Earth faults and VSD systems.

[beyond86]

Hello!
I need your help to clarify some aspects of VSD working.
I made the model of VSD which fed a motor (model.png in attachments). The VSD connects to the grid via transformer 35/5 kV Yg/D.
I can't understand, why phase voltages change on the motor side when the earth fault occurs on the network side? I agree that health phase voltages increase to line voltage values on the network side when earth fault occurs, but why it happens on the motor side?

 

[beyond86]

Also, look at scope.png for a better understanding.

 

[jraef]

Are these real world measurements or a model from some sort of software? If the latter, the model is not understanding how a VFD works.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[beyond86]

It's the model from software, but the question arose from the real situation.
We have VSDS which controls the synch. motor 24MV.
Ground protection located only motor side Y. Simple SLD here:

https://i.ibb.co/4t0zg1C/12-12-Pulse-LCI-design-driving-a-six-phase-synchronous-machine.png

The manufacturer told us, that this ground protection can also operate when ground faults occur on the network side of VSD.
I created a more detailed model of this VSDS and the manufacturer was right. No matter where a ground fault occurs, this protection can sense this type of fault.
The new model here:

https://i.ibb.co/17K3Bns/model-new.png

The new data of scope here:

https://i.ibb.co/7NP3ZGT/scope-new.png

And I can't understand, why it's happening, why phase voltages change on the motor side?

 

[beyond86]

Gents, I got it at last. This protection covers all motor sides and network sides.