May be Temperature kills motors

[Jed057]

Dear anyone,

Motor 2100 kW ,6.6 kV, 50 Hz
according to motor datasheet,Motor insulation class F and temperature rise is Class B (Ambient Temp 40 deg)
but the problem is during operation at full load temp reach 140 deg C. so, Vendor recommends that we have to change setting from original (We have RTD in winding of this motor)

Alarm setting from 120 deg C--------------->150 deg C
Trip setting keep at 160 deg C

Do you think this new setting is safe for this motor??


young engineer

 

[rbulsara]

Your trip setting is not changing, so what is the worry?

For the best recommendation consult the motor manufacturer.

Rafiq Bulsara

http://www.srengineersct.com

 

[rbulsara]

If anything I would review the Trip setting of 160C. The class F winding is rated for 155C.

The alarm should be set at little above the rated temperature rise plus the ambient.

Rafiq Bulsara

http://www.srengineersct.com

 

[edison123]

Yes. Temperature is a major killer of winding insulation. If the specified temp. rise is class B and the ambient is 40 deg C max, then 120 deg C should be the trip. For Class F temp rise, the trip is 140 deg C. Even though class F is rated for 155 deg C, that's for the hottest spot and your RTD's is not necessarily the hottest spot and hence the allowance.

Your high winding temp is may be due to overload, improper cooling, dust accumulation etc. I would eliminate the root cause of this high temp instead of meddling with temp trip levels.

Muthu

http://www.edison.co.in

 

[j3n5]

I agree with Muthu,

your motor is running too hot. Does it have a VFD? Are the voltages balanced?

Most of the failure modes of your motor's insulation system are chemical processes with exponential dependency to absolute temperature (according to Arrhenius). The cooler the motor, the longer the lifetime (lower failure rate).

F-class insulation is guaranteed to last for 20.000 running hours with hot-spot temp at 155°C at 40°C ambient. The reason for having B-class temprise but F-class insulation is that you want a longer lifetime than these 20.000 hours.

Note that your RTD is not located at the hot-spot. You may calculate 5° temperature gradient from the hot-spot to your RTD.


My advice is free of charge and of respective quality

 

[esee135]

You could get lucky and run for years, but the key word is lucky so you'll accelerate your life expectancy like tipping over the bad end of the bath tub curve.

For some of the older motors/gens I've worked on, the use of hard board papers and poorly delaminated insulation layers are common, the added heat never helps.

In general, a lot of people are spec'ing Class B operation of a Class F rated machine. The idea is, yes it's rated for higher temps, but the head room buys you longevity. Hope your iron doesn't buckle on you at 160degC...

 

[wolf39]

Jed057:

I have some more questions regarding your motor:

Motor speed?
Year of construction?
Post-impregnated stator winding?
Constant or variable load conditions?
Low voltage conditions?

You would be well advised to follow Muthu's hints. Clean the coolers and stator winding.

Regards

Wolf

http://www.hydropower-consult.com