Current Imbalance in Double Wind Motor

[eaglet]

We are finding current imbalance of up to 7% in several motors on our test stand. The strange thing is that the imbalance is only seen in one of the windings. If we were having a problem with our power supply, wouldn't we be seeing the imbalance in both windings? Any suggestions as to what would be causing these problems?

 

[moturcu]

As long as you do not change the phase order (not to cause direction reserval), the same phase winding will be excited with the same phase voltage.

I would try two times phase order change so that direction will not change. This may help to understand the nature of the problem.

 

[Shortstub]

If the motors are randomly-wound, then, there is a high probability of a problem with your test-stand metering. Have you made any other parameter measurements?

 

[moturcu]

eaglet:
After second reading your post, I understand you have got 2 set of 3phase in the motors. If this is the case, unavoidable unbalance occurs between phase leakage reactance.

Because one set will occupy lower part of the slots, the other set will occupy upper part of the slots. The one which occupies lower part of the slot will have higher leakage reactance and lower phase current. The only solution to the problem is to distribute the sets in slots so that half will be upper and the other half will be lower.

 

[GusD]

HI eaglet

The problem you are experiencing is not uncommon, specially when motors are running at little or no load.
Some winding arrangements don't magnitize the core in a symmetrical manner reason for the current unbalance.The unbalance should disappear once motor is under load.
If you had a System Voltage unbalance most likely you would have unbalance on both windings.

GusD

 

[jbartos]

Suggestion to eaglet (Industrial) Jun 25, 2003 marked ///\\We are finding current imbalance of up to 7% in several motors on our test stand. The strange thing is that the imbalance is only seen in one of the windings. If we were having a problem with our power supply, wouldn't we be seeing the imbalance in both windings?
///Yes. It will show in both windings.\\ Any suggestions as to what would be causing these problems?
///Revisit the winding showing up to 7% of current imbalance for its quality.\\\