Effects of rewinding ind. motors with higher resistance that the initial?

[iwen]

I wonder where I work, 3-phase ind. motor with 80 ohms resistance per phase from the manufacturer was re winded and the new resistance per phase was 89 / 90 / 94 Ohms in the 3 phases. when the motor was put back, it burnt within few hour, why was this?

 

[Phrak]

Infantile mortality due to shorted winding?

Why the large disparity in resistance? Did someone loose count?

 

[iwen]

Infantile mortality due to shorted winding?

Why the large disparity in resistance? Did someone loose count?

So does it mean that had it been there was no short winding the motor couldn't burn although with high resistance? if so what are the effects of such higher resistance?

 

[hisham.i]

We can think about the higher resistance in the winding as an extra resistor in series with the initial windings, so the same concept as using a rheostat in starting induction motors, thus the high resistance indicates a low motor speed, but it does not cause to burn the motor.

 

[m.s.j]

It is very clear, Increasing of Ri2 losses and consequent unbalance core fluxes (negative sequence rotary field) due to phases emf unbalancing without any cooling system modification can be caused motor burning.

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[Phrak]

There are several souces for an inbalanced reistance that I can think of:

1) Mis-wired phases
2) Variations in wind length, e.g.: An outer winding is longer than an inner winding
3) Turns count variation
4) Shorted turns
5) Wire gauge doesn't match