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A current transformer (CT) system centered on Rogowski coil is introduced to measure the low frequency heavy current of the linear induction motor (LIM) powered by the H-bridge sine pulse width modulation (SPWM) inverter. The frequency of the output current of the inverter ranges from 1 hertz to 200 hertz. The current test apparatus is made of the sensor head of Rogowski coil and the post-processing circuit. The post-processing circuit has characteristics of high reliability, high accuracy, low saturation, and low distortion. The voltage from the processing circuit is acquired by the Nicolet acquisition system, which has a fast speed of analyzing the current in real time. The fundamental current can be gained by means of the Fourier transformation. Both theory analysis and experimental results can verify the feasibility of the proposed CT instrumentation.