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VSD on Wound Rotor Motor
Excessive sparking on the slip-rings of wound rotor motor

We have a 32kW 400V WRM starter via 1 step Resistor. Once started a VFD is used to control Speed. There is excessive sparking on the sliprings when exceeding 90% rated speed.

Any suggestions?

1 out of 1 members thought this post was helpful...

If a VFD is not seeing an inductive load then the o/p voltage and current will not necessarily be sinusoidal. The sparking rather confirms that.

The start up resister is rather redundant and do not need to have any switchgear between VFD and motor. The exception to this is the local isolator.

Thanks for the reply.

The existing VFD is not rated for the starting current of the motor hence the resistor start. Sparking only occurs with the resistor is out of circuit (contactor closed) and the VFD at more then 90% (45Hz).