{'fraction_non_alphanumeric': 0.01909307875894988, 'fraction_numerical': 0.0, 'mean_word_length': 5.484536082474227, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Electrical Tree Initiation Properties in Cross-Linked Polyethylene Under DC-Impulse Composite Voltages

DC cables may be subjected to impulse overvoltage during operation, which may cause electrical tree inside the cable insulation. So, it is necessary to investigate the influence of impulse voltage on the insulation of dc cable. The initiation characteristics of electrical trees in cross-linked polyethylene under dc-impulse composite voltages were investigated in this paper. The influences of pre-stressed dc voltage, impulse voltage, polarity, and space charge accumulation on the initiation characteristics were analysed. The experimental results indicated that the impulse voltage would facilitate the electrical tree initiation and had an obvious polarity effect. Electrical tree initiation voltages under positive impulse voltages were lower than those under negative ones, which was independent of the polarity of the pre-stressed dc voltage. With the increase of the pre-stressed dc voltage, the initiation impulse voltages declined when dc and impulse voltages were of the same polarity. In the presence of opposite polarity, the initiation impulse voltage did not change obviously at first and then increased with the pre-stressed dc voltage.