Phase converters

[Bert_]

This is mainly in response to Matt Matt's request for some pictures of a site that I was working on recently. When 3 phase power is cost prohibitive there are options to run some pretty large machinery.


This site runs off a single phase service. The service is a couple of 600A switches that are fed by a 167KVA transformer, will do about 700 amps continuous or more for short periods. That's the biggest common single phase transformer out there and he has to be a little careful not to run everything at once.
One switch runs a rotary phase converter, the other runs the rest of the site.




The big leg off center in the photo is 120' tall and has a 40hp motor that is run by a VFD with single phase input. Inside the building in the background is a pit with a 15hp motor also powered by a VFD with single phase input.

Tall circular grain dryer in the center has a 75hp blower that runs off the phase converter. There is also a 30hp transfer system plus a 7.5 and 3 hp conveyor running on the phase converter.

The blue leg has a 10hp single phase motor.
Not shown in the photo is five or six 10hp single phase fans one the grain bins. There are also a few augers used to transfer grain that I don't remember the hp.

 

[rsanter]

Are you sure 3ph is not available to the site?

 

[Bert_]

Are you sure 3ph is not available to the site?

Oh it's available, just have to get out the checkbook... The 3 phase primary is about 3 or 4 miles away. Last quote from the utility was $120,000+ to build new line.

This site is at the point where he really should just spend the money and get 3 phase run. But the phase converter is a lot cheaper.

 

[Matt Matt]

Bert, thanks for the pictures. I enjoy seeing documentation of how others are doing exactly what this grain farmer is doing.

I am a wee bit shocked to see 39 amp. three phase idling. On a 60 hp idler. Is there a name plate on the idler Motor? Or any motor specs, shaft diameter, Frame size... anything?

Phase-O-Matic & Roto-Phase, i’m still trying to figure out if they are using motors twice the size. Or if they’re using a ton of balancing caps as the amperage always seems to be very high on idle.

I pull about 2.8 A off my 5 RPC (NARPC) and almost 5.5 A off my homemade 20 hp RPC at Idle.
I pull a peek 28 A starting my 5hp RPC. And 78 A starting my 20 hp RPC .

 

[Bert_]

It uses a a bunch of capacitors. They are housed the the rectangular box with the pictured name tag and that is mounted to the top of the idler. It does not have any other tags other than a Lincoln electric sticker on the motor, I would say the idler is a 60 hp motor.

I am honestly surprised at how well this is running the 75 hp blower in the new dryer. The voltage on the generated leg droops quite a bit when the blower is starting but once running all three lines are within a few volts of each other.

 

[matt_i]

That's a head scratcher. You'd think the utility had to upgrade all of the 3-4 miles of lines to supply ~600A on 240vac single phase to that site plus whatever else tees off, running the 3rd line & supplying the two additional transformers wouldn't be a lot more.

If they could make the jump to 480v all of the amperages on the secondary/consumer side would halve into the ~300-350 range.

I can see there's a lot of room to buy RPCs and VFDs if the true cost is $120k though.

 

[nadogail]

I once found a guy selling info on how to build your own rotary phase converter from industrial salvage.

the whole concept seemed to be pretty simple, until I retired I was saving capacitors from HID lighting fixtures.

 

[Stuart in MN]

That's a head scratcher. You'd think the utility had to upgrade all of the 3-4 miles of lines to supply ~600A on 240vac single phase to that site plus whatever else tees off, running the 3rd line & supplying the two additional transformers wouldn't be a lot more.

To go with a true three phase service, they would also have to rebuild all the poles from point A to point B to hold that third conductor.

 

[Matt Matt]

It uses a a bunch of capacitors. They are housed the the rectangular box with the pictured name tag and that is mounted to the top of the idler. It does not have any other tags other than a Lincoln electric sticker on the motor, I would say the idler is a 60 hp motor.

I am honestly surprised at how well this is running the 75 hp blower in the new dryer. The voltage on the generated leg droops quite a bit when the blower is starting but once running all three lines are within a few volts of each other.

I know the system very well. I built one, but repaire many.... I am a junkie. Old-school.
If you do get any real specs on the idler motor, I would be interested.

 

[Bert_]

I think the primary is a #2 at 7200V. There is probably some voltage drop issues when stuff get's fired up but it hasn't been an issue. Secondary voltage is tapped fairly high, I measure almost 250V when there isn't much load.

To go with a true three phase service, they would also have to rebuild all the poles from point A to point B to hold that third conductor.

They would need a 3rd and 4th conductor...
I suppose they could add one wire and use an open delta 240V transformer bank but that wouldn't make much sense if they were rebuilding the line. Once in a while they can bring in one phase from the north and one from the south, or visa versa, if there is single phase primary on another phase nearby. Then they would do the open delta.

Single phase primary is usually one line and a neutral. Around here it is a 13.8KV/7200V Y system.

I know the system very well. I built one, but repaire many.... I am a junkie. Old-school.
If you do get any real specs on the idler motor, I would be interested.

This one doesn't use any extra starting capacitors or contactors. The 600A fuse disconnect is used to start it. It does recommend wiring additional capacitors to the load side of the starter of large motors. Keeps the voltage from being so high on the generated leg with minimal load.

Sorry no specs other than it looks like it started as a standard 60hp motor.