Electrical Machines-II

1.      a) Explain in detail the principle of flux in transformer is always constant at all loads.

b) Derive the emf equation of transformer? Draw the NO-Load phasor diagram? (6+9)

2.      a) Define voltage regulation of a transformer. Deduce the expression for the voltage regulation.

b) Derive the equivalent circuit diagram of single phase transformer? (7+8)

3.      a) The number of turns on the primary and secondary windings of a single phase transformer is 350 and 35 respectively. If the primary is connected to a 2.2 kV 50 HZ supply. Determine the secondary voltage.

b) Describe the procedure for conducting sumpners test on pair of transformers? (5+10)

4.      What are the different losses occurring in a transformer on load? How can these losses be determined experimentally? (15)

5.      A 5 KVA, 1000/200V, 50Hz single phase transformer gave the following test results:

Open-circuit test: (l.v side): 200V, 1.2 A, 90 W

Short-circuit test (h.v Side): 50 V, 5 A, 110 W

Compute the parameters of the approximate equivalent circuit referred to l.v side. Also draw the exact equivalent circuit referred to l.v side. (15)

6.      A three phase transformer is used to step down the supply voltage from 10000 V to 440 V. If the output capacity of the transformer is 132 kVA, find the secondary and primary currents of the transformer. (15)

7.       a) Why does the magnitude of the magnetic field remain constant, and also what is the speed of rotation of the magnetic field, so formed? Also what is meant by the term ‘Synchronous Speed’.

b) Derive the relationship between mechanical power developed, rotor input and rotor copper loss. (6+9)

8.  Explain the speed control of induction motor form stator side? (15)