# GTU previous years question papers -BE- Sem-III -Electrical Machines and Electronics -May 2012

GTU previous years question papers

GUJARAT TECHNOLOGICAL UNIVERSITY

BE SEM-III Examination May 2012

Subject code: 131901

Subject Name: Electrical Machines and Electronics

Instructions:

1. Attempt all questions.

2. Make suitable assumptions wherever necessary.

3. Figures to the right indicate full marks.

Q.1 (a) Explain the Construction of DC Machine

(b) Explain working principle of transformer under lagging power factor load

Q.2 (a) Explain speed control of dc shunt and series motor by armature control and flux control method

(b) Determine Armature torque and Shaft torque of 220 V , 4-pole,series motor with 800 conductors wave connected supplying a load of 8.2KW by taking 45 A from the mains. The flux per pole is 25 mwb and its armature circuitresistance is 0.6 ohm

OR

(b) Explain Three point dc shunt motor starter

Q.3 (a) Explain construction of single phase transformer

(b) Explain different methods of speed control of three phase induction motor

OR

Q.3 (a) What are the conditions to be fulfilled for parallel operation of two

synchronous machine? Give any one method of synchronizing

(b) Describe construction features and operating characteristic of a shaded pole motor. also give its applications

Q.4 (a) Write short notes on substation Equipment

(b) A 12-pole,three phase, 600 V,50 Hz star connected induction motor has rotor resistance and stand-still reactance of 0.03 and 0.5 ohm per phase respectively. Calculate (1) Speed of maximum torque (2) Ratio of full load torque to maximum torque,if the full-load speed is 495 rpm

OR

Q.4 (a) Explain Comparison of DC and AC transmission system

(b) Explain different methods to improve power factor

Q.5 (a) Explain De-morgan’s theorm

(b) What are the causes of low power factor also list disadvantage of low power factor

OR

Q.5 (a) Define rectification. Draw and explain operation of three phase full wave rectifier

(b) Draw Functional block diagram of 8085 microprocessor and explain in brief