be predicted closely for any current level. Suggested methods for loss determination include wattmeter, voltage drop, and bridge methods. As with transformers, the winding resistance (either AC or DC) is a linear function of the winding temperature. Variations of the winding resistance for temperature is accounted for by (θ + Tk ) Rs = Rm s (θ m + Tk ) where Rs is the winding resistance at the temperature of interest, Rm is the resistance measured at the known temperature, θs is the temperature of interest in oC, θm is the temperature in oC corresponding to the known resistance, and Tk is 234.5 for copper and 225 for aluminum. In order that the winding not change temperature while the measurements are taking place, the current is specified by the standard not to exceed 15% of the rated continuous current. Since the power loss is produced by I2R heating, the power loss varies with temperature by the same factor as the resistance. The reported losses of a reactor are corrected to 75 oC. This expression just presented assumes that the environmental temperature is not changing. The physics of operation for a reactor is the same as a transformer. The major difference between the two devices is the magnetic field in the vicinity of the winding. In a transformer, the net ampere-turns of the winding are sufficient to drive the magnetic flux in the core necessary for rated voltage. The net ampere-turns are small and would be zero in an ideal transformer having an infinitely permeable magnetic path. While under load, the transformer winding currents differ in sign and vary by a factor of approximately the turns ratio (the slight difference producing the net ampere-turns to drive the magnetizing flux). The opposite and almost proportional winding currents create “load” magnetic flux essentially confined to the space around the turns of the windings in addition to the magnetizing flux that is confined to the highly permeable core steel. The place in the windings where the magnetic field strength is greatest is the space between the two windings. In a reactor, there is no secondary winding to provide balancing ampere-turns. Owing to the one winding, the reactor magnetic field in the vicinity of the winding is free to flow through the path of least reluctance such as steel core clamps or tank walls. As a result, the expectation is that the stray loss of a reactor is a bigger portion of the power losses than for a transformer. In regard to the influence of temperature on power losses, the same relation holds with reactors as it would hold with transformers, i.e. the winding power loss increases with temperature increase while the stray losses decrease with temperature increase. Since the stray

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loss is a larger fraction of the overall power losses, the expectation is that the reactor rejected heat is even more insensitive to ambient temperature than the transformer. Steady state operation is assumed and any heat lost by the reactor is heat added to the environment containing the reactor.

Measurement Uncertainty According to IEEE Std. C57.16, the uncertainty for power loss values is that the losses on any individual unit may not differ by more than 6 % from the average loss of all units of the same design. If a manufacturer does not follow C57.16, then the uncertainty of any power loss data presented by that manufacturer is not known and there is no information concerning the method by which the losses were measured.

Manufacturers A list of reactor manufacturers was created. A total of 34 reactor manufacturers were found from the NEMA web site. Examination of company web sites disclosed that some of these companies were only indirectly related to the manufacture of reactors. Ten companies were contacted by e-mail in the survey and no responses were received. The web sites of the reactor manufacturers were studied to observe the standards claimed to be followed in the production process. The only observed standard, which specifically deals with reactors, listed on the web sites studied was UL 506 – 2000, Specialty Transformers. UL 506 does not require power loss measurements. The web site investigation has turned up extensive tables of loss figures for series/load reactors on one manufacturer’s web site.

Information Deficiencies The extensive table of reactor losses provided by one manufacturer serves as a starting point for constructing the tables required in this work. The quality of the published loss information is not known. Since a large number of manufacturers do not follow IEEE Std. C57.16, there is little expectation for any information to be available on loss measurement uncertainty or loss measurement test methods. Also, the influence of the environmental temperature on power losses cannot be determined from the loss information found. For these reasons, reactors have been placed in category II.

Test Plan The test plan for reactors involves several steps. These are: 1) The circuit of Figure 3 will be used to excite the reactor with AC voltage and to measure the power loss. The insulated box of Figure 1 will be used for power loss verification and for controlling the ambient temperature of the reactor. The circuit of Figure 3 will supply in excess of 600 amp AC at 16 volts AC with the 15:1, 240V AC, 10kVA transformer. The series inductor is used to limit test circuit current. The wattmeter is used to measure the power delivered to the test leads and the reactor.

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TRP – 1104 Heat Gains from Electrical and Control Equipment in Industrial Plants Owing to the high current, the current sensor of the wattmeter will be supplied through a CT. The expense of the test circuit is listed at the end of this section. The test apparatus allows the determination of power loss uncertainty in the manufacturer supplied loss data. It should be appreciated that Figure 3 is a three phase circuit although it is drawn as a single phase circuit for conceptual purposes. In order to measure the power loss, the “two wattmeter” method will be used. The addition of a second wattmeter will require additional expense. The expenses are included at the end of this section. The goal of the design of the experimental apparatus is to achieve a measurement uncertainty of no larger than ±10%.

Transformer Current Limiting Inductor 240 VAC 10 kVA

Wattmeter 15:1

Test Leads

Reactor Load

CT

Figure 3: Apparatus for Testing Losses in Reactors

2) In order to measure the power loss of a reactor being used in a DC application, the motor – generator set of Figure 1 will be used. The AC motor of the motor-generator set will be supplied at rated voltage and the field winding of the DC generator will be adjusted to supply DC current levels of up to 100 amps DC. The apparatus of Figure 1 will be used to control the ambient temperature and to measure the power loss 3) Based upon the results of the first two steps, a decision will be made regarding the necessity of additional tests to provide the amount of information required to complete the goal of this study. 4) The final step of the test plan involves the organization of the data into tables to provide power loss information. In order to perform these test procedures, a 10 kVA transformer must be purchased. It is anticipated that the transformer expense is $1000. Likewise, the wattmeter will require an additional $600 bringing the total to $1600. No other additional resources are needed for completion of the two test setups. In order to conduct the reactor tests, three different sizes

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(small, medium, and large or 2, 200, and 750 amps AC) from two different manufacturers are required. If these units will be purchased and are listed in an equipment table contained in a later section of this report. The funds for the 10 kVA transformer are available from the project budget. The purchase of the transformer offers the opportunity to test this device.

References IEEE Std. C57.16 – 1996, Requirements, Terminology, and Test Code for Dry-Type Air-Core Series-Connected Reactors. UL 506 – 2000, Specialty Transformers.

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Composite Equipment Three of the equipment items placed in Category II involve a construction of smaller, standard items that might be common to more than one device. These three items are medium voltage and DC switchgear, panelboards, and motor control centers. Some of the items that these devices have in common are busses, circuit breakers, and space heaters. The unit substation is added to these three items since it can be found as a part of switchgrear and motor control centers. The approach to be taken toward quantifying the heat loss from these devices is to be determined from the heat loss of the components that make up each of these devices. Some of the components are already treated in this study such as circuit breakers and adjustable speed drives. Table 6 contains a list of the composite equipment and the components into which they are divided.

Motor Control Centers LV Circuit Breakers Disconnect Switches

Medium Voltage and DC Switchgear MV Circuit Breakers Bus Bars

Motor Starters

Potential Transformers

Bus Bars

Control Power Transformers

Space Heaters

Current Transformers

Auxiliary Compartments for Relays Auxiliary Compartments for Relays and Instruments and Instruments Adjustable Speed Drives Space Heaters Enclosure Enclosure Unit Substations Panelboards LV Circuit Breakers LV Circuit Breakers Bus Bars Bus Bars Auxiliary Compartments for Relays Enclosure and Instruments Space Heaters Unit Substation Transformers Enclosure Table 6: Components of Composite Equipment To determine the losses of these devices, attention will be devoted to the individual items. The losses of bus bars can be calculated through analytical means. Space heater losses are easy to predict through nameplate values. The losses of the various transformers can be obtained through manufacturers and has been addressed elsewhere in this study. Low and medium voltage circuit breakers are addressed within this study. The enclosure losses arise by passing current carrying conductors near a conducting surface. This is a quantity that depends upon the construction of a particular device and is by no means a quantity that depends only upon the size or rating of a particular device. This information has been found from one manufacturer and it is anticipated that it will vary from manufacturer to manufacturer. The only items appearing in

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Table 4 once are adjustable speed drives, motor starters, and disconnect switches. Adjustable speed drives are covered in this study. Information is lacking on motor starters and disconnect switches. In the sections to follow here, each of the composite equipment items will be covered. It will be seen that there exists published manufacturer loss values for motor control centers, switchgear, and panelboards. For some of the composite equipment components, loss values are available from manufacturer web sites or catalogs. Motor control centers, panelboards, switchgear, and unit substations will be covered in the same fashion as the other equipment items. The individual components of each composite item will be discussed. If the individual component has already been treated in a previous part of the report, reference will be made to that part. If the individual item has not been treated, then whatever test or measurement method needing application is discussed.

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Motor Control Centers Motor control centers provide the capability of combining electric motor control devices and other related components. The motor control center consists of free standing, floor-mounted, vertical sections that are bolted together and consist of totally enclosed, dead front structures. The vertical sections are linked together by a common, horizontal, electric power bus. The vertical section themselves are used to house motor controllers mounted one above the other. The controllers are normally linked together within the vertical section by vertical power busses tied to the common power bus. The motor control center is essentially a shell or closet into which a variety of equipment can be installed. This equipment can consist of combination motor-control units, adjustable speed drives, and lighting panelboards. NEMA Std. ICS 3 contains a more extensive list of the equipment possibilities that can be included in a motor control center.

Review of Environmental Heat Gains Standards In addition to NEMA Std. ICS 3, other standards relevant to motor control centers are NEMA Std. ICS 1; 2; and 2.3 in addition to UL 845. Owing to the variety of ways a motor control center can be utilized, the choice of equipment included with the motor control center establishes the level of losses. The bare motor control center consists of empty enclosures and a power bus. Of itself, the bare motor control center produces no losses. When equipment is added, there is a loss associated with the added equipment and electric current flowing in the power bus. The bus losses are usually reported with the device losses. NEMA Std. ICS 3 outlines the method of measuring the electrical resistance of the power bus. This resistance is usually not reported on the equipment nameplate nor listed in the manufacturer literature.

Equipment Heat Loss No standard has been found that treats heat losses or efficiency of motor control centers. As with the other equipment, thermal equilibrium is assumed. Any heat lost by the equipment is added to the environment. As an illustration of the diverse range of equipment in a motor control center, consider that the motor control center can be made up of combination starters (circuit breaker or fusible disconnect), main and branch feeder breakers, main and branch feeder switches, relays, timers, and other control devices, and busses. The conclusion reached in this examination of motor control centers is that greater attention has to be devoted to the loss values of the installed equipment types and the determination of the bus losses.

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Measurement Uncertainty No information is available concerning the measurement uncertainty of motor control center power losses. The quality of the loss figures associated with a motor control center obtained from manufacturers depends on the quality of the loss figures associated with the installed equipment.

Manufacturers A list of motor control center manufacturers was assembled and a survey on equipment heat losses was performed through e-mail and through examination of company web sites. A total of 28 manufacturers of motor control centers was found on the NEMA web site and all off these manufacturers were contacted in the survey. Two manufacturers responded to the survey. From an examination of manufacturer web sites, power loss information was found bring to three the number of manufacturers reporting power loss data.

Information Deficiencies For those manufacturers who list motor control center heat losses on their web sites, a menu approach was taken. The deficiency in the published loss information is the equipment contained in the “typical” motor control center. When specific equipment items are tabulated, the means used to measure the power losses and the uncertainty of the tabulated loss numbers is not presented.

Test Plan The test plan consists of determining the heat loss of the individual components making up a motor control center. Each of the items listed in Table 6 under the heading of motor control center will be discussed in this section. Should a measurement technique or apparatus be required, then the details of that issue are discussed. Low Voltage Circuit Breakers: The information relevant to low voltage circuit breakers has been covered in the section treating circuit breakers. Disconnect Switches: A disconnect switch is similar to a circuit breaker in that there are electrical resistive power losses, some caused by the switch material and some contributed by the contacts of the switch. No information has been found concerning either resistance or power loss values. Of the equipment listed in the TRP 1104 Work-statement, the disconnect switch is found as part of a combination motor starter. The testing of the disconnect switch will be performed with the motor starters. Motor Starters: The motor starter consists of relays, coils, switches, and panel lights among other equipment. The motor starter remains in the circuit as long as the electric motor it is attached to continues to run. The losses of the starter consist of resistive heating. Data has been located from one manufacturer regarding power losses from motor starters. No rejected heat uncertainty

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information is available form this manufacturer. It is necessary to test the losses of the motor starters. Transformer Current Limiting Inductor 240 VAC 10 kVA

Test Leads

Starter Load

Wattmeter 15:1

CT

CT

Balanced Short

Figure 4: Apparatus for Testing Motor Starters

In order to perform this test, the circuit of Figure 4 will be used. This circuit is similar to that of Figure 3. The circuit leading up to the starter is three phase. It is shown as single phase in the illustration so as not to clutter the diagram. As in Figure 3, the two wattmeter method of measuring power will be used. Three CTs will be used to step up the transformer secondary line current to as much as 2000 amp. Three identical CTs will be placed on the starter side to monitor the current. This will require four additional CTs with an added total expense of $600. Through proper calibration, the goal of the apparatus and experimental design is to achieve a measurements uncertainty no greater than ±10%. To be tested will be NEMA types 1 and 3 combination motor starters. We have received a type 1 starter from the General Electric Company and we will purchase types 1 and 3 starters from another company. This equipment is listed in a later section of this report. The testing of any starter is limited to 2000 amp. The purchase of the CTs is within the project budget. Bus Bars: Bus bars are used to convey electric current through the motor control center. The bus bar can be constructed either from copper or aluminum. The bus bar has a large cross sectional area to reduce the electrical resistance per unit length of conductor. The power losses of the bar are still subject to skin effect and enclosure. The bus bars run from the feeder lines to the individual equipment housed in the motor control center. While power loss values per unit length have been found for copper conductors, the best way to approach the power losses is through calculation. As with cables, good analytical models of the bus bar are available. Some of these are found in the Anders book mentioned in the section on Cables and Cable Trays. Another is ANSI/IEEE Std. C37.23 which treats isolated phase buses. The plan is to develop tables of losses for the buses on a per unit length basis and to also estimate the total length of bus found in a motor control center.

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Space Heaters: The purpose of a space heater is to eliminate moisture or the keep equipment fluids from becoming too viscous. The heater has a nameplate with the watt losses specified. The plan is to test a few of these devices with the apparatus of Figure 1. If the devices deliver the power claimed on the nameplate, then no further testing will be performed. If the nameplate value is not an accurate representation of the total power losses, then additional testing will have to be performed. Auxiliary Compartments for Relays and Instruments: These compartments are used in switchgear for housing relays and instruments. Total losses in these compartments depend on the number of relays and instruments in these compartments. Since these losses are much smaller in comparison to losses in the rest of the switchgear, instead of providing losses for individual relays and meters the manufacturers give loss for the whole compartment for typical configurations. However, it is not clear if these values are actually measured or estimated. Owing to the great variations in what might occupy an auxiliary compartment, the plan is to collect and average manufacturer information regarding the losses of auxiliary compartments. Adjustable Speed Drives: Adjustable speed drives were covered in a previous section. Enclosure: The magnetic field generated by the current flowing in different equipment creates eddy currents in the enclosure in which the equipment is placed. For example, the current flowing in the circuit breaker would induce eddy current in the metal cabinet in which the breaker is mounted. These eddy current losses could be substantial. In fact one of the manufacturers reported losses in the enclosure to be equal to that in the breaker itself. Other manufacturers did not provide any information on the effect of enclosures. At this stage we are not sure of the level of losses in the enclosure. We feel that the values provided by one manufacturer more of less ad hoc values. Thus, we plan to test the effect of enclosure. The approach would be to determine losses in the circuit breaker without an enclosure and then the same test with the enclosure. Difference in the two values would give losses due to enclosure. This test can be repeated for different type of enclosures to get a better feel of this effect. We don't expect to obtain exact values of losses in enclosures of different type of switchgear equipment. However, these tests will provide a better judgment on the effects of enclosure. At the least, we will be able to establish the magnitude of these losses in relation to losses in the equipment. In other words, we will be able to corroborate or refute one manufacturer's claim on losses in the enclosure.

References NEMA ICS 1-1993 Industrial Control and Systems – General Requirements. NEMA ICS 2-1993 Industrial Control Devices – Controllers and Assemblies. NEMA ICS 2 – 1996 PART 8: Industrial Control and Systems Controllers, Contactors, and Over-load Rlays Rated Not More Than 2000 Volts AC or 750 Volts DC – Part 8 Disconnect Devices for Use in Industrial Control Equipment.

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NEMA ICS 2.1 – 1990 Devices for Motor Service – A Guide for Understanding the Differences. NEMA ICS 2.3-1995 Instructions for the Handling, Installation, Operation, and Maintenance of Motor Control Centers Rated Not More Than 600 Volts. NEMA ICS 3-1988 (R1993) Industrial Systems. ANSI/IEEE C37.23 – 1987 (1991) Guide for Metal-Enclosed Bus and Calculating Losses in Isolated-Phase Bus.

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Medium Voltage and DC Switchgear Switchgear is made up of several electrical sub-components, each of which contributes to the rejected heat. According to IEEE C37.20.2, the term switchgear denotes a general term covering switching and interrupting devices and their combination with associated control, metering, protective, and regulating devices; also assemblies of these devices with associated interconnections, accessories, and supporting structures used primarily in connection with the generation, transmission, and conversion of electric power. A switchgear assembly is a general term referring to metal-enclosed switchgear, metal-enclosed bus, and control switchboards. The switchgear described by standards C37.20.1 to C37.20.3 are all specific cases of metal-enclosed switchgear. According to C37.21, a control switchboard is a type of switchboard including control, instrumentation, metering, protective (relays) or regulating equipment for remotely controlling other equipment. Control switchboards do not include the primary power switching devices or their connections. Metal-clad switchgear have voltage levels which range from 5 kV to 38 kV while station type cubical switchgear range in voltage levels from 15.5 kV to 72.5 kV. Since the voltage levels for medium voltage switchgear range from 5 kV to 15 kV, both of these types of switchgear need to be examined.

Review of Environmental Heat Gains Standards From a review of standards, it is not clear if there is one procedure for determining the heat loss. From C37.09, it is stated that the dc resistance of the current-carrying circuit from terminal to terminal of each pole unit in the close position shall be measured with at least 100 A flowing in the circuit and shall not exceed the limit set for the rating of the breaker by the manufacturer. In order to quantify the heat dissipated by the switchgear, it is necessary to include the heat lost from all of the various parts and accessories of the switchgear. DC switchgear is covered by IEEE C37.20.1 and heat loss measurements are not specified by the standard.

Equipment Heat Loss No standard addresses switchgear heat loss, however, some manufacturer web sites have been found which have power loss values.

Measurement Uncertainty No information on measurement uncertainty applied to heat loss from switchgear has been found.

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Manufacturers A list of switchgear manufacturers was assembled and a survey on equipment heat losses was performed through e-mail and through examination of company web sites. Some of the manufacturers responded to the e-mail and loss data were found on some company web sites. Table 9 contains this information.

Information Deficiencies Those manufacturers who listed heat loss from switchgear in a catalog, a menu approach was taken. The deficiency pertaining to the information is first how to subdivide the equipment, uncertainty of loss numbers, and loss number validity.

Test Plan The plan of representing information regarding the power losses from Medium Voltage and DC Switchgear is to address the heat loss from the individual parts. Each of those parts will be mentioned here. Medium Voltage and DC Breakers: These components were discussed in the section on circuit breakers. Bus Bars: Bus bars were discussed in the section on motor control centers. Control Power Transformers: Control Power Transformers are used in medium voltage switchgear to provide low voltage for instruments and other control equipment in the switchgear. These are standard power transformers for which sufficient data are available. Hence, the procedure of the test plan is to gather loss information regarding these devices by contacting manufacturers. Potential Transformers: Potential transformers are used in conjunction with voltage measurements in medium voltage switchgear. Potential transformers are very widely used in power industry and significant information on losses in them is available. Therefore, we haven't planned any tests for potential transformers. The procedure of the test plan is to gather loss information regarding these devices by contacting manufacturers. Current Transformers: Current transformers are used in conjunction with current measurements of very high magnitude. Significant information on losses in current transformers is available and thus they will not be tested with the exception of the two CTs purchased for the test apparatus. Auxiliary Compartments for Relays and Instruments: These components were discussed in the section on motor control centers. Space Heaters: These devices were discussed in the section on motor control centers.

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Enclosure: These components were discussed in the section on motor control centers.

References IEEE C37.09 – 1999, Test Procedure for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis. IEEE C37.20.1 – 1993, Standard for Metal-Enclosed Low-Voltage Power Circuit Breaker Switchgear. IEEE C37-20.2 – 1993, Standard for Metal-Clad and Station-Type Cubicle Switchgear. ANSI C37.20.3 –1999, Metal - Enclosed Interrupter Switchgear. ANSI/IEEE C37.21 – 1985 (R1998), Standard for Control Switchboards. NEMA SG 5 – 1995, Power Switchgear Assemblies. IEEE C37.100 – 1992, Standard Definitions for Power Switchgear.

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Panelboards Standards relevant to panelboards are listed at the end of this section. According to NEMA PB 1, a panelboard is defined as “a single panel or group of panel units designed for assembly in the form of a single panel, including buses, and with or without switches or automatic overcurrent protective devices, or both, for the control of light, heat or power circuits designed to be placed in a cabinet or enclosure accessible only from front.” Panelboards operate at 600 V or less with a 1600 or less amp mains and 1200 amp or less branch circuits. The panelboards under consideration exclude the familiar residential variety.

Review of Environmental Heat Gains Standards The standards do not discuss heat loss. In order to estimate the heat loss of these devices, a closer look has to be taken at the individual components that make up the panelboard.

Measurement Uncertainty No information regarding panelboard heat loss measurement uncertainty has been found.

Manufacturers A list of panelboard manufacturers was assembled and a survey on equipment heat losses was performed through e-mail and through examination of company web sites. One manufacturer responded to the e-mail and loss data were found in a catalog.

Information Deficiencies The manufacturer who listed heat loss from panelboards in a catalog did not provide the information as to what was included with the panelboard. The deficiency pertaining to the information is first how to subdivide the equipment, verifying loss numbers, and loss number uncertainty. Some measurement of component losses will have to be performed.

Test Plan The plan of representing information regarding the power losses from panelboards is to address the heat loss from the individual parts. Each of those parts will be mentioned here. Low Voltage Circuit Breakers: Power losses from these devices were addressed in the section on circuit breakers. Bus Bars: Bus bars were discussed in the section on motor control centers. Enclosure: The losses created by the equipment enclosure have been discussed in the section on motor control centers.

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References NEMA PB 1 – 1995, Panelboards. NEMA PB 1.1 – 1996, Instructions for the Safe Installation, Operation, and Maintenance of Panelboards. UL 67 – 1993, Panelboards.

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Unit Substations The unit substation consists of a power transformer, buses, enclosure, and breakers among other equipment. The substation is usually located with other equipment such as motor control centers or switchgear. The bulk of the substation losses is contributed by the transformer.

Review of Environmental Heat Gains Standards No standards were found which discussed heat loss from the unit substation.

Heat Losses No information on the heat losses of unit substations has been found. However, power loss information from several of the components of unit substations is known.

Measurement Uncertainty No information regarding unit substation heat loss measurement uncertainty has been found.

Manufacturers No list of unit substation manufacturers was compiled since the bulk of the losses is from the transformer and since the approach in this work is to estimate the heat loss through the rejected heat of the individual components. No manufacturers were contacted regarding the power loss of unit substations.

Information Deficiencies The information deficiency is the loss data in a format it can be used by the design engineer. Likewise, the quality of the information varies from good for transformers to uncertain for circuit breakers.

Test Plan The plan of representing information regarding the power losses from unit substations is to address the heat loss from the individual parts. Each of those parts will be mentioned here. Low Voltage Circuit Breakers: Power losses from these devices were addressed in the section on circuit breakers. Bus Bars: Bus bars were discussed in the section on motor control centers. Auxiliary Compartments for Relays and Instruments: Information regarding heat losses from these devices was presented in the section on motor control centers.

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Space Heaters: Information regarding heat losses from these devices was presented in the section on motor control centers. Unit Substation Transformers: Power losses from unit substation transformers were covered in the section on transformers. Enclosure: The losses created by the equipment enclosure have been discussed in the section on motor control centers.

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Category III Category III is made up of manual transfer switches. This device is discussed here. In order to accumulate the necessary information, a series of tests need to be performed. For each size and make, it is hoped that five independent tests of loss determination can be made.

Manual Transfer Switches Applicable standards for non-automatic (manual) transfer switches are shown in the references at the end of this section. NEMA ICS 10 defines a non-automatic transfer switch as “a device, operated by direct manpower or electrical remote manual control, for transferring one or more load conductor connections from one power source to another.” The switches are rated 600 V or less and are used in single-phase or polyphase application.

Review of Environmental Heat Gains Standards While NEMA ICS 10 specifies the design tests for transfer switches, the standard also specifies that the transfer switches covered by the standards must also pass the production tests specified in UL 1008. The UL 1008 production tests for transfer switches do not include a heat loss measurement. In the design test specified by UL 1008, no direct measurement of heat loss is made. However, a possible way of determining the transfer switches heat loss is through the resistance test used to determine temperature rise of the conductors in the transfer switches. The resistance of the circuit is measured at a known temperature. By measuring the resistance of the circuit after carrying rated current, the temperature rise of the conductor can be determined. There is an alternate way of measuring the temperature rise through the use of thermocouples, thus, it cannot be expected that all manufacturers would follow only the resistance method of determining the temperature rise. The design test of NEMA ICS 10 specifies that the temperature rise is to be determined, but does not specify how the temperature rise is to be determined. The thrust of this discussion is that a possibility exists that design test data may be available to predict the transfer switches heat loss.

Measurement Uncertainty No information regarding power loss measurement uncertainty for transfer switches has been found.

Manufacturers Through the NEMA web site, no manufacturers of non-automatic transfer switches could be found. By using the search key word “transfer switch,” only manufacturers of automatic transfer switches could be found. We have found that Cutler-Hammer makes transfer switches of the non-automatic variety. In examining the web site of manufacturers of transfer switches, no loss information has been found. No survey was taken of transfer switch manufacturers.

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Information Deficiencies Since no standards could be found and no information could be found from manufacturers, transfer switches were placed in Category III.

Test Plan The transfer switch can be treated the same as a circuit breaker and the apparatus/method used to test a circuit breaker can be used here. The plan is to test as many as possible since no data has been found on the heat losses of these devices. Owing to the extent of the project budget, the purchase of these devices with project funds for testing purposes is not possible. It is necessary to rely on equipment donations and/or loans in order to conduct these tests.

References NEMA ICS 10 – 1999, Industrial Control and Systems, AC Transfer Switch Equipment. UL 1008 – 1996, Automatic Transfer Switches.

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Summary of Phase II Information The recommended ranges of equipment sizes to envelop the testing work in included in Table 7. The type, number, and sizes of equipment to be purchased for testing are also listed in Table 7. No equipment will be tested at a manufacturer’s factory. The type, number, and sizes of equipment to be tested at in-use locations as well as the location of each site is also contained in Table 7. Letters of equipment loaning, donation, and permission for testing are included in the Appendix. The test apparati to be used in the investigation together with the level of measurement uncertainty have been documented in the test plan. In regards to testing standards, all power equipment having applicable testing standards have been identified. In performing the heat loss measurements, it is not necessary to follow any testing standards since these are usually not addresses by the manufacturing standards. In the case of where the testing standards exist, the published data eliminates the need for further testing. In regard to data acquisition standards, those honored by the selected National Instruments hardware (in this case the 6024E data acquisition card and the SC-270 terminal board with cold junction compensation) and the software package LabVIEW published by National Instruments will be followed. A budget for the Phase II work is shown in Table 8. A time schedule for completion of the work is provided in Table 9. Table 10 lists all the equipment connected with this work. The first column lists the equipment type while the second column shows any sub-categories of equipment. The third column shows the source of the loss information such as manufacturer, testing of loaned equipment, and/or testing of purchased equipment. The fourth column shows the activity that connected with the equipment, which can be testing, calculating (such as bus bar losses), and/or assembling the tables for the final report. For any verification tests to be performed with the equipment, the test apparatus uncertainty is listed in column five. Column six contains either a GO or NO GO as far as the completion of the data gathering and loss verification testing is concerned. If column six contains a NO GO then an explanation is listed in the seventh column. These explanations consist of either “Wait Equipment” indicating the a discussion(s) is (are) being held on equipment loans or “No Equipment Source” indicating that there are currently no prospects of being able to borrow the equipment. Several pieces of equipment such as bus bars and low voltage circuit breakers are listed in Table 10 more than once. By considering the unique equipment items listed with a GO and NO GO in Table 10, it is seen that 75 % of the equipment contained in the TRP 1104 Work-statement is involved in the Phase II activity. For the 25 % of the equipment for which verification measurements are not planned, we will be able to collect and pool loss data from manufacturer web sites and catalogs for all equipment items with the exception of the manual transfer switch.

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Uncertainty of Results The testing apparati will be designed and calibrated so that the uncertainty of any measured test results is no greater than ±10%. In as many cases as the budget and the equipment donations permit, the testing will try to envelop or bracket the range of equipment specified in the TRP 1104 Work-statement. In the following explanation, the expectation of uncertainty of results will be addressed. Consider that there are two pieces of equipment from two manufacturers. Consider further that the equipment brackets the necessary range of equipment. Each piece of equipment is tested at a given load level and ambient condition. The measurements are averaged at either end of the equipment range. In addition to computing a mean, a standard deviation is also computed at each end of the range. Given the standard deviation at each end, the 95% confidence interval for the true mean value at either end can be expressed as µ ± t1,95σ / 2 where µ is the mean and σ is the standard deviation. The quantity t1,95 is the Student t value for a 95% confidence interval for the mean of two numbers. Now suppose each measurement has an uncertainty of ±10% or ±0.1 (expressed as a fraction). The uncertainty of the mean of each data point is ±

(± 0.1)2 + (± t1,95σ / 2)2

which shows that the uncertainty of a given data point cannot be determined in advance but only after the tests are performed. The uncertainty of the data is a product of the testing procedure. There are times when an experimenter can make the second term under the radical very small by including a large number of independent tests such as repeating a pressure or temperature measurement, say a hundred time or more. In this case, the designer of the experiment can state the uncertainty of the results ahead of time. For us, an additional independent measurement represents a test on another manufacturer’s device. We do not have the luxury of having a hundred devices of the same size to test! What is possible is to show how big or small the uncertainty of the data will be given a particular standard deviation. This allows one to appreciate how the standard deviation influences the result, but this is only an academic exercise. Suppose it were possible to organize many samples of a particular type and size of an equipment item from several manufacturers into a collection and it was also possible to randomly select items from this collection. Further suppose that the sample standard deviation remained the same as you drew 30 random samples from the collection. The uncertainty of the mean of this sample is

±

(± 0.1)2 + (± t 29,95σ / 30)2

where the ratio of the second terms under these last two radicals is

(t

(2) / (t1,95 (30) )) = (2.042 * 2 /(12.707 * 30)) 2 = 0.00011 which makes the second term small compared to the first term under the radical. This might be a good way to conduct the testing, however it would be hard to assemble a large collection of the same size product from many manufacturers owing to the expense. 2

29, 95

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If there were only five manufacturers of a given product and it was possible to test all of the products, then you would have a fairly good estimate of the mean value of the heat loss. Certainly, the uncertainty of this mean estimate can be reduced through further testing as shown above but the significant information is not the fine estimate of the mean value but rather the mean value and the spread of the data. If the data spread is small, then the mean is a representative number of the heat losses. If the data spread is large, then the engineer may want to use a heat loss value larger than the mean. The significance of this discussion is that the loss values going into the mean calculation should be as good as you can produce (± 10%). However, the significance of the mean heat loss value is as important as the spread of the data, i.e. the sample standard deviation. To arrive at a good estimate of the mean value and the standard deviation of the test data, the recommendation is that 75% or more of the products (of a given size and equipment type) available from different manufacturers be tested. The figure of 75% is arrived at through the consideration of the uncertainty of the sample mean. Suppose there are n manufacturers of a particular size device where n is greater than or equal to 5. This size requirement on n comes from the behavior of the Student t table. For degrees of freedom of 5 or more, the table entries do not change rapidly with degrees of freedom. Since tν,95 (where ν is the number of degrees of freedom) does not change rapidly with increases in ν and since the standard deviation is not that sensitive to additional sample, the uncertainty in the mean value for performing a test on 75% of the manufacturers would be u 75% = ±

(± 0.1)2 + (± υ 0.75n,95σ / (0.75n ))2 .

The uncertainty of the mean value obtained by testing all of the manufacturers would be

u100% = ±

(± 0.1)2 + (± υ n,95σ / n )2

.

If σ was very large compared to the measurement uncertainty of 10%, then the limiting value of the ratio u100%/u75% of these two uncertainties would be 0.75. If σ was very small compared to the measurement uncertainty, then the limiting value of the same ratio is 1.0. Thus, if only 75 % of the manufacturers were tested, then the uncertainty of the mean will be in the range from being the same as to 25 % larger than the mean obtained from testing all of the manufacturers.

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Electric Power Equipment to be Tested Testing Range 25 - 50 hp

Size to Test 25 & 50 hp

100 - 600 Amp

100, 400, 600 Amp

Inverters

20 - 30 kVA

Reactors

2 to 750 Amp

Adjustable Speed Drives Battery Chargers

Low Voltage Circuit Breakers

Number to Test 2

Number of Manufacturers 2

Equipment Source ---

3

2

---

20 & 30 kVA

2

2

---

2, 200, 750 Amp

3

2

Purchase

7412

2

1

Purchase

8800

800, 1600, 2000, 800 Amp/ 800 A frame 3200, 4000 Amp 2000 Amp/2000 A frame Frames

Medium Voltage Circuit Breaker

Equipment Cost

5 - 15 kV Current

5 and 15 kV

4

1

Loan/Site test

Combination Motor Starters

NEMA Type 1-3

Types 1 & 3

2

2

Donation/Purchase

2195

Space Heaters

Not Determined Two sizes

2

2

Purchase

100

TOTAL

Reactors: GE (Enclosed Units) 2A

Olsun Electric

Motor Starters: Cutler-Hammer

Low Voltage Circuit Breakers: General Electric (Spectra Line) (65k - AIC)

200 A 750 A TOTAL

155 690 2800 3645

2A 200 A 750 A TOTAL

570 1269 1928 3767

TOTAL REACTORS

$7,412

NEMA Type 1 NEMA Type 3 TOTAL

604 1,591 $2,195

800 A Frame 2000 A Frame TOTAL

2800 6000 $8,800

Table 7: Electric Power Equipment to be Tested

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Phase II Budget The expenses for Phase II are estimated here. The funds remaining in the TRP 1104 budget are sufficient to cover the test apparatus construction, personnel salaries, equipment purchase, and travel. Table 8 shows the how these funds will be used. Table 8 shows the estimated cost for acquiring the equipment or test articles for performing measurements.

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Phase II Time Schedule Phase II Time Schedule for Completion of Work Month July

August

September

October

November

December January

February

Activity Purchase components and build test apparatus Purchase equipment for testing Calibrate the test apparatus Send request for shipping loaned equipment Begin cable and bus loss calculations Begin testing purchased equipment Test loaned equipment Acquire and organize published loss information Continue cable and bus loss calculations Continue testing and calculations Teleconference with PMS to assess progress Begin work on Part B, Phase II report Conclude Part A, testing and calculations Continue work on Part B, Phase II report Transmit Part A Report Transmit current Part B Guide document to PMS Teleconference with PMS for first coordination meeting Continue work on Phase II report Continue work on Phase II report Incorporate comments from first review Continue work on Phase II, Part B Guide report Transmit draft of Phase II, Part B Guide to PMS Teleconference with PMS for second coordination meeting Incorporate comments from second review Deliver Phase II final report to TC 9.2

Table 9: Phase II Time Schedule

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Equipment Category Sub-Categories

Information Source

Actions

Verification GO/ Reason for NO GO Test NO GO Uncertainty

Transformers Unit Substation Power and Lighting Potential Control Power Current

Manufacturer Manufacturer Manufacturer Manufacturer Manufacturer + Purchase/Test

Assemble Tables Assemble Tables Assemble Tables Assemble Tables Assemble Tables

N/A N/A N/A N/A N/A

GO GO GO GO GO

Synchronous Induction DC

Manufacturer Manufacturer Manufacturer

Assemble Tables Assemble Tables Assemble Tables

N/A N/A N/A

GO GO GO

Cables and Cable Trays

Calculations

Study/Assem. Tables

N/A

GO

Adjustable Speed Drives

Manufacturer/Tests

Test/Assem. Tables

< 10%

GO

Batter Chargers

Manufacturer/Test

Test/Assem. Tables

751-3196 > > > > > ---------> > From: Warren N. White[SMTP:[email protected]] > > Reply To: [email protected] > > Sent: Wednesday, March 07, 2001 2:52 PM > > To: Kurtz, James W. > > Subject: equipment > > > > Jim: > > > > This is a follow up to our conversation on Wednesday, March 7. There > are > > two time frames I am working with. The first involves lining up > > equipment to test. My hope is that I can complete the location of > > equipment to test by the end of March. The second time frame involves > > receiving and completing the tests on the equipment. In this regard, I > > would prefer to complete all testing by the end of this coming summer. > > > > One constraint that I have to observe is that ASHRAE (organization > > funding the investigation) needs to be informed that equipment is > > available to be tested. A letter from TVA describing the equipment > that > > you will allow me to test will help here significantly. > > > > Should you have any other questions, please don't hesitate to call or > > e-mail. > > > > Thank you for your help and time! > > > > Warren White > > > > > > [email protected] Dr. Warren N. White, Associate Professor Mechanical and > > Nuclear Engineering Department 324 Durland Hall Kansas State University > > Manhattan, KS 66506-5106 USA Voice: (785) 532-2615 FAX: (785) 532-7057 > > > [email protected] > Dr. Warren N. White, Associate Professor > Mechanical and Nuclear Engineering Department > 324 Durland Hall > Kansas State University > Manhattan, KS 66506-5106 > USA > Voice: (785) 532-2615 > FAX: (785) 532-7057

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E-Mail Regarding Battery Chargers from TVA

Attach is a list of equipment we have been asked to help provide. This is all indoor type equipment. Please check at your plant sites to see if they have any surplus. Ken, Mr. White said he might be able to use one of the towmotor chargers. going to call you.

He is

Thanks BOB PHILLIPS 423-751-6753 [email protected] > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >

---------From: Higley, Arthur F. Sent: Wednesday, March 07, 2001 1:21 PM To: Phillips, Bobby L.; Allen, Kenneth W. Subject: FW: equipment list Revised list, can we help? ---------From: Pinkleton, Hugh M. Sent: Wednesday, March 07, 2001 10:11 AM To: Higley, Arthur F.; 'Bob Kleeb' Cc: Kurtz, James W. Subject: FW: equipment list BOB AND ART SEE E-MAIL BELOW FROM JIM KURTZ CONCERNING EQUIPMENT FOR KANSAS STATE. LET ME KNOW IF WE HAVE ANYTHING AVAILABLE. THANKS ---------From: Kurtz, James W. Sent: Wednesday, March 07, 2001 10:05 AM To: Pinkleton, Hugh M. Subject: FW: equipment list Hugh, I talked to Dr. White about the restrictive listed as asked if he could use other equipment. He said he could use other equipment. For example: He can use battery chargers up to 250 VDC, any rating. Inverters of almost any size Any circuit breaker up to 15KV (accept small less that 200 amps) If you find something and want to know if he can use the equipment then please contact him. He needs a listing of equipment before the end of the month.

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TRP – 1104 Heat Gains from Electrical and Control Equipment in Industrial Plants

James W. Kurtz, Manager Substation Project's Protection & Control 751-3196

---------From: Hall, David Sent: Friday, February 16, 2001 12:13 PM To: Kurtz, James W. Cc: Denney, Roy C. Subject: FW: equipment list Please review this list for potential items that we could loan them for testing, get vendors to give them, etc. ---------From: Warren N. White[SMTP:[email protected]] Reply To: [email protected] Sent: Thursday, February 15, 2001 5:37 PM To: Hall, David Subject: equipment list David:



Thanks for taking the time to discuss my measurement needs on the phone. The equipment list is attached and it is in pdf format. look forward to hearing from you again and I hope we can work out a suitable deal regarding the equipment.

I

Sincerely, Warren White

[email protected] Dr. Warren N. White, Associate Professor Mechanical and Nuclear Engineering Department 324 Durland Hall Kansas State University Manhattan, KS 66506-5106 USA Voice: (785) 532-2615 FAX: (785) 532-7057

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ASHRAE Research Project 1104-TRP PHASE II PART A: TEST REPORT Warren N. White, Ph.D. Department of Mechanical and Nuclear Engineering and Anil Pahwa, Ph.D. Department of Electrical and Computer Engineering

Kansas State University June 6, 2003

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Table of Contents Page List of Figures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii List of Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

v

Introduction and Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

Phase II Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

Medium Voltage Switchgear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6

Cables and Cable Trays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9

Cable Trays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9

Loss Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9

. Spreadsheet for Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Examples and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Uncertainty in Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Limits on Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Motor Control Centers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Motor Starters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Motor Starter Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Inverters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Battery Chargers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Low Voltage Breakers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Unit Substations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

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Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Adjustable Speed Drives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Medium Voltage Breakers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Appendix 1 Raw Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

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List of Figures FIGURES

Page

Figure 1: Typical Arrangement of Cables in a Cable Tray. . . . . . . . . . . . . . . . . . . 10 Figure 2: Snap Shot of Spreadsheet for Calculation of Losses in Cable Trays. . . . . . . . . 13 Figure 3: Extreme Range of Losses for 600V Cable Trays with 40% Packing Factor and 60% Diversity Factor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Figure 4: Extreme Range of Losses for 5 kV Cable Trays with 40% Packing Factor and 60% Diversity Factor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Figure 5: Extreme Range of Losses for 15 kV Cable Trays with 40% Packing Factor and 60% Diversity Factor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Figure 6: Circuit for Measuring Heat Loss of Combination Motor Starters . . . . . . . . . . 21 Figure 7: NEMA 0 Power Losses with Enclosure . . . . . . . . . . . . . . . . . . . . . . . 22 Figure 8: NEMA 0 Power Losses without Enclosure . . . . . . . . . . . . . . . . . . . . . 23 Figure 9: Power Losses of NEMA 1 Combination Starter with Disconnect with Enclosure. . 23 Figure 10: Power Losses of NEMA 3 Combination Starter with Disconnect with Enclosure . 24 Figure 10a: Power Losses of NEMA 2 Combination Starter with Disconnect with Enclosure Figure 11: Inverter Losses as a Function of Load. . . . . . . . . . . . . . . . . . . . . . . . 28 Figure 12: 130 Volt DC Battery Charger Load and No Load Losses. . . . . . . . . . . . . . 29 Figure 13: 260 Volt DC Battery Charger Load and No Load Losses. . . . . . . . . . . . . . 29 Figure 14: 60 Amp Frame Circuit Breaker Losses. . . . . . . . . . . . . . . . . . . . . . . . 31 Figure 15: 60 Amp Frame Breaker Losses Without Enclosure . . . . . . . . . . . . . . . . . 32 Figure 16: Figure 16: 100 Amp Breaker Power Losses in Enclosure . . . . . . . . . . . . . . 32 Figure 17: 100 Amp Breaker Heat Loss Without Enclosure . . . . . . . . . . . . . . . . . . 33 Figure 18: 200 Amp Breaker Power Loss With Enclosure (250 Amp Frame) . . . . . . . . . 33 Figure 19: 200 Amp Breaker Heat Loss Without Enclosure (250 Amp Frame) . . . . . . . . 34

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Figure 20: 800 Amp Breaker Heat Loss Without Enclosure . . . . . . . . . . . . . . . . . . 34 Figure 21: 800 Amp Breaker Heat Loss With Enclosure . . . . . . . . . . . . . . . . . . . . 35 Figure 22: 1200 Amp Breaker Heat Loss Without Enclosure. . . . . . . . . . . . . . . . . . 35 Figure 23: 1200 Amp Breaker Heat Loss With Enclosure . . . . . . . . . . . . . . . . . . . 36 Figure 24: Comparison of Measured and Reported Breaker Losses . . . . . . . . . . . . . . 37 Figure 25: Unit Substation Power Loss Calculation Spreadsheet. . . . . . . . . . . . . . . . 41 Figure 26: Reactor Losses - 240 Volt Applications . . . . . . . . . . . . . . . . . . . . . . . 44 Figure 27: Reactor Losses - 480 Volt Applications . . . . . . . . . . . . . . . . . . . . . . . 44 Figure 28: Reactor Losses - 600 Volt Applications . . . . . . . . . . . . . . . . . . . . . . . 45 Figure 29: 230 Volt Drive Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Figure 30: 460 Volt Drive Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Figure 31: 600 Volt Drive Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Figure 32: Drive Losses as a Function of Current . . . . . . . . . . . . . . . . . . . . . . . 48 Figure 33: Thermal Chamber Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Figure 34: 1200 Amp, Medium Voltage Breaker Losses. . . . . . . . . . . . . . . . . . . . 51

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List of Tables TABLES

Page

Table1: General Purpose Dry Type Units Having an 80 oC Temperature Rise . . . . . . . .

2

Table 2: General Purpose Dry Type Units Having a 115 oC Temperature Rise . . . . . . .

2

Table 3: General Purpose Dry Type Units Having a 150 oC Temperature Rise . . . . . . .

3

Table 4: Nonlinear Dry Type Units Having an 80 oC Temperature Rise . . . . . . . . . . .

3

Table 5: Nonlinear Dry Type Units Having a 115 oC Temperature Rise . . . . . . . . . . .

4

Table 6: Nonlinear Dry Type Units Having a 150 oC Temperature Rise . . . . . . . . . . .

4

Table 7: General Purpose Liquid Filled Units . . . . . . . . . . . . . . . . . . . . . . . . .

4

Table 8: NEMA TP1 Efficiencies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Table 9: Manufacturera A and D Medium Voltage Switchgear Equipment Power Losses. . . 7 Table 10: Manufacturer E Medium Voltage Switchgear Equipment Power Losses. . . . . . 8 Table 11: Losses in Cable Trays for 600 V Cables . . . . . . . . . . . . . . . . . . . . . . . 15 Table 12: Losses in Cable Trays for 5 kV Cables . . . . . . . . . . . . . . . . . . . . . . . 16 Table 13: Losses in Cable Trays for 15 kV Cables . . . . . . . . . . . . . . . . . . . . . . . 17 Table 14: Starter Watts Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Table 15: Comparison of Motor Starter Losses . . . . . . . . . . . . . . . . . . . . . . . . . 25 Table 16: Motor Starter Coil Losses and Overall Losses . . . . . . . . . . . . . . . . . . . . 26 Table 17: Motor Control Center Bus Losses . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Table 18: Inverter Losses as a Function of Load . . . . . . . . . . . . . . . . . . . . . . . . 27 Table 19: Circuit Breaker Heat Loss at Rated Frame Current . . . . . . . . . . . . . . . . . 30 Table 20: CT Circuits Used to Test Low Voltage Breakers . . . . . . . . . . . . . . . . . . 31 Table 21: Coefficients for Breaker Loss Calculation . . . . . . . . . . . . . . . . . . . . . . 37

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Table 22: Nominal Efficiencies for General Purpose Motors. . . . . . . . . . . . . . . . . . 38 Table 23: Arrangement of Motor Averages. . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Table 24: Reactor Power Losses at Rated Current . . . . . . . . . . . . . . . . . . . . . . . 42 Table 25: Regression Constants for Drive Losses. . . . . . . . . . . . . . . . . . . . . . . . 48 Table 26: Adjustable Speed Drive Losses – Tested Values . . . . . . . . . . . . . . . . . . 50

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Introduction and Executive Summary The Phase II report for “Heat Gain from Electrical and Control Equipment in Industrial Plants” is divided into two separate documents being Part A and Part B. Part A of the report, which this document constitutes, consists of a compilation of heat loss data and a documentation of the testing methods used to measure the heat loss of specific power equipment items. The Part B document contains heat loss information together with instructions on using the heat loss information in determining the heat load. The Part A document contains the heat loss information accumulated through the data gathering methods specified in the Phase I report of this investigation. The data gathering methods consist of both compiling industrial catalog data when it was believed that this information is representative of actual losses as well laboratory tests where a sample of certain equipment items were tested to verify published loss information. The deciding factor between testing and simply accepting catalog data is the availability and adherence to published testing and/or manufacturing standards. In some cases there is both an absence of standards and an availability of only very crude estimates (if at all) of heat loss information. These three scenarios represent the spectrum of the information presented in this document. Some of the presented results consist of graphs and/or tables of how the heat loss values vary as a function of load. In addition to the graphical and tabulated representation of losses, formulae are also presented for the calculation of losses since this might prove the most convenient for the engineer. The means of using the data for calculations is contained in the Part B portion of this report. In the situations where it was necessary to make equipment tests, the methods by which the tests were performed are documented. The order in which the data is presented consists of the order in which the data collection for the various equipment types was performed. This order is different than the organization of equipment coverage in the Phase I document where the three categories defined in the RP 1104 work statement were used to organize the discussion of heat losses.

Phase II –Test Results Transformers No load, full load, and total heat loss data for transformers were obtained from three different manufacturers. When more than one set of loss values was available for the same size unit, both an average and a standard deviation was computed. If only one set of loss values was available, then the standard deviation is reported as N/A. The results of the data collection are shown in Tables 1 through 7. Tables 1 through 3 present information concerning general purpose dry type units. Tables 4 through 6 pertain to dry type, nonlinear units. Table 7 contains data concerning liquid filled units. In each table involving the nonlinear units, losses are shown for units having a K factor of 4 and 13. Since only one value was found for each size of nonlinear unit, no average heat loss or standard deviation is reported. The same is true for the liquid immersed Phase II – Part A

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units. The K Factor reported in Tables 4 through 6 is defined as the ratio between the additional losses due to harmonics and the eddy losses at 60 Hz. It is used to specify transformers for nonlinear loads.

Table1: General Purpose Dry Type Units Having an 80 oC Temperature Rise

Table 2: General Purpose Dry Type Units Having a 115 oC Temperature Rise

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Table 3: General Purpose Dry Type Units Having a 150 oC Temperature Rise

Table 4: Nonlinear Dry Type Units Having an 80 oC Temperature Rise

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Table 5: Nonlinear Dry Type Units Having a 115 oC Temperature Rise

Table 6: Nonlinear Dry Type Units Having a 150 oC Temperature Rise

Table 7: General Purpose Liquid Filled Units

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KVA

15 30 45 75 112.5 150 225 300 500 750 1000 1500 2000 2500

Dry Type Low Voltage 75 oC – 35% Load 97.0 97.5 97.7 98.0 98.2 98.3 98.5 98.6 98.7 98.8 98.9 -------------

Dry Type Medium Voltage 75 oC – 50%

Liquid Immersed Medium Voltage 85 oC – 50%

96.8 97.3 97.6 97.9 98.1 98.2 98.4 98.5 98.7 98.8 98.9 99.0 99.0 99.1

98.0 98.3 98.5 98.7 98.8 98.9 99.0 99.0 99.1 99.2 99.2 99.3 99.4 99.4

Table 8: NEMA TP1 Efficiencies Table 8 shows NEMA Class 1 transformer efficiencies. These efficiency values represent lower bounds on the peak efficiency that a transformer must meet or surpass before is may be given the Class 1 designation. For dry type, low voltage units, the peak efficiency usually occurs at 35 % of full load while for medium voltage, dry type units and medium voltage liquid immersed units, the peak efficiency usually occurs at 50 % of full load. Using the idea of peak efficiency, values of load and no load losses can be determined. From the definition of efficiency, we have pf ⋅ kVA ⋅ 1000 ⋅ lf η o = 100( )% (2) pf ⋅ kVA ⋅ 1000 ⋅ lf + NL + Load Loss ⋅ lf 2 where ηo is the efficiency in percent, lf is the load fraction, pf is the power factor, NL is the no load loss, Load Loss is the full load loss, and the units of both the numerator and denominator are power. By setting the efficiency expression for a given unit type, kVA, and power factor equal to the corresponding value obtained from Table 8 for the appropriate load fraction, i.e 0.35 or 0.5, we get one equation for the two unknowns of NL and Load Loss. Since the peak of the dη efficiency vs. lf curve occurs at the given value, i.e. 0.35 or 0.5, the slope of the curve, , is d (lf ) zero at this point and relation provides another equation for the two unknown losses. Solving the two derived equations for the two unknown losses produces η   1 − o  ⋅ pf ⋅ kVA ⋅ 1000  100  Load Loss = (3) ηo 2lf ⋅ 100 Phase II – Part A

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and  100  (4) NL = pf ⋅ kVA ⋅ 1000 ⋅ lf ⋅  − 1 − lf 2 ⋅ (Load Loss ) η  o  where ηo comes from Table 8 and lf is either 0.35 or 0.5 depending if a low or medium voltage unit, respectively, is under consideration.

Given the full capability of the of the unit in kVA, then the losses are approximately 2  T + T REF   watts transformer total losses = NL + (Load Loss )(lf )  K o  T C + 75   K

(5)

where TK is 234.5o C for copper windings or 225o C for aluminum windings, and TREF is the reference temperature, and lf is the load fraction. Only the dry type units require temperature correction.

Medium Voltage Switchgear Owing to the unavailability and expense of medium voltage switchgear, no testing was possible within the scope of this project. While there are proprietary models and software packages used by manufacturers for estimating the heat loss of these devices, the only devices uncovered in this effort were simplified models for determining rejected heat. Likewise, some manufacturers publish some general tables for predicting the heat loss. Tables 9 and 10 list the data obtained from three different manufacturers. Although this information was obtained from the latest versions of manufacturers’ documents, some of the information still matches data contained in the 1985 paper of McDonald and Hickok listed in the Phase I report.

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Manufacturer

A

D

Equipment

Watts Loss

1200 Amp Breaker 2000 Amp Breaker 3000 Amp Breaker 600 Amp Unfused Switch 1200 Amp Unfused Switch 100 Amp CL Fuse 1200 Amp Breaker 2000 Amp Breaker 3000 Amp Breaker 3500/4000 Amp Breaker 2-1200 Amp Beakers - Stacked 1-1200 Amp & 1-2000 Amp Breker - Stacked Each Vertical Section with Simple Relaying & Control Each Vertical Section with Simple Relaying & Control Each PT Rollout Each CPT rollout up to 15kVA Equipment Heaters if Supplied

600 1400 2000 500 750 840 675 1335 2030 2765 1220 1880 150 330 50 600 300

Table 9: Manufacturers A & D Medium Voltage Switchgear Equipment Power Losses

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Equipment

Watts Loss

Breakers 1200 Amp Breaker 2000 Amp Breaker

413 845

CTs – Sets of three 600:5 – Turns Ratio 1200:5 – Turns Ratio 2000:5 – Turns Ratio 3000:5 – Turns Ratio 4000:5 – Turns Ratio Auxiliary Frames

23 45 75 113 150

Each Frame

150

Main Bus Per Frame 1200 Amp 2000 Amp 3000 Amp

108 180 115

4000 Amp

204

Control Power Transformers CPT – 5 kVA, 1 Phase CPT – 105 kVA, 1 Phase CPT – 15 kVA, 1 Phase CPT – 25 kVA, 1 Phase CPT – 50 kVA, 1 phase CPT – 45 kVA, 3 Phase CPT – 75 kVA, 3 Phase Heaters

60 115 175 295 450 520 885

150 Watt 300 Watt heater at 75 Watts

150 75

Table 10: Manufacturer E Medium Voltage Switchgear Equipment Power Losses According to manufacturer E, the influence of the enclosure is to double the heat losses. Phase II – Part A

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The information from manufacturer E comes in the form of a spreadsheet. A copy of this spreadsheet has not been included in this document since it is possible to identify the manufacturer. Using the information provided by manufacturer E, eliminating that information pertaining to old technology equipment (available only as replacement parts), and incorporating the information from the other two manufacturers, provides a new spreadsheet useful to calculating the rejected heat from medium voltage switchgear. This spreadsheet is contained in Part B of this report. No accuracy information is available on any of this data.

Cables and Cable Trays Cable Trays In industrial facilities, power cables are routed in cable trays, which come in 6 to 30 inch widths in 6-inch increments. Trays will have some eddy current losses, but they are extremely small and, thus, are neglected. The bulk of the cable losses are the resistive losses in the main conductors. Thus, if the number of cables and their physical arrangement in the trays are known, total losses per foot at the room temperature of that specific cable tray can be computed. The main difficulty arises due to the temperature of the cables in the trays and since resistance of the conductors increase with temperature, the heat generated also increases. The temperature of the cables depends on loading of the cables, size of cables, and packing of the cables. There are almost infinite combinations of these variables. However, normal industry practice and some simplifying assumptions make the task tractable.

Anders (1997) discusses a method for calculating the steady-state temperature of cables in opentop trays. This method is based on a paper by Harshe and Black (1994) and it removes the conservatism in the thermal models used in IEEE Std 835-1994 for generating the ampacity tables. These tables are based on complete packing of the tray by cables and maximum current loading of the cables. The method of this paper allows partial packing of the tray and allows inclusion of load diversity. Details of the method are provided in the next section. Loss Calculation The model of Harshe and Black (1994) assumes that the current in all the cables in the bundle is known. The model has two options for heating within the tray. One of the options assumes that cables generate heat uniformly across the cable tray and the second option assumes that the heavily loaded cables are located at the cable tray centerline and the lightly loaded cables are placed above and below the centerline. The uniform loading option is used for calculations presented in this report.

Figure 1 shows a typical arrangement of cables in a tray. For a bundle of n identical three-phase cables carrying a current I per phase with a resistance R per phase, heat balance equation considering flow of heat from center of the bundle to the surface and then from surface to the air by radiation and convection is given by

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This equation assumes that the cables are located indoors in still air and the heat flow is taking place above and below the tray with no sideways heat flow. The equation presented by Harsh and Black (1994) considers cables of different sizes and numbers in a cable bundle. The calculations become very complex for a general case; therefore, we have modified it for identical cables. The variables and symbols used in this equation are Wtotal - Watts generated within the cable bundle per unit length (W/m) hs - Convective heat transfer coefficient (W/m2-oC) As - Surface area of the cable bundle per unit length (m) θ s - Surface temperature of the cable bundle (oC) θ amb - Ambient air temperature (oC) σ - Stephan-Boltzmann constant (W/m2-K4) ε - Emissivity of the cable bundle surface

H

w Figure 1: Typical Arrangement of Cables in a Cable Tray In general, the temperature at the bottom surface of the bundle will be different from the top surface, but as a simplification they are considered to be the same. However, the convective heat transfer coefficient for the top and the bottom are different. The coefficient for the bottom surface is 0.25

  gβ  hB = 0.248 k air w  ν 2 (θ s − θ amb )    and the coefficient for the top surface depends on the value of the Rayleigh Number (Ra): − 0.25

hT = 0.496 k air w

Phase II – Part A

−0.25

 gβ    ν 2 (θ s − θ amb )   

10

0.25

for 105 < Ra