Rotating imbalance from faulty rotor bar joints

[wetwind]

I have recently had some rotors tested(with a core loss tester) and the results showed some high resistance joints between the rotor bars and the short circuit ring(these are brazed joints). I know that these high resistance joints will cause vibration issues, high current draw, and heating issues. I would like to calculate(or estimate)the amount of force or imbalance that would occur from a high resistance joint in a rotor circuit. Any help would be appreciated.

 

[electricpete]

The main effect would be uneven heating causing a rotor bow. The formula would be

Force = S[·]W[·]A[·]G
Where Force is in units of lbf

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[electricpete]

Another effect which might occur is movement of bars within the slots. Same formula.

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[jraef]

E-pete, you had me going there for a second. I found myself trying to interpret the electrical meanings for S, W, A,... oh no!

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[electricpete]

Glad you liked my formula. Maybe I should have created variables: S = Speed;
W = Weight of rotor; A = cross sectional area; G = acceleration of gravity (required for English units).

Actually I wasn't trying to be a wise guy in response to the original question. I suspect any attempt at calculating this would be very involved, require many gross assumptions, and be very inaccurate.


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[davidbeach]

No, no, no. Obviously, as this is an electrical forum, S = apparent power in VA, W = power in Watts, A = Current in Amperes, and G = Conductance in mhos or Siemens.

Unfortunately, the formula then also needs a term (or terms) that can cancel the extra m*A[sup]3[/sup]/s from the results.