Aging of Isolating Materials in Power Cables

There is more than 160 years that polymers are using in cable industry. Polyethylene of low and high density [ LDPE , HDPE ] and crosslinked polyethylene [ XLPE ] gradually succeeded paper and polyvinylchloride[ PVC]. This paper discusses some aspects of aging processes of polyethylene working conditions. Electrical and water treeing are considered, dependent upon morphology and induced characteristics of the insulating material. Subsequently presented interim tests on crosslinked polyethylene and ethylene propylene [ EP ] isolated cables aged under identical conditions for 36 months at 30oC (±5oC) with and without application of voltage transients. Aging voltages were from 1 to 2.5 times of rated voltage. Failures during aging have occurred in EP isolated cable while none have occurred in XLPE isolated cable. Both type of cables experienced a large drop in ac and impulse voltage breakdown strength early in the aging process. Voltage transients have slightly affected the ac and impulse voltage breakdown strength.

Keywords:

aging of isolating materials , electric treeing , water treeing , accelerated aging