全尺寸直流电缆脉冲电声法(PEA)空间电荷测量系统设计及声信号衰减与色散补偿

PEA Method Based Full-size DC Cable Space Charge Measurement System Design and Acoustic Signal Attenuation and Dispersion Correction

脉冲电声法(PEA)空间电荷测量是交联聚乙烯(XLPE)绝缘直流电缆材料选型与评价的主要技术手段,被广泛应用于直流电缆薄膜试样。但应用该方法测量厚尺寸平板试样和大尺寸同轴试样以研究材料体效应对空间电荷的影响时,声波信号在材料中传播时的衰减与色散将直接影响电荷密度测量的精度和空间分辨率。提出了在空间电荷校准过程中利用理论计算直流电场的方法确定内外电极表面的电容电荷密度,然后计算确定在绝缘介质中传播的脉冲声波信号传递函数(该函数含有衰减和色散系数),再对原始信号进行反卷积分运算以去除系统响应。在频域利用测量信号乘以传递函数获得脉冲声波信号经过衰减、色散恢复后的信号,从而保证大尺寸直流电缆试样测量中电荷密度及空间分辨率的测量精度。同时,设计了全尺寸直流电缆空间电荷测量系统,并在Lab VIEW环境下开发了数据采集与处理系统。

Pulsed electro-acoustic method（ PEA） based space charge measurement is one of the main technical means for cross-linked polyethylene（ XLPE） insulated DC cable material selection and evaluation,which is widely used in the DC cable film specimen.However,when PEA is applied to a thick flat sample or a large scale coaxial cable sample to evaluate the influence of the sample itself on space charge,the attenuation and dispersion of the acoustic signal propagation in the sample affect directly the accuracy and resolution of space charge measurement. In this paper,the charge densities inside and outside the electrode surface are determined by calculating DC electric field using theoretical method during space charge calibration process. Then,the transfer function,which includes the attenuation and dispersion coefficients,of pulse acoustic signal transfering in the insulating medium is calculated,and the system response is removed from the original signal with deconvolution operation. In the frequency domain,the pulse acoustic signal after attenuation and dispersion correction is obtained by a product of the measurement signal and the transfer function to ensure the accuracy measurement of charge density and spatial resolution of the full-size DC cable sample. M eanwhile,a PEA method based full-size DC cable space charge measurement system is designed,and a data acquisition and processing system is developed under Lab VIEW.