300 A current sensor using amorphous wire core [invertor control of AC motors]

A noncontact small-size 300-A current sensor for inverter control of AC motors was constructed using zero-magnetostrictive amorphous wire cores combined with a hybrid-integrated circuit including a multivibrator bridge. The sensor head cores could be set close to a conductor bar by using a negative feedback circuit, which simultaneously improved linearity, stability against temperature changes, signal-to-noise ratio, and dynamic range. Experimental results for detection of DC and AC currents up to 300 A showed good linearity with less than 0.5% FS nonlinearity, temperature stability with less than 0.3%/°C FS variation up to 80°C, and cut-off frequency of 5 kHz. The noise due to external disturbance by adjacent bar current could be reduced to less than 0.3% FS by the sensor´s dual-core arrangement and the use of a simple silicon steel shield shell. Both size and weight could be reduced as compared with conventional current sensors