Test: Induction Machine - 1 - Electrical Engineering (EE) MCQ

The split phase induction motor has two windings, the main winding and the auxiliary winding. These windings are displaced in space by 90^o electrical. The auxiliary winding has higher current ratio between resistance and reactance, by designing it at a higher current density.

The rotor operates at synchronous speeds without current-conducting parts. Rotor losses are minimal compared to those of an induction motor.

Once started at synchronous speed, the motor can operate with sinusoidal voltage. Speed control requires a variable-frequency drive.

A reluctance motor is a type of electric motor that induces non-permanent magnetic poles on the ferromagnetic rotor. The rotor does not have any windings. It generates torque through magnetic reluctance.
A. Reluctance motors are not self starting
B. Reluctance motors start as induction motor and runs as synchronous motors
C. Reluctance motors needs no DC excitation

In DC series motor, the AC currents through the field and armature winding will be unidirectional by commutator and brushes. So torque will be unidirectional but pulsating due to AC.

A Capacitor Start Motors is a single phase Induction Motor that employs a capacitor in the auxiliary winding circuit to produce a greater phase difference between the current in the main and the auxiliary windings. Due to greater phase difference capacitor Start motors have very high starting torque for a single-phase AC motor.

The capacitor helps the motor to get starting torque by phase splitting. If the capacitor is short circuited,there will be no starting torque and as single phase induction motor is not self starting,it will not start rotating. single phase induction motor is not self starting. capacitor is used to start the motor.

In a three-phase induction motor,

• The stator is stationary, and the rotor is a rotating part
• Both the stator field and rotor field rotate with synchronous speed
• The rotor rotates with a speed less than synchronous speed

Negative slip indicates that the motor is running above synchronous speed. This can happen only when it is driven by a prime mover. This motor becomes an induction generator. For it to generate, it must be connected to a power supply, from where it can draw magnetising current.

Rotor voltage frequency = 120/f = 2 Hz 

Rotor voltage frequency = S x supply frequency 

2 = S x 50 

S = 2/50 = 0.04 = 4%

When the motor is stationary,rotor conductors are being cut by rotating flux at synchronous speed.therefore,the frequency of rotor current(or emf)is the same of supply frequency