Two Speed motor problem 1

[Drivesrock]

Hi all. In my company's shop we have an ABB two speed motor for repair, two seperate windings in the same stator - 6 pole and 8 pole, both Delta connected. It was badly burnt so re-wound but now we have the following problem:

The 8 pole machine runs fine no load - expected no-load current of 26%. Then we connect to the 6 poles.
The 6 pole machine draws approx rated current in two phases and higher in the third.
We are using a VFD for the tests but we did perform one off DOL start of the 6 pole machine and same 'bad' result.

Plenty of electrical checks and reworking polarities etc etc so we know the 6 pole and 8 pole windings have not been internally connected. The surge test results of the 6 pole connections showed a problem until we opened the 8 pole windings.

We opened the 8 pole delta connections and the 6 pole motor runs fine. So there seems to be some interaction between the windings causing the 6 pole machine to behave this way.

We rewound again (just in case) but did the 6 pole machine first, performed a surge test to check it was ok. Then we installed the 8 pole windings and we get the 'bad' surge test results in the 6 pole machine again - ie one phase different to the other two.

So we are expecting to run the 6 pole machine and get the high current again.

The motor terminal box doesn't have links to open the 8 pole windings if we want to run the 6 pole machine.

ABB won't supply the motor winding schematic. The motor nameplates are attached.

Any ideas anyone?

 

[edison123]

We had similar problems with delta connected two windings in our shop too. When one winding was energized, the other winding would also have induced currents, which overheated the motor and made the motor noisy. We rewound both the windings with Wye connection and both the problems went away.

Muthu

http://www.edison.co.in

 

[waross]

A six pole winding will induce unbalanced voltages in an adjacent eight pole winding.
If a delta winding does not have balanced voltages there will be circulating currents.
When running on the eight pole winding you most likely have circulating currents in the six pole winding, but possibly not as severe.
The solution, as noted:
Either break the delta on the unused winding or use wye connections.
With the wye connection there will still be unbalanced voltages induced in the unused winding but there will be no path for circulating currents to flow.

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

 

[panter]

Your people likely did not analyze good old coils and place where must be beginning of both windings which I guess is the problem .If they did not keep the old head of the winding or they do not have a good winding pattern it will be difficult to do a good job.

 

[dArsonval]

Certain two winding motors during the repair process can differentiate “the men from the boys”.

Couple / three things. It was noted that the motor nameplates are attached. “Attached” meaning photos?

Regarding the original winding; was it wound as a concentric winding or in a lap winding arrangement?

Some windings absolutely have to be placed back in the machine the exact same way they were originally
engineered for the apparatus. Panter's reply is eluding to this necessity.
Switching things around along the way, is going to get ‘ya all tangled up further.

It’s unfortunate ABB is unwilling to supply a winding diagram, because it would likely show
the location or relation of the two windings in respect to the actual stator slot placement etc.
That information is what would be very helpful.
Manufacturers data is typically laid out in a flat or straight line, compared to what one sees in a text book, or
when referring to EASA diagrams which are shown in a circular scheme.

One might ask, how would that matter? A coil is a coil. Well….

I seemed to be clicking on these forum questions lately that are just
not solvable without knowing so many other factors.

The combinations of all the answers given here so far are valid.
But unfortunately, these answers still don’t solve your problem.
And mine isn't going to either.

I can think of three different people I’ve met in the motor repair industry that spent most of their life winding motors,
and I’m confident that one of them would know how to better explain an answer to your two winding dilemma.
Do they participate in forums like this? Nope. They’re just not interested.

I wish you luck with this. If and when you solve the problem, come on back and tell us what you ended up doing.

John

 

[zlatkodo]

Sometimes this problem can be solved relatively easily.
We have solved a similar case recently (6 and 4 poles).
Contact us with exact diagrams you use ( for both speeds) and nameplate photo.

 

[MarioOliveira]

as 6-pole inputs are correct? In, In, Out, In, Out, Out