101 / 2018-08-24 16:53:21

Experimental Study on Surface Charge Accumulation and Dissipation of HVDC GIL Post Insulator

HVDC GIL,post insulator,surface charge,accumulation and dissipation

The High Voltage Direct Current (HVDC) gas insulated transmission line (GIL) has the advantages of large conveying capacity, small transmission loss, and high safety performance. In the special environment with large altitude difference, harsh natural conditions and high environmental protection requirements, it is the first choice to replace the overhead line and high voltage DC cable for power transmission. Studying the law of charge accumulation and dissipation of GIL post insulators in DC electric field, especially the charge accumulation behavior when there are tiny defects on the surface of insulator or electrode, is the premise of reducing surface flashover and near-field gas breakdown, and also is the key to developing HVDC GIL core product technology. A set of post insulator surface charge measurement system was established. The electrostatic probe can measure the potential distribution of the entire surface of the insulator only by the accumulated charge. The accumulation and dissipation laws of the surface charge of insulators with different voltages (+200kV-+450kV), gas pressure (1atm and 4atm absolute values) and polarity reversal were studied. The results show that with the increase of positive voltage, the surface potential of the insulator near the high voltage electrode is negative and its absolute value is gradually increased. The surface potential of the insulator near the ground electrode is positive, and its potential is gradually increased but the increase is smaller than the potential nearby the high voltage electrode . Under the same voltage and pressurization time, the higher the gas pressure, the less accumulated charge and the faster it dissipates; The spark discharge near the insulator has a significant polarity effect on the surface charge accumulation: the spark discharge caused by the positive rising voltage causes the insulator surface potential of the insulator to be negative on the high voltage electrode side and positive on the ground electrode side, and the spark discharge generate when the negative voltage rising causes the surface potential of the insulator to be all negative, and the absolute value of the potential is significantly larger than the positive polarity discharge; When the positive polarity reverse to the negative polarity, the insulator surface potential is negative, and the absolute value of the potential increases by an average of 97% after the reversal. When the negative polarity changes to the positive polarity, the potential on the high voltage side changes from negative to positive, and the potential on the ground side remains basically unchanged. Comparing the surface potentials in SF6, N2 and CO2 gas atmospheres, it can be seen that the surface potential of SF6 gas is the lowest, followed by N2, the highest is CO2, and the surface potential fluctuation in the SF6 gas environment is the smallest compared to other gases. The results of this paper provide more comprehensive experimental data for the actual operating behavior characteristics of the post epoxy resin insulator, which has certain reference value for guiding the design of HVDC GIL gas-solid insulation structure.