Electrochemical treeing in PE and XLPE insulated cables - frequency effects and impulse degradation

Abstract

This paper describes the effect of rrequency on the rate of growth of electrochemical trees in PE and XLPE insulation, extruded into thin wall mini-cables over a #14 AWG copper wire (round and square conductors). The cables were subjected to treeing tests at several frequencies in the range of 60 to 8000 Hz.The tree grvwth rate is increased by increasing the frequency, and there appears to be saturation in this effect at approximately 1000 Hz. At all frequencies the tree growth rate in XLPE was considerably less than that in PE.The results of dielectric tests on cables subjected to accelerated treeing tests indicate that the trees reduce both DC and impulse breakdown strength of the mini-cables. When trees penetrate the wall, the impulse strength drops to about 40% of its original value in both PE and XLPE cables. As the streamer trees grow in length, a substantial reduction in DC breakdown strength was observed.

The effects of water immersion on the electrical properties of miniature XLPE cables

“…These results were surprising considering the effects of frequency reported by Srinivas et al 14 who observed a steady decrease in the time to grow a tree 0.375 mm long for frequencies up to 1.5 kHz. However in a later publication, 13 the same authors presented additional data.…”

Condition assessment of XLPE insulated cables based on polarization/depolarization current method

“…In order to obtain XLPE samples with water trees, numerous studies have been performed to explore how water trees grow, how they bring about the failure of XLPE cables and how they can be detected [5][6][7]. It is found that the magnitude and frequency of the applied electric field have an observable effect on the growth of water trees.…”