Rajiv Gandhi Proudyogiki Vishwavidyalaya 2007 B.E Basic Electrical Engineering raury 2005 - Question Paper

this ques. paper is of year 2005 not 2007..

Basic Electrical Engineering February 2005 ques. Paper

1.
(a) Derive the expression for the active power and reactive power consumed by a balanced 3-phase delta connected load in terms of line voltage, line current and power factor.
(b) Three inductive coil every having a resistance of 20 ohm and reluctance of 15 ohm are connected in star across a 3-phase, 400 V, 50 Hz supply. compute the readings of 2 watt meters connected in the circuit to measure the power input.

2. A steel ring of 25 cm mean diameter and of circular part three cm in diameter has an air gap of 1.5 mm length. It is wound uniformly with 750 turns of wire carrying a current of 2.1 A. Calculate:
(i) Magneto motive force
(ii) Flux density in air gap
(iii) Magnetic flux
(iv) Relative permeability of steel ring
Assume that iron parts takes about 35% of the total magneto motive force.
3. A transformer has its maximum efficiency of 0.98 at 15 k VA at unity power factor. During the day it is loaded as follows:
12 hours - two KW at 0.5 p.f. lagging
6 hours - 12 KW at 0.8 p.f. lagging
6 hours - No load
Find the all day efficiency of the transformer.
4. A steel ring of 25 cm mean diameter and of circular part three cm in diameter has an air gap of 1.5 mm length. It is wound uniformly with 700 turns of wire. relative permeability of steel is 972. Calculate:
(i) Components of no-load current
(ii) Efficiency on full-load at 0.8 p.f. lagging
(iii) Regulation full-load at 0.8 p.f. lagging
5. Derive the expression of torque developed in doubly excited magnetic system. Clearly state the assumptions made.

6. (a) Derive the expression for the induced e.m.f. in the armature of a DC machine.
(b) An eight pole alternator running at 750 rpm supplies power to a 6-pole, 3-phase induction motor, the induction motor has full-load slip of 3%. obtain the full-load speed of the induction motor and the frequency of its rotor e.m.f.

7. A 3-phase, 50 Hz, 20 pole salient pole alternator with star connected stator winding has 180 slots on the stator. every slot consists of eight conductors. The flux per pole is 25 mWh and is sinusoidally distributed. The coils are full pitched. compute :
(i) The speed of the alternator
(ii) Winding factor
(iii) generated e.m.f. per phase
(iv) line voltage per phase
8. Write short notes on the kind of en closers?

Earning:   Approval pending.