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1. unacademy

Ba C ks i d e Electrical

Power

b / ts systems

(solutions) cx
150-154 @Wadhwa

2. Y unacademy

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K.Anvesh sameer

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Masters in Power engineering

Electrical engineer at Hyderabad

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3. unacademy

Ba C ks i d e Electrical

Power

b / ts systems

(solutions) cx
150-154 @Wadhwa

4. Y unacademy

150. If one phase of supply goes off in the case of 3-phase induction motor, the
motor then.

(a) Comes to a stop

(b) Draws double the initial current and continues to run

(c) Draws 1/ V 3 times the initial current and continues to run
(d) None of the above.

5. © unacademy

150.Ans:

Q This condition is called as Single Phasing

Q If motor is running before Single phasing occurred keeps on running as single phase
motor + Make characteristic Noise

Q What Happens to currents in star connected stators?

Q Currents are same

P= V3VI cosy > 3 phase

P= Vicosp > 1 phase

So , the Load taken by the motor is reduced (143 times)
Motor operates at 57.7% of it’s rating

Q If the Stator is Delta connected > One of the windings get overloaded ( current is not
same in all phases)

Q Heat increases ( due to increased rotor losses)

Q Protective devices must be set

6. Y unacademy

150. If one phase of supply goes off in the case of 3-phase induction motor, the
motor

(a) Comes to a stop
(b) Draws double the initial current and continues to run

(c) Draws 1/ V 3 times the initial current and continues to run
(CL None of the above.

7. Y unacademy

151. Induction generator works between the slip

(al<s<2 (b)0.1<s<1.0
(c)s<0.0 (d) None of the above.

8. 151.Ans:

in & Mode

N„?N,

a $<0

© unacademy

9. Y unacademy

151. Induction generator works between the slip
(a)l<s<2 (b)0.1<s<1.0
Yrs < 0.0 (d) None of the above.

10. Y unacademy

152. The motor which can be used on both a.c. and d.c. is

(a) Reluctance motor (b) Induction motor
(c) D.C. series motor (d) None of the above.

11. © unacademy

152.Ans:

DC series motor can be run using both AC and DC.

Operating with AC > Losses are high

These losses can be reduced by slight modifications in the construction.
Such type of motor is also called as UNIVERSAL MOTOR

12. Y unacademy

152. The motor which can be used on both a.c. and d.c. is

(a) Reluctance motor (b) Induction motor
Y d.c. series motor (d) None of the above.

13. Y unacademy

153. If transformer frequency is changed from 50 Hz to 60 Hz, the ratio of eddy
current loss 50 Hz to 60 Hz at constant voltage is

(a) 5/6 (b) 25/36
(c) 6/5 (d) 1.0.

14. 153.Ans:

We, =W

© unacademy

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wad 4 et
$ so eo ta

CARS

We, xv? (te fon 50 Hz)

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15. Y unacademy

153. If transformer frequency is changed from 50 Hz to 60 Hz, the ratio of eddy
current loss 50 Hz to 60 Hz at constant voltage is

(a) 5/6 (b) 25/36

(c) 6/5 Y 1.0.

16. Y unacademy

154. An alternator of 300 kW is driven by a prime mover of speed regulation 4%
and another alternator of 200 kW driven by a prime mover of speed regulations
3%, the total load they can take is

(a) 500 kW (b) 567 kW
(c) 425 kW (d) 257 kW

17. 150.Ans:

Machine 1

300 KW

ea -- -- ee ee

E

200
Max P2 = 200 KW

F

Y unacademy

DE _ CE
AB CB
PES
300 4
Pl = 225
P2 = 200

P1+P2 = 425KW

18. Y unacademy

154. An alternator of 300 kW is driven by a prime mover of speed regulation 4%
and another alternator of 200 kW driven by a prime mover of speed
regulations 3%, the total load they can take is

(a) 500 kW (b) 567 kW
425 KW (d) 257 kW

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