Effect of dc testing on extruded cross-linked polyethylene insulated cables
- Detroit Edison Co., MI (United States)
- Essex Cable Co., Lafayette, IN (United States)
This project was initiated to investigate the effect of dc testing on extruded crosslinked polyethylene (XLPE) insulated cables. A series of experiments were conducted in the laboratory, where the samples were aged under accelerated conditions of 60 Hz, 150 v/mil, nominal 90{degree}C conductor temperature load cycled daily, with tap water in the conductor strands and outside of the sample. DC test voltages at the factory level (70 kV), at the field proof level (55 kV), and the maintenance level (40 kV) were employed. The effect of dc testing on unaged and aged cables was studied using ac breakdown strength measured periodically and time to failure as criteria for life. The test program also encompassed aged and new cables spliced together. The effect of dc on such systems was investigated. Application of dc factory, proof and maintenance testing did not affect the ac breakdown strength. DC acceptance (maintenance level of 40 kV for 15 minutes) testing of aged XLPE insulated cables reduces its remaining life. DC voltage testing at 40 kV of XLPE cable that failed during ac aging reduces its remaining life, when subjected further to ac voltage after splicing with a new cable section. Statistical analysis of the data revealed a probable existence of an inflection point in the aging time, beyond which cables subjected to multiple dc voltage applications during aging start to fail at an increased rate. DC testing of new cable at factory level (70 kV) does not cause any reduction in its service life. Water tree growth appears to increase upon dc testing. Recommendations are made to operating utility companies not to do dc acceptance (proof or maintenance) testing at 40 kV on XLPE insulated cables, failed once in service and then spliced. DC testing can be done at 55 kV in the field on a new cable prior to energizing when there is no aged cable spliced in the system.
- Research Organization:
- Electric Power Research Inst., Palo Alto, CA (United States); Detroit Edison Co., MI (United States); Essex Cable Co., Lafayette, IN (United States)
- Sponsoring Organization:
- Electric Power Research Inst., Palo Alto, CA (United States)
- OSTI ID:
- 10138387
- Report Number(s):
- EPRI-TR--101245; ON: UN93009484
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
240300
36 MATERIALS SCIENCE
360606
AGING
BREAKDOWN
DIELECTRIC PROPERTIES
DIRECT CURRENT
ELECTRIC CABLES
ELECTRICAL INSULATION
ELECTRICAL INSULATORS
ELECTRICAL TESTING
EXTRUSION
FAILURE MODE ANALYSIS
PHYSICAL PROPERTIES
POLYETHYLENES
POWER TRANSMISSION LINES AND CABLES