# GTU previous years question papers -BE- Sem-III -Electrical Machines and Electronics -Dec 2009

GTU previous years question papers

GUJARAT TECHNOLOGICAL UNIVERSITY

B.E. Sem-III Examination December 2009

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 working principle of DC generator. Also explain commutator action. 07

(b) Explain parallel operation of alternators. 07

Q.2 (a) Explain the different methods of speed control of DC shunt and series motor. 07

(b) How the rotating magnetic field is produces in three phase induction motor, when three phase supply is fed to it? Explain with the help of phasor diagram. 07

OR

(b) Explain shaded pole induction motor in detail. 07

Q.3 (a) State the types of instrument transformer and derive the EMF equation of single phase transformer. 07

(b) A long shunt compound generator delivers a load current of 50 A at 500 V

and has armature, series field and shunt field resistances of 0.05 ohm, 0.03 ohm and 250 ohm respectively. Calculate the generated voltage and the armature current. Allow 2 V brush contact drop. 07

OR

Q.3 (a) What are the causes of low power factor? Explain various methods of power factor improvement. 07

(b) A 500 V shunt motor runs at its normal speed of 250 r.p.m. when the armature current is 200 A. The resistance of armature is 0.12 ohm. Calculate the speed when a resistance is inserted in the field reducing the shunt field to 80 % of normal value and the armature current is 100 A. 07

Q.4 (a) List the different equipments used in transformer substation with their function. 07

(b) A synchronous condenser absorbing 60 kW is connected in parallel with a factory load of 240 kW having a lagging power factor of 0.8. If the combined load has a power factor of 0.9 lagging, what is the value of the leading kVAR supplied by the motor and at what power factor is it working? 07

OR

Q.4 (a) Explain the full wave rectifier in detail with the help of circuit diagram and waveforms.     07

(b) Compare AC and DC transmission. 07

Q.5 (a) State and explain Boolean Laws. 07

(b) Describe various types of tariffs. 07

OR

Q.5 (a) Draw block diagram of 8085 microprocessor. 07

(b) Explain inverting and non-inverting comparator. 07