脉冲方波频率对局部放电特性的影响及机理分析

为探讨脉冲方波电压频率对局部放电特性的影响,基于超高频(UHF)检测方法和IEEE 488.2传输协议,构建了宽频、高速数据采集局部放电测试系统.利用该系统,研究了变频电机耐电晕漆包线的局部放电脉冲幅值、相位和时频特性.研究结果表明:频率200 Hz以上的高频脉冲电压使空间电荷扩散效应减小,增大了局部放电初始电子产生的概率,使得局部放电瞬时电压降低,出现幅值小于200 mV的局部放电脉冲.在高频脉冲电压下,当局部放电发生在电压上升时段时,快速变化的电压幅值将改变局部放电特性,使得局部放电脉冲在1～2 GHz高频能量的比重增大.因此,根据相关标准检测变频电机局部放电时,为易于激发绝缘薄弱点处局部放电,宜采用频率低于200 Hz的低频脉冲方波电压,且局部放电超高频传感器在1.2 GHz及以上频率处应具有较好的增益特性,并采用500 MHz的高通滤波器,以提高测试系统的信噪比. 

Influence of Frequency of Impulsive Square Wave Voltage on Partial Discharge Characteristics and Its Mechanism

To probe into the influence of frequency of (impulsive) square wave voltage on partial discharge (PD) characteristics, a system for PD detection specially used at square wave voltage was designed by resorting to the ultra-high frequency (UHF) detection method and the IEEE 488.2 protocol. By utilizing this system, PD features of corona resistance enameled wires, i.e., magnitude, occurring phase and time/frequency characteristics, were investigated. The research results show that high-frequency (above 200 Hz) square wave voltage will make space charge decaying rate reduce to increase the probability of initial electrons for PD, decrease instantaneous voltage when PD occurs and result in PD events with voltage magnitudes below 200 mV. Under high-frequency square wave voltage, when PD occurs at the rise time of voltage, PD features will be changed to make energy components with 1 to 2 GHz frequency increase. So when PD of inverter-fed motors is detected on the basis of related standards, low-frequency (below 200 Hz) square wave voltage should be used to induce the PD of insulation weak points easily. Furthermore, to increase the signal-to-noise ratio, UHF sensor should have a better performance in the frequency range equal to and higher than 1.2 GHz, and 500 MHz high-pass filter ought to be adopted.