service fator of motor
service fator 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 fator of motor
Operation at service factor load will allow insulation temperature approx 10C above rated continuous temperature which equates to approximate doubling of insulation aging rate (in a theoretical sense).
Operation at service factor also can put increased stress on other components beside the insulation.
Different people appraoch service factor differently. Try searching the motor forum. Hopefully some folks here on the pump forum will add their perspective as well.
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RE: service fator of motor
As usual, electricpete has the correct scoop, the pump design should not use the service factor, leaving room for field problems such as low voltage, unbalanced voltage, wire size, poor splices, higher flow rates than planned, sags in the power grid voltage, and for longer motor life.
Our solution is to trim (or have the manufacturer trim), the impeller such that no service factor is used anywhere on the pump curve, even at flow rates higher than the BEP or design flow rate. This can be hard to accomplish though, far more time and effort is required to get this done.
PUMPDESIGNER
RE: service fator of motor
You may find that it is less costly to replace the motor than to live with reduced efficiency and the Capex for increase power factor correction equipment.
Specifiers belive in their ignorance that service factors are good for the plant. Overdesign can be as bad as under desgin.
eg What is the point of designing a motor for a pump for the full HQ curve when the static head and system friction will prevent the pump ever reaching that point? Costs increase for the larger motor, coupling and baseplate on the pump. Then there is the foundation, cable size, switchgear, switchroom, transformer etc all increasing for no real benefit.
Unless the duty of a pump is to be increased or the unknowns are so great dont use a highly inflated service factor.
RE: service fator of motor
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RE: service fator of motor
But there are other problems to consider also.
We use concentric, modified concentric, and turbines.
The concentric and modified concentrics are naturally less efficient than the volute designs, but the few points of efficiency are well worth it to get rid of radial thrust causing short life on the bearings.
Again, it will come down to hiring a professional who cares and takes the time to do it the way you need it done, and who is not afraid to lose work because he charges more.
PUMPDESIGNER