Electrical machine BEU previous year question solution 2021 beu pyq solution

Bihar engineering university(BEU) previous year question solution. Electrical machine BEU pyq solution . BEU question paper solutions is very important for exam . BEU organizer electrical machine . BEU pyq solution electrical machine 2021.

1(a). Explain how the primary current increases as the current in current on the secondary side of the transformer is increased. (b) Define reluctance and inductance. (c) Explain why open-circuit and short- circuit tests should be performed on LV and HV sides respectively.

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2(a). Transformer is a constant-flux machine. Justify with the help of equivalent circuit. (b) Derive a condition for efficiency of a transformer.

3 (a) What is meant by commutation in d.c. machine? Differentiate between good commutation and bad commutation. Enumerate the mechanical and electrical conditions leading to poor commutation in d.c. machines.

(b) Explain the advantages of four-point starter over the three-point starter.

BEU previous year question solution

4 (a) Describe and compare the various methods of speed control of d.c. motors.

(b) Explain the terms base speed’ and ‘speed regulation’ of d.c. motor.

5(a) A 250 V d.c. series motor has armature and series filed resistance of 0.25 2 and 0-15 respectively.

(i) Calculate the current for developing a torque of 80 Nm at 1200 r.p.m.

(ii) Calculate the percentage reduction in flux when the motor runs at 1800 r.p.m. at half the current obtained part (i).

(B) For a commutator machine with 6 poles and 40 coils, determine for a simplex lap winding-

(i) the number of commutator segments;

(ii) back pitch and front pitch;

(iii) commutator pitch.

6.(a) A5 kVA, single-phase transformer has a core loss of 40 watts and full load ohmic loss of 100 watts. The daily variation of load on the transformer is as follows:

7 am to 1 pm: 3 kW at p.f. 0.6 1 pm to 6 pm: 2 kW at p.f. 0.8

6 pm to 1 am: 6 kW at p.f. 0.9

1 am to 7 am : No load. Determine the all-day efficiency of the transformer.

(b) What is an equalizer ring? Explain how it performs its two functions.

7(a) The following test data were taken on a 30 kVA, 2400/240 V, 50Hz, transformer:

Open circuit test: V = 2400 V, 1-03 A, P= 230 W

Short circuit test: V70 V, I= 18-8 A, P= 1050 W

Determine the primary terminal voltage, real and reactive power input and efficiency, when a current of 12.5 A at 240 V is drawn from the low voltage side by a load of 0-8 p.f. lagging.

(b) Explain why the e.m.f. generated in the armature of a d.c. motor is called back e.m.f’.

8( a) Discuss how the parallel operation of two single-phase transformers is affected by-