# 3 Phase to 2 Phase

Discussion in 'General Electronics Chat' started by viju, Apr 6, 2012.

1. ### viju Thread Starter Senior Member

Sep 28, 2008
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0
I have a welding machine which is powered through 3 phase system.But machine input power is 2 phase. While operating the machine (which is 250 KVA) I have great amount of imbalance in the system resulting in voltage drop particularly while running back up generator.

Can I connect a suitable Scott - T transformer so that primary of transformer is balanced?

But the phase angle in three phase system 120 deg and Scott - T would be 90 degrees. How do I calculate the effective voltage so that I can feed the welding machine with 2 phase with 90 degree phase angle?

Help would be greatly apprciated.

2. ### crutschow Expert

Mar 14, 2008
13,492
3,372
A Scott-T of the proper current and voltage should convert the 3-phase power to the 2-phase power required for your welding machine. I don't understand your question.

3. ### viju Thread Starter Senior Member

Sep 28, 2008
120
0
When I connect the welding machine from 3 phase source phase angle would be 120 degrees.But when I connect Scott - T transformer phase angle between phases would be 90 degrees. Am I right.

Will it create any problem? Will the effective voltage to the welding machine vary?

4. ### shortbus AAC Fanatic!

Sep 30, 2009
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1,680
Very unusual to find something that is two phase. Sure it is not single phase 220 volts? 220V sometimes has the 120V used for controls or displays on the machine.

Two phase power uses a four wire plus ground system. 200 single phase will use two "hot" wires, a "neutral"(to allow the 120V) and ground.

5. ### BSomer Member

Dec 28, 2011
433
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It shouldn't affect your machine in any way. The Scott-T was designed for the balancing of the load accross a 3 phase system when connecting a 2 phase device, typically a motor.

6. ### viju Thread Starter Senior Member

Sep 28, 2008
120
0
Shortbus --- You are right.

I was wrong. Machine is supplied 440V with two phases of the three phase system (Line to Line).

Transformer should be three phase to single phase but at voltage of 440 V.

My question is whether the phase angle would affect the machine

7. ### shortbus AAC Fanatic!

Sep 30, 2009
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Even though the three phase is 120° out it shouldn't hurt the welder thats expecting 180°. If the lights are dimming its probably because the line is not at high enough current. A thee phase to single phase transformer that big will be expensive, though it will spread the load across all three phases.

8. ### crutschow Expert

Mar 14, 2008
13,492
3,372
The phase angle is relative to the other phases. If you only have single-phase then the phase angle has no meaning (expect between voltage and current, which is the power factor).

strantor likes this.
9. ### viju Thread Starter Senior Member

Sep 28, 2008
120
0
Thank you people. Is there any other solution other than going for 3 phase to single phase transformer.Because this imbalance would create more neutral current.

10. ### shortbus AAC Fanatic!

Sep 30, 2009
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I think you mean "reactive current". But this is beyond my knowledge on how to solve it. I do know its done with capacitors though. Has to do with "power factor".

11. ### PaulEE Member

Dec 23, 2011
423
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three phase motor, two phase generator. sorry, couldn't resist.

12. ### strantor AAC Fanatic!

Oct 3, 2010
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1,989
Your welder won't care, but other devices running on the same power might care.
You could load the other phase with some other single phase load.

13. ### jimkeith Active Member

Oct 26, 2011
539
99
I think that the real issue now is:
250KW is an insanely high single phase load--other solutions?

Not without getting into the unit and making substantial, expensive modifications--like changing out to a 3phase transformer... If output is AC, you are stuck with single phase.

My take is that the type of installation where such a welder is used, probably has multiple such welders so that the total 3 phase load may be reasonably balanced or that such imbalance is insignificant relative to total load.

Last edited: Apr 8, 2012