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The usage of harmonic electric field on detecting faulty insulators on high voltage DC transmitting lines

Since now few people have thought about online detection of DC insulator on high voltage transmitting line. In this paper, a new method of detecting composite insulator and porcelain insulator on DC line is put forward. It diagnoses insulator by the distribution of harmonic electric field. Around insulators on DC transmitting line there exists strong harmonic electric field. Through the distribution of this electric field along insulator, conductive defect can been found, because the abnormal changes of the distribution curve identify defects at where changes take place. The sensitivity of this method was studied at laboratory by defective insulator and artificial defect. The results identify that this method can find defect of 5 cm length at high voltage part or 15 cm length at middle part of composite insulator at the best, or one piece of zero porcelain insulator. Experiment on real 500 kV DC line was made and the result proved this method is feasibility.