IEC motrors and Service Factor 1

[jraef]

Is there any kind of terminology in the IEC motor specs that equates to Service Factor in the NEMA motor specs? I read a brochure from ABB motors that states that IEC designs using Class F insulation provide the same extra duty capacity as a 1.15 Service Factor. Any thoughts on this?

"Venditori de oleum-vipera non vigere excordis populi"

 

[aolalde]

The insulation class by itself does not imply the possibility of running a motor with service factor (SF). Not for NEMA and I am almost certain that is not for IEC. (I don’t have that standard, but it was developed by international agreement).

NEMA MG1 states;
{Any alternating-current motor having a SF is suitable for continuous operation overloaded up to the horsepower (HP) obtained by multiplying the rated HP by the SF SHOWN ON THE NAMEPLATE.

A motor operating continuously at any SF greater than 1.0 will have a reduced life expectancy compared to operating at its rated nameplate HP.
INSULATION LIFE and BEARING LIFE are reduced by operating at the SF load.}

 

[jraef]

Thanks.
I knew that about NEMA, although the condensed version that I have states that a litle less severely. What I was after was any statement in IEC standards that might equate.

"Venditori de oleum-vipera non vigere excordis populi"

 

[UKpete]

jraef

For industrial motors IEC60034-1:1996 applies (formerly known as IEC 34-1) "Rating and performance". There is simply no IEC equivalent to service factor, I didn't even know what it meant until I started seeing references to SF on this forum. I have just flicked through my copy just to make sure.

The motor rating plate usually gives the rated values of voltage, current, speed, power factor, temperature class etc, and unless otherwise stated these are for S1 duty (continuous running). Incidentally, although the motor may be capable of running over a specified voltage range, the rated values do not imply any other capability other than at the rated voltage.

In the UK (IEC territory) it has long been accepted practice to rate industrial induction motors to class B temperature rise whilst using class F insulation, except on some larger machines. However, I have never seen it equated to a particular value of service factor as you have seen ABB refer to. But I wouldn't expect to in a European brochure as we don't use the term; I have read plenty of ABB material but I guess they only make the reference in the US.

The respective temperature rises for classes B and F for a typical induction motor are 80 and 105 deg.C, I would think it reasonable that for the same motor life, the motor with class F insulation would be capable of 15% higher output than an equivalent motor with only class B. This assumes that the winding temperature goes up with the square of increased power.

When I first came across SF I thought it was a good idea, now I am a bit dubious. Having been brought up without it, it seems like an uneccessary complication but I could still be persuaded.

 

[Modula2]

We normally operate Nema motors within the rating, not at the SF even when available. Thermal is only one motor design factor affected by shaft power. It is good to know that all factors have been accounted for, if the motor is operated beyond it's rated load. Does the Iec rating system mean that we should be extra cautious when applying an Iec motor, with a lower ratio of load to motor power? How does Iec allow a motor to be operated beyond it's rating? In Nema, it could operate continuously at the SF, sacrificing insulation life by thermal.

 

[UKpete]

I would be suprised if there is any real difference in lifetime between similarly-rated IEC and NEMA (SF 1.15) motors. Most large manufacturers produce both types and you basically get what you pay for (their sales-reps would be in a good position to give an informed and unbiased opinion on any differences).

NEMA MG-1 only specifies service factor in relation to thermal performance; any reference to bearing life is a bit vague.

I don't think NEMA or IEC actually specify a typical motor life (i.e. continuous hours at the rated condition) - it is largely down to the reputation of the manufacturer.

 

[jraef]

Thanks UKpete.
Your answers were helpful to solidify what I suspected and I voted you a star. I see a lot of OEMs here in the US use the Service Factor rating of the motor as a way of fudging on applications where they need a little more HP than the nameplate rating at a given speed, and yet NEMA MG-1 says specifically that they can't. I take the stand that the SF only allows for temporary variations in line voltage or brief load fluctuations, but the continuous rating remains just as shown on the nameplate. It appears that IEC rules are essentially the same, other than the fact that variables may perhapse not be tolerated as loosely as they can be in NEMA designs using higher SF ratings. Ergo IEC ratings are the same as NEMA 1.0 Service Factor and if you want more out of it, buy a bigger motor.

"Venditori de oleum-vipera non vigere excordis populi"

 

[RRaghunath]

I am in IEC area and not much familiar with NEMA. I find the discussion as above interesting.

I thought IEC motors are rated to take on 10% overload on continuous basis. That is 1.10 service factor in NEMA terms.

The overload rating always apply when the voltage and frequency of the power system are rated levels, whether it is NEMA definition or IEC.

Appreciate any comment.

Thanks in anticipation.

 

[mikeflux]

Just to set the record straight rraqhunath, the IEC standards are all nominally based on a so called S1 , Continuously Maximum Rated duty cycle which has no provision for any continuous overload.
IEC also recognises other various intermittant/cyclic duty cycles designated S2 - S9, but none of these allows for any continuous overloads as such.
In the dim and distant past the old, very old , British Standard BS 168 did allow for a continuos 10% overload as well 25% for 2 hours but this is long gone.

Regarding the initial querry the current ,UK , ABB position is as follows :-
ABB use class F insulation systems as a minimum, with as standard an allowed class B temperature rise. The use of Class F insulation with a Class B temperature rise gives ABB products a 25 deg C safety margin. This can be used to increase the loading by up to 12% for limited periods , to operate at higher ambient temperatures or altitude, or with greater voltage and frequency tolerances. It can also be used to extend insulation life.

 

[jraef]

So I have concluded that this was/is something unique (as in "marketing spin") to ABB motors, not design criterea for IEC motors in general. This was about recommending Service Factor settings on motor protection systems when protecting IEC motors. We have decided to insist that Service Factor settings be always set to 1.0 when protecting IEC motors, and only increased for NEMA motors when the user truly understands the ramifications of doing so.

(LOL... like that will ever happen!)

 

[RRaghunath]

Thanks mikeflux, for the response. I am still left with the impression that the IEC rated motors are capable of taking overload of 10% continuously provided the system parameters are rated (rated voltage and rated frequency).

I explain - these motors are rated as per IEC to deliver rated output at voltage and frequency varying. The permissible variation is +/-10% voltage and +/-5% frequency and 10% combined.

Having said that, a motor designed to deliver rated output at -10% voltage would certainly be able to carry higher load during rated voltage operation. Hope you agree with me.

Thus, is this additional load carrying capability not akin to 'service factor' in NEMA terminalogy.

 

[magneticted]

rraghunath,regarding the voltage as you know in Europe we now have the Euro Voltage, whereas since 1995 all new motors now have a 230v or 400 v windings suitable for +/-10% volts. And within this voltage range the motors will still be within class "B" limits, for motors with class F insulation system.Therefore the motor output can be increased providing the class F temperature limit is not exceed.

ABB stance is we follow IEC , there is no reference in IEC to service factors or overload capabilities, other than duty S1 ( continous )or duty cycles S2-S9 ( intermittent )as mikeflux correctly pointed out.

ABB literature does point out that the load can be increased by upto 12% for limited periods, but this is a general statement. We can of course utilize the full class F temperature rise for increased output's or high ambient's and can be offered as a continous duty condition.If that's want the customer requires.( Not what IEC states )In doing so we will not call it a service factor, but a motor output with class F rise. The % figure is determined case by case, and is an internal issue, which is not conveyed to the customer, whatever it may be. So there is no misunderstandings. Concluding one should not mix up NEMA standards with Service factors or any other NEMA terminology, with IEC motors or vice - versa. IEC Motors from ABB which have output's corresponding to class F rise, are commonly called "High Output Motors "