## 09/03/2020

### Single Phase Induction Motor Interview Question Answer - 1

Describe the different types of single-phase induction motor.

Types of single-phase induction motor

Split phase induction motor

Capacitor start induction run motor

Repulsion motor: (1) Compensated repulsion motor (2) Repulsion start induction run motor and (3) Repulsion induction motor

AC series motor

Unexcited synchronous motor: (1) Hysteresis motor and (2) Reluctance motor

Which type of construction the single-phase induction motor consists of?

The single-phase induction motor consists of

Stator : It consists of starting and running winding. Both windings are placed 900 with respect to each other.

Rotor : It is squirrel cage type.

Centrifugal switch : It is provided in motor to cut out starting winding.

Give reason: The single-phase induction motor is not self-starting.

Single phase induction motor not self-starting

The single-phase winding produces pulsating or alternating flux which acts on the stationary squirrel cage rotor. This flux does not produce any rotation therefore the single-phase induction motor is not self-starting. (The forward and backward rotating torque in the single-phase induction motor is equal and opposite at standstill therefore the net torque is zero.)

What is backward rotating slip of the induction motor if the forward rotating slip is s?

2 – s

On which factor the starting torque of the split phase induction motor depends?

The starting torque in the split phase induction motor is directly proportional to sin α. (Where α is angle between starting winding current and running winding current)

Describe the function of the centrifugal switch in the single-phase induction motor.

Function of the centrifugal switch

The function of the centrifugal switch is to disconnect starting winding from the main supply when the motor speed reaches 70 to 80% of the full load speed.

Where the relay coil is connected in the split phase induction motor?

The relay coil is connected is in series with main winding whereas the pair of its contacts are connected in series with the starting winding.

Which winding has high resistance in the split phase induction motor? Main winding or starting winding

The main winding of the split phase induction motor has high reactance but low reactance whereas the starting winding has high resistance but low reactance.

State the applications of the split phase motor.

Applications

Centrifugal pumps

Fans

Blowers

Washing machines

Duplicating machines

Oil burners

Refrigerators

Give reason: The split phase induction motor is constant speed motor.

Speed Regulation

The speed of the split phase induction motor varies about 2 to 5% between no load to full load therefore it is called as constant speed motor.

How the phase split is done in the capacitor start induction motor?

The phase split in the capacitor start induction motor is done by connecting a capacitor is in series with the starting winding.

Which type of capacitor is used in the capacitor start induction motor?

Short duty electrolyte capacitor

Which type of induction motor has high starting torque, split phase or capacitor start induction motor? Why?

High starting torque

The capacitor start induction motor has high starting torque as compared to split phase motor because the angle between starting winding current and running winding current is 800 in the capacitor motor as compared to 300 in the split phase motor.

Why the capacitor is provided in series with starting winding in the capacitor start induction motor?

Function of capacitor

To provide necessary phase difference between starting and running winding.

It provides necessary high starting torque.

Describe the function of capacitor in the capacitor start and capacitor run motor.

Function of capacitor

It increases the power factor

High efficiency

Noiseless operation

Which motor works as unbalanced two phase motor?

Single value capacitor run motor

Whether any centrifugal switch is necessary in the single value capacitor run motor?

No

Which type of capacitor is used in the single value capacitor run motor?

Continuous duty rating motor, Pyranol insulated foil paper capacitor

State the applications of the single value capacitor motor.

Application

Induction regulator

Furnace control

Rheostat

Arc welding control

What do you mean by single value capacitor motor and two value capacitor motor?

Single value capacitor motor

The single value capacitor motor is one in which one capacitor is used during starting as well as running condition.

Two value capacitor motor

The two-value capacitor is one in which high value of capacitor is used during starting condition and low value of capacitor is used during running condition.

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