Why Starting Current of Induction Motor Is Higher Than the Synchronous Motor

986 Words Mar 18th, 2013 4 Pages
2012
Sidra Inam
University of Engineering & Technology
12/10/2012
2012
Sidra Inam
University of Engineering & Technology
12/10/2012

Why Starting Current of Induction Motor Is Higher Than the Synchronous Motor
Why Starting Current of Induction Motor Is Higher Than the Synchronous Motor

Starting Current Of Induction And Synchronous Motors:-
Starting Current of both motors were different, when analyzed using ETAP. Starting current of Induction motor was more than that of the synchronous motor. However Induction motor is used for Stable operation in running condition [1]
Reason:-
Before Complete description following parameters should be known * Current in rotor in case of Induction motor is “AC” and in case of
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Large synchronous motors are usually started acrossthe- line. Occasionally, reduced voltage starting methods, such as autotransformer or part-winding starting, may be employed. [6]

As the motor speed increases, the discharge resistor provides the torque required for the motor to reach synchronous speed. Once synchronous speed is reached, the starting resistor is switched out of the field circuit and excitation can be applied to lock the stator and field poles in sync. The DC excitation system is used to apply current to the field winding creating a rotating electromagnet field that couples the rotor field to the rotating AC field in the armature winding when the motor is operating at synchronous speed.

Starting and pull-in torque’s vary with the square of the applied voltage, and the starting current is proportional to the applied voltage, exactly as on induction motors. [7]

Summary:-

Synchronous motor efficiencies are higher than those of induction motors. Their inrush currents are low. They can be designed with torque characteristics to meet the requirements of the driven load and available power supply. A synchronous motor’s speed/torque characteristics are ideally suited for direct drive of large horsepower, low rpm loads such as reciprocating compressors. Their precise speed regulation makes them an ideal choice for certain industrial processes. That is why starting current of synchronous motor is less when compared with induction
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