Two Marks Questions with Answers

Two Marks Questions with Answers

Q. 1 What is the use of circle diagram of an induction motor ?

Ans. :

The circle diagram is useful in predicting the performance parameters of an induction motor such as motor input, losses, power factor, slip, efficiency at any load condition and also the maximum quantities as maximum torque, maximum power factor, maximum output etc.

Q. 2 Which two tests are conducted to obtain the data for the circle diagram ?

Ans. :

1. No load test or open circuit test

2. Blocked rotor test or short circuit test

Q. 3 How to conduct blocked rotor test on induction motor ?

Ans. :

In this test, the rotor is locked and it is not allowed to rotate. The reduced voltage (about 10 to 15 % of rated voltage) just enough such that stator carries rated current is applied. Now the applied voltage Vsc, the input power Wsc and a short circuit current Isc are measured.

Q. 4 How to conduct no load test on induction motor ?

Ans. :

In the no load test, the motor is made to run without any load i.e. no load condition. The speed of the motor is very close to the synchronous speed but less than the synchronous speed. The rated voltage is applied to the stator. The input line current and total input power is measured. The two wattmeter method is used to measure the total input power.

Q. 5 State the effect of increase in load on the power factor, efficiency, input current and slip of an induction motor.

Ans. :

As the load on an induction motor increases the power factor increases, the efficiency increases upto certain load and then decreases, the input current increases and slip also increases.