What are the effects of dV/dt on a Motor when using a VSD?


15 October 2021

As there is an impedance mismatch at the termination of the motor cable to the motor, there will be a reflected wave which travels back along the motor cable causing
overvoltage’s. Overvoltage’s on the motor terminals can cause both partial and corona discharge which eventually wears down the winding insulation to failure. 

Corona discharge occurs when the overvoltage is large enough to cause electrons to flow from one winding to another whilst ionising the air between the conductors. They cause damage to the internal and external insulating material respectively. As the motor cable length increases the peak voltage increases. This can increase to a value of 2 to 2.5 times the DC bus voltage. 

Schneider Electric Offer Sinus filters or dv/dt filters to reduce the overvoltage across windings and high frequency currents in differential mode. Check out our current ATV600 or ATV900 catalogue for more information on output filters to help you with overvoltage mitigation.