直流叠加冲击电压下XLPE/EPDM界面的空间电荷特性

Space Charge Characteristics of XLPE/EPDM Interface Under DC Superimposed Impulse Voltage

在直流输电线路中,电缆线路易受到操作或雷电过电压的侵扰,导致线路在直流电压的基础上叠加冲击电压,再加之电力设备绝缘的感/容效应,导致各元件间的电磁能量转换过程造成线路系统发生震荡,产生上百乃至上千赫兹的高幅值冲击电压波,严重影响电力设备绝缘长期运行可靠性。为此基于实验室已有的直流叠加冲击电压下PEA法空间电荷测量系统,分别测量了直流电压、冲击电压、直流叠加冲击电压作用下XLPE/EPDM复合介质中空间电荷特性。实验结果表明,在直流电压作用下,随着电场的升高,两种介质的电导率特性发生反转,导致界面电荷量逐渐发生变化;冲击电压作用下,正冲击导致界面处出现负电荷的积累,负冲击导致则界面处出现正电荷的积累,电荷量会随着场强增大而增加;当直流叠加同极性冲击,等效直流电场倍增,由两种材料电导率大小的反转导致界面电荷呈现先减小后反向增加趋势;当直流叠加异极性冲击,在叠加期间,由于等效直流电场的降低以及暂态电场极化的影响,导致界面电荷减少。

Among DC transmission lines, cable line is susceptible to operation overvoltage and lightning overvoltage, which causes the line to superimpose impulse voltage on DC voltage. In addition, the inductance/capacitance effect of power equipment insulation leads to the electromagnetic energy conversion process between the components that causes the line system to oscillate, generating hundreds to thousands hertz high-amplitude impulse voltage waves. These situations seriously impair the long-term reliability of power equipment insulation.Consequently, the space charge of XLPE/EPDM composite sample under DC voltage, impulse voltage and DC superimposed impulse voltage was measured based on DC superimposed impulse voltage PEA measurement system in laboratory. Experimental results show that, under DC voltage, conductivities of two media are reversed which causes gradual change of interface with the increase of electric field;under impulse voltage,positive voltage causes accumulation of negative charge at the interface, negative voltage causes accumulation of positive charge at the interface, and the amount of charge increases with the increase of electric field. When DC superimposed same polarity impulse voltage is applied, the equivalent DC voltage field is multiplied and space charge at the interface decreases first and increases in opposite direction due to the reversal of two material’s conductivities. When DC superimposed opposite polarity impulse voltage is applied, space charge at the interface decreases due to the decrease of equivalent DC voltage field and transient electric field polarization in the superposition period.