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02000EE202052003

A 3-phase, 4 pole, 50 Hz, synchronous generator has 48 slots in which double
layer winding is housed. Each coil has 10 turns short pitched by an angle of 36°
electrical. Flux/pole is 0.025 Wb (sinusoidally distributed). Then, for a 3phase,
Y connection, find (i) the line to line induced emf (11) the fifth harmonic
component of line to line induced emf.
List the effects of armature reaction in a synchronous generator at upf, zero pf
lag and zero pf lead?
PART (^

Answer any two full questions, each carries 10 marks.
Describe the synchronising procedure using dark lamp and bright lamp
methods.
Explain clearly how a rotating magnetic field is setup around the stator of a 3-
phase Induction motor when a 3-phase supply is fed to it.
Define slip related to an Induction motor. What is the expression for slip?
Draw the phasor diagram of a salient pole alternator supplying a current which
leads line voltage V and lags the generated voltage E.
Draw and explain the V-curve and Inverted V-curve of a synchronous motor

PART D

Answer any two full questions, each carries 10 marks.
A 4 pole, 50Hz, 415V, 37kW, delta connected , 3-phase Induction motor gave
the following test results:
No load test: 415V, 16A, 1.75kW
Blocked rotor test: 100۷, SSA, 1.85kW
Draw the circle diagram and find the input line current and input power factor at
full load. Assume rotor Cu loss at standstill is equal to half of total Cu loss.
Describe the following single phase Induction motors: (i) Capacitor start type

and (ii) split phase type with torque-speed characteristics and phasor diagram
Find the line current drawn from the supply when a 3-phase Induction motor is
started using (i) a star-delta starter, (ii) Auto transformer of ratio 0.5, if the line
current drawn from the supply is 6A without any starter.

Explain the double revolving field theory related to single phase Induction

motor.

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