Basic Study of Transient Breakdown Voltage in Solid Dielectric Cables. Final Report

摘要

A comprehensive review of the technical and scientific publications relating to crosslinked polyethylene (XLPE) and ethylene propylene rubber (EPR) insulated cables revealed that there is very little known with respect to the life expectancy, the final factory voltage test background and the mechanism of voltage breakdown of these cables. In this study a new methodology for the investigation of breakdown voltages of XLPE and EPR insulated cables was developed which is based on the investigation of breakdown voltages at various voltage transients such as unipolarity pulses and dual-polarity pulses, and a.c. voltage at power and high frequency. Also, a new approach to statistical testing was developed which allows one to establish a correlation among the breakdown voltages obtained with various voltage transients. Finally, a method for the determination of threshold voltage regardless of the magnitude of apparent charge was developed. Extensive statistical testing of breakdown voltages was conducted using: impulses with front durations from approximately 1.5 to 1000 mu s and times to half-values from 40 to 3000 mu s; dual-polarity pulses consisting of d.c. voltage and standard impulse of opposite polarity; combined a.c. and d.c. voltages; and a.c. voltages at power and high frequencies. Based on the results of this testing, a model of breakdown and electrical aging of XLPE and EPR insulated cables was developed as well as life expectancy characteristics for high voltage stress XLPE insulated cables operated in a dry environment at room temperature and at 90 exp 0 C. Life expectancy characteristics for EPR insulated cables are approximated. A test procedure including requirements for full-reel factory voltage withstand and partial discharge testing of finished XLPE and EPR insulated cables is proposed. Cables that pass the proposed tests will exhibit a smaller rate of failure in service than cables tested in accordance with present practices. (ERA citation 06:030541)