温度梯度场下电缆本体脉冲电声法空间电荷测量声波纠正

Correction of Acoustic Wave in PEA Space Charge Measurement on Cable Under Temperature Gradient

采用脉冲电声(PEA)法测量电力电缆本体空间电荷时会因电缆筒柱形结构和温度梯度场的作用而使PEA声波在电缆本体中的传播声速发生变化,导致空间电荷测量波形幅值的衰减和采样时间的变化。为此,首先研究了温度梯度场下交联聚乙烯(XLPE)电缆本体PEA测试信号的纠正问题。实验研究发现:PEA系统中声波沿XLPE电缆绝缘径向传至压电传感器时,不仅会受到与切片试样中相同的吸收衰减和散射衰减,而且会因电缆的圆柱型结构而导致声波辐射面扩大并发生扩散衰减,扩散衰减与声波所在位置的半径的平方根成反比;温度梯度场下声速沿电缆本体绝缘径向呈线性分布,且温度越高,声速就越低。然后将电缆本体中声波衰减因子离散成1个传递矩阵,针对试样处在常温和温度梯度场下的不同情况,分别在频域下获取了整个电缆本体绝缘中的空间电荷恢复方程;同时为解决不同温差下以时间为横坐标来比较空间电荷的位置分布的困难,采取将时间轴转换为对应的试样厚度方向的距离来进行比较。纠正结果表明该纠正方法是有效的。

In pulsed electroacoustic（PEA） measurement of power cable, propagation velocity of PEA acoustic waves varies because of cable＇s temperature gradient and cylinder structure, and consequently induces attenuation to the amplitude of obtained space charge waveform as well as variation of sampling time. Hence, we experimentally studied the correction of these PEA measurement signals. The results show that, when acoustic wave propagates from cable insulation to piezoelectric transducer, it attenuates not only because of absorption and scattering which is similar to that in film samples, but also because of the enlarged radiating surface in cylinder structure. The diffusion and attenuation is inversely proportional to the square root of the radius of sound wave location. Meanwhile, sound speed is linearly distributed along radial cable insulation in temperature gradient field, and it also decreases with the increase in temperature. Then we discretized the acoustic attenuation factors in cable body into a transfer matrix, and obtained equations of space charge recovery in frequency domain under the conditions of room temperature and temperature gradient field, respectively. Since it is difficult to compare the space distribution of space charges using time as the abscissa, the corresponding distance in the specimen thickness direction is used as an alternative. The results prove the proposed correcting method to be effective.