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MU Electrical Engineering (Semester 5)
Electrical Machine - 2
May 2015
Total marks: --
Total time: --
INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

1(a) Define inrush current in three phase transformer
5 M
1(b) Explain the Dd0 phasor group of three phase transformer connection along with connection diagram and phasor diagram.
5 M
1(c) Name the different methods of starting of single phase induction motor and explain any one.
5 M
1(d) Explain the working principle of three phase induction motor.
5 M

2(a) A three phase, star connected , 400V, 50MHz, 4 pole induction motor has the following per phase constants in ohm referred to stators
R1=0.15, XR1=0.45, RR2=0.12, XR2=0.45, XRm=28.5
10 M
2(b) Explain star-delta starter for a 3 phase induction motor. Derive the expression for starting current and starting torque.
10 M

3(a) Explain the necessity of controlling voltage along with frequency fro speed control of an induction motor for v/f control method. Also draw torque-speed characteristics for constant v/f ratio at different frequencies.
10 M
3(b) Explain double field revolving theory for a single phase induction motor.
10 M

4(a) A 500 KVA , 3 phase transformer, having per phase leakage impedance of 0.004+j0.018 ohm is connected in parallel with another transformer of the same voltage ration having a rating of 1000 KVA and per phase leakage impedance of 0.002+j0.012 ohm. Find the load shared by each transformer and their operating power factors for a load of 1500 KVA at 0.8 pf lagging.
10 M
4(b) Conditions required for successful parallel operation of three phase transformers.
10 M

5(a) Draw & explain torque-speed characteristics of 3 phase induction motor at variable rotor resistance.
10 M
5(b) Develop equivalent circuit for a single phase induction motor
10 M

Write a short note on:
6(a) Excitation phenomenon in 3 phase transformer
10 M
6(b) Oscillating Natural
10 M
6(c) Double cage induction motor
10 M

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