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Code No: 3220204
II B. Tech II Semester Regular Examinations April/May 2009
ELECTRICAL MACHINES - II
( Electrical and Electronics Engineering )
Time: 3 Hours
Max. Marks: 80
Answer any FIVE questions.
All questions carry equal marks
* * * * * *
1. (a) State and Explain the Principle of operation and constructional details of single-phase
(b) A 1 – phase transformer has 500 turns in the primary and 1200 turns in the Secondary.
The cross – sectional area of the core is 80 sq.cm. If the primary winding is connected to
a 50 HZ supply at 500 V, Calculate (i) peak flux density and (ii) Voltage induced in the
2. (a) How does a transformer can be resolved into an equivalent circuit?
(b) A 600 KVA, 1- Phase transformer when working at u.p.f has an efficiency of 92% at
full load and also at half-load. Determine its efficiency when it operates at unity p.f and
3. (a) Explain the requirements for parallel operation of 1 – phase transformers.
(b) Two 1 – phase transformers A and B rated at 250 KVA each are operated in parallel
on both sides. Percentage impedances for A and B are (1 + j6) and (1.2 + j 4.8)
respectively. Compute the load shared by each when the total load is 500 KVA at 0.8 p.f
4. Discuss various possible poly phase connections in poly phase transformers.
5. (a) Obtain the expression for slip and frequency of rotor current.
(b) A 4 – pole, 3 – phase induction motor operates from a supply whose frequency is 50
(i) The speed at which the magnetic field of the stator is rotating.
(ii) The speed of the rotor when the slip is 0.0