Fuse protection for a VFD/Motor

[WastefulMiser]

What type of fuse would you use in an upstream fused load break switch which feeds a 400HP VFD with a bypass contact? 4160V/3/60.

Class R for motors or Class E for transformers or something else? VFD manufacture's responsibility?

Any guidance or thoughts would be appreciated.

 

[Thedroid]

I would consult the drive manufacturer.

The MV drives I've worked with had class R fuses upstream, but were protected by a GE 735 relay.

I don't think that an MV fuse would melt fast enough to provide any meaningful protection to the drive.

I also would not want to rely on fuses for an MV motor. I would feel much better with a Multilin 269 or 469 or something similar.

 

[WastefulMiser]

I would consult the drive manufacturer.

The MV drives I've worked with had class R fuses upstream, but were protected by a GE 735 relay.

I don't think that an MV fuse would melt fast enough to provide any meaningful protection to the drive.

I also would not want to rely on fuses for an MV motor. I would feel much better with a Multilin 269 or 469 or something similar.

I was more worried about popping the fuse during inrush current -- either motor (bypass contactor) or VFD. From what I've seen a 400HP VFD has about a 500kVA transformer inside of it.

I've actually never seen MV VFD's protected with a fused LBS ... only CB's. This could very well be a common practice as I'll admit there is a lot I haven't seen.

Thank you for your reply.

 

[weressl]

What type of fuse would you use in an upstream fused load break switch which feeds a 400HP VFD with a bypass contact? 4160V/3/60.

Class R for motors or Class E for transformers or something else? VFD manufacture's responsibility?

Any guidance or thoughts would be appreciated.

You would probably want to isolate the ASD in the bypass mode. The ASD would most likely require a different fuse than the FVNR starter. Multilin on the bypass and the ASD's usually have a protective module in teh software that provide a tailored protection that a Multilin would have difficulty accomplishing on a varied frequency line. If you have RTD's and you want them to be used in both protective mode, further tinkering is required.

 

[WastefulMiser]

You would probably want to isolate the ASD in the bypass mode. The ASD would most likely require a different fuse than the FVNR starter. Multilin on the bypass and the ASD's usually have a protective module in teh software that provide a tailored protection that a Multilin would have difficulty accomplishing on a varied frequency line. If you have RTD's and you want them to be used in both protective mode, further tinkering is required.

Thank you for the reply.

First off, I am not designing this -- this is what's on the drawing I saw and I am just trying to understand if I am missing something which seems to be the case.

They show the VFD and the bypass contactor coming off the same node from the fused LBS. And correct me if I am wrong, but this is drawn incorrectly, eh?

The two ways to do it possibly do this is:

1) (2) Fused LBS (more than likely motorized than manual) --- (1) for the VFD and (1) for the bypass

2) (1) Fused LBS going to the VFD which contains (2) contactors --- (1) for the VFD and (1) for the bypass.