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3phase Motors Running On Single Phase


solas

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I have a lathe with a 3phase cage motor. In my home workshop I do not have 3Phase supply. I have been told by a Russian friend that back in Russian his father (without the use of an inverter) has modified or connected 3induction motors to run on single phase. How can this be done?

Solas

 

Oops! that should read

 

I have a lathe with a 3phase cage motor. In my home workshop I do not have 3Phase supply. I have been told by a Russian friend that back in Russian his father (without the use of an inverter) has modified or connected 3phase induction motors to run on single phase. How can this be done?

Solas

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Hello solas

 

There are ways that you can connect a three phase motor up to a single phase supply using capacitors to give some phase shift.

This will cause the motor to rotate, but it will not give the same performance as it would when connected to a three phase supply. The ratings will be severely crippled and at the end of the day, you would be best to fit an inverter or a single phase motor.

 

Best regards,

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Hi Mark

Thanks for your help at this post and at others. I am trying to deepen my knowledge about electrics and electrical systems. I understand a little about Capacitor start and capacitor run motors and how the capacitor gives rise to an artificial phase differance that give the stator field a 'kick' to get it rotating. I presume that running 3phase cage motors on single phase utilises the same effect. For my understanding could you explain what wiring arrangement would be used? In the meantime I am going to start investigating inverters.

 

Solas

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Hello solas

 

the capacitor gives rise to an artificial phase differance that give the stator field a 'kick' to get it rotating.

 

Not quite, the capacitor introduces a phase shift so that the field is driven by two displaced phases which results in a rotating field. A single phase field is actually two fields rotating in opposite directions so that they are in phase at 0 degrees and 180 degrees. The result is no rotation. see http://www.lmphotonics.com/single_phase_m.htm Although with a DC circuit, the capacitor may give a "kick" with the AC circuit, the effect is continuous. There is no kick.

The capacitors used to fool a three phase motor to operate on single phase are doing the same thing, but essentially, most of the flux is going to come from one winding instead of three, and the windings are displaced by 120 degrees and the flux vectors will be 180 degrees plus 90. Hence the considerable derating in performance.

 

Best regards,

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Mark thanks very much. I will think about this and digest it.

My father always said, that a person that really understands something can always explain it in simple terms. You are a man that has real understanding.

Solas

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