Electroluminescence in XLPE under impulse voltage stress

Time resolved electroluminescence (EL) measurements were performed on high voltage cable grade crosslinked polyethylene (XLPE) insulation with positive, negative and alternating polarity impulses at various repetition rates. To create divergent fields in the insulation, needle electrodes made of semiconductive polymer were used. It is shown that the EL emission probability is lower for unipolar as compared to alternating polarity impulses and more EL pulses are emitted during the negative than the positive polarity. However, the EL emission probability is independent of the impulse repetition rate from 0.001 to 1500 Hz and this shows that for up to 16 min there is practically no decay of the space charge near the semicon tip. The EL pulses are always grouped within two distinct time periods between which there is no EL activity