SKM modelisation

[Acristi]

Hello
Could somebody tell me how can I modelised a VFD in SKM?

Thank you
Cristian

 

[davidbeach]

What type of VFD (how many quadrants), does the VFD have bypass contactors, and do you have the DC module for SKM?

 

[Acristi]

Unfortunaty I don't have more information about VFD (it's a GE).
Yes, I have a DC module in SKM.

Thanks

 

[davidbeach]

Well, you could model it in SKM as a rectifier, a DC bus, and an inverter. But without good information on the VFD you'd still be out of luck.

If it has a bypass contactor, I'd just ignore the VFD for fault calculations. If there is no means of bypassing the VFD and the VFD can not feed back into the line, I'd just ignore the motor for fault calculations. With a four quadrant drive you might get some fault current back out but not as much as the motor itself would produce. I don't really know what a four quadrant drive does during faults, you might well not get any fault contribution.

So, with bypass contactor ignore the VFD for fault calculations and without bypass contactor ignore the motor for fault calculations. For load flow you need to account for the VFD losses as well as the motor loads. Beyond that it really depends on what you are trying to get out of your model.

 

[Acristi]

Thank you very much!
I will try to modelise all posibility and I will analyse the results.

 

[Acristi]

I want to find the Arc Flash - Incident energy, working distance and PPe category.

 

[davidbeach]

Most VFDs will shut down their output almost instantaneously (much faster than the instantaneous of a breaker) for faults on their output. I would expect that there would be very little incident energy on the output side of a VFD (without bypass contactor). On the input side the VFD won't make any difference.

 

[Acristi]

Thank you very much for your answers.