变压器局部放电检测声阻抗匹配研究

局部放电检测技术是变压器绝缘诊断的重要手段之一，而外置式超声法是目前使用较多的超声检测法。针对当前外置式超声检测法灵敏度较低的问题，文中研究了声阻抗匹配提高变压器局部放电超声信号透射强度的可行性。经理论分析发现，通过在变压器油和外壳之间加入匹配层，且满足匹配层声阻抗介于变压器油和外壳的声阻抗之间，能增大超声波信号的透射系数，获得了透射系数随频率变化的规律及中心频率和匹配层厚度的关系。模拟试验表明，在变压器油与变压器外壳之间加入声阻抗匹配层后，测得的超声波信号幅值约为未设置声阻抗匹配层侧的2倍，超声波信号的透射系数得到了显著增强，试验结果验证了声阻抗匹配提高实测超声波信号强度的可行性。

Research on Acoustic Impedance Matching of Partial Discharge Detection for Transformer

Partial discharge detection is one of the most important methods for transformer insulation diagnosis, and the sensor -externally -installed method is the most used ultrasonic detection method at present. In view of the low sensitivity of current external ultrasonic detection method, the feasibility of improving transmission intensity of ultrasonic signal of transformer partial discharge by acoustic impedance matching is studied. By theoretical analysis, it is found that the transmission coefficient of ultrasonic signal can be increased by adding matching layer between transformer oil and shell when the acoustic impedance of matching layer is between those of the transformer oil and shell. The variation rule of transmission coefficients with frequency and the relationship between center frequency and thickness of matching layer are obtained. The simulation test results show that when the acoustic impedance matching layer is added between transformer oil and shell, the amplitude of the measured ultrasonic signal is about double that of the ultrasonic signal measured in opposite side without the acoustic impedance matching layer, and the transmission coefficients of ultrasonic signal is significantly enhanced, which verifies the feasibility of improving the intensity of the measured ultrasonic signal by the acoustic impedance matching.