2 Phase drive 1

[Wilderbeast]

We are working on a project an are trying to source a 0-240V, 40A, two phase VFD. So far the electrical engineers have had no success, I thought i'd give this forum a go and see if anyone can help.

 

[jraef]

2 phase is extremely uncommon, a relic of bygone days that exists in 3 or 4 places in the US that I know of and dwindling as we speak. I would be very surprised f you really have 2 phase power.

I think your problem might be in the semantics here. If you have 240V as an input source, either as two hot lines and a neutral coming from a utility distribution transformer, or 2 hot lines off of a 3 phase system, that is considered "Single Phase" power. There are HUNDREDS of VFDs capable of single phase input which will give you three phase output, in fact with attention to details, you can do that with almost any VFD. At 40A, you will need to double the size of the VFD because the input current is higher per-pole than the 3 phase it was designed for.

If your motor is single phase, that is an entirely different problem.

Please state EXACTLY what you have so we can help you through it.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[Marke]

We do come across two phase applications here in NZ from time to time where they run two phases only and so we need to run a drive off 400V two phase rather than 400 volt three phase.
What we do, is use a three phase drive with twice the rating of the motor so that we do not kill the capacitors.
The ripple current is much higher than with three phase input for which the drives are designed.

Best regards,

Mark Empson
L M Photonics Ltd

 

[stevenal]

Is that two phase input to the VFD? Output? Both? If not both, what is required on the other side?

faq238-777

 

[jraef]

We do come across two phase applications here in NZ from time to time where they run two phases only and so we need to run a drive off 400V two phase rather than 400 volt three phase.
What we do, is use a three phase drive with twice the rating of the motor so that we do not kill the capacitors.
The ripple current is much higher than with three phase input for which the drives are designed.

Actually, that happens a lot here too with 480V systems fed out to far flung farms, but we still call it single phase.



"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[waross]

Hi Mark.
What I think of when I see two phase is the old original systems with 3, 4, or 5 wires and 90 degree phase separation.
We have three phase with three or 2 transformers (Open delta).
And we have single phase supplies derived from a single phase transformers or from one side of a three phase bank.
A possible point of ambiguity is supplies derived from two phases and neutral of a wye system. We usually, (us old dinosours anyway) call such a supply a 120/208, or two phases rather than two phase. These systems all have the well known 120 degree phase separation. Some of us reserve the term Two Phase for systems with 90 degree separation.
I understood the OP to mean two phase output. We'll have to wait and see.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[roydm]

Marke, Can you tell us a bit more about the 2 phase system.
Is it just 2 phases of a 3 phase system or are the phases 90 degrees from some special transformer connection?
I have seen 2 phase motors in shearing sheds, are they specially wound or 3 phase motors adapted?
Roy

 

[ScottyUK]

Roy, the old two phase systems over here are two phases in quadrature. There are, or were until relatively recently, fragments of this old system supplying outlying parts of north-east England. Connection between a two phase and three phase system can be achieved using a Scott connected transformer, not of my invention BTW, which uses two transformers. See

http://en.wikipedia.org/wiki/Scott-T_transformer

for a bit more detail.

Motors were specifically wound for two phase duty.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[roydm]

Thanks Scotty, that's an interesting article. I have seen the odd 2 phase installation in rural NZ but just assumed it to be 2 of 3, so the motors would be specially wound with 90° coil displavement as well?
Single wire earth return systems were also quite common. The house I was raised in was wired for DC (but connected to 230AC) with a marble switchboard. To replace a blown fuse you turned off the main switch and put in a new piece of wire across a couple of terminals because the fuses were not removable.
Roy

 

[Wilderbeast]

We are controlling a vibratory conveyor Eriez which is 400vac 2 phase using a variac. The fluctuations in supply voltage mean the unit is constantly driving up and down giving unreasonable wear to the brushes and causing klarge carbon deposits that can short.
I trialed a thyristor unit but the waveform it produced effected the conveying severely. a vsd would be better as it would give more of a sine wave output rather than a chopped wave produced by the thyristor chopping the peaks of the voltage.

 

[waross]

Wilderbeast
After reviewing the posts above, can you tell us if you are using:
True 2 phase, (Only two phases supplied at a 90m degree phase angle).
Two phases and a neutral from a three phase system, (Two phases at a 120 degree phase angle).
or
Two lines from a three phase system (Actually single phase at the load).
Can you describe your conveyor drive? I have never seen a vibratory drive with brushes anywhere.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[roydm]

Wilderbeast, have you considered a constant voltage transformer to supply your variac. As Waross says you conveyor sounds unusual, I am familliar with vibratory feeders from Eriez but they just have coils.
Roy

 

[Wilderbeast]

The brushes are on the variac the conveyor is just 4 simple coils. The voltage is 400v ac.

 

[waross]

What roydm says. Or you may want to lessen the sensitivity of the control circuit so that the variac is not thrashing so much.

Bill
--------------------
"Why not the best?"
Jimmy Carter