Induction motor stator orientation

[Tanweer Ahmed]

Hello Engineers,
We just received a new 200kW 4P induction motor. Due to machine space restriction the MTB needs to be on other side of the motor. The motor terminal box is casted with the motor housing. Therefore, in order to change the MTB orientation we have to rotate the complete stator.
My question: What are the critical matters that must be taken care while doing so.

 

[waross]

Mechanical issues.
Are the end bells interchangeable?
Will the rotor still be centered in the stator after the switch?
Usually the answers are yes.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[electricpete]

I agree with Bill, it's just mechanical. You would flip the stator frame end-for-end but put the endbells back in their original positions (now flipped with respect to the stator).

In theory you could change the airgap during such evolution if there were offset bores on both the stator and endbell at one end that compensated for each other in the original configuration. And unfortunately it's very difficult to check airgap in small motors (maybe with odp you have a bit of access but none with TEFC). It's also remotely possible that original lack of perpendicularity between shaft axis and endbell flange on the stator could have been compensated for by opposite lack of perpendicularity between endbell flange and bearing seat on the endbell... that's quite a stretch but could induce a rotor bow and 1x vibration (btw any change in shaft extension position with respect to mounting holes will become irrelevant once the machine is aligned to the driven equipment). I guess in theory there's nothing that requires the OEM to set it up so that axial positioning would be unchanged during such swap, but it seems like every OEM builds their motors symmetrically so this can be done without any effect on axial position of shaft extension.

With all that said, I can remember about 5 times we have swapped endbells to correct terminal box location at our plant for small NEMA frame motors, and we have never encountered any problem with interchangeability of the endbells, or axial positioning, difficulty of alignment, or unusual vibration afterwards.

Also of course if rotation was correct in original orientation then a lead swap is required for new orientation. There may be auxiliary junction boxes for space heater or rtd to think about. Since it's a congested area make sure any air ports (side or end for odp, end for TEFC) are not blocked by whatever is next to the motor.

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(2B)+(2B)' ?

 

[che12345]

Dear Mr. Tanweer Ahmed
T. " .... , in order to change the MTB orientation we have to rotate the complete stator...."
C1. The " best?" way is to {rotate} the [stator as a complete motor]. Refrain from removing the end covers as far as possible. Mechanical foot-mounting dimensions would likely to be different but the (shaft height) [remains the same].
C2. You may need to change the direction of rotation:
a) if it is DOL starting, irrespective of whether it is in Star or Delta; reversal any of the two incoming phases would change the rotation.
b) if it is Star-delta starting, consult the Electrical PE to look into the recent development on Star-delta connection. The century-old method of reversal of two incoming phases is NOT? the best/correct way. Look into the recent contactor manufactures' publications. For ( CW or CCW rotation ) , the connection/wiring is different!.
It is NOT simply by reversing any of the two incoming phases!. Be aware.
Che Kuan Yau (Singapore)