Study on the Influence Factors and Criteria of PDC Diagnosis Method

Published in 2015

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Summary

When the insulation of 10 kV XLPE cable is diagnosed with polarization and depolarization current measurements, the length of cable has a strong influence on the measured current, which makes it difficult to set the proper measuring range when obtain the current. To solve this problem and design the PDC diagnostic apparatus, this paper built the polarization and depolarization model based on Debye model firstly, then the 10kV XLPE cable samples which were accelerated ageing at a 10 kVrms and 5 kHz ac voltage for 250h and 400h were polarized under -1kV for 1800s and depolarized for 1800s, polarization and depolarization current during this period were measured, lastly, the influence of cable length on polarization and depolarization current were analysed based on the model and experimental result. The analysis shows that the polarization current amplitude appears linear growth with the increase of cable length and it is limited by the charging resistor, the depolarization current amplitude first increase and then decrease with the increase of cable length. For 10kV XLPE cable, when the polarization voltage is -1kV, the charging resistor is 1MO, the polarization current amplitude cannot beyond 1mA no matter how long the cable is, and the maximum depolarization current amplitude will reach to maximum 7036nA when the length of cable is 900m and depolarization measurement time is 0.4s.