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Q5. With reference to three phase induction motors:

a) Explain the phenomenon of crawling and cogging in these motors (6)

b) A three-phase induction motor is wound for four poles and is supplied from a 50 Hz System calculate:

a) The synchronous speed

b) The speed of rotor when the slip is 4 per cent.

c) The rotor frequency when the speed of the rotor is 600 r/min. (10)

Q6. A) What is back emf? Derive the relation for the back emf and the supplied voltage in terms of armature resistance. (6)

b) A three-phase induction motor is wound for four poles and is supplied from a 50 HZ system.

Calculate:

(i) The synchronous speed

(ii) The speed of the rotor when the slip is 4 percent

(iii) The rotor frequency when the speed of the rotor is 600 r/min. (10)

Q5. A 400V, 4-pole, 50 Hz, 3-phase, 10 hp, star connected induction motor has a no load slip of 1% and full load slip of 4%, find the following:

(i) Syn speed

(ii) No -load speed

(iii) Full load speed

(iv) Frequency of rotor current at full load

(v) Full – load torque (16)

Q6. a) Describe the working of a single-phase full wave rectifier with a resistive load. Draw the load voltage and current waveforms. (8)

b) Diode half wave rectifier supply a resistive load of 100Ω from a 100 V ac r.m.s voltage source. The diode is a resistance of 5Ω during conduction state. Calculate

i) The DC output voltage

ii) DC average load current (8)