Abstract
This paper focuses on the electrical tree growth characteristics in epoxy resin with dc-impulse voltage caused by line fault and switching surges in liquid nitrogen (LN2). Electrical tree initiation tests were conducted on molded epoxy resin with a needle–plate system. The test samples were stressed with a dc voltage amplitude of 10 kV and an impulse voltage amplitude of 24 kV at 77 K. With a wide range of voltage frequencies and different impulse polarities, four different waveforms of dc-impulse voltage were used as applied voltage. Result shows that the electrical tree tends to grow longer when the dc and the impulse are of the same polarity. The impulse frequency plays a crucial role in tree initiation and growth process. The tree initiation probability increases with the frequency rising from 50 to 400 Hz in epoxy resin. Different charge transportation processes are discussed based on four different voltage waveforms. The collision ionization and charge recombination have a decisive effect on electrical tree initiation. The impulse voltage is worth regarding in the operation of a superconducting cable system.
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