Winding Temperature Stabilization

[petronila]

Dear Friends,
The Following name plate belongs to an electric motor manufactured in 1994 By SIEMENS in SPAIN:
1LA14502KF
Frame: 450
Ins.Class F (B heating)
550 kW
I= 62 A
Ia/In = 560 A
2980 rpm
Cos Phi = 0,9
Eff = 96,3 %

The motor was tested in Factory with this results:

Load% 104,9
V - 6.130 V
I - 62,2 A
597,5 Kw
Cos - 0,904
Eff - 0,9657
In this conditions the Winding temperature was Stabilize at 92,92 ºC.

Today some body are trying to use this motor with a new pump and loading with 592 kW.

The question is How to determine by calculations the new Winding temperature stabilization at 592 KW with out a new dynamometer test (Only taking account the above factory datas).

Thanks for the Inputs

Regards

Petronila

 

[electricpete]

I would make the following approximations:

Temperature rise above ambient is proportional to losses.

No-load losses are about 20% of full-load losses. The remaining 80% of full-load losses are load losses which vary approximately with load^2

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[TomG33]

THe answer to your question lies in the motor name plate data. It says the insulation class is "F" and it inferrs that the motor is designed for a class "B" rise, meaning that the motor is designed for insulation class B operation. What this means is that the motor is designed to limit the copper temperature to be below 80 Degrees C above the the nominal 40 degrees C ambient. (120 Degrees actual copper temperature) when operating at 1 per unit load.
the standard also implies that if the motor is run at 1.15 Per unit load, the temperature rise will be less then 90 degrees c above the nominal Ambient (130 Degrees actual copper temperature).
The actual insulation Material used is class F which means it is good for 155 Degrees c copper temperature, so in the worst case you have a 25 degree C margin.



Your 592Kw is only 1.076 P.U. (550Kw Base) so for a good first guess, your maximum design copper temperature will be 40 Ambient + 80 For 1.0 PU operation + ((7.6/15)* 10) for the 7.6% overload. or aproximately 125 Degrees C.
THe motor Insulation is rated for an absolute copper temperature of 155 Degrees C so you should be able to operate the motor at 592 Kw with at least a 30 Degree c temperature margin before insulation life is affected.

Look Here for a little more information on the temperature classes.

http://www.engineeringtoolbox.com/nema-insulation-classes-d_734.html

Regards
Tom Grayson

 

[petronila]

Thanks Pete and Tom,

Tom in this order of ideas, the motor could be labelled with a new name plate ¿¿ What new data could we use??

Thanks

Petronila

 

[rotman]

I think it's not necessary to change the rating plate of this motor for using it with new pump. Motors are hardly ever operated exactly at rated load (normally less, but - if thermal margin allows, as in this case - can be 'overloaded' as well). If this could be useful for maintenance, I'd suggest to intall additional plate with motor parameters for the new load conditions (for load 107.6% of rated load we can assume the same cosfi and eff values as for rated conditions, so the actual data would be: 592 kW and 66 A).

 

[TomG33]

I agree, Rotman.
In reality, You ave not changed the motor, Just it's load. Renameplating the motor should be done only if the motor is physically changed to operate differently.
All you will have done is to change the load, and verified that it is operating within the design limitations of the motor.
of course the temperature calculations are based on the motor having the correct maximum ambient and umimpeded ventilation. IF your ambient is cooler then this 40 Degrees C, you are ok, If you are above 40 Degrees C then you need to watch what is happening. But still, 25C margin looks pretty good.