Why only equilizer winding completely burnt in 60kW TEFC motor, after full load run for 8 hours ?

[Tirthraj]

Hi,

There is problem reported in our 60kW DC Motor.
We had run this DC motor on full load & after running of 8 hours , the motor was failed.

And during failure analysis it observed that all winding like field winding, IP winding, series winding & Armature winding found healthy, even commutator was also healthy.

After opening of layers of armature winding it was observed that equalizer winding was completely burnt.

Kindly suggest the possible causes of failure...


Regards,
Mahesh

 

[electricpete]

Conductor failure in general can be initiated due to excess current or due to insulation breakdown.

Your description "completely burnt" seems to point in the direction of excess current. It was the entire length of the equalizer? All equalizers?

What is ratio of equalizer conductor area to armature coil conductor area? Should be at least 1/3, maybe more depending on design, per EASA.

The purpose of the equalizer is to prevent differential voltages of points that are supposed to be equal voltage (allows small current circulating in small loop to avoid larger current circulating in larger loop). The unbalance can arise from uneven airgap, problems with magnetic circuit, perhaps more. It seems that excess unbalance could overload the equalizers (the unbalance circulating current also flows in armature coils, but those have larger conductors).


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(2B)+(2B)' ?

 

[Tirthraj]

Thanks,

I presumed the same.....


Regards,