电老化过程中直流电场对油纸绝缘空间电荷特性的影响

Effect of DC Electric Field on Space Charge Characteristics of Oil-paper Insulation in Electrical Aging Process

通过研究不同电老化过程中直流电场对油纸绝缘的空间电荷特性的影响,可为换流变压器在长期高场强运行下油纸绝缘的空间电荷特性提供试验依据。利用电声脉冲法研究了油纸绝缘在20 k V/mm的直流电场下老化1 000 h不同阶段下的空间电荷特性,结果表明:在电老化的不同阶段,油纸绝缘在极化过程中的空间电荷特性主要表现为都出现了同极性电荷注入和积聚;随着老化程度的加深,油纸绝缘内部积聚电荷量越大,去极化电荷消散速率越慢,老化过程中陷阱密度和深度都在增大,促进空间电荷被陷阱捕获而积聚;整个电老化过程中,快速运动电荷量变化不大,而慢速运动电荷量逐渐增大主要是由于陷阱密度的增大,导致电荷迁移率下降;电老化过程中电荷的积聚导致极化过程中电场畸变明显,容易产生大电流而使击穿电压下降。

By studying the effect of DC electric field on space charge characteristics of oil-paper insulation in the different aging processes, we call provide experiment references for space charge characteristics of oil-paper insulation of converter transformers while it is running for a long time under high electric field intensity. Therefore, we studied the variations of space charge characteristics of oil-paper insulation with electrical aging for 1 000 hours under electric field of 20 kV/mm by using the pulsed electro-acoustic method. The results show that the variation rules of space charge characteristics are similar at different aging status. As the space charge is caught by the trap, homo-charge injection and accumulation are easy to take place. As the degree of aging deepens, the amount of charge accumulation inside the sample becomes larger, and the dissipation velocity of charge during depolarization becomes slower, since both trap density and trap level are in- creasing. Throughout the electrical aging process, the amount of fast moving charge does not remarkably change, while slow moving charge grows gradually with the trap density increasing, which decreases the mobility rate. Charge injection caused by electrical aging leads to electric field distortion inside the samples during polarization, which easily promotes the generation of large current and lowers the breakdown voltage.