The Institution of Engineers,India 2010 A.M.I.E Section A , Electrical science winter - Question Paper

W10: 5 AN: AN 210 (1410)

ELECTRICAL SCIENCE

Time: Three hours

Maximum marks: 100

 

Q 1.        (a) A negative point charge of 1 C is situated at x = 0 in free space. Calculate electric field intensity at a point on positive x axis 3 m from origin.

(b)    What do you understand by the term electric potential?

(c)     State and explain Thevenins theorem.

Q 2.        (a) An arc lamp (which my be regarded as non inductive) takes 10 A at 50 V. find the impedance of a choke of 1 ohm resistance to be connected in a series with the arc lamp so that the lamp may be used at 200 V 50 Hz supply. Also, find the total active power and power factor.

(b)    Explain the term series resonance?

(c)     Define the terms impedance and admittance.

(d)    What is the use of phasor diagram?

 

Q 3.  (a) An air cored toroidal coil has 3000 turns and carries 0.1 A current. The length of magnetic circuit is 15 cm and cross-sectional area of coil is 4 cm‚. Find H, B, and flux.

(b)    What is meant by the term reluctance?

(c)     Explain eddy current loss and hysteresis loss in a magnetic circuit.

(d)    What is meant by saturation of a magnetic circuit?

Q 4.    (a) What is the difference between balanced and unbalanced load?

(b)    A star connected three phase load has a resistance of 6 ohms and an inductive reactance of 8 ohms in each branch. The line voltage is 220 V. find line current, total active power, and phase voltage.

(c)     What is the use of symmetrical components?

 

 

 

Group B

 

Q 5.        (a) Distinguish between radial, ring and parallel feeders?

(b)    Why are conductors of overhead lines stranded?

(c)     What is ACSR conductor?

(d)    A 400m long distributor has the following unity power factor loads tapped off R phase: 100A load at 100 m from feeding point

120 A load at 250 M from feeding point

80 A load at 400 m from feeding point.

The resistance of conductor is 0.25 ohm/km length. Voltage at feeding point is 240 V. Find the voltage at the far end. Neglect voltage drop in neutral conductor.

Q 6.        (a) What are various losses in a transformer?

(b)    What is meant by voltage regulation of a transformer? Derive a formula for calculating voltage regulation.

(c)     Write the names of different parts of a D.C. machine.

(d)    Name different types of D.C. motors.

Q 7.        (a) An 8 pole lap wound d.c. generator has 960 conductors, a flux of 40 mWb per pole and is driven at 400 rpm. Find open circuit voltage. Derive the expression used.

(b)    Name some applications of single-phase motor.

(c)     Explain the process of self-excitation in d.c. generators.

 

Q 8.        (a) Explain the principle of operation of three phase induction motor.

(b)    The input to a three- phase 50 Hz 4 pole induction motor is 150 kW. Stator losses are 5kW, mechanical losses are 3kW and full load slip is 0.05. find frequency of rotor e.m.f. at standstill, frequency of rotor e.m.f. at full load, and rotor copper losses.

(c)     Briefly describe the principle of operation of synchronous generator.

 

 

 

Group C

Q 9.        Answer the following in brief:

(i)   Name some applications of capacitors.

(ii) How are electric field intensity and potential related?

(iii)           Name some applications of principle of superposition.

(iv)           How are magnetic materials classified?

(v) What is meant by relative permeability?

(vi)           How are induced e.m.f. s classified?

(vii)         What are the factors on which inductance of a coil depend?

(viii)       What is meant by step up and step down transformers?

(ix)           What is back e.m.f.?

(x) Why is rotor core loss negligible in three phase induction motor?