II/IV B.Tech Degree Examinations, June 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) What is the function of yoke in a DC Machine?
b) Draw the external characteristic of DC shunt Generator?
c) Why there is need for starter in a DC motor?
d) Define regulation of a Transformer.
e) What is the condition for Maximum efficiency of a Transformer?
f) Draw the vector diagram of a Transformer under No Load conditions.
g) Define slip.
h) What is the difference between stepper Motor and other motors?
i) List various types of Single phase Induction Motors.
j) What is Synchronous Impedance?
k) List starting methods of Synchronous Motor.
l) Define Pitch factor.
UNIT - I [1 x 12 = 12M]
2. a) Derive the torque equation of a DC Motor.
2. b) A DC Shunt Generator is supplying load connected to a bus bar voltage of 220 V. It has an armature resistance of 0.025 ohms, field resistance of 110 ohms. Calculate the value of load current and load power when it generates an emf of 230 V. (OR)
3. a) Explain how to find critical resistance from occ of a shunt generator.
3. b) With a neat diagram describe a 3 point Starter.
UNIT - II [1 x 12 = 12M]
4. a) Derive the condition for maximum efficiency of a Transformer.
4. b) Calculate the equivalent circuit parameters of single phase, 4 KVA, 200/400 V, 50 Hz transformer referred to LV side. The following are test results.
OC test: 200 V, 0.7 A, 70 W (LV side)
SC test: 15 V, 10 A, 80 W (HV side) (OR)
5. a) Derive an expression for voltage regulation of a Transformer.
5. b) The maximum efficiency of a 500 KVA, 3300/500 V, 50 Hz single phase transformer is 97% and occurs at 75% full load, UPF. If impedance is 10% calculate regulation at FL 0.8 lagging.
UNIT - III [1 x 12 = 12M]
6. a) With the help of vector diagrams explain the concept of Rotating Magnetic field.
6. b) A 4 pole 50 Hz, 3 phase Induction motor has rotor resistance and reactance per phase of 0.03 ohms and 0.12 ohms respectively. What is the value of speed at which maximum torque occurs? Find the amount of external rotor resistance per phase to be inserted to obtain 75% of maximum torque at starting? (OR)
7. Write short notes on
a) With the help of neat diagram explain about a capacitor start single phase Induction Motor
b) Explain the principle of operation of any one stepper Motor.
UNIT - IV [1 x 12 = 12M]
8. a) Derive an expression for Pitch factor.
8. b) A 16 pole 3 phase Alternator has a star connected winding with 144 slots and 10 conductors per slot. The flux per pole is 0.03 wb and speed is 375 rpm Find line voltage. (OR)
9. a) Derive the expression for regulation of an Alternator.
9. b) What do you mean by Hunting?