The most important advantage of an induction motor is that its construction is quite simple in nature. The construction of the Stator is similar in both Synchronous motors as well as induction motors. However, a slip ring is required to feed DC Supply to the Rotor in the case of a Synchronous Generator. These Slip rings are not required in a Squirrel cage induction motor because the windings are permanently short circuited. When compared with a DC Motor, the induction motor does not have Brushes and hence, maintenance required is quite low. This leads to a simple construction.
The working of the motor is independent of the environmental condition. This is because the induction motor is Robust and mechanically strong.
A Squirrel cage induction motor does not contain Brushes, Slip rings and Commutators. Due to this reason, the cost of the motor is quite low. However, Slip Rings are used in Wound type induction motor to add external resistance to the rotor winding.
Due to the absence of Brushes, there are no sparks in the motor. It can also be operated in hazardous conditions.
Unlike synchronous motors, a 3 phase induction motor has a high starting torque, good speed regulation and reasonable overload capacity.
An induction motor is a highly efficient machine with full load efficiency varying from 85 to 97 percent.
Disadvantages of Induction Motor
A single phase induction motor, unlike a 3 phase induction motor, does not have a self starting torque. Auxiliaries are required to start a single phase motor.
During light load conditions, the power factor of the motor drops to a very low value. This is because during the start, the motor draws a large magnetising current to overcome the reluctance offered by the air gap between the Stator and the Rotor. Also, the induction motor will take very less current from the supply main. The vector sum of Load current and Magnetising current lags the voltage by around 75-80 degrees and hence, the power factor is low. Due to high magnetising current, the copper losses of the motor increase. This in turn leads to decrease in the efficiency of the motor.
Speed control of an induction motor is very difficult to attain. This is because a 3 phase induction motor is a constant speed motor and for the entire loading range, the change in speed of the motor is very low.
Induction motors have high input surge currents, which are referred to as Magnetising Inrush currents. This causes a reduction in voltage at the time of starting the motor.
Due to poor starting torque, the motor cannot be used for applications which require high starting torque.
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