University of Mumbai 2007-5th Sem B.E Electrical and Electronics Engineering Electrical Machine-II Old - Question Paper
10
Con. 5376-07.
(OLD COURSE)
(3 Hours)
CD-8187 [Total Marks : 100: (1) Question No. 1 is compulsory.
N.B.
1.
(2) Attempt any four out of remaining questions.
(3) Assume any data if necessary.
(a) Explain cogging and crawing in induction motors.
(b) Explain mechanical forces in transformer.
2. (a) The power input to the ROTOR of a 440 V 50 Hz, 6 pole. 3$ induction motor is 10 80 kW. The rotor emf is observed to make 100 revolution per minute. Calculate
(i) slip (ii) rotor speed (iii) mechanical power developed (iv) rotor cu loss (v) rotor resistance per phase if rotor current is 65 A.
Draw and explain the power stages in 3 phase induction motor. Prove that : 10
(b)
PQ : PCf ; Pm = 1 ; s : (1 - s) where S is slip.
(a) Explain oscillating neutral in transformer.
3.
10
10
(b) Explain excitation phenomenon in transformer.
4. (a) Draw and explain torque speed characteristics of three phase induction motor. Explain 10 3 zone operation.
(b) What is necessity of starter in three phase induction motor ? Explain autotransformer 10 starter, star delta starter. Derive their starting torques In terms of starting torque for DOL starter.
5. (a) Explain split phase induction motor and capacitor start capacitor run motor. Draw 10 circuit diagrams, phaser diagrams and torque speed charactristics.
(b) A 230 Vt 50 Hz. 4 pole, single phase induction motor has following constants and losses : 10 It = 2-3 a r2* 4-2 1.2 x, = 3-2 U x2 = 3-2 fl xm = 74 Cl Core loss = 98 Watts Friction and windage loss = 30 watts
If the motor is running with a slip of 0 05 at rated voltage and frequency, then compute the stater current, pf, power output, torque and efficiency with its auxiliary winding open.
6. (a) Two 3 phase transformers have the following per phase parameters, referred to secondary. 10
re1 = 0-004 n xet =0*018 0
re2 = 0-002 U xe2 = 0 012 O No. 1 transformer is of 500 KVA and No. 2 is of 1000 KVA. They are connected for parallel operation. How will they share a load of 1500 KVA at 0-8 pf lag ?
(b) Expjain back to back test on transformers.. 1
(ii) Slip at max torque
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