TED (r0) _ 4039

(REVrSroN - 2010)

FIFTH SEMESTER DIPLOMA EXAMINATION IN ELECTRICALAND ELECTRONICS ENGINEERING

- OCTOBER, 2OI6

INDUCTION MOTORS

(Maximum marks : 100)

[Note :- A4 Size graph sheet to be supplied]

PART-A(Maximum marks : l0)

I Answer the following questions in one or two sentences.

fTime : 3 loxs

Marks

Each question carries

(sx6=30)

2 marks.

1 . Define slip of an induction motor.

2. What are the two tlpes of rotors used in 3Z induction motor ?

3. What are the two main losses n a 30 induction motor ?

4. List any two melhods of speed control of 3U induction motor fiom stator side.

5. State the working principle of a universal motor. (5x2=10)

PART - B

(lvlaximum marks : 30)

Answer any .five of the following questions. Each question carries 6 marks.

l. Explain how the rotor roates in a 30 induction motor

2. Derive the condition for maximum torque in a 30 induction motor.

3. t,ist the various speed control methods ofa 32 induction motor.

4. What is the necessity of stafiers in 3Z induction motor ? Also list the various

methods of stating.

5. Explain the working of double cage rctor induction motor.

6. Draw the circuit diagram ofan auto-tansformer starter.

7. Write any six applicatiors of single phase induction motor.

[8s]

www.madinpoly.com

2

Marks

PAR| - C

frvlaximum marks: 60)

(Answer one fullquestion from each unit. Each full question carries 15 marks')

UNrr - I

ill (a) A 3A, 4-ple,400[ 50 Hz induction motor, when nuuring on full load,

the frequency of the rotor emf is found to be 2.5 Hz. Calculate :

(i) synchronous sPeed

(ii) slip

8(iii) rotor speed at full load.

(b) Explain the main parts of a 3A shp ring induction motor. 7

On

IV (a) Explarn how rotating magnetic field is produced n 3A induction motor. 7

(b) A 3g induction motor has 4-poles and is supplied from 50Hz system.

Calculate :

(i) the speed of the stator flux.'(ii) rotor speed when slip is 0.04.

(iii) frequency of rotor current at 600 r.p.m. 8

UNrr - II

V (a) Explain the effect of supply voltage on torque and speed in 32 induction

motor.

(b) A 100 kW (output), 3300 Y 50IIz,3A sulr connected induction motor has a

synchronous speed of 500 rpm. The firll load slip is 1.8 % and full loadpower factor 0.85. The stator copper loss : 2440 W.Iron loss : 3.5 kW.Rotational losses: 1200 W. Calculate :

(i) the rotor copper loss

(ii) the line current

(iii) tull load effEciency

On

Vl (a) Explain the various power stages of 3A induction motor.

(b) An 18.65 kW 4-pole, 50Hz,3Z induction motor has friction and windage

. losses of 2.5 percent of the output. The flrll load slip is 4o . Calculate for fullload

(i) the rotor copper loss

(ii) the rotor input

(rn) .the shaft torque 8

www.madinpoly.com

3

Marks

UNlr - III

VII (a) Describe the rotor rheostat method of speed control of 3a induction motor. 5

(b) Explain no load and blocked rotor tests of an induction motor with neatdiagrams. l0

On

VII (a) List any tluee applications of 3A induction motor.

(b) A 3A 4-pole, 50H2,200Y 3.73kW star connected induction motor gavethe following test data. No load : line voltage 200V line cument 54,total input 350 W Blocked rotor : line voltage l00Y line current 26A,total input 1700W. Draw the circle diagam and estimate the following forfirll load conditions.

(i) the line current

(ii) power factor

(iii) the maximum torque in terms of the full load torque.

The rotor copper loss at standstill is half the total copper loss.

UNlr -- IV

D( (a) Explain the double-field revolving theory in lA induction motor.

(b) Explain the working of a repulsion start motor.

On

X (a) Explain the working bf a shaded pole single phase motor. 8

(b) Draw and explain the construction and working of an ac series motor. 7

t2

8

www.madinpoly.com