Hall Ticket No Question Paper Code: AEE007
INSTITUTE OF AERONAUTICAL ENGINEERING
(Autonomous)
B.Tech IV Semester End Examinations (Supplementary) June, 2018
Regulation: IARE R16
AC MACHINES
Time: 3 Hours Max Marks: 70
Answer ONE Question from each Unit
All Questions Carry Equal Marks
All parts of the question must be answered in one place only
UNIT I
1. Explain the constructional details and working principle of three phase induction motor with
neat sketch.
A three phase, 50Hz, 8 pole, induction motor has full load slip of 2%. The rotor resistance and
stand still rotor reactance per phase are 0.001ohm and 0.005 ohm respectively. Find the ratio of
the maximum to the full load torque and speed at which the maximum torque occurs.
2. Draw and explain the torque-slip characteristics of the three phase induction motor with different
modes of operation.
A three phase star connected 400V, 50Hz four pole induction motor has the following per phase
parameters in ohms, refer to the stator. R1=0.15, X1=0.45 R21=0.12, X21=0.45 Xm=28.5
compute the stator current and power factor when the motor is operated at rated voltage and
frequency with s=0.04.
UNIT II
3. What are the different staring methods for induction motor and explain the auto transformer
starting method for three phase induction motor?
A six pole, 50Hz three phase induction motor running at 960rpm on full load slip develops
a torque of 149.3N-m at its pulley rim. The friction and windage losses are 200W and stator
copper and iron loses equal 1,620W. Calculate the
i. Output power
ii. The rotor Copper losses
iii. The efficiency at full load.
4. With the neat circuit diagram explain indirect method to determine the efficiency of three phase
induction motor.
With the aid of torque-speed characteristic explain the operation of induction generator.
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UNIT III
5. Describe the difference in construction of rotors of alternators used in hydroelectric plants and
steam plants. Draw neat sketch of two types of rotors.
A three phase, 6 pole synchronous generator has a resultant air gap flux of 0.06wb per pole. The
flux is distributed sinusoidally over the pole. The stator has 2 slots per pole per phase and 4
conductors per slot are accommodated. The coil span is 1500 electrical. Calculate the phase and
line induced voltages when the machine runs at 375 rpm.
6. What do you mean by synchronizing of alternator? Describe any one method of synchronizing.
With the aid of circuit diagram for inductive impedance between two voltages sources and is
associated phasor diagram and derive the expression for power developed.
UNIT IV
7. Explain different methods of starting synchronous motor.
A 2000V, three phase, star connected synchronous motor an effective resistance and synchronous
reactance of 0.2 ohms and 2.2 ohms per phase respectively. The input is 800KW at nominal
voltage and the induced line emf is 2500V. Calculate the line current and PF.
8. Explain the effect of excitation on armature control and power factor for synchronous motor.

A 6600V, star connected three phase synchronous motor works at constant voltage and constant
excitation. Its synchronous reactance is 20 ohm per phase and armature resistance is negligible.
When the input power is 1000KW, the power factor is 0.8 leading. Find the power angle and
power factor when the input is increased to 1500kW.
UNIT V
9. Explain the principle of operation of the single phase induction motor by the double field revolving
theory.
Explain the operation of capacitor start-run induction motor.
10. Draw and explain the equivalent circuit of a single phase induction motor without core losses?

Find the mechanical power output of 185W, 4 pole, 110V, 50Hz single phase induction motor,
whose constants are given below at a slip of 0.05. R1=1.86 ohm, X1=2.56 ohm R2=3.56 ohm,
X1
2 =0.45 X2=2.56 ohm, Xm=53.5 ohm, friction and windage losses are 13.5W.