Fault Current Calculations involving motors with VSD's 1

[ScottPET]

When performing fault current calculation study on a system with a motor controlled by a VSD, I am of the understanding that, for an overcurrent fault upstream of the VSD, fault contributions by this motor need not be considered as the VSD will not allow them to pass. Is this correct ?

With this in mind, for a separate overcurrent fault between the VSD and the motor, would the VSD limit/block the fault current from the main utility/generator supply to the installation ? Would this second fault solely consist of the contributions from the motor ?

 

[Marke]

Hello ScottPET

The VSD will prevent the motor from contributing to the fault current upstream of the VSD.
The output of the VSD is a different situation. The fault current will be limited by the output of the inverter so you will not see the full fault current capacity of the supply, but the level is going to be dependent on the internal design of the inverter. I am not aware of any rules for calculating this.
Best regards,

Mark Empson

http://www.lmphotonics.com