37Kw Motor pulling double rated currect

[Colesy]

Hi Guys
Some help if possible please.
Recently (July) installed a Soft Start Control (Trip Class 20) to a 37Kw Mill Motor (Rated 74Amps) DO Delta
The motor gradually over a period of 8hours runs normally to start at 60+Amps but by the end of the day she pulls a steady 121Amps from each phase, increasing throughout. No loose connections anywhere.
My question is, could it be the windings are cooking, could it be too much mechanical load or could it be a fault within the soft start. The latter I wouldn't think personally as its the motor which determines what power to pull. The motor casing is constantly about 80degC when running and it's been like this since July.
Voltage is maintained at 408Vac across each phase all the time and frequency is consistent 50Hz.
I may have answered my own questions but looking to you guys for advice.
Cheers,
Colesy

 

[Pat H]

I'd guess its the loading. If it was cooking the windings I wouldn't expect it to cure over night then start again.
can you run the motor off load at the start of the day and then check it at the end of the day for current draw?

 

[Colesy]

Good point Pat H, it points to the mechanical loading throughout the day.

 

[Pat H]

Could be a bearing somewhere siezing up.

 

[timbobelfast]

I would do a full detailed inspection of the motor, especially the Rotor. Wouldn't hurt to measure the windings to check they are balanced etc!
What's this motor coupled to? Pump or agitator etc?

You might need to review the mechanical loading also.

 

[Lucien Nunes]

I would be surprised if the frame remained at a constant temp with the line current varying from 74 to 121A, as the copper loss would increase more than 2.5 times even if the motor is OK. A winding fault sufficient to increase the current by that amount would probably make itself known pretty quickly, so I would hazard a guess that an increase in mechanical load is at least partly responsible.

A soft-start should cut itself out of circuit once its job is done and you can confirm this by measuring the voltage between input and output terminals, which should be negligible once the bypass contactor closes.

I wonder why the overload relay is not catching it before it gets to 121A, or has someone conveniently adjusted that to keep production running?

 

[Marvo]

That's a massive overload that would normally produce a lot of heat in the motor. Unless the motor is only running for very short periods of time and with a long 'off' time between runs then I'd expect overheating to be noticeable within minutes and probably catastrophic in a relatively short space of time after that depending on the insulation class.

If it was a bearing that was winding up tight and causing that much mechanical overload it would have have failed shortly afterwards. Also you'd get noise and heat from a failing bearing so I'd guess that maybe you're missing something.

What protection is on the motor? Can you give full motor details and some explanation of it duty?