Insulation breakdown

[Guardiano]

Hi,
Any reason about the cause of failure? The unit is a 250 k W compression chiller.
Thanks
Guardiano

 

[waross]

Is this running on a VFD?
Is this running on an ungrounded system?
Have you had any electrical storms in the area?


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricpete]

From the looks of it, turn-to-turn failure.

Suspects in general would include contamination and (as Bill suggests) steep front voltage spikes from some external origin.
No contamination is visually evident, was the winding cleaned?
Voltage spike scenario gets more likely if the failed coil is the line end coil or an electrically-adjacent coil in the circuit.


=====================================
(2B)+(2B)' ?

 

[waross]

Hi Pete. I thought that the feature in the lower part of the picture may be fish paper installed between phases, hence a line end failure.
Was the inside of the stator polished with a buffing wheel?
Was this done shortly before the failure?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Guardiano]

Thanks Waross and electricpete for your replies. The compression chiller is not on a VFD and the low voltage system is solidly grounded. There was no storm in the area recently and the windings were cleaned and not contaminated.
Waross, the polished area on the stator is from origin. I am suspecting repeated starts, due to reduced load, but I don't have any records to support this statement. The compressor is star/delta started.
Guardiano

 

[petronila]

Hi Guardiano,

If the motor was maintenanced could be possible that the winding was contacted by the rotor once the rotor was installed again.

Regards

Carlos