Re: Service Factor
What NEMA say is concerning service factor is that a motor must deliver full hp and torque when loaded to at or below service factor ratings and tha the motor will operate within its rated temp. When motors are loaded beyond thier service factor amps the winding temp will increase and thermal degrdation of the magnet wire and insulation system is rapidly compromised. Torque beginsto drop rapidly at this point and the motors ability to sustain the load drops. As the winding temp increases the winding resistance begins to change and the current continues to increase until it reaches the "knee" of the saturation curve when the winding has absorbed all it can stand. Then the motor rapidly begins to stall and all the smoke is let out which is what keeps motor winding shops and new manufacturers in business. Motors are designed with a service factor to allow for temporary overload conditions and this service factor is not supposed to be used for design and application to the load. that si if you had a 1.2 hp calculated laod requirement you would not apply a 1 hp motor with a 1.25 service factor to run this load. You jump up to the next size motor at 1.5 hp instead.In all my years in the motor shop business engineers who skimped on H.P. requirements helped keep us going.
[ March 05, 2004, 01:42 PM: Message edited by: stew ]
