November 2010 BE 411302/511302/515306/516303/6C0022 Electrical Technology Sathyabama University

Register Number

                               

SATHYABAMA UNIVERSITY

(Established under section 3 of UGC Act, 1956)

Course & Branch: B.E/B.Tech-CSE/MECH/M&P/E&C/BME

Title of the Paper: Electrical Technology                  Max. Marks: 80

Sub. Code: 411302/511302/515306/516303/6C0022 Time: 3 Hours

Date: 24/11/2010                                                         Session: FN

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PART - A                (10 X 2 = 20)

Answer ALL the Questions

1.     Classify the DC generators based on excitation.

 

2.     What is the purpose of starter in DC motor?

3.     What is the purpose of laminations in the transformer core?

                                                 

4.     Define all day efficiency.

5.     Define ship.

6.     Why is induction motor known as rotating transformer?

7.     Define distribution factor in synchronous generator.

8.     What is the purpose of damper winding?

9.     Mention the types of stepper motor.

10.   Mention any two applications of permanent magnet DC motor.

 PART – B                      (5 x 12 = 60)

Answer All the Questions

11.   (a) Discuss the process of self excitation in a DC machine. What conditions must be fulfilled for the machine to self excite?         (7)

        (b) A 4 pole lap wound shunt generator supplies to 50 lamps of 100 watts, 200V each. The field and armature resistances are 50 and 0.2 ohm respectively. Assowing a brush drop of 1V per each brush, calculate armature current, generated EMF.         (5)

(or)

12.   (a)  Explain about the various methods of speed control for DC series motor.                                                                             (5)

        (b) A 6 pole, lap wound 400V series motor has the following data: Number of armature conductors = 936; Flux/pole = 0.05 wb; Total motor resistance = 0.7 ohm; Iron and friction loss = 2.5 kW; If the current taken by the motor is 80A, find the

(i) total torque                 (ii) Power output                     (7)

13.   (a)  Derive the EMF equation of transformer.                       (5)

(b) A 10kVA, 2500/250V, single phase transformer gave the following test results

O.C. Test: 250V, 0.8A, 50W

S.C. Test: 60V, 3A, 45W

Calculate the efficiency at

(i) Full load upf      (ii) half full load, 0.8 pf lagging     (7)

(or)

14.   Obtain the equivalent circuit of transformer from first principle.

15.   (a) With the neat sketch, discuss about the construction of squirrel cage induction motor.                                             (7)

        (b) A 6 pole, 3 phase, 50Hz motor with star connected rotor, the rotor resistance/phase is 0.3 ohm and reactance/phase at standstill is 1.5 ohm. An emf of 175V is induced between the slip rings on open circuit. Find

(i) Slip at a speed of 950 rpm

(ii) Rotor frequency and reactance at a speed of 950 rpm.                                                                                                    (5)  

(or)

16.   (a)  Derive the torque equation of induction motor.

(b) Discuss about any one starter for starting AC 3 phase induction motor.

17.   Discuss about the procedural steps in calculating the regulation of synchronous generator using synchronous impedance method. Also draw the phasor diagram if the generator is loaded with the lagging pf load.

(or)

18.   Is synchronous self starting? Discuss in detail about the starting of synchronous motor with the aid of neat diagram.

19.   What is a Linear Induction motor? Discuss about the construction and operation of linear induction motor. Mention its applications.

(or)

20.   Write short note on the following:

(a) Position Synchros

(b) Brushless DC motors

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