温度对油-纸界面处微水迁移与局部放电的影响

Effect of Temperature on Moisture Migration and Partial Discharge at the Oil-Paper Interface

变压器内部温度的改变会使油-纸绝缘中水分分布和聚集位置发生改变,而局部高含水量会严重影响油-纸绝缘的电气强度。因此,有必要研究温度对油-纸绝缘界面处微水迁移与局部放电(PD)的影响。该文利用楔形-板电极,研究了升温、起泡及降温过程中不同含水量(W_(C)=3.61%和5.76%)的油-纸绝缘体系在水分瞬态作用下的PD特性。在温度变化过程中,持续监测油的温度、含水量和水活性,并采用升压及恒定电压法进行PD试验。试验结果表明,温度升高,油-纸界面处局部放电起始电压(PDIV)短时增加,随后PDIV开始逐渐降低且PD强度突然增强。两种含水量体系的油中含水量均逐渐增加。油浸纸板含水量越高,从纸板进入油中的水分越多。气泡出现,PDIV快速下降,油中含水量急剧增加。降温阶段,两个体系的PDIV呈现先减后增趋势,与之相对应,PD强度呈现先增后减趋势,且PD均保持在一个相对较高的水平。油温降至室温,PD并未完全消失。该研究成果对油浸式电力设备中水分的实时监测及其绝缘性能的评估具有重要理论价值。

The increase and decrease of internal temperature in transformers can cause changes in the distribution and accumulation of moisture in the oil-paper insulation,and high moisture content can seriously affect the electrical strength of the oil-paper insulation.Previous simulations and tests were conducted at temperatures not exceeding 80℃and without bubble interference.Few scholars have raised the temperature to the initial temperature bubble effect to study the moisture migration and partial discharge(PD)characteristics under extreme temperature conditions.Therefore,it is necessary to study the effects of temperature changes during the heating,bubbling and cooling phases on the moisture migration and PD at the oil-paper insulation interface.In this study,using wedge-plate electrodes,the PD characteristics of oil-paper insulation systems with different moisture content(W_(C)=3.61%and W_(C)=5.76%)were investigated under transient moisture conditions during the processes of heating,bubbling,and cooling.During the temperature change process,the temperature,moisture concentration,and moisture activity of the oil were continuously monitored,and PD tests were conducted using the voltage rise and constant voltage methods.For the voltage rise,the voltage was increased at a rate of 1 kV/(10 s)and the partial discharge inception voltage(PDIV)was measured by this method to determine the PD charge threshold for the first PD event as 100 pC.If the applied voltage reached the PDIV,it was immediately recorded and the voltage was reduced.The rest of the tests were performed at a constant voltage.All tests were performed in an electromagnetically shielded room to avoid interference with PD measurements from external activities.The experimental results showed that as the temperature increased,the PDIV at the oil-paper interface briefly increased,followed by a gradual decrease in PDIV and a sudden increase in PD intensity.The moisture content in the oil gradually increased in both systems.The higher the moisture content in the oil-immersed paperboard was,the more moisture entered the oil.Bubbles appeared,PDIV rapidly decreased,and the moisture content in the oil sharply increased.During the cooling stage,PDIV in both systems showed a decreasing-then-increasing trend,and correspondingly,PD intensity showed an increasing-then-decreasing trend,maintaining a relatively high level.Even when the oil temperature dropped to room temperature,PD did not completely disappear.The research findings have important theoretical value for the real-time monitoring of moisture in oil-immersed electrical equipment and the evaluation of its insulation performance.