Drive Vfd

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Frequently Asked Questions...

3 phase 10kw motor is showing voltages on its housing when it is used with frequency drive(vfd).frequency 4kHz

when the motor is switched on with normal 3 phase supply on 50hz frequency then the motor operate correctly and not showing voltages on its housing.whenever we connect the motor with frequency drive for speed control then at high frequency(50hz--4khz) the housing or the body of the motor and all attached metal parts showing voltages and the voltages are varied with speed control of motor(127--240 volts).we applied this operation on two different motors.but the result is same.why the motors are showing leackage current or voltages with frequency drives?

Best Answer...


Firstly the motor should be earthed so you would never see voltages on it.

The drive operates differently than the mains. The dc is switched by PWM at very high frequencies (much higher than the output frequency its operating at) which can create induced voltages. The insulation should also be inverter rated, usually class F or better.