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coolyaar
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Join Date: Jul 2011
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Motor Insulation Class F/B

06/03/2012 12:40 PM

our 3.3KV,450KW motors have insulation class F/B on nameplate.what does that mean?

as for as i know a motor should have only one overall insulation class i.e. either class F=155 degree or class B=130 degree.

clarification required please.

tanx in advance.
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lyn
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#1

Re: motor insulation class F/B

06/03/2012 1:53 PM

NEMA Insulation Classes

Class dismissed.

Oh, this↓ might help.

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lyn
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#2

Re: motor insulation class F/B

06/03/2012 3:00 PM

Is the motor rated 50/60Hz?
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SolarEagle
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#3

Re: motor insulation class F/B

06/03/2012 3:02 PM

" stator windings may be Class B but the more difficult to cool rotor winding may be Class F."

http://en.wikipedia.org/wiki/Insulation_system

http://elpaso.apogee.net/md/mfnrins.asp

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debata07
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#4

Re: Motor Insulation Class F/B

06/04/2012 5:26 AM

This means that the motor is manufactured with class F insulation. But its cooling circuit will be so designed that the temperature rise of the motor is not allowed to exceed 130 degree celsius, although the motor can withstand 155 degree. This will provide a substantial margin for temperature rise and the expected life of insulation of the motor will be more.
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rudy.leurs
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#5

Re: Motor Insulation Class F/B

06/04/2012 5:29 AM

good answer debate 07,

you hit me in reaction time
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rudy.leurs
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#6

Re: Motor Insulation Class F/B

06/04/2012 5:32 AM

I think that the windings are made from materials with an isolation class F (155°C)

But , at nominal load, the temperature rise of the winding will be limited to class B (120°C)

So in case of an overload,

- you have an extra safety margin from 35°C before the winding gets damaged

- the overload protection has more time to trip.
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electricalexpert65
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#7

Re: Motor Insulation Class F/B

06/04/2012 12:10 PM

A class 'B' insulating material will give a service life of about 20, 000 operating hours, at its maximum permissible temperature of 130 deg. C, under standard conditions of instllation, operation & maintenance. So, also a class 'F' insulating material will give a service life of about 20, 000 operating hours at its maximum possible temperature of 155 deg. C.

But, when you subject a class F material only to class B limits, it gives an extended service life of about 1, 00, 000 hours at an operating temperature of 130 deg.C.

Also, as standard service conditions cannot be guaranteed, the insulation service life of the motor increases even under the worst possible conditions of service - if a class F material is provided but its temperature rise is limited to that of Class B.
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