Download PTU B-Tech EEE 2020 Dec 4th Sem Asynchronous Machines Question Paper

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Total No. of Pages : 02
Total No. of Questions : 18

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B.Tech. (EE) (2012 Onwards)/(Electrical & Electronics)(2011 & 2012 Batch)/(Electrical Engineering & Industrial Control)(2012 to 2017)/ (Electronics & Electrical)(2012 Batch) (Sem.-4)
ASYNCHRONOUS MACHINES
Subject Code : BTEE-401
M.Code : 57104
Time : 3 Hrs. Max. Marks : 60

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INSTRUCTIONS TO CANDIDATES :

1. SECTION-A is COMPULSORY consisting of TEN questions carrying TWO marks each.
2. SECTION-B contains FIVE questions carrying FIVE marks each and students have to attempt any FOUR questions.
3. SECTION-C contains THREE questions carrying TEN marks each and students have to attempt any TWO questions.

SECTION-A

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Answer briefly :

1. “The rotating fields of the stator and rotor are stationary with respect to each other”. Justify the statement.
2. Why is the efficiency of a 3-phase induction motor less than that of a 3-phase transformer?
3. Explain the function of two stator windings in a single-phase induction motor.
4. Draw the neat diagrams of single-phase capacitor-start capacitor-run induction motor.

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5. Name the four types of starters used for 3-phase induction motor.
6. Why does a 3-phase induction motor always run at a speed less than the synchronous speed?
7. What is the effect of introducing resistance in the rotor circuit of a 3-phase induction motor?
8. State the condition for maximum torque in a 3-phase induction motor.
9. A voltmeter gives 120 oscillations per minute when connected to the rotor of an induction motor. Find the slip of the motor. The stator frequency is 50 Hz.

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10. In case of induction motors, explain why the air gap length is kept as small as is mechanically possible?

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SECTION-B

1. Derive the condition for maximum torque in a 3-phase induction motor.
2. Explain the principle of operation of a self-excited 3-phase induction generator. Give the condition under which this generator may fail to build-up.

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3. When main winding of a single-phase induction motor is connected to 200 V, 50 Hz source, it takes a current 50 A at an angle of -60° at standstill position. Find the rotor circuit parameters. Neglecting stator leakage impedance and magnetizing current.
4. Explain how the speed of a 3-phase induction motor can be controlled by injecting a voltage in the rotor circuit of 3-phase induction motor.
5. Describe the construction and working of universal motor.

SECTION-C

1. Explain how the stationary, pulsating m.m.f. wave of a single phase induction motor can be considered as equivalent to two equal but oppositely rotating m.m.f. waves.

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2. Describe the constructional features and working of a single-stack 3-phase 6/4-pole variable reluctance stepping motor.
3. The starting torque of 100 Nm is developed in a 3-phase squirrel-cage induction motor by an auto-transformer starter with a tapping 40%. Find the starting torque, if the tapping of the auto-transformer is changed t0.80%.

NOTE : Disclosure of Identity by writing Mobile No. or Making of passing request on any page of Answer Sheet will lead to UMC against the Student.

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