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Impulse tests and AC tests were also carried out on shorter samples, which were removed every few weeks during the aging process. The impulse strength of the EPR cables dropped slightly and then leveled off, while the impulse strength of two of the TR-XLPE dielectrics dropped continuously during the tests with no evidence of leveling off. The third type of TR-XLPE showed a tendency for the impulse strength to level off at a value similar to that of the EPR cables.
Wet electrical AC aging of the shorter samples of model cable was continued until the strength of both the TR-XLPE and EPR cables had dropped to the point that frequent failures at 150 V/mil AC made continued aging impossible. This occurred at about 45 weeks for both the TR-XLPE and EPR model cables. The AC failure of the TR-XLPE cables was traced to large water trees, which extended fully through the dielectric. The impulse strength of the EPR and one of the TR-XLPE cables leveled off early in the aging process, while the impulse strength of the other two TR-XLPE cables dropped to levels below that of the EPR cables, and continued to drop with no sign of leveling off. This suggests that the service life of these dielectrics could be dictated by a loss of impulse strength, which precedes a loss of AC strength. The finding that the AC end of life for the TR-XLPE model cable was associated with the formation of large water trees is consistent with a water tree-based mechanism for reduction of impulse strength as hypothesized previously.
This presentation shows how in-situ diagnostic measurements of PD and 0.1 Hz. DF were correlated with laboratory accelerated cable life testing (ACLT) data in an attempt to make estimates of remaining cable life.
The following presentations are part of the Subcommittee A general session
This presentation describes work carried out in the UK over the last 25 years to study the ageing of extruded dielectric cables under wet conditions. Cables manufactured in the 1970’s and 1980’s were aged at working voltage, 50Hz or 500Hz, and maximum operating temperature of 90oC for up to 10 years immersed in water. The results of these tests are reviewed and also compared with the results on 1990’s cable, tested to the UNIPEDE regime at 2.5 times working voltage and a temperature of 30oC for 2 years immersed in water.
The long term tests at working voltage showed the initial accelerating effect of testing at 500Hz and the reduction in ramp breakdown strength to a plateau. A high level of ramp breakdown strength was retained, supporting the absence of service failures due to water treeing with these cables from the 1970’s and 1980’s.
UNIPEDE testing of the 1990’s cable resulted in the ramp breakdown strength reducing to a plateau after approximately 1 year, exhibiting a similar performance to that in the long term tests on the earlier cables. Although comparisons such as these are not easy, the UNIPEDE regime may nevertheless be considered a useful tool in detecting cables with a limited performance under service conditions.
Present power applications and demonstration projects use Nb-Ti and bismuth-based superconductors (BiSrCaCuO) and future applications may use yttrium-based superconductors (YBaCuO). Superconducting magnetic energy storage (SMES) systems made with Cu/Nb-Ti are being used for power conditioning. Superconducting transmission lines and electric motors made with Ag/Bi-based superconductors are being used in demonstration projects. The hope is to develop low-cost, coated, yttrium-based superconductors for future power applications. Currently, only short lengths (0.1 m to 10 m) of yttrium-based superconductors have been made with good properties.
A second leak on the same line was reported approximately 24 hours within the completion of the repair of the first leak. A crew was dispatched to inspect the manhole where the recent leak was repaired. Because the latest repair was found intact a patrol was dispatched to inspect the whole line. No evidence of a fluid leaks was discovered in ComEd or other utility manholes during this line patrol. Pressure tests indicated that the leak was on the return line and not in the cable pipe. The return line leak was located and repaired with the line in service and under a static pressure.
The results of the example show that multiple method can give a high Accuracy of PD localization
Abstract: Extruded insulations have been used in medium voltage power cables since the sixties. These materials have high breakdown strength and a low dielectric constant, making them ideal insulating materials for power cables. However, cables installed in the late sixties and early seventies began failing after only five to ten years in service. The majority of the failures were caused by tree-like growths, referred to as water trees, in the insulation. Extensive studies were made to determine the mechanisms of water treeing, in the development of accelerated aging tests on cables, and to develop tree retardant materials to suppress water trees. The presentation will briefly review the aging mechanisms, the parameters that affect tree growth, and also the different accelerated tree-growth and accelerated aging tests.
Biography: John Densley, ArborLec Solutions - John Densley was graduated from Queen Mary College, University of London, with a B.Sc. and Ph.D. degrees in 1964 and 1967. In 1968, he joined the Power Engineering section of the National Research Council of Canada, where he became leader of the electrical insulation research group. In 1991, Dr. Densley joined the Research Division of Ontario Hydro, now Ontario Power Technologies, where he continued his research in the area of electrical insulation until his recent retirement. Dr. Densley is now a consultant with ArborLec Solutions Inc. He is a Fellow of the IEEE, active in the PES Insulated Conductors Committee, the Dielectrics and Electrical Insulation Society, and is a Registered Professional Engineer in the Province of Ontario.
Abstract: Wet testing of cables in various stages of completion to compare materials or attempt to predict relative longevity in service has been conducted since the early 60's or longer. The direction of the temperature gradient and location of the test water have a controlling influence on the test results. These factors determine if the test must be limited to comparing very similar materials or if the test can also be used to compare dissimilar materials. As a service life predictor, the most valuable data points may be the outliers which, unfortunately, are all to commonly ignored.
Biography: Carl C. Landinger, PE, Dir. Of Technology, Hendrix Wire & Cable - Carl Landinger received his BSEE degree from Marquette University, Milwaukee, WI. Prior to joining Hendrix in 1990 he held various technical positions at Wisconsin Electric Power Co., applications engineer for Anaconda Wire & Cable, chief engineer for Wis. Electric Cooperative Assoc., manager of insulated conductor engineering for ALCOA Conductor Prod. Co. and was manager of technology for Conductor Products Inc.
He has taught numerous short courses at Texas A&M, Univ. of Wis., Iowa State and Univ. of W. Virginia. He has presented numerous technical papers at national and regional technical meetings.
Abstract: The AWTT is part of a qualification test designed to assure that cables meet basic performance requirements. The primary information provided is the reduction in ac dielectric strength as the cable is aged in water up to a year under relatively moderate accelerated test conditions. It also provides specific, minimum performance requirements that cables have to meet in order to be considered qualified. It is also often used as a performance comparison test. The test setup is well defined, and the test conditions are specifically established. This presentation will provide a review of the AWTT test procedures, typical AWTT data as well as the pros and cons of the data generated by the AWTT.
Biography: Richard A. (Rick) Hartlein - Mr. Hartlein spent the first 25 years of his career working at the Georgia Power Research Center evaluating transmission and distribution materials, developing material specifications and industry standards, managing research and testing programs and providing engineering services. He came to Georgia Tech in 1996 where he helped to establish NEETRAC, the National Electric Energy Testing, Research and Applications Center. As NEETRAC’s Underground Systems Program Manager, Mr. Hartlein works to develop and manage research and testing projects related to electric utility underground cable systems. He also participates in a variety of industry technical organizations related to this field and is the past Chair of the IEEE Insulated Conductors Committee.
Abstract: A review of the various ACLT protocols being employed at General Cable's Marshall Technology Center is presented. The difference between a time-to-failure ACLT protocol and a retained breakdown strength ACLT protocol will be explained. ACLT test variables and their influence on test results will be discussed. Mathematical aging model development using ACLT test techniques will be discussed and an aging model for XLPE cables operating in a wet environment will be presented. Finally, a relationship between ac breakdown strength and cable life for XLPE-insulated cables will be presented.
Biography: Mark D. Walton (M'90, SM'94) was born in Crockett, TX on June 10, 1950. He received his BSEE degree from the University of Texas at Arlington in 1972 and his MSEE degree from the University of Houston in 1976. From 1973 to 1979 he was with NASA at the Johnson Space Center in Houston, TX. He joined Alcoa Conductor Products Co. (ACPC) in Scottsville, TX in 1979 where he was employed as a senior electrical engineer in their R&D Laboratory. He joined Conductor Products Inc. (CPI) in 1984 with ACPC's departure from the power cable business. He has managed to stay employed with CPI's acquisition by Reynolds Metals Co. in 1989, RMC's acquisition by BICC Cables Corporation in 1992, and BICC's acquisition by General Cable Corporation in 1999. He is currently Manager of Customer Testing Services at General Cable's Marshall Technology Center. He is a senior member of the IEEE and a voting member of the Insulated Conductor Committee (ICC) of the IEEE. He is also a member of Eta Kappa Nu, Tau Beta Pi, and is a registered professional engineer in the State of Texas. He has authored or co-authored several IEEE technical papers and 3 EPRI reports. He holds one U.S. patent.
Abstract: After all the negative experience collected so far with poor performing extruded cables, it is very important to know if a new cable insulating material will be susceptible to water treeing or not. By applying accelerated aging, in a relative short period of time the material is being tested for how it will perform under service conditions during cable life. However, accelerated aging under power frequency conditions usually takes a long time of about 2 years before any decisive conclusions about the performance of the insulating material under service conditions with respect to water treeing can be drawn. Apart form the high testing costs; this long period of time may cause liability problems, because usually the cable is already in service before the accelerated aging test has been completed.
Extensive testing of laboratory models as well as cable samples demonstrated clearly that accelerated aging under 500 Hz conditions could reduce the necessary aging time from 2 years to 3000 h, (about 4 months), without influencing the aging mechanism as observed under power frequency conditions.
In this presentation a survey will be given of test results to prove the accelerating effect of 500 Hz testing voltage. Besides information will be given about practical testing experience in the Netherlands, where according to the national standard this type of testing is being used for several years successfully.
Biography: Willem Boone obtained his Masters Degree in Electrical Engineering from Delft University of Technology in The Netherlands and has thirty five years of experience with KEMA in the field of Electrical Power Transmission and Distribution. Mr. Boone is recognized world-wide as an expert in power cables, and he has made a significant contribution to the development of testing methods and related international standards for the electrical cable industry. He is now the manager of KEMA Diagnostic Services in the USA, offering diagnostic cable testing services to the utility customers. He is chairman of a CIGRE working group on Maintenance of HV power cables and he is an active member of the Insulated Conductors Committee of the IEEE.
Abstract: HD 605 ‘Electric cables - Additional test methods’, prepared by CENELEC TC20 for Europe, specifies the test methods for distribution and power station cables with extruded insulation for rated voltages from 0.6/1kV up to 20.8/36kV. As published in 1996, HD 605 included a large number of different long duration test methods to assess the resistance to water of medium voltage extruded insulation cables. CENELEC TC20 agreed that a study be carried out to formulate a harmonized test regime.
There were three basic test methods in HD 605, namely the so-called UNIPEDE, VDE and Temperature Gradient regimes. An attempt was made to harmonize these three regimes but, after due consideration, it was agreed as a first step to rationalize the variations existing in the UNIPEDE regimes. This involved the study of a number of parameters, including cable construction, preconditioning, water type, aging voltage/stress, aging temperature and test duration. Tests were made at a number of establishments by cable manufacturers, utilities and test houses throughout Europe and included comparison with the VDE regime. The Temperature Gradient regime was left for future consideration.
This presentation outlines the test methods, the tests carried out and the results obtained to achieve harmonization of the UNIPEDE and VDE regimes, a harmonized test method having been submitted in 2000 for inclusion in HD 605. Tests are in progress to this regime and results are expected to be available in 2002. Future considerations include shortening of the test duration, taking into account not only the results of the harmonized regime but also higher frequency aging and the temperature gradient regime.
Biography: Vic Banks, Pirelli Cables (UK), Energy Cables Division - Vic Banks graduated from University College London with a B.Sc. in 1963. Joined BICC Research and Engineering Division, London to work on a number of oil-filled paper cable insulation projects, which resulted in the development of paper/polypropylene laminate (PPL). Became leader of the High Voltage group in 1977 to evaluate the performance of fluid-filled PPL cables and accessories for voltages up to and including 400kV. Also carried out studies to assess medium voltage (MV) extruded insulation cables, particularly the long term performance, and to develop a range of accessories. Transferred to BICC Cables, Power Division, Wrexham in 1988 to continue work on MV extruded insulation cables, including investigation of water treeing under an EEC contract in liaison with universities and other cable manufacturers. In 1990, became Standards Manager and member of a number of national, European and international standards technical committees. Continued in this position and work in the standards arena for first BICCGeneral and then Pirelli Cables. At present, the memberships include chairman of IEC TC20 WG16 ‘High voltage cables’ and CENELEC TC20 WG09 ‘Cables for use by electricity supply companies’ Task Force ‘Long duration tests’.
Abstract: Together with the improvement of designs, materials and compounds, test methods for accelerated aging under wet conditions have also been developed. One goal has been to have a tool for discriminating between "bad" and "good" cables. Standardized wet aging test methods for extruded medium-voltage cables such as the North American AWTT according to AEIC Specification CS5-94 and the German VDE test according to DIN VDE 0276 are able to differentiate between insulation systems. The retained AC breakdown strength after aging is the most important criterion. Water tree investigations only provide additional information. Wet design cables that perform well in these tests should have a life expectancy of more than 50 years.
Biography: Lauri Hiivala received a Bachelor of Applied Science in Electrical Engineering from the University of Toronto in 1965. Since graduation, he has been with Nexans Canada in Toronto. He has held various positions involving the design and development of power cables and accessories from 300 V to 500 kV. He is currently Director of Application Engineering, Energy Networks Division.
His professional activities include being Member, IEEE Power Engineering Society; Past Chairman, Insulated Conductors Committee; Chairman, ICEA Liaison Group 690 Utility Power Cable Standards Technical Advisory Committee (UPCSTAC) and Canadian Specialist, IEC TC 20 WG 16 Cables with Extruded Insulation and their Accessories. Other memberships include CIGRE and the Association of Professional Engineers of Ontario.
Abstract: Low temperature, voltage accelerated aging of medium voltage cable has been used successfully at CTL Laboratories for over 15 years to simulate URD cable aging in the field. This aging method is being used at present, in a number of cable projects. In one of these projects, the laboratory aging at 2.5 times rated voltage is being compared with aging in the field at 2.5 times rated voltage and also field aging at operating voltage. The rate of degradation of the low temperature aged cable justifies the use of this low cost technique, in the accelerated test aging of the cables. The presentation will provide details of the methodology and overall results.
Biography: Carlos Katz has been active in the field of power transmission and distribution cables for over 40 years. He held research and engineering positions at General Cable Corporation and Phelps Dodge Cable and Wire Company until he became co-founder of Cable Technology Laboratories, Inc., in 1978.
Mr. Katz had conducted many analytical and laboratory investigations of degradation and failure of cable insulation and accessories for both distribution and transmission cable systems. He was instrumental in developing methods to extend the service life of extruded distribution cable. Mr. Katz is the author or co-author of more than 35 technical papers and holds 16 USA Patents. He is a Fellow of the IEEE, a voting member of the ICC and a member of CIGRE.
Abstract: The ACLT has historically been used to evaluate the performance of 15 kV class cable cores – that is cables with a 175 mil wall, no jacket and a conductor that is not water blocked. However, utilities commonly employ cables with a water blocked conductor and a jacket and they often use cables with a wall thickness that is greater than 175 mils thick. These changes to the cable structure can have a profound influence on cable performance. For this reason, Georgia Tech NEETRAC has explored the use of ACLT to test complete cable designs instead of cable cores. This presentation will cover how the cable design aging test is conducted and provide results from an early design test program.
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