变压器工频短路电流测量技术研究

针对变压器工频短路电流测量需求,研究了外积分式罗氏线圈技术和光纤电流传感技术。建立了2种传感器的低频数学模型,基于MATLAB/Simulink仿真计算传感器对工频短路电流的响应特性,结果表明:罗氏线圈对工频短路电流的测量精度受其下截止频率影响,下截止频率越低,测量精度越高;光纤电流传感器理论上可以精确复现工频短路电流。采用多种电流传感器进行变压器工频短路电流现场对比测试,结果表明:电流比较仪、光纤电流传感器及下截止频率为0.02Hz的罗氏线圈测得的电流波形吻合较好,而下截止频率为0.2Hz的罗氏线圈测量结果出现了明显的偏移,且无法归零,与仿真分析结论基本一致。对于外积分式罗氏线圈,为保证高精度测量,建议下截止频率应低于0.1Hz;光纤电流传感器具有极好的直流及低频响应特性,是工频短路电流高精度测量的理想方案。

Research on Measurement Technology of Power Frequency Short-circuit Current of Transformer

Aiming at the requirements of transformer power frequency short-circuit current measurement, the external integral Rogowski coil technology and fiber-optic current sensing technology are studied. The low-frequency mathematical models of the two sensors are established which based on MATLAB/Simulink to calculate the response characteristics of the sensor to the power-frequency short-circuit current. The results show that the measurement accuracy of the Rogowski coil for the power-frequency short-circuit current is affected by its lower cut-off frequency. If the cut-off frequency is lower, the measurement accuracy will be higher. The optical fiber current sensor can theoretically accurately reproduce the power frequency short-circuit current. Multiple current sensors are used for the field comparison test of the transformers power frequency short-circuit current. The results show that the current waveforms measured by the AC/DC current comparator, the fiber-optic current sensor, and the Rogowski coil with a lower cut-off frequency of 0.02Hz agree well, the measurement result of the lower cut-off frequency in Rogowski coil at 0.2Hz shows a significant deviation and could not be reset to zero, which is consistent with the simulation analysis conclusion. It is recommended that the lower cut-off frequency should be lower than 0.1Hz for the external integral Rogowski coil in order to ensure high-precision measurement; fiber-optic current sensor has excellent DC and low-frequency response characteristics, it is an ideal scheme for high-precision measurement of power frequency short-circuit current.