Spring 2002 - Accelerated Cable Testing and Its Correlation to Field Testing
For the spring 2002 ICC Educational Program we had the pleasure of
featuring a renown group of experts in the field of accelerated laboratory aging of medium
voltage extruded power cables. Their presentations covered various accelerated cable aging
tests used in North America and Europe. Each aging test was described, typical data will
be presented and where possible, correlation to field aging was discussed.
- Aging of Medium Voltage Extruded Dielectric Cables Under Wet
John Densley, ArborLec
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. These slides are
available in a 131 kB PowerPoint file or as a much
smaller (72 kB) PDF file.
- Its All In The Interpretation Outliers Count
Carl C. Landinger, PE, Dir. Of
Technology, Hendrix Wire & Cable
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. These
slides are available in a 80 kB PowerPoint file or
as a much smaller (38 kB) PDF file.
- AEIC Accelerated Water Treeing Test History, Test Program,
Results, Pros and Cons
Rick Hartlein Georgia
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. These slides are available in a 828 kB PowerPoint fileor as a much smaller (110 kB) PDF file.
- Accelerated Cable Life Testing
Mark D. Walton, Manager of
Customer Testing Services, General Cables Marshall Technology Center.
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. These
slides are available in a 752 kB PowerPoint file or as
a much smaller (313 kB) PDF file.
- Accelerated Cable Aging At 500HZ, Time Is Money!
Willem Boone, MSc, KEMA
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. These slides are
available in a 2749 kB PowerPoint file or as a much
smaller (31 kB) PDF file.
- Harmonization of Long Duration Test Method in Europe
Vic Banks, Pirelli Cables (UK),
Energy Cables Division
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. These
slides are available in a 340 kB PowerPoint file or as
a much smaller (23 kB) PDF file.
- Comparative Wet Aging Tests of Medium Voltage XLPE Cables (AEIC
AWTT & DIN VDE 0276)
Lauri Hiivala, Nexans Canada
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. These
slides are available in a 9759 kB PowerPoint file or
as a much smaller (152 kB) PDF file.
- CTL Aging of Medium Voltage Cables
Carlos Katz, Chief
Research Eng., Cable Technology Laboratories, Inc.
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. These
slides are available in a whopping 15MB PowerPoint file
or as a much smaller (296 kB) PDF file.
- Using ACLT as a Cable Design Aging Test
Rick Hartlein Georgia
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. These slides are available in a 992 kB PowerPoint file or as a much smaller (97 kB) PDF file.