Largest HP Motor on 480V

[designer82]

What is the largest HP Motor you would put on a 480V bus started across the line?

Then same question again started with a VFD?

Thanks

 

[augie47]

As far as ACL, a more relevant question might be what is the largest motor your POCO will allow ACL.
Locally, depending on the location, they often restrict anything over 100 HP.

 

[don_resqcapt19]

I have done a 500 hp at 480 volts and a 4500 hp at 4.16kV across the line in industrial facilities.

 

[ramsy]

I have done.. a 4500 hp at 4.16kV across the line in industrial facilities.

That's the next motor going in my truck

 

[Jraef]

I have run across utilities that start requiring RV starting at 50HP, but yeah, 100HP is probably the most common. The biggest I have seen starting ATL is 500HP on irrigation pumps in Eastern Washington for irrigation pumps that started once per year and ran for 6 months. The farmer applied for and got a variance because of how seldom they started. I got involved because that was ending and they were going to have to change to RVAT or RVSS starting because the water level had dropped so low that they could no longer run that long without stopping, so the variance reasoning had been voided.

The biggest AC motors I have seen run on LV VFDs are 3,000HP on a test stand for an OEM that makes cryogenic pumps used in natural gas processing and tankers. Most of the time these motors are used at MV, but every once in a while they get a request for LV motors that will run on somewhere between 400 to 690V and they have to test them. That of course means these pumps are being started and run on LV drives at the end user facilities somewhere too, but I have only seen the test stand drive. It was in Reno, NV up until recently, they moved it to Pennsylvania somewhere a year or two ago.

Prior to that the largest 480V drives I had done on a VFD was 1500HP on some pumps, but have recently quoted a job that needs 2,000HP, but will more likely go MV.

 

[petersonra]

I think the largest VFD I ever worked on was like 600 horsepower. For testing fire pumps.

 

[garbo]

What is the largest HP Motor you would put on a 480V bus started across the line?

Then same question again started with a VFD?

Thanks

At one place that I worked at we had dual 13,200 service that feed 480 volts thru out the plant. We had two 450 HP chillers that started across the line. Had some kind of arm that adjusted compressors to start unloaded. At a large five Millon square foot hospital/ research center campus they had two 1,750 HP chillers feed from a 13,200 volt breaker into a 18' long panel that had a transformer reducing power down to 4,160 volts that went thru a Johnson Control VFD to feed 4,160 volt chiller motors. Amazing thing on some 100 HP Chillers the VFD'S we're water cooled.

 

[zbang]

I thought most larger chillers started unloaded. Not true?

 

[Besoeker3]

As far as ACL, a more relevant question might be what is the largest motor your POCO will allow ACL.
Locally, depending on the location, they often restrict anything over 100 HP.

I agree. I think its something like for UK. I think some were around 180kW with star/delta starters.

 

[paulengr]

What is the largest HP Motor you would put on a 480V bus started across the line?

Then same question again started with a VFD?

Thanks

Largest motors period I’ve seen is 1200 HP. It was stupidly large for 480. Contactors give out at about 800-1000 A forcing you to use breakers. Largest VFD driven motor period was built by ABB. It runs a wind tunnel, 150,000 HP. The VFD is underpowered.

Above about 400 HP there is a mechanical issue. If you allow the full starting torque on ATL you end up grossly over sizing shafting. So some soft starting helps greatly.

On those sizes for that reason there is always some kind of soft starting. Today we use SCR electronic soft starts mostly. In the past I’ve seen wye delta and sometimes auto transformer.

A big problem with VFDs and even ATL motors is that they have a tendency towards bearing fluting in a big way. One particular very noisy VFD (AB Powerflex 700) and motor required a massive common mode filter to get the bearing currents under control.

As to practicality IEEE Red Book has a lot to say about system sizing. Based on experience on conventional starting the economics favor 4160 starting at around 500 HP. On VFDs this goes up quite a bit, approaching around 700-800 HP but be careful. Depending on the application you may run into an issue that an “800 HP” VFD may only be sufficient on a 500 HP “heavy duty” application.

Don’t be afraid of MV VFDs. At one time the only way to do large ones was to step down to 480, parallel several large VFDs, then step back up. Now up to 1250 HP there are lots of cascaded H bridges (cheap, simple, transformerless) and there’s no real practical limit except that again around 5000 HP it starts to be necessary to go to 7200 or higher since contactors in MV only go to around 800 A. They’re still expensive but it’s mostly due to the necessity of a lot more steps to avoid the lower surge limits than a cheap 6 pulse inverter.

As to VFDs these are massively expensive and impractical unless you need variable speed at the high end. And at larger sizes not very competitive with cycloconverters. Wound rotors are variable torque (with liquid rheostats). Starters can be soft starting or capacitive starters or wound rotor.