AEIC CG5 2005-Underground Extruded Power Cable Pulling Guide

AEle CG5 2005

AEIC UNDERGROUND EXTRUDED POWER CABLE PULLING GUIDE (2nd EDITION)

Association of Edison Illuminating Companies 600 North 18th Street, Post Office Box 2641 Binningham Alabama 35291-0992 June 2005

www.aeic.org Copyright © 2005 by the Association of Edison Illurninating Companies No part ofthis specification may be reproduced in any form without the prior written Permission of the Association of Edison Illurninating Companies. AlI rights reserved.

AEIC CG5 2005

Copyright © 2005 by the Association of Edison Illuminating Companies No part ofthis specification may be reproduced in any form without the prior written Permission of the Association of Edison Illuminating Companies. AlI rights reserved.

Please contact us at our website at: http://www.aeic.org

AEIC CG5 2005

TABLE OF CONTENTS DISCLAIMER ........................................................................................................ 1 SCOPE ....................................... ........................................................................... 2 1.0 INTRODUCTION .... ... ................. .... ... ................................ .. ... ............... ....... 3 2.0 CABLE REMOVAL ....................................................................................... 3 3.0 HISTORY ....... ..................................................................................... ....... 4 4.0 ECONOMIC CONSIDERATIONS ... .. ........................................................... 4 5.0 NOMENCLATURE ......................... .. .......... ........................... ....................... 4 5.1 Definition of Symbols ...................................................................... ...... 5 6.0 DESIGN CRITERIA & PULLING LlMITS ................................................ ...... 5 6.1 Cable Diameters and Weights ........... .. ....... ...... ............... .................... 5 6.2 Jamming ................................... ....................... .................................... 6 6.3 Cable Configuration in Duet.. .. ............................................................. 6 6.4 Cable Clearance ................................................................. ........ .. ... .... 7 6.4.1 Clearance Formulas ............. ...................................................... 7 6.5 Minimum Bending Radius .................................................................... 8 6.6 Duet Size ...................................................... .............. .. ......... ....... .. ... 10 6.7 Coefficient of Friction ......................................................................... 11 6.8 Weight Correction Faetor. ....... ........................................................... 14 6.9 Sidewall Bearing Pressure .... .................................................. .......... 14 7.0 DESIGN LIMITS ................ ................. ........... .......... ............................... .... 15 7.1 Tension Limits - Eyes and Bolts ....................................................... 15 7.2 Tension Limits - Grips ....................................................................... 16 7.3 Maximum Sidewall Bearing Pressure ............................................... 17 8.0 PULLING TENSION FORMULAE .. .. .......................................................... 19 8.1 Straight Pull ....................................................................................... 20 8.2 Siope - Upward Pull .... .. ....... .. ....... ................................. ...... .. ....... .... 20 8.3 Siope - Downward Pull ...................... ............................................... 20 8.4 Bends ......................... ........... ... ............... ........ ... ........................ ... .... 21 8.4.1 Horizontal ....... .. ... .... ..... ....... .. .......... .... ... ............. .. .......... .. ....... 21 8.4.2 Convex Upward ........................................................................ 21 8.4.3 Convex Downward .................... ............................................... 22 8.4.4 Concave Upward ...................................................... ................ 22 8.4.5 Concave Downward .... .. ... ........................................................ 22 9.0 SIDEWALL BEARING PRESSURE FORMULAE ... ..................... ...... ... ..... 24 10.0 CALCULATION SEQUENCE ..................................................................... 25 11.0 SAMPLE CALCULATI ONS ... ..... .. ... ............ .............................. ................. 26 12.0 INSTALLATION CONSiDERATIONS ........ .......................................... ... .... 45 12.1 Pulling Lines and Duet Wear ...... ........ ....................... ....... .......... ....... 45 12.2 Surging .......... .... .. ...... ............ ............. ... .. ...... .. .................................. 45 12.3 Siaek Pulling .............. ................ ........................................................ 45 12.4 Looping ......... .... ................................... ........... ... ....................... ......... 46 12.5 Lubricants ... ... .... ........ ..... ... ... ...................... ....... ... ......... .. .. .............. .. 46 12.6 Pulling Speed ...................... ... ........... .. .. ............ ............ ... ...... .. ...... ... 46 12.7 Pulling Direction .................................................. ......... .... ......... .... ..... 46 12.8 Caution ... ................ .... ...... ................ .. .. ..... .. ... .......... ... .. .................... 47 12.9 Swivels and Other Deviees ....... ........................................ ... ....... ....... 47 12.10 Riser Poles ............. ..... ......................... ........................ ... ........... ...... 47 12.11 Cable Installation Guide ............................................................ .. ..... 48 13.0 REFERENCES ......................................................................................... .. 49 14.0 APPENDIX ......................................................................................... .. ...... 50

AEIC

UNDERGROUND EXTRUDED POWER CABLE PULLING GUIDE

AEIC UNDERGROUND EXTRUDED POWER CABLE PULLING GUIDE (2nd EDITION)

OISCLAIMER This guide was prepared by the Cable Engineering Committee of the Association of Edison lIIuminating Companies. Most of the data presented in this guide is derived from EPRI project EL3333, which was conducted to correlate calculated values to actual field conditions. Other valuable sources of pulling data are available from cable and cable lubricant manufacturers. Use of this guide is voluntary and the existence of the guide is not intended in any respect to preclude the manufacture or use of products not conforming to the guide. While care has been taken in preparing this guide, AEIC makes no warranty or representation in connection with its use. Persons electing to use the guide are reminded that they should independently evaluate their specifie needs and requirements before doing so. Users are also cautioned that there may be requirements issued by governmental and regulatory authorities which are not addressed by this guide. Because this guide is subject to review and revision, those who use it are cautioned to obtain the latest version.

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UNDERGROUND EXTRUDED POWER CABLE PULUNG GUIDE

SCOPE This guide outlines the pulling parameters that need to be considered when installing underground power cable in duct. Only extruded power cable is covered. Installations with more than three cables in a conduit are not included. Cable installations in trays or racks are also not included. A variety of pulling guides and computer software are available from many power cable manufacturers and cable lubricant manufacturers. Several of these guides provide a basic introduction to cable pulling criteria and are listed in references [1] - [3]. This guide is intended to complement these publications. Cable specialists from each electric power utility may desire to use this guide to develop their own simplified version which incorporates criteria unique to their systems. Cable pulling is not an exact science: it involves a complicated combination of variables, which are often difficult to accurately predict. The information presented in this guide is a compilation of data obtained through mathematical modeling, experimentation, and experience. The best judgment of the AEIC Cable Engineering Committee was used to resolve conflicting data and controversial information. Personnel who do not necessarily have an in-depth technical background can use the guide. The guide can also be used by engineers with a need for a detailed design guide. ln the body of this guide a simplified approach is used to calculate pulling tensions and sidewall bearing pressures (SWBP) for the most commonly encountered conditions in the field. It incorporates tension and sidewall bearing pressure limits developed under EPRI Project EL-3333, "Maximum Safe Pulling Lengths for Solid Dielectric Insulated Cables", as weil as the many design parameters which must be considered when these new limits are employed. The more detailed considerations that utilize more complex formulae are addressed in the appendix. The major points covered in the guide include: Factors that influence pulling tensions such as cable type, conduit type and size, lubricants and installation practices Calculation of maximum pulling lengths allowable without damaging the cable Limits on cable tension and sidewall bearing pressure Design constraints

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1.0

INTRODUCTION

A guide of this nature cannot cover ail of the possible cable and conduit parameters that can be encountered in the field. The intent of this guide is to provide the most recently available state-ofthe-art technical information that interested parties can use to design a cable/conduit system. The major topics covered are: • • • • • • • • • • • • • •

One or three equally sized cables in a duct New information covering only extruded cables 0.6 kV to 138 kV cable Aluminum and copper conductors Cables with bare concentric wires, bare lead sheaths, jacketed lead sheaths, jacketed wires, jacketed LC shields and jacketed fiat straps Tension and sidewall bearing pressure limits Grips and eyes Dynamic and static coefficients of friction Coefficients of friction at high and at low sidewall bearing pressures Coefficients of friction for lubricated cable and duct Minimum bending radius Formulae and Sample Calculations Jam ratios and clearance considerations Installation considerations • • • • • • •

2.0

Pulling lines and duct wear Surging Slack pulling Looping Lubricants Pulling speed Pulling direction

CABLE REMOVAL

Removing cable from an old duct may be more difficult than pulling cables into a new duct. Silt and debris can collect in duct over the years and make cable removal extremely difficult. Also, when pulling lubricant dries out, it can adhere to both cable and duct resulting in a friction factor that is higher than that encountered if the same cable were installed with no lubricant. Usually, the cable being removed will be scrapped, so damage to the cable during removal is not a concem. The primary consideration is that pulling tensions not exceed the tensile strength of the cable. Currently, there is very little information on the effective static and dynamic friction coefficients encountered when removing cable. If excessive tensions are expected, flooding the duct with water can aid removal. Water itself is a lubricant. When wetted, the silt and de bris in the duct will not adhere as strongly to the cable. Also, the effective weight of the cable in a flooded duct will be reduced due to the buoyancy of the cable in water. As pulling lengths are increased, additional consideration must be given to subsequent cable removal.

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3.0

UNDERGROUND EXTRUDED POWER CABLE PULLING GUIDE

HISTORY

Maximum safe pulling lengths for cables were established by field experiences of users and cable manufacturers during the early 1900's. The 1931 Underground Systems Reference Book stated ... "satisfactory operation of installed cables is assured provided that it has suffered no mechanical injury. " Buller analyzed effects of duct curvature in bends in 1949 (4) and Rifenberg established a more exact engineering method in 1953(5). These formulae and definitions of the associated conditions were used to gain additional confidence in longer and more complex pulls. By the mid 1970's it was generally known that sorne of the factors limiting longer cable pulls, such as sidewall bearing pressure, were neither realistic nor based on a strict engineering analysis. The time had come to update available information on pulling tension limits for extruded power cable. As a result, an Electric Power Research Institute (EPRI) project was funded to quantify the factors that influence the maximum pulling lengths for pipe-type cable. This was published as EL2847 (6). The advent of extruded dielectric cables and the lack of information on pulling factors for these newer designs of cable led to the funding of an additional EPRI project. These results have been published as EL-3333 (7). This last research project has demonstrated the ruggedness of modem extruded cable constructions and has shown the need to compile the information into a comprehensive pulling guide. Use of these recent research results will not only enhance underground system reliability, but also minimize cable system costs.

4.0

ECONOMIC CONSIDERATIONS

Determining the maximum safe pulling lengths for power cables is an essential element necessary for designing the most cost effective and reliable cable system. When there is no equipment or physical limitations, the number of cable splices and splicing chambers can be minimized. Also, cable damage can be avoided.

5.0

NOMENCLATURE

There are many terms unique to cable/duct installations. Before a subject of this type can be discussed in detail, the terminology must be completely understood. Therefore, the definitions used in this guide are listed as follows: Cable Entrance Duct section closest to cable feeding equipment. This is the lowest tension point of the cable in the duct section under examination. Cable Exit Duct section closest to the cable pulling equipment. This is the highest tension point of the cable in the duct section under examination. Extruded lEncapsulating) Cable Jacket Cable jacket that substantially encapsulates the metallic shield. Tubed or Sleeved Cable Jacket Cable jacket that is loosely applied over the metallic shield. Usually a separator tape separates the jacket and the metallic shield. CG52005

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5.1

Definition of Symbols Cable entrance tension Cable exit tension Inside radius of duct bend Inside bending radius of cable Duct centerline radius Total weight per unit length of cables in duct Angle Coefficient of friction Length of cable in section Sidewall bearing pressure Weight correction factor Inside diameter of duct Nominal outside diameter of one cable 1.05 x d Area of circle 1 mil (.001 ") in dia. Clearance Jam ratio Lead sheath cross-sectional area Lead sheath outside radius Lead sheath inside radius 3.1416 2.7183 Factor for determining minimum bending radius

T1 T2

R Re Rel W

e K

L SWBP Wc

D d d' cmil C

J A1ead

Ra Ri 1t

e F

Pounds Pounds Feet Feet Feet Pounds/Foot Radians or Degrees* Dimensionless Feet Pounds/Foot Dimensionless Inches Inches Inches Circular Mils Inches Dimensionless Square Inches Inches Inches Dimensionless Dimensionless Dimensionless

*(Radians = Degrees x 1t/180)

6.0

DESIGN CRITERIA AND PULLING LlMITS

6.1

Cable Diameters and Weights

Cable diameters and weights listed in manufacturers' catalogs' and specification sheets are generally approximate and subject to normal manufacturing tolerances. Possible variations in cable diameters are taken into consideration in the formulae for cable clearance and jam ratio. Catalog weights are generally adequate, except for marginal cable pulls for which more accurate weights should be requested from the cable manufacturer. Actual cable weights should be used if available. Assemblies of triplexed cables will weigh more per foot than paralleled cable. The cable manufacturer should be contacted to determine the weight of triplexed cables. The weight of parallel cables, whether they are delivered on individual reels or on multiple reels, will be the cable weight per unit length times the number of cables.

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6.2

Jamming

The Jam ratio (J), is defined as the ratio of the inside diameter of the duct (D) to the cable diameter (d), Le. J= Dtd

6-1

When this ratio is close to 3.0, one of the cables in a three-cable pull may slip between the other two cables causing the cables to jam in the duct. This is most likely to occur when the cables are pu lied around a bend. Jamming is not usually a problem for essentially straight cable pulls. The following guidelines are suggested to minimize the risk of such an occurrence during cable installation in a duct. If J is between 2.8 and 3.0, jamming could occur and it is not recommended that cable pulls with this jam ratio be performed unless the conduit run is free of elbows or sharp bends. Recognized variations in cable and conduit diameter and ovality in conduit diameter at bends are taken into account in these limits. Triplexed cable assemblies tend to maintain a triangular configuration during a cable pull and therefore jamming is not likely to occur regardless of the calculated jam ratio. Pull lines, especially synthetic or fiber ropes can wear a groove in conduit bends. Jamming can occur in these bends for single cable and parallel multiple cable pulls when the cable diameter is slightly larger than the diameter of the groove. This happens because of a tendency for the cable to wedge into the groove and is an especially acute problem for cables with tubed jackets. Therefore, the pulling line diameter should be greater than the cable diameter or at least 0.5 inches smaller in diameter than the cable diameter.

6.3

Cable Configuration in Duet

The relative position of three parallel cables pulled in a duct is important because it affects the weight distribution of the cables and hence the normal (perpendicular) force between the cable and the duct. When pulling three parallel cables, the configuration of the cables is govemed by the ratio of the inside diameter of the duct to the nominal diameter of the cable. This parameter was defined earlier as the jam ratio, J. Based on field experience, observations made in EPRI Project EL-3333 and on information presented in Rifenburg (5), the following general trends can be expected for cable configuration in duct. If J< 2.4, cables are triangular If 2.4 < J < 2.6, cables tend toward triangular If 2.6 < J < 2.8, cables are either triangular or cradled If 2.8< J < 3.0, cables tend toward cradled If J> 3.0, cables are cradled Note: Jamming can occur when 2.8 ~ J ~3.0. However, if the sidewall bearing pressure, SWBP, is greater than1000 Ib.lft. and if 2.6rce required to start a cable in motion. The dynamic coefficient of friction dictates the force required to keep a cable in motion. The static coefficient of friction is greater than the dynamic coefficient of friction. Most pulling calculations are made using the dynamic coefficient of friction because most cable pulls are continuous and it is the force on a cable during a pull that is of concern. If a pull is stopped before it is complete, a higher tension is required to restart the pull than is required to maintain the cable in motion. Cable pulls should be started (or restarted) slowly. The coefficient of friction is a function of the materials that are in contact with each other and the pulling lubricant that is used. The coefficient of friction for both single and three cable pulls was measured experimentally under EPRI project EL-3333. The friction factor measured for three cables was not the same as that predicted by the commonly used Rifenberg relationships. Thus, for tension calculations performed in this guide, separate friction factors are provided for single cable and three-cable geometries. The three-cable geometry friction factors are based on the EL3333 measured values. The weight correction factor, Wc, is used in this guide for three cable pulls to account for different cable/duct geometries. Under the EPRI EL-3333 project it was observed that the normal force between the cable and conduit significantly affects the dynamic coefficient of friction in lubricated ducts. As the normal force increases, the friction factor decreases. This phenomenon occurs because the function of the lubricant changes. At low normal forces, the pulling lubricant layer between the cable and the conduit is relatively thick. Under this condition, shear forces in the compound must be overcome for this cable to move. However, when the force is high, the lubricant layer is very thin and the boundary layer phenomenon takes over, allowing the pulling compound to act as a more effective lubricant. The data indicates that at the side wall bearing pressure SWBP of approximately 150 pounds per foot, the dynamic coefficient of friction is significantly reduced. In effect, this means that the lower coefficient of friction can be used when the cable is being pu lied around bends where the pulling tensions and radii are such that the sidewall bearing pressure is 150 pounds per foot or greater. The higher value of dynamic coefficient of friction should be used for essentially straight pulls and lead-in bends at the start of the pull and bends where the SWBP is less than 150 pounds per foot. A tabulation of dynamic coefficients of friction for various cable materials, ducts, and lubricants are listed in Tables 3 and 4. Values are shown for low bearing pressures and for bearing pressures of 150 pounds per foot and higher. The friction factor was not measured for ail cable/conduitllubricant combinations. If values for specifie combinations are not shown, the cable, conduit, or lubricant manufacturer should be consulted.

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Table 3 Recommended Dynamic Coefficients of Friction for Straight Pulls and Bends with SWBP < 150 Ib.lft. (soap and water based lubricants) Duct Material PVC

PE

FIBRE

Cable Outer Covering Installation Temp. XLPE PE PVC N CN Pb p