Is there too many amps or spikes to input of drive?

[Judis]

I have 480v, 200amp fusible disconnect going to a main cabinet of a Ward/ Flex machine. At the bottom of these fuses there are four small motors and an old dc drive that moves a 500vdc, 300amp SHUNT motor. When this machine is running at a good rate it has 22amps being read at the input fuses and around 50amps at the motor.

I decided to add a 480vac, 50hp blower motor at the bottom of these fuses as well (46amps while running) You can see the blower motor from the main cabinet, its about 50' away. Just before the dc drive there is a "Line Reactor" that helps wilt isolating spikes and I also wired a 480v to 480v, wye isolating transformer after a 60amp fusible disconnect, to an AB motor contractor for the blower motor circuit.

I'm hoping that the amps and the spikes would be maintained enough having the line reactor and the isolation transformer in between the dc drive that runs the main motor of the machine, wanting to keep the drive healthy? I could have run a separate line to the blower from across the plant but I was hoping to save time and money!
Judis

 

[ptonsparky]

I think I would be more worried about how you set up the isolating transformer. Size. Primary and Secondary overcurrent. Grounding of the secondary. 60 amp fused disconnect seems small from here.

 

[petersonra]

I doubt it is going to matter all that much. The drive does not really care all that much up minor voltage excursions at its input terminals. The worst thing likely to happen is the drive trips.

You might consider installing line reactors on the VFD if it bothers you.

 

[herding_cats]

Adding a line reactor will reduce the amperage. Though expensive, a powerhouse unit might be a good fit. Sized by kVAR. If you want it professionally sized, get me all the data from the primary load: kW, kVA, kVAR, peak amperage on start.

 

[petersonra]

Adding a line reactor will reduce the amperage. Though expensive, a powerhouse unit might be a good fit. Sized by kVAR. If you want it professionally sized, get me all the data from the primary load: kW, kVA, kVAR, peak amperage on start.

Line reactors do not reduce the amperage. They will attenuate high frequency line noise or spikes. They will also introduce a small amount of voltage drop going to the input terminals on your VFD.

 

[herding_cats]

Line reactors reduced amperage related to voltage drop and poor power factor yes. These reductions in amperage prevent the drive from tripping:

https://acim.nidec.com/drives/kbelectronics/-/media/kbelectronics/documents/white-papers/applications-of-line-and-load-reactors-with-variable-frequency-drives.ashx?la=en#:~:text=Line%20reactors%20help%20protect%20VFDs,back%20into%20the%20utility%20grid.

 

[herding_cats]

From the data sheet in the link above, the RMSA and kVA reductions on a 100 kW VFD:

 

[herding_cats]

The reduction in Amperage is through the increased power factor. Line reactors a a great way to solve a tripping drive. In some cases the drive was sized too small and a LR 3-5% won’t fix it.
Go to the next sized drive.

 

[Jraef]

There is no VFD here, it's a DC drive.

Generally you put a "Drive Isolation Transformer "ahead of a DC drive because of the line notching and common mode noise that the old SCR based DC drives created. Once you go to the expense of the Drive Isolation Transformer, the line reactor would be redundant and only serve to drop the voltage a little. So why was that added?

When this machine is running at a good rate it has 22amps being read at the input fuses and around 50amps at the motor.

That would imply that the isolation transformer is ALSO dropping the line voltage down to the motor, i.e. its a 480V feed to the transformer, but a 240V DC drive and motor. That's not at all unusual.

The rest of this scheme sounds odd to me with regard to tapping off of the "bottom of the fuses" in several places. I don't quite follow the description, but it sounds concerning with regard to circuit protection.

 

[Judis]

I doubt it is going to matter all that much. The drive does not really care all that much up minor voltage excursions at its input terminals. The worst thing likely to happen is the drive trips.

You might consider installing line reactors on the VFD if it bothers you.

I've installed a lot of machines and circuits in the past. We have plenty of parts and pieces that I through together all over. 50hp seemed a little chancy and be so close to the drive. The machine has a line reactor on it. These are older machines and the drives in them seem to run forever.
I tested good and I knew the amps would go down quite a bit but with the transformer when from 46amps to 20amps after the motor start up rush, which jumped to 236amps .
It's an old dc drive, that I have looked at for awhile but it's definitely not a vfd. So far so good.

 

[Judis]

There is no VFD here, it's a DC drive.

Generally you put a "Drive Isolation Transformer "ahead of a DC drive because of the line notching and common mode noise that the old SCR based DC drives created. Once you go to the expense of the Drive Isolation Transformer, the line reactor would be redundant and only serve to drop the voltage a little. So why was that added?


That would imply that the isolation transformer is ALSO dropping the line voltage down to the motor, i.e. its a 480V feed to the transformer, but a 240V DC drive and motor. That's not at all unusual.

The rest of this scheme sounds odd to me with regard to tapping off of the "bottom of the fuses" in several places. I don't quite follow the description, but it sounds concerning with regard to circuit protection.

True that about the drive isolation transformer.
I've installed a lot of machines and added a few circuits along the way but never installed a 50hp motor so close to an input of a dc drive. Yes, after the motor rush the amps went down to 20amps. Before the the transformer it was 46amps.
Working great!

 

[Judis]

I think I would be more worried about how you set up the isolating transformer. Size. Primary and Secondary overcurrent. Grounding of the secondary. 60 amp fused disconnect seems small from here.

The transformer is 75kva, 480 D primary and 480 Y secondary. Transformer took amps down to 22amps.
60 amp fuse I figured by 46amps x 125%=57.5. Compensating for motor rush. Seems to work good so far.
And still has plenty of rpm's to do the job.Thanks

 

[Judis]

The reduction in Amperage is through the increased power factor. Line reactors a a great way to solve a tripping drive. In some cases the drive was sized too small and a LR 3-5% won’t fix it.
Go to the next sized drive.

This machine has a line reactor that was originally manufactured with it.
No tripping drive, 50hp blower motor seems to be testing well.
60amp fuse are compensating for motor rush and no drive fault lights, so far.Thanks

 

[Judis]

I think I would be more worried about how you set up the isolating transformer. Size. Primary and Secondary overcurrent. Grounding of the secondary. 60 amp fused disconnect seems small from here.

Transformer is 75kva, 480 D to 480 Y. It's an Acme brand, general purpose transformer.
I figured fuse by 46amps x 125%= 57.9, which makes my 60amp fuse.
I tried 30amp for the heck of it and they all 3 blew immediately but 60amp fuse are doing well. I might try 50amp fuse to see if it handles that motor start rush.
I've read that transformers if they are grounded on the primary only for isolation and to prevent any type current loop.
Circuit is working good.Thanks

 

[ptonsparky]

60 is marginal, but if it’s running you’re good.

75000/480/1.73=90

90 *1.25 =113 for wire size.