NETA Handbook Series I, Online Diagnostics Vol 1-PDF.pdf

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On-Line Diagnostics Handbook Volume 1

Published by InterNational Electrical Testing Association

THE “GO-TO” STANDARDS FOR ELECTRICAL SAFETY AND RELIABILITY

How Do You ensure Safety and Reliability?

The ANSI/NETA Standards for Acceptance and Maintenance Testing Specifications for Electrical Power Equipment and Systems!

Hire a NETA Accredited Company! ANSI/NETA MTS-2011 - New Edition This standard should always be referenced when writing maintenance specifications or performing routine testing on electrical power systems.

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ANSI/NETA ATS-2009

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STANDARD FOR

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On-Line Diagnostics Handbook Volume 1

Table of Contents Elements of a Comprehensive Power Quality Audit: A Case Study ................................1 Frank P. DeCesaro, P.E., Thomas M. Blooming, P.E., Jerry R. Murphy, P.E., and Dan K. Walsh, P.E.

Partial Discharge — 101 Unsolved Mysteries —Part One ..............................................7 Gabe Paoletti, P.E.

Predictive Mechanical and Electrical Inspection Utilizing Ultrasonic Monitoring Technology ............................................................10 Dwayne Bateman

Understanding and Analyzing Event Report Information from Transformer Differential Relays ......................................................................13 David Costello

Partial Discharge — 102 Unsolved Mysteries —Part Two ............................................17 Gabe Paoletti, P.E.

Partial Discharge — 103 Unsolved Mysteries —Part Three ..........................................21 Gabe Paoletti, P.E.

Software for Collection and Analysis of Digital Fault Records ....................................24 Amir and Maria Makki and A.T. Giuliante

Eastman Chemical Company Motor Analysis… Stepping out of the Box .....................28 Tom Whittemore, Jr., Paul Aesque, and Danny Hawkins

Using Partial Discharge Surveys to Increase Electrical Reliability ...............................32 Don A. Genutis

Advancements in Condition Assessment and Diagnostics Related to the Monitoring of Partial Discharges in Medium Voltage Equipment .....................35 Claude Kane

Experience with On-line Diagnostics for Bushings and Current Transformers .............41 Robert Brusetti, P.E.

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On-Line Diagnostics Handbook Volume 1

Table of Contents (continued) Power Quality Instrumentation: Standards, Pitfalls, and Shortcuts ...........................45 Alex McEachern

Power Quality Investigations — Part One – The Case of the Ghostly Ground .................................................................49 Roderic L. Hageman

Not All Problems Are Power Quality ........................................................................53 Rod Olinger

A New Approach to Maintenance Monitoring of Major Assets ...................................55 Ramesh Anand and Jeff Benach

Dynamic Resistance and Vibration Testing of Power Circuit Breakers ..........................60 Don Spieth

Power Quality Investigations — Part Two – Continuing Detective Work .......................................................................66 Roderic L. Hageman

NOTICE AND DISCLAIMER NETA Technical Papers and Articles are published by the InterNational Electrical Testing Association. Opinions, views, and conclusions expressed in articles herein are those of the authors and not necessarily those of NETA. Publication herein does not constitute or imply any endorsement of any opinion, product, or service by NETA, its directors, officers, members, employees, or agents (hereinafter “NETA”). All technical data in this publication reflects the experience of individuals using specific tools, products equipment, and components under specific conditions and circumstances which may or may not be fully reported and over which NETA has neither exercised nor reserved control. Such data has not been independently tested or otherwise verified by NETA. NETA makes no endorsement, representation, or warranty as to any opinion, product, or service referenced in this publication. NETA expressly disclaims any and all liability to any consumer, purchaser, or any other person using any product or service referenced herein for any injuries or damages of any kind whatsoever, including, but not limited to, any consequential, special incidental, direct, or indirect damages. NETA further disclaims any and all warranties, express or implied including, but not limited to, any implied warranty or merchantability or any implied warranty of fitness for a particular purpose. Please Note: All biographies of authors and presenters contained herein are reflective of the professional standing of these individuals at the time the articles were originally published. Titles, companies, and other factors may have changed since the original publication date. Copyright © 2009 by InterNational Electrical Testing Association, all rights reserved. No part of this publication may be reproduced in any form or by any means, electronic or mechanical, without permission in writing from the publisher.

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On-Line Diagnostics Handbook — Volume 1

Elements of a Comprehensive Power Quality Audit: A Case Study NETA World, Summer 2000 Issue by Frank P. DeCesaro, P.E., Cooper Power Systems Thomas M. Blooming, P.E., Keweenaw Power Systems of Minnesota, LLC Jerry R. Murphy, P.E. and Dan K. Walsh, P.E., Reedy Creek Energy Ser vices, Inc

Reedy Creek Improvement District (RCID) is a local government that provides municipal utility ser vices for the Walt Disney World (WDW) resort. Reedy Creek Energy Services (RCES) is the division that plans, designs, operates, and maintains utility systems, including distribution of electricity, for RCID. The advent of sensitive electronic devices such as computers and programmable logic controllers has caused an increased awareness of power quality among all utilities. RCES focuses on a proactive power quality program by determining existing power quality levels and addressing problems to improve the quality level to exceed industry standards. In the future, this time-stamped baseline will compare power quality activities as Walt Disney World and the RCID system continue to grow.

The RCID Electrical System History The RCID electric system began in 1970 as a single substation with a load of less than 20 MW, served directly by a central Florida utility. Today, RCID is its own control area with a network of seven substations and eighty-five 12 kV feeders. In the summer of 1998, RCID experienced a peak load of 180 MW. The size of the RCID system ensures that there will be some power quality problems similar to other utilities, but the power quality challenges are heightened by the combination of four theme parks as well as numerous resorts, restaurants, shops, water parks, and monorails.

Measurement Strategy A measurement survey was designed to compare electrical characteristics of the RCID system to industry standards. Simultaneous measurements were performed at trans-

mission, distribution, and utilization voltages. This enabled identification of coincidental activity between power quality disturbances throughout the RCID system. RCID has over 1200 meters as a customer load. The economics and logistics of performing a power quality measurement survey prohibit a 100 percent sampling of individual site loads. A plan was developed that obtained power quality measurements at two (of seven) selected 69 kV buses, all fourteen 12.47 kV substation buses, all seventy-four feeder circuits that carried significant load, and seventy-one unit substation/transformer loads. The two 69 kV buses and two of the fourteen 12.47 kV buses were monitored using high frequency voltage dividers and current transducers. This was done to investigate whether high frequency electrical transients were injected into the RCID distribution system from either transmission connections to other utilities or from the switching of 69 kV breakers and capacitors within the RCID system. The 12.47 kV measurements were performed by connecting to system potential transformers (PTs) and current transformers (CTs). Low-voltage measurements were usually performed by directly connecting to low-voltage busbars and to system CTs. It was occasionally necessary to measure the current directly using Rogowski coils placed around the conductors. Week-long measurements were taken at all of the 12.47 kV buses and main feeders. Four-day measurements were taken at the direct 69 kV and 12.47 kV connections. Fifteen-minute spot measurements were taken on all 12.47 kV feeders and selected unit substation/transformer loads. The 69 kV and 12.47 kV direct measurements and the unit substations/transformer load measurements were performed in conjunction with the 12.47 kV weeklong measurements.

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On-Line Diagnostics Handbook — Volume 1

Transient Measurement Considerations Recent advances in electronic and computer technology have revo lu tion ized power quality metering. Today, equipment has the capability of capturing and recording waveforms, power consumption, harmonics, voltage flicker, voltage and current rms trends, and transient voltages. However, care must be taken in selecting the voltage or current transducer to scale system quantities to levels that can be safely monitored by the instrumentation. Reliable use of any transducer is dependent on whether it provides adequate operation at the frequency of the disturbance being analyzed. Erroneous interpretations can occur if the transducer frequency response is below that of the instrumentation.

Voltage Transducers Transducers available for voltage monitoring include:

a) Voltage transformers (VTs), which historically have been called potential transformers (PTs)

b) Voltage dividers, either resistive, capacitive, or a combination of both

c) Capacitive coupled voltage transformers (CCVT)

Measurements of high frequency voltage impulses require the broad bandwidth of a voltage divider rather than the limited response of a VT. Laboratory measurements of the frequency response characteristics of a VT and resistively compensated capacitive divider were performed and are displayed in Figure 1. This indicates that VTs should not be considered for disturbances beyond 10 kilohertz. It also indicates that a resistively compensated capacitor voltage divider is capable of accurately monitoring voltage transients up to one megahertz.

last from microseconds to seconds in duration. Transducers selected for metering these currents must be capable of handling the currents passing through them. Transducers must also be capable of safely monitoring current on the high-voltage system and providing a safe, low voltage, accurate representation that can be recorded. There are numerous types of transducers capable of current monitoring. The most common are CTs, current monitors, and Rogowski coils. All are used to transform primary currents to values suitable for meters, relays, and other measuring or control devices. They provide isolation between the electrical system and the metering equipment. Each type has specific characteristics that the user should be aware of before use. For CTs, errors are introduced at both high and low frequencies. As frequency increases, core losses, particularly eddy current losses, introduce errors. Parasitic capacitance of the current transformer winding will provide a path for very high frequency currents that can resonate with the inherent inductance of the unit. These effects can typically be noticed above five kilohertz. Lower frequencies will introduce errors because of core saturation effects. Some transient currents are asymmetric in nature and contain dc components which can saturate the CT and result in distorted waveforms. Current monitors are internally terminated current transformers which give an output voltage proportional to the current being measured. They can be used for measuring waveforms from microamperes to values in excess of 500 kA. Current monitors consist of a magnetic core, a secondary winding, resistive termination, and an electromagnetic shield. Current monitors can be obtained that have frequency responses as low as one hertz and as high as 200 megahertz. Rogowski coils are comprised of a coil of wire closely wound on a circular piece of plastic which is surrounded by insulation. These coils create a differential voltage proportional to the current passing through it and must be connected to an electronic integrator. Rogowski coils can have bandwidths of one megahertz or more. Even though they do not saturate, they cannot measure dc.

Precautions

Figure 1 — Voltage Transducer Frequency Response Plots

Current Transducers Currents during electrical power system disturbances can greatly exceed normal system ratings. Overcurrents on the electrical system can have dc components along with fundamental, harmonic, and transient frequencies. They can

Performing meaningful measurements on electrical power systems requires the user to have knowledge of the events expected. Transducer and recorder characteristics must be selected to properly replicate the events. Erroneous selection of either component can lead to incorrect interpretations. Many instances have been encountered where high frequency events which exceeded the frequency response of the VTs were analyzed. Another common source of error is recording data with proper transducers but using inadequate recorder-digitizing rates to accurately represent the data. This can lead to improper conclusions.

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On-Line Diagnostics Handbook — Volume 1 Results One aspect of the RCES power quality audit was to determine whether the 69 kV transmission system experienced high frequency voltage transients that would be coupled to the 12.47 kV distribution system. Measurements included the use of specialized 115 kV class and 35 kV class capacitive voltage dividers, with a one megahertz bandwidth, to directly monitor the 69 kV and 12.47 kV systems simultaneously. The power monitor used sampled impulses at two megahertz. High-voltage monitoring was performed at two RCES substations for a period of four days each. The 69 kV metering recorded approximately five events at each substation. Although the frequency of the events exceeded the capabilities of the recorder, it was observed that they did not propagate to the 12.47 kV system. Also, simultaneous measurements proved that switching surges on the 12.47 kV system did not get coupled to the 69 kV system.

Power Quality Criteria The goal of a power quality audit is to determine if electrical power delivered by the utility is acceptable when compared to industry standards or criteria. Criteria items include voltage regulation, harmonic current and voltage, voltage notching, voltage sags and swells, voltage flicker,

voltage and current imbalance, as well as reliability indices. Table 1 lists standards that apply to specific power quality concerns. The power quality audit produced a document based on the standards and considerations which will be adjusted as standards are refined. Each monitored location was compared to the established criteria of Table 1. Results indicated that the RCID system does not experience voltage and currents outside of the power quality criteria. There were several voltage sags outside acceptable limits. One was determined to be from a transformer needing to have its voltage taps increased. Other violations resulted from faults that occurred during the monitoring period.

Flicker Voltage flicker is the amplitude modulation of the fundamental frequency voltage waveform by one or more frequencies, typically in the zero-to-thirty hertz range. At some magnitudes, this modulation causes a visible brightening and dimming of lights connected to the modulated voltage, hence the term flicker. At voltage magnitude variations normally found in electric utility networks (