service factor of motor
service factor of motor
(OP)
I often see the service factor of motor when I select e-motor , but I don't know the exact meaning of service factor,I often see factor 1.1 and 1.0 , Could any one explain what is service factor and what do we need to pay attention to when we select factor ?





RE: service factor of motor
We don't use SF much in Europe and when we do, I have a feeling that we do not really know what we are talking about.
I know that a 1.15 SF motor can be overloaded a lot more - heard up to 80 percent for a limited time - than can a SF 1.0 motor. But there must be a lot more to it. Technical and historical reasons. Data, tables, nomograms. We want to hear it all!
Gunnar Englund
www.gke.org
RE: service factor of motor
The differ numbers refer to how much. For example a 10 hp motor with a 1.15 service facture means that it can be load to 11.50 hp or 10 hp x 1.15 sf =11.50 hp
RE: service factor of motor
The S.F is a factor by wich the motor can be overloaded beyond the full load, a 1.1 Services Factor means that the motor can operate at a 10% 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.For main breakers and Wire sizing You have to take acount the S.F Amperes, normally S.F * FL Amps.
Best Regards
Petronila
RE: service factor of motor
any one can give other comments ?
RE: service factor of motor
RE: service factor of motor
www.nema.org
As I recall, the continuous HP rating for a motor is for an ambient temperature of up to 40 degrees C. The Service Factor rating is for operation at an ambient temperature of 20(?) degrees C.
RE: service factor of motor
Lets asume you have 10 HP motor coupled to one Pump,for a S.F 1.0 motor the name plate motor´s amperage is 14 Amps.This motor is not designed to drawn more than 14 amps under normal conditions. But the pump sometimes requiere 15 amps, this is a 1 amp beyond the name plate, for it this s.f 1.0 motor will be overloaded.Yo will need a 10.7 HP motors but you don´t find this motor at trade, (The next hp is 15HP)so what to do??
You call to motor´s dealers and sayds I have this problem, then the recommend use a 10 HP S.F 1.1 Motor, so whats that?? this is a motor that could provide you 1.1*14 amps = 15.4 Amps. Now you can supply the overload to this pump
with out use of more spencive 15 HP motor (And maybe you need some arrangments to install because could be different FRAME).And with out risk to burn the motor.
Regards
Petronila
RE: service factor of motor
That NEMA link is worth a PLS.
Gunnar Englund
www.gke.org
RE: service factor of motor
Because of this, many OEMs, especially pump and compressor OEMs, regularly utilize the service factor of motors in order to avoid going up one size in a given application. They only need it to last out the warranty period so the somewhat nebulous long term efects are not important to them (on the surface IMHO). On consumer goods and some industrial pre-packaged systems, this is often hidden by saying things like "developes XX HP" instead of actually stating a HP rating. People will argue all day as to whether that is a good idea or not, but I am just stating a defacto application.
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: service factor of motor
Yes, Try to be in acordance about this concept is very hard, I think the design manufacturers always are above the rated values because they want to keep your good names in Industrie, for it is possible some motors don´t fail quickly even overloaded, my point of view about the Services Factor is exposed in my last post, this is usefull when you have sligt or very short time overloads.
Thanks for your comments.
Regards
Petronila
RE: service factor of motor
As I said, I have been unsure about service factor and how to use it. The NEMA paper pointed to by sreid probably says it all, but the practical interpretation varies a lot. The example with 80 percent "short term" overload with a 1.15 SF motor is what I have experienced in a machine specification. How many minutes "short term" actually is, is not specified.
I think that the less creative European way of doing it leaves less to be guessed. Rated power = Rated power - and that's it.
Gunnar Englund
www.gke.org
RE: service factor of motor
RE: service factor of motor
A motor with a service factor of more than 1.0 does not reach its thermal limit at nameplate load but rather at some higher load. The motor's design life however, is only acheivable at nameplate load. Operation at levels above nameplate, ie, in the service factor range, will not result in overtemperature but will result in shortened motor life.
I guess the bottom line is that a motor with a service factor over 1.0 has extra thermal capacity built into it but not extra mechanical/electrical life.
Or, to look at it another way, you can get extra continuous output from a high service factor motor but it will cost you in motor service life.
RE: service factor of motor
http://ww
you can learn a bit about S.F. there.
You should like this one Gunnar!
remember: An opinion is only as good as the one who gives it!
RE: service factor of motor
RE: service factor of motor
A higher S.F. motor can be used to give you a little margin for either case.
In power plants, we typically specify motors to be 1.15 S.F., and that the motor must drive the load without going into the S.F. This provides some coverage for "unanticipated" load conditions, as well as some "extra life"!