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5th October 2010, 12:26 PM #91
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The short answer I got is that the power is the same.
Originally Posted by Stustoys
The question was. What difference in power is there between running a 3 phase induction motor on 415V 3ph in star configuration versus 240v 3ph delta configuration?
Taking a typical small 4 pole induction motor, there are a total of twelve windings in all, 4 coils on each leg.
The delta configuration draws more current. because there are only 4 coils (1 leg) between the phases, whereas the star configuration has 8 coils (2 legs) between the phases.
The lecturer that would have been able to provide the detailed math analysis was away yesterday. (I for one, would still like to see the maths!)
Regards
Ray
PS: Bigger Motors (say more than 5hp) are nearly always designed to run 415V delta. If you ran them 415V star you would get 1/2 power and reduced current.
This reduced current in star is why you have star-delta starters, to reduce starting current.
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6th October 2010, 07:58 AM #92
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Thanks Ray, I'm still trying to getting a handle on this.
So a dual voltage motor can't be run in 415V delta?
Stuart
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6th October 2010, 02:31 PM #93
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Hi Stuart, Originally Posted by Stustoys
I suspect the answer is mostly no..
I asked the same question, you are asking, and the answer I got was that you wire it according to the nameplate, (remember we are talking small motors a few kW at most..) will specify voltage and current for each configuration.
But, I think we need to clarify, what you mean by the term "Dual Voltage" there are motors which are wound with extra tapping points on the coils, between the poles, so there is a lot of potential for confusion. Going from 4 pole 415 to 2 pole 240v.... and the combinations are endless....
In my case, the 2hp motor on the mill, was setup 415v star only, and we had to pull it apart (with Son-in-laws help) it to bring out the extra 3 wires so I could run it on 240v 3phase. So the nameplate info didn't help at all.
Regards
Ray
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10th October 2010, 06:32 PM #94
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A new booklet on the subject of 3 phase converters is coming out soon:
Workshop Practice Series No. 47 Three-Phase Conversion - due late November 2010
Jordan
