Voltage drop due to Phase shifting transformer

[NickParker]

Although there is no inrush current drawn by the motors operated with VFD's, what about the Inrush current drawn by the phase shifting transformers? Does starting of new VFD with already running VFD, create significant voltage drop because of the Inrush of the phase shifting transformer? I'm concerned about the momentary voltage dip which may trip the running VFD.

 

[ScottyUK]

'It depends'

How stiff is your supply? If you have big drives on a small supply transformer and you're on the end of a long high impedance line then you'll quite possibly have problems. If the drives are small and you're on a large transformer fed directly from the transmission system then you probably won't. There are a myriad of possibilities in between the extremes. If you want a more definite answer you can model the network in software.

The DC link capacitors will provide some decoupling between the input and the output.

 

[MatthewDB]

Are you shutting off the power to the VFD, or just stopping it? You only get inrush on energization. If you're leaving power on to the VFD input, then there will be no inrush associated with starting another VFD.

If you're killing power to the VFD and phase shift transformer, stop doing that. It's not good for the drive to cycle power and they won't last as long.