DC motors and AC short circuit analysis

[buckeyemurphy]

When doing an AC short circuit study, do DC motors contribute to fault currents and therefore need to be included when building a system?

 

[davidbeach]

It depends. Where does the DC come from?

 

[buckeyemurphy]

Inverter

 

[davidbeach]

Not likely, how would the energy get from the DC to the AC?

 

[Skogsgurra]

Inverter you say? I think that you mean a thyristor rectifier (SCR). If it is a one quadrant drive, then the DC can not be fed back to the mains. But if it is a four quadrant drive with regeneration, then it definitely feeds back.

Such a drive usually has very fast acting (semiconductor) fuses which are current limiting. I do not think that your short circuit analysis will suffer much if you leave contribution from the DC motors out. Unless, of course, there are very large DC drives, and many of them.

Gunnar Englund

http://www.gke.org