Motor ratings

[ksps100]

Dear ALL,

We have a motor that is rated as Class B,Ambient=40Deg C,and Service Factor-1.15.

My spec calls for all motors to be rated Class F, Ambient=50Deg C .Service Factor to be defined by Vendor

Will the change of Service factor from 1.15 to 1 enable the motor to be rated for Class F and Ambient=50Deg C.
I have no knowledge of such calculations.
Whats the relationship between Service Factor and Insulation class?

These are 3 phase motors.

Could somebody guide me

Thanx

 

[Marke]

Hello ksps100

The class commonly describes the quality of the insulation that is used in the motor providing for a different maximum operating temperature of the windings.
Having said that, there are motor wound with high temperature insulation and designed for a low temperature rise. - they could tolerate a higher operating temperature.
You really need to present your requirements to the manufacturer for comment as there are too many unknowns.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[aolalde]

To make an evaluation, the full load temperature rise is required.

Class B insulation is adequate to operate up to 130 °C.
Class F insulation is adequate to operate up to 155 °C.

The maximum temperature rise of a motor with insulation class F installed in a place with 50°C ambient is limited to 95°C.
50+95 = 145 with allowance 10 °C for hot spots.

If the class B insulation motor has 80 °C rise the total temperature for 50 °C ambient will exceed the insulation limits.
50+80+10 = 140 °C

 

[easpe]

Below is taken from reliance electric, SF and IC are by design and not so much a function of one to the other. At minimum I always use a sf of 1.15 and class f motors. If the motor is in place you can IR and amp it to see if design conditions are exceed. Seen lots of pump installs where class b motor run above 130deg just shortens their life.
So no to changing the service factor changes temp rating if that the question. The nameplate will give all the motor ratings.

SERVICE FACTOR
1. When used on a motor nameplate, a number which indicates how much above the nameplate rating a motor can be loaded without causing serious degradation, (i.e., a 1.15 S-F can produce 15% greater torque than the 1.0 S-F rating of the same motor).

2. When used in applying motors or gearmotors, a figure of merit which is used to "adjust" measured loads in an attempt to compensate for conditions which are difficult to measure or define. Typically, measured loads are multiplied by service factors (experience factors) and the result in an "equivalent required torque" rating of a motor or gearmotor.



INSULATION CLASS
Since there are various ambient temperature conditions a motor might see and different temperature ranges within which motors run and insulation is sensitive to temperature; motor insulation is classified by the temperature ranges at which it can operate for a sustained period of time.

There are four common classes:

Class AC Motor DC. Motor W/1.00 S.F.
Max. Total Temperature Range
(Including Ambient and Temperature
110ƒ Hot Spot) Range DC Motor Total
Temperature Range
A 105ƒC A 110ƒ C
B 130ƒC B 140ƒ C
F 155ƒC F 170ƒ C
H 180ƒC H 195ƒ C

When a motor insulation class is labeled on the nameplate the total insulation system is capable of sustained operation at the above temperature.

 

[petronila]

Hello ksps100,

The S.F is a factor by wich the motor can be overloaded beyond the full load, a 1.15 Services Factor means that the motor can operate at a 15% overload with out damaging, if a motor has a S.F of 1.0 then the motor has no overload capacity and probably will overheat if is overloaded for a period of time.In your case you can reverse this concepts, you have a Class B motor with 1.15 S.F that means the motor could be operated at 15 % beyond the full load amperaje, if you reduces the S.F to 1.0 then you most to operate your motor at Full load only,and your gonne have an "Overloading SAVE" and "Temperature Save", I think your S.F 1.15 motor could operate for ambient up to 30 Degrees C.
Another think , if the manufacturer was classified this motor B with a 1.15 S.F the most probably is the real insulation´s motor be Class F.

Best Regards

Petronila

 

[ksps100]

Dear All,
Thanks so much for your advice.

The change of Service Factor from 1.15 to 1 does give a Temperature Save(We observed it by experimenting here)
i.e:Although the nameplate of the motor is stating SF=1.15, we want to change the Data sheet to limit the SF=1.0,so that the Operations team is not permitted to overload these motors( Even though the nameplate permits it)
However my objective is to prove that such a reduction in the Service Factor enables the motor to have a Insulation class equivalent to a Class F motor.
I could not get any calculations from the manufacturer for a relationship between the Service Factor and Temperature rise.
Is there some formula for such a calculation?
Thank you
With Best Regards
ksps

 

[petronila]

ksps 100,

I think you are not going to find this formula.

The insulation class Labelled on the nameplate seems unimportant unless you increse the ambient temperature or the motor´s loads. In your case due to your CLASS B, S.F 1.15 is running at S.F 1.0 rated the motor class F.

OCT 15: if the manufacturer was classified this motor B with a 1.15 S.F the most probably is the real insulation´s motor be Class F.This is a common practice by the manufacturers.

Regards

PETRONILA

 

[aolalde]

The "insulation class" depends on the materials used in the motor construction not on the load applied.
Ask to the manufacturer what is the insulation class in your motor.

 

[petronila]

Hello aolalde,

The Motor´s insulation class is B.

Regards

PETRONILA

 

[ksps100]

Dear ALL,
Thank you for your useful insights.
The manufacturer sent us revised data sheet( but no calculations!).
SF is revised to 1. And manufacturer warrantied that the Motor can be treated "equivalent" to a Class F motor.

Thanks all again.
With Best Regards
ksps