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4.

Rotor currents will have both sf and a (2-s) f component frequency where s is the slip and f is the supply frequency.

Of these statements:

(a)

1 and 4 are correct

(b)

1 and 2 are correct

(c)

3 and 4 are correct

(d)

2 and 3 are correct

Q.14:- While a 2-phase ac servomotor is in operation, if the voltage across the control field winding becomes zero, then the motor has a tendency to run as a single-phase induction motor. To prevent this

(a)

rotor having high mass moment of inertia is used for such a motor

(b)

drag cup type of light rotor with high rotor resistance is preferred

(c)

a low rotor resistance is used

(d)

The number of turns in the control field winding used is less than the main reference wingding.

Q.15:- The inertia constant of a 100 MVA, 11 KV water wheel generators is 4. The energy stored in the rotor at the synchronous speed is

(a)

(a) 400 MJ(b) 400 KJ

(b)

(c) 25 MJ(d) 25 KJ.

Q.16:- A separately excited dc generator is feeding a shunt motor. If the load torque on the motor is halved approximately.

(a)

Armature currents of both motor and generator are halved.

(b)

Armature current of motor is halved and that of generator is unaltered.

(c)

Armature current of generator is halved and that of motor is unaltered.

(d)

Armature currents of both motor and generator are unaltered.

Q.17:-Which variety of coal has lowest calorific value?

(a)

Steam coal

(b)

Bituminous coal

(c)

Lignite

(d)

Anthracite

Q.18:- The Current through an electrical conductor is 1 ampere when the temperature of the conductor is 0°C and 0.7 ampere when the temperature of the conductor is 1200°C must be

(a) 0.08 A(b) 0.16 A(C) 0.32 A(d) 0.64 A

Q.19:- The velocity of a travelling electrmagnetic wave I freee space is given by

(a) μ ε(b)(c)                            (d)

Q.20:- When a thyristor is negatively blased

(a)

all the three junctions are negatively blased .

(b)

outer junctions are positively blased and the inner junction is negatively biased.

(c)

outer junction are negatively baised and the inner junction is positively biased a.

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