Double-ring High-frequency Common-mode Current Sensor Based on Magnetic Shielding Principle
Insulation failure is an important cause of power equipment failure and shutdown.Compared with the partial discharge method and the high frequency injection method,the high frequency common mode leakage current method has the characteristics of non-intrusion and high sensitivity,but the high frequency common mode current detection faces the interference of high amplitude and multi-band differential mode current.Therefore,a double-ring current sensor is proposed based on the principle of magnetic shielding.The inner ring uses magnetic aggregation effect to isolate the differential mode current magnetic field and the outer ring detects the high frequency common mode current signal based on the principle of Roche coil.By analyzing the magnetic field distribution of common mode and differential mode current,the parameters of the double-ring sensor are designed and the shielding effect of the magnetic ring is analyzed.Finally,a 3 kW permanent magnet synchronous motor is tested.Experimental results show that the proposed double-ring high frequency common mode current sensor can effectively suppress the interference of high frequency differential mode current and has good stability.Compared with the single-ring sensor,the differential mode component is reduced by about 40%which greatly improves the accuracy of online insulation monitoring.
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