II/IV B.Tech Degree Examinations, January 2014
First Semester
Electrical Technology
Time : 3 hours
Maximum Marks : 60
Answer question No.1 Compulsory
Answer ONE question from each Unit
1. Answer the following [12 x 1 = 12M]
a) Write the generated emf equation for dc generator.
b) Write the advantages of dc shunt generator & dc shunt motor.
c) What is the function of armature in dc generator?
d) Draw the torque speed characteristics of dc series motor.
e) Define transformer from basic principles.
f) Write the expression for transformer efficiency suitable for any load condition.
g) Define voltage regulation for a transformer.
h) Draw the torque slip characteristics of 3-phase induction motor.
i) Write the principle of operation of induction motor in few sentences.
j) Write the applications of single phase induction motor.
k) Define synchronous impedance for synchronous generator.
l) Write the different constructional parts of 3-phase alternator.
UNIT - I [1 x 12 = 12M]
2. With neat diagram give the constructional features of dc machine. (OR)
3. A 4 pole 500 V dc shunt motor has 700 wave connected conductors on its armature. The full load armature current is 60 A and flux per pole is 30 m Weber. Calculate the full load speed if the motor armature resistance is 0.2 ohm and the brush drop is 1 V per brush.
UNIT - II [1 x 12 = 12M]
4. a) Derive the relationship between line and phase quantities of star connected poly phase system.
4. b) What are different losses in transformer? Derive the condition for maximum efficiency of a transformer. (OR)
5. a) Derive the emf equation of a single phase transformer and explain voltage transformation ratio.
5. b) A short circuit test when performed on the HV side of a 10 KVA 2000/400 V single phase transformer gave the following data- 60 V, 4 A, 100 W. If the LV side is delivering full load current at 0.8 pf lag at 400 V, find the applied voltage to HV side
UNIT - III [1 x 12 = 12M]
6. Explain with the help of suitable diagrams, how rotating magnetic field is produced in a three phase induction motor. (OR)
7. a) Describe the construction and working principle of stepper motor with relevant diagrams.
7. b) Using double field revolving theory explain the torque-slip characteristic of a single phase induction motor and prove that it cannot produce any starting torque.
UNIT - IV [1 x 12 = 12M]
8. a) Derive from basic principles the emf equation of three phase synchronous machine.
8. b) Derive the expression for voltage regulation of alternator by using synchronous impedance method (OR)
9. a) Explain the construction and working principle of three phase synchronous motor and write its applications also.
9. b) Explain the different starting methods of synchronous motor.