改进电声脉冲法的交流空间电荷测量新方法

New Method for Space Charge Measurement Under AC Stress Via the Pulsed Electroacoustic Method

提出一种交流电压下的电声脉冲法空间电荷测试新方法。采用电脉冲作为触发源,利用数字示波器的长存储功能同时获取空间电荷信号和高压交流电压信号,从而避免了传统交流空间电荷测试方法的硬件同步。通过调整脉冲发生器的频率可获取不同相位下的高压交流下的空间电荷响应,并通过平均若干个交流周期的空间电荷信号获得足够信噪比的相位相关的空间电荷信号。通过对低密度聚乙烯工频50 Hz下的空间电荷测量结果表明,在交流电场下,下电极附近区域会形成异号电荷;与传统的交流空间电荷测量系统相比,由于测量时间得到很大程度缩短空间电荷信息能够最大限度保存,并且新系统较老系统有更高的相位分辨率,空间电荷衰减图形更能逼真的反映电荷动态变化。

A new method for space charge measurement resorting to the pulsed electroacoustic （PEA） method under HV AC stress is presented. This work consists in using a long memory digital oscilloscope to simultaneously measure both the piezoelectric signal and the applied AC stress for each voltage pulse. There is no need for synchronization between pulse generation and HV AC stress,and hence no hardware change of classic PEA system. The phase of the HV AC stress can be resolved into different profiles by frequency adjustment of the pulse generator. Several periods of the HV AC stress are necessary for obtaining the set of profiles. Preliminary results obtained on a low density polyethylene （LDPE）film under 50 Hz AC stress show that heterocharge can be formed in the region close to the lower electrode under AC electric field. The results captured from the new system have better phase resolution than the old system. The space charge decay profile measured by the new system can reflect vividly on the charge＇s dynamic changing. The utmost space charge information can be saved as the measurement time is dramatically shortened by the improved system.