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Home Work #1

ELE-300 Induction and Synchronous Machines

D.O.A: 25/08/10 D.O.S:9/9/10

1. How equivalent circuit model of a Induction motor is developed?

2. Explain the production of torque in 3-phase induction motor.

3. How flux and mmf wave produced in induction motor?

4. A 6-pole, 50 Hz, 3-phase induction motor has a rotor resistance of 0.25 ohm per phase and a maximum torque of 10 Nm at 875rpm. Calculate (a) the torque when slip is 3%, and (b) the resistance to be added to the rotor circuit to obtain the 60% of the maximum torque at starting. Explain why values are obtained for the resistance. which value will be used? The stator impedance is assumed to be negligible.

5. What are various information obtained from torque and slip characteristics of induction motor?

6. Compare various speed control method of induction motor.

7. What information are obtained from circle diagram of induction motor?

8. A 400 V, 1450 rpm, 50 Hz wound rotor induction motor has the following circuit model parameters.

R1 = 0.3 ohm R2' = 0.25 ohm

X1 = X2' = 0.6 ohm Xm = 35 ohm

Rotational loss = 1500 W

(a) Calculate the starting torque and current when the motor is started direct on full voltage.

(b) Calculate the full load current, Power Factor and torque (net).

Also find internal efficiency and overall efficiency. Internal efficiency is defined as

Pout (gross) / Pin; Pout (gross) = (1 - s) PG

(c) Find the slip for maximum torque and the value of the maximum torque.dsmfk