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Rotating imbalance from faulty rotor bar joints

Rotating imbalance from faulty rotor bar joints

Rotating imbalance from faulty rotor bar joints

(OP)
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.   

RE: Rotating imbalance from faulty rotor bar joints

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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RE: Rotating imbalance from faulty rotor bar joints

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

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RE: Rotating imbalance from faulty rotor bar joints

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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RE: Rotating imbalance from faulty rotor bar joints

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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RE: Rotating imbalance from faulty rotor bar joints

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*A3/s from the results.

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