Insulated Conductors Committee

 E4- Minutes


Spring 2005

Spring 2005 - Secondary Cable Technology - A Review of Secondary Underground Cable Basics

Abstract:  The topic of 600 volt underground secondary cable is seldom discussed at ICC meetings where medium and high voltage underground cables receive most attention. However, underground secondary cables form an important part of a utility system considering larger utilities install more than 1 million ft. of underground secondary cable per year and spend several million dollars annually on secondary underground cable repair costs. This Educational Program will focus on the topic of underground residential and commercial services and underground streetlight cables. Presentations from the cable manufacturers will cover the manufacture, design, materials and industry specifications covering secondary cables. Learn about the latest secondary cable design technologies and their potential benefits. Presentations from the utilities will focus on their experience with underground secondary cables and splices. The Educational Program will also feature a presentation on the results of a utility survey on secondary cables conducted specifically for the benefit of utilities attending this session. All files are available in the PDF format

For additional details on the presentations please refer to the abstracts listed below:

Fall 2005

Fall 2005 Educational Program - EPR Insulation & Cables
bullet Evolution of EPR Compounding (3.6 MB PDF)
Carl Zuidema, The Okonite Company
Abstract: There are four elastomeric materials that have found widespread use as the primary dielectric in wire and cable for power delivery: cis-polyisoprene, (natural rubber), polybutadiene co-styrene - (SBR), polyisobutylene co-isoprene - (IIRR) polyethene co-propene - (EPR). The art of rubber compounding began with the invention of vulcanization of natural rubber by Charles Goodyear in 1844. This talk will focus on the development of rubber technology as applied to the dielectric of electrical wire and cables. We will briefly review the development of natural rubber compounds, the invention of synthetic rubber and the particular compounding requirements of each of these. An emphasis will be placed on the relationship between polymer structure and physical properties, as well as the relationship between compounding variations and finished properties. This leads to a discussion of the different types of EPR compounds, defined by the ICEA as classes I, II, III and IV. Manufacturing methods for mixing and processing EPR will be reviewed. Lastly we will discuss semi-conducting EPR compounds as used for cable shields.
  • Q: John Rector, Black & Veach – How dependent are different cable designs on EPR compounds and what makes EPR not suitable, say for wet design
    A: EPR’s are good for wet cable designs and the fillers in the insulation compound are critical for its suitability for wet designs; if the fillers are altered it may make them not suitable
  • Q: Rick Hartlein, Neetrac – Are butyl rubbers Type I rubber; it will be good to have reference(s) where its characteristics are described
    A: Yes the butyl rubbers are Type I with poorer mechanical properties; useful references will be added to the slides. (The slides are revised to include general references for further reading on rubbers)
  • Q: Carlos Katz, Cable Technology Laboratories – In the case of semiconducting EPR, are the fillers replaced 100% or less by carbon black?
    A: It depends on the conductivity of the carbon black; for example more than 100% replacement may be required if lower conducting black is used
  • Q: Ajit Hiranandani, DTE – Is chemical treeing mechanism in EPR different from that in XLPE?
    A: Treeing is not a recognized mode of failure in EPR and hence not as extensively studied as in the case of XLPE

 

bullet Black EPR (63 KB PDF)
Ronald F. Frank, Cable Engineering Consultant
Abstract: Data is presented on 5kV to 46kV shielded cable insulated with black EPR made by one cable manufacturer from 1964 to 1970. To achieve maximum performance characteristics at this time a small amount of carbon black was added to the EPR compound, which gave it a black color. Service experience with this cable has been good.
  • Q: Rick Hartlein, Neetrac – How could one recognize butyl rubber as distinct from black EPR? A: At temperature >85oC, butyl rubber will revert back to its thermoplastic nature and will easily separate out from the conductor whereas EPR will not
  • Q: H. Sarma, Kriya Consulting – Any information known on the type of carbon black used in these compounds, high or low structure or thermal or UV grade etc? A: Reinforcement SRF grades were predominantly used in these early compounds
  • Q: Larry Salberg, KSC – Have the other manufacturers of black EPR also used the same criteria for the color change? Also whether all the details of the presentation will be included in the minutes and in which format? A: The presentation in its entirety will be included in the minutes. This will also detail properties and typical formulations used (see the minutes for Word document). The advantage of the light beige color is to provide a good contrast between the insulation and the black insulation shield. The other suppliers moved over to the other distinct colour such as pink. There was yet another IPCA requirement on wet electrical aging in 90oC water that forced the change from black to other colours.
  • Larry Kelly, Kelly Cables added an increasingly greater demand for 69 kV cables with 650mil wall insulation and requirements such as flexibility, improved loss index (dielectric constant x dissipation factor) and strippability providing evidence that there is residual conducting residue on the insulation necessitated the change in colour of the EPR insulation
    (see a detailed tabulation of Test requirements, typical formulations and electrical stability of EPR cables in the technical write-up)

 

bullet EPR Mechanical and Thermal Properties (549 KB PDF)
Steven Boggs,
Electrical Insulation Research Center Institute of Materials Science, University of Connecticut
Abstract: The mechanical and thermal characteristics of several EPR compounds will be discussed based on new experimental data for several EPR compounds. The thermal conductivity, thermal expansion, heat capacity and mechanical properties of these compounds were measured as a function of temperature using modern equipment and the data presented.
  • Q: Larry Salberg, KSC – The outliers (or the compound with properties distinct from the rest of the group) in thermal conductivity (EPR1) and low temperature elasticity (EPR4) seem to be different. Is this correct and if so any explanation?
    A: Yes the data is correct. Of the 4 compounds studies, EPR1 was with the higher filler content and hence the conductivity higher whereas EPR4 is of the lowest and hence LT elasticity is the greatest. So essentially the measurements reflect the filler content
  • Q: Rick Hartlein, Neetrac – How the thermal needles are inseted into the slabs for conductivity measurements and whether the results will be dependent of sample origin, cable Vs molded slabs?
    A: The test samples are molded cylinders containing the needle; thermally conducting filling compounds are used to improve the interface contact between the measurement needle and the sample. The measurements are not orientation dependent and hence will not be affected by their origin as to cable Vs slab
  • Q: Haridoss, Kriya Consulting – How does the EPR designations in your presentation correspond to ICEA Type I, II, III, IV?
    A: They 1,2,3, 4 designations are the same for all graphic representations.

 

bullet Accelerated Wet Testing of Medium Voltage EPR-insulated Cables (926 KB PDF)
Edward E. Walcott, William S. Temple
, General Cable Corporation, Suffern, NY and John T. Smith, III, General Cable Corporation, Scottsville, Texas
Abstract: A brief history and overview of North American accelerated wet-aging test procedures is presented. A review of accelerated wet-aging time-to-failure and fixed time aging tests (followed by electrical test diagnostics) for medium voltage EPR insulated power cables is presented. A discussion of the relevance of these tests to actual field service performance is also discussed.
  • Q: Larry Kelly, Kelly Cables – Are the 2 EPR cables used for the comparison of ACLT performance extruded with the same conductor shield?
    A: Two EPR cables with two different conductor shield, together a set of 3 test cables are used for this comparative study to demonstrate the effect of insulation and conductor shield on ACLT performance
  • Q: Larry Salberg, KSC – do the data indicate higher the use temperature longer the life of the EPR cable?
    A: Yes they do; but a lower temperature and higher stress ACLT will be a better discriminating test
  • Larry Kelly, Kelly Cables emphasized high temperature operation of EPR cables is the norm and the higher reliability of EPR cables has been substantiated by the field experience. Steve Boggs, Univ. Connecticut commented that preconditioning the test cables for equivalent moisture conditions is necessary to compare their performance at high and low temperatures and the time to reach equilibrium moisture content will affect the cable failures at high and low temperatures. John Smith, General Cable acknowledged Steve’s comment and added that it is the combination of high stress and low temperature is more useful for comparative evaluations.
  • Q: Steve Graham, Duke Power – asked about the differences in the test water between AWTT and ACLT
    A: Mark Walton, General Cable - AWTT is with tap water as specified by AEIC and ACLT is with deionized water
  • John Cancelosi, The Okonite Cables, commented that the charts on ACLT for cables with different insulation and conductor shields should probably include comments about the origin of the compounds as to commercial or experimental. Upon further consideration, since this is an educational program the authors feel that identifying the compounds, even to the extent of "commercial or non commercial", is not appropriate and really does not effect what is being said with regard to the points discovered about wet accelerated aging of EPR cables
  • Q: Ajit Hiranandani, DTE – Will one be able to predict the life expectancy of the cables in service using ACLT?
    A: No
  • Haridoss Sarma, Kriya Consulting added that it is always a challenge to evaluate what we can learn from these test results and to use the results to the benefit of life time presicability

 

bullet In Service Performance of EPR Cables Installed in the Memphis Light Gas And Water (MLGW) Electrical Distribution System (128 PPT)
P.Cox, MLGW
Abstract: This presentation will provide a brief background relating to the decision to install EPR insulated cables rather than HMWPE and XLPE cables, 25 year performance history, and field aging studies performed at MLGW.
  • Q: Ed Walcott, General Cable – what is the cable design, jacketed or unjacketed
    A: All unjacketed design
  • Mark Walton, General Cable commented the 350-400 v.mil residual voltages after field aging correspond closely to the values obtained in EPRI projects dealing with laboratory aging
  • Q: Larry Salberg, KSC – the failure rate of 0.16 per 100 conductor miles correspond to what installed length in total?
    A: Do not know exactly but certainly lots of it as this was a big project for Memphis Light Gas & Water
  • Jim Fitzgerald, The Okonite Company commented that all these URD cables are usually operated not necessarily at high temperatures and still performing reliably contrary to the prediction from the laboratory ACLT at ambient temperature

 

bullet Performance Evaluation of EPR Underground Distribution Cables
Carlos Katz,
Cable Technology Laboratories, Inc.
Abstract. - Because of the increased usage of EPR insulated cables and the limited data available, starting in 1994, EPRI, ESEERCO and Orange & Rockland Utilities (O&R) funded a project to develop information to quantify the aging of various EPR cables. Five types of EPR cables, manufactured by different companies, were aged for 7 years at three locations: namely, in CTL laboratories under 2.5V0, in the field at O&R at 1 and 2.5 V0. The field sides were part of actual utility circuits. Laboratory load conditions were adjusted to mimic field conditions. Cables were periodically tested for a number of properties. Test results indicate that there is no major difference in the overall performance of the five EPR insulated cables. However, differences in the characteristics of the components may lead to conditions, which can result in premature failure, as it occurred on a number of occasions while aging one of the cables in the laboratory. Other circumstances lead to the field development of partial discharges in another cable.
  • Q: Serge Pelissou, IREQ – How can the stability on ACBD test be explained?
    A: From the range of values
  • Q: Ben Lenz, Imcorp – How are the test cables chosen? Are these jacketed or unjacketed? Having a jacket, would it reduce pitting that was observed after aging?
    A: Test cables were unjacketed. Having a jacket would probably resuce pitting; but if the neutral wires are loose with moisture migrating from outside, pitting is still a possibility
  • Steve Boggs, Uconn, commented that the specification range of volume resistivity of the insulation shield is not necessarily adequate.
  • Q: John Smith III, General Cable – Do the VT Vs Life characteristic curves predict differently for different EPR?
    A: Yes; but in general to 50 years life time. The data is not included in this presentation.

 

bullet EPR Use at High Voltages – Cost Justification (300 KB PDF)
Rachel Mosier, Northeast Utilities
Abstract: Northeast Utilities (NU) has been installing 115-kV ethylene propylene rubber-insulated (EPR) cables since 1999. We use these cables in our substations where we do not have room for overhead lines. Our service reliability is excellent, having never suffered a failure for any reason on these lines. However, the losses in an EPR cable are relatively high compared to other types of insulation. This presentation will detail how NU cost-justifies an EPR cable by calculating the point at which the cost of losses per foot of the EPR cable exceeds the cost per foot savings of the EPR cable over other types of insulation.
  • Q: Rick Hartlein, Neetrac – Lead sheathed designs are used for economic comparisons. Has any attempt been made to compare the economics of EPR design to metallised laminate structures with alternate insulation?
    A: No; however it is not expected to change very much with a net result of favoring EPR design. If vault can be eliminated, they may be more comparable.
bullet Transmission Class EPR Power Cables (2.9 MB PDF)
Robert E Fleming, The Kerite Company
Abstract: This segment of the EPR Power Cables Session will focus on Transmission Class Cables. It includes a brief history of early Underground Transmission Projects, increase in installed cable and Current Type Projects. Also included is information on Underground verses overhead and EPR verses Alternate Designs and Materials. The advantages and disadvantages of EPR cables as far as electrical, mechanical, installation, maintenance and testing of the new cable installation will also be presented.
  • Q: Randy, Southwire Co – what type of sheath was used?
    A: Bonded
bullet AEIC Guide for Reduced Diameter Cable (49 KB PDF)
Michael L. Walker,
Reliant Energy
Abstract: This presentation will provide an overview of The Association of Edison Illuminating Companies’ (AEIC) guide for reduced diameter cables. Many cities in the United States and countries around the world have and aging underground cable system. This guide was developed to provide an alternative to complete duct bank replacement.
  • No questions
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