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# ELECTRICAL ENGINEERING - page 10 / 15

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combination of dissimilar metals, when used to produce an emf, is called a thermocouple, and has many uses in the measurement of temperature.

12:- (b)

‘Shall be slightly greater than  and therefore, slightly greater core loss Current flowing through is now somewhat less than and therefore reduced copper loss in it

Note: - If the shunt branch is shifted to 2-2’, then the answer would be (c). It depends on which approximate circuit is used. The one given above is more common.

13:- (c) The motor will not stop. It will continue to run as a single phase motor with two phases of the windings connected in series (for a star- connected) and third phase open; while for a delta – connected motor, one phase of the winding and two other phases in series of the winding are in parallel. The field in the air gap is pulsating which can be resolved into a forward rotating components. The rotor, therefore, has both s f and (2 – s) f component frequencies.

14:- (b) Drag cup type of light rotor with high rotor resistance is preferred.

15:- (a) Inertia constant H

Mega joules of energy stored in the rotating mass of the alternator at

=

Thus, 4 =

E      =    400 MJ.

16:- (a) Since field winding currents of the two machines are not disturbed and the torque is proportional to the product of armature current and field flux, when the torque reduced to half, the armature current in both also reduces to half.

17:- (c) Lignite coal has lowest calorific value.

18: (b) Let  be the temperature coefficient.

Then  = Ro (1 +  t)

Where  is resistance at t° C and is resistance at 0°C

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