48. A synchronous machine under steady state has initial load angle 6, and mechanical power

49.

50.

51.

52.

input ?,,) as shown in below figure. A sudden increase in mechanical power input from ಲ
to P,,, causes the rotor oscillations between points a to c on the power angle curve, then :
(4) during the rotor swing from a— b->c: the rotor speed at point ‘b’ is greater than
at point ‘a’ and rotor speed at point ‘c’ is greater than at point ‘b’
(B) during the rotor swing from c— b-— a: rotor speed at point ‘b’ is greater than at
point ‘c’ and rotor speed at point ‘a’ is greater than at point ‘b’
(C) during the rotor swing from c— b-— a: rotor speed equals synchronous speed at
point ‘c’ and ‘a’ and at point ‘b’ it is higher than the synchronous speed

(D) during the rotor swing from a—b->c: rotor speed equals synchronous speed at
points ‘a’ and ‘c’ and at point ‘b’ it is higher than the synchronous speed

Of the following statements (i-iv) about protective devices, choose the correct option among
those listed :

@ Interrupting rating of MCBs is upto 1800 A and that of MCCBs ranges from 10000A to
2,00,000A

൯൬ The current rating of an MCB is upto 100 amperes, while an MCCB has a current
rating of between 10 to 200 amperes

(10) MCBs contain a movable tripping circuit while MCCBs have fixed tripping circuit.

(iv) Both MCBs and MCCBs protect circuits against overloading and short circuit.
(^) (0), Gi), (iii) are correct ൯) 0, ii), (iv) are correct
(C) 0), ൬, ന) are correct (0) Qi, (iii), (iv) are correct

Choose the right option from those listed concerning statements (i-iv) about protective
devices :

൫ RCCB disconnects an electric circuit as soon as it detects earth leakage current.

Gi) MCB affords over current and earth leakage protection.

(ii) The short circuit current rating of a 16 A, ‘C’ type MCB is approximately 10 kA.

(iv) Incorrect short circuit withstand capacity of a circuit breaker can cause fire and can be

fatal.
(^) (0), Gi), (iii) are correct ൯) 0, ii), (iv) are correct
(C) (i), Gi), (iv) are correct (0) Qi, (iii), (iv) are correct

Compute the ratio of illuminance at a point 5 metres just below a lamp emitting 100 candelas
to the illuminance at a point 5 metres away from the first point on the same horizontal
plane:
(ಯ) 1:2 (8)
(© 1:2.83 (0)

21
2:1

An average illuminance of 50 lux is needed in a 4 metre X3 metre rectangular room.
Estimate the number of lamps each having 300 lumens to obtain the required illuminance :

(A) 2 © 4
(0 5 0) 6

080/2028 12 A