## December 17, 2011

### ELECTRICAL TECHNOLOGY ECE JNTU previous years question papers

ELECTRICAL TECHNOLOGY JNTU previous years question papers

Time: 3 hours Max. Marks.80

All questions carry equal marks

1.a) Explain briefly the essential functions of armature and field coils in a dc machine.
b) Develop an expression for EMF in a dc machine.
c) A 4 pole, long shunt, lap wound generator supplies 25 Kw at a terminal voltage of 500 V. The armature resistance is 0.03 O, series field resistance is 0.04O and shunt field resistance is 200O. The brush drop is IV. Determine the emf generated. 

2.a) Discuss the various methods of speed control of a D.C motor?
b) A 2- pole, D.C. shunt motor operating from a 200 V supply takes a full load current of 35 Amps drawn from the supply. The no load current being 2 Amps. The field resistance is 500O and the armature resistance is 0.6O. Calculate the efficiency of the motor on full load. [8+8]

3.a) Explain the principle of operation of transformer
b) Obtain the approximate equivalent circuit of a given 200/2000 V single phase 30kVA transformer having the following test results.
O.C test: 200 V, 6.2 A. 360 W on Lv side
S.C. test: 75 V, 18 A, 600 W on hv side. [8+8]

4.a) Derive the condition for maximum efficiency of a single phase transformer.
b) A 20 kVA, 2200/220 V, 50 Hz transformer is tested for efficiency and regulation as follows:
O.C. test: 220 V, 4.2 A, 148 W (LV side)
S.C test: 86 V, 10.5 a, 360 W (HV side)
Determine:
i. Efficiency at full load and 0.8 pf lag and

5.a) Derive the expression for develop torque in a 3 phase induction motor and find the condition for maximum torque.
b) The starting and maximum torques of a 3 phase induction motor is 1.5 times and 2.5 times its full load torque. Determine the percentage change in rotor circuit resistance to obtain a full load slip of 0.03. Neglect stator impedance

6. a) Derive EMF equation of Alternator.
b) A 3- phase, 2.5 MVA, 6.6 KV synchronous generator gave the following data for open circuit test at synchronous speed.
If (A) 16 20 25 32 45
Voc (line) V 4400 5500 6600 7700 8800
with armature short circuited and full load current flowing the field current is 18A. Find the field current and voltage regulation when the machine is supplying full load current at 0.8 P.F log by at rated voltage. Neglect armature resistance use M.M.F method. [8+8]

7. a) Explain the methods of starting and principle of operation of single phase induction motor?
b) Explain the operation of a shaded pole type motor. [8+8]

8. With neat sketch explain the Basic principle of Moving iron instrument

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