Running a 20HP motor from single phase power ??

[milmat1]

We have a project that will require running a 20HP motor, Only single phase 240VAC is available.

I need to gather some power requirements for the customer / sales dept. But first must decide the best way of doing this..

What are the options for doing this ??

 

[junkhound]

3 phase vfd fed by dc from pfc boost supply on the 240 line.

 

[Besoeker]

We have a project that will require running a 20HP motor, Only single phase 240VAC is available.

I need to gather some power requirements for the customer / sales dept. But first must decide the best way of doing this..

What are the options for doing this ??

What voltage is the motor?

 

[petersonra]

We have a project that will require running a 20HP motor, Only single phase 240VAC is available.

I need to gather some power requirements for the customer / sales dept. But first must decide the best way of doing this..

What are the options for doing this ??

any reason you cannot use a 240V single phase motor? it is not exactly an easy size to come by but it might be the simplest answer.

no matter what you do, you will using around 100A at full load.

if a single phase motor is not an option, you might be able to use some kind of phase converter or VFD. Would be a big VFD. Maybe 75 HP or so.

 

[Jraef]

This is not going to be simple no matter what, but start with the simplest options:

Option 1: 20HP 230V single phase motor. Standard off-the-shelf NEMA single phase motors stop at 10HP 240V then specialty farm duty / grain dryer motors go up to 15-16HP, but as petersonra said, you might find larger if you look around and/or are willing to wait or have a motor shop build one for you. And as he said, expect the FLC to be about 100A, which means your source power transformer feeding the circuit will need to be at least 60kVA, which means in the single phase transformer world, a 75kVA transformer. That's going to be hard to find in a single phase service, a 200A service will typically be fed by a 50kVA transformer, and the next size up for service drops is 400A, which would be a 100kVA transformer. So that's what you would need to have at your single phase service. If you don't, it likely is not going to be allowed by your utility.

Option 2: There are what are called "written pole" motors that run as 3 phase motors, but from a single phase source. It will not really change anything about the FLC issue as far as what is drawn from your source, but it may allow you to start it from a 200A service rather than having to go to a 400A service.
http://www.written-pole.com/singlephase/singlephase.html

Option 3: as mentioned, is to buy a VFD that allows a single phase input at that size, then can run a 3 phase motor. You can still do this with a 200A service. All VFDs are technically capable of doing this, but some can, some cannot because the mfrs did not anticipate this use and did not provide a way to defeat the Phase Loss protection for the input power on 230V drives this large. For this to work, you must at least DOUBLE the size of the VFD compared to the motor, so you would buy at least a 40HP 230V VFD to run a 20HP motor from single phase (because of the higher input current and DC bus ripple from single phase). So problem #2 of this will be that many VFD mfrs do not make a 40HP 230V rated drive, partly because it is so uncommon; generally people using motors that big use 480V.

So option #4: get a 240-480V single phase transformer, about 37.5kVA, and then get a 480V VFD that accepts single phase input (again, be careful) and a 20HP 460V rated motor. You can still do this with a 200A service.

Option #5: get a 3 phase service from the utility.

 

[ptonsparky]

Notice anything missing?

None of the options are inexpensive.

 

[Barbqranch]

How often will this be used? If only once in a while, it might be cheaper to rent a generator.

 

[jim dungar]

Option 3: as mentioned, is to buy a VFD that allows a single phase input at that size, then can run a 3 phase motor.

Option 3A?
Phase convertor assuming speed control is not required. Must know the load characteristics. The digital ones can even be used to supply CNC machines.

 

[Jraef]

Option 3A?
Phase convertor assuming speed control is not required. Must know the load characteristics. The digital ones can even be used to supply CNC machines.

Yep, missed that one.

 

[kwired]

Notice anything missing?

None of the options are inexpensive.

Correct, and unless the ability to have three phase is a long way away, it is still worth consideration to at least have POCO run necessary equipment to supply with an open delta.

VFD's and phase converters - all tend to require more service down the road then a basic magnetic motor starter.

I do like the idea of bumping to 480 volts if you decide you need to do a VFD or phase converter.

 

[Iron_Ben]

We have a project that will require running a 20HP motor, Only single phase 240VAC is available.

I need to gather some power requirements for the customer / sales dept. But first must decide the best way of doing this..

What are the options for doing this ??

Fifteen years ago we used a rotary phase converter to run a 60 HP pump motor from single phase for about a year during construction of a Wal-Mart distribution center in the boondocks. It was noisy and we were holding our breath for the first week or so but it never gave a lick of trouble. I think it was manufactured by GWM but am not certain. There are more manufacturers of "add-a-phase" units out there than you might think.

 

[kwired]

Fifteen years ago we used a rotary phase converter to run a 60 HP pump motor from single phase for about a year during construction of a Wal-Mart distribution center in the boondocks. It was noisy and we were holding our breath for the first week or so but it never gave a lick of trouble. I think it was manufactured by GWM but am not certain. There are more manufacturers of "add-a-phase" units out there than you might think.

Rotary phase converter involves an idler motor nearly same size as the motor being driven. Not saying it don't work but does cost you. It does work better then a static converter made from capacitors, which need to be sized and even fine tuned to the load being driven. I think a basic static converter also needs the motor to be over sized for the driven load So if OP needs 20 HP for his load and uses a static converter he may find he needs a 25 or 30 hp motor to run it off a static converter. This type of converter works best if the load doesn't vary from my experiences.

 

[Phil Corso]

Gentlepeople...

Sounds like another "Bear & Wall" story:

1) What is the source's electrical capacity?

2) What are the driven-load characteristcs?

3) What is the required breakaway-torque?

4) What is the required acceleration-torque?

5) What is the desired acceleration-time?

6) How about using two motors; one as a "pony", the other to carry the balance of load?


Regards, Phil Corso

 

[kwired]

Gentlepeople...

Sounds like another "Bear & Wall" story:

1) What is the source's electrical capacity?

2) What are the driven-load characteristcs?

3) What is the required breakaway-torque?

4) What is the required acceleration-torque?

5) What is the desired acceleration-time?

6) How about using two motors; one as a "pony", the other to carry the balance of load?


Regards, Phil Corso

I can agree, just knowing what the motor is to drive can make a big difference in what options may be best.

 

[milmat1]

It will run 50-75% of the time.
The motor can be whatever I decide as it hasn't been purchased yet.
I am really pushing sales dept to discuss this with the customer and explain that while this can be done it will add cost and it will not be an efficient running machine. And with the derated VFD the supply would be close to 200 Amps.
When running the VFD on single phase power you must derate the VFD by 50%. So I would need a 240V 50HP drive. ($$$$)..

I am really pushing for them to get 3 phase power ran to the location but I don't know the reason yet for there reluctance.

 

[Jraef]

...
I am really pushing for them to get 3 phase power ran to the location but I don't know the reason yet for there reluctance.

Usually, cost. If there is no other 3 phase on the street where they are, the PoCo often makes them pay for the cost of running the extra cables and/or the transformer. If the shop in in a far flung rural area, that could be miles of cable and hugely expensive. On the other hand if other people on the same block already have 3 phase it may not be that expensive. Sometimes the money guys ask the questions of the wrong people and ASSume it will be more than what it really will. The only valid answer has to come from the PoCo.

 

[Phil Corso]

Milmat1...

Considering long-range operation, you must consider replacement of the motor when necessary. Based on that alone, a 3-phase solution will be much more economical.

Phil

 

[kwired]

It will run 50-75% of the time.
The motor can be whatever I decide as it hasn't been purchased yet.
I am really pushing sales dept to discuss this with the customer and explain that while this can be done it will add cost and it will not be an efficient running machine. And with the derated VFD the supply would be close to 200 Amps.
When running the VFD on single phase power you must derate the VFD by 50%. So I would need a 240V 50HP drive. ($$$$)..

I am really pushing for them to get 3 phase power ran to the location but I don't know the reason yet for there reluctance.

If it takes a long distance just to get three phase primary to the site, you already have some $$$$ involved before even considering transformers and site distribution equipment, POCO is not likely going to run it for no additional charges. If there is three phase already near the site, it usually makes most economical sense to upgrade existing or add additional three phase service to your facility.

 

[junkhound]

When running the VFD on single phase power you must derate the VFD by 50%. So I would need a 240V 50HP drive. ($$$$)..

Use your imagination: 20 HP VFD, for a 230 Vac 3 phase input unit the internal dc link is typically 400 volts. Find a power factor corrected boost supply that puts out 400 Vdc, use that for the vfd input, then no derating of the vfd.

Can you belt couple 2 ea 10 hp single phase motors?

70% of the time = say 5000*20KW = 100000 kw-hrs per year. At 10 cents kwhr, 10 grand per year for power to run the thing.

Single phase is at best about 84% efficient (17.8 kW) , good 3 phase 20 HP is 93% or better (16.1 kW) Good VFD and dc supply is 90%, or total of 17.8 kW again, break even.

$850 per year operating expenses. Say the business has and ROI of 8%, so you can figure break even to go 3 phase is to spend about $10K to upgrade to high efficiency 3 phase; the $10 K is your break point for poco charge to put in 3 phase. You can figure in the maintenance savings for 3 phase also.

 

[Phil Corso]

Junhound...

You should never operate induction motors coupled to the same drive-train, unless they have some form of "slip" between them! VFDs provide the required slip!

Regards, Phil Corso