A synchronous generator is running over excited with a Ef=1.40pu. This machine, with a synchronous reactance of 1.2pu, is delivering a synchronous power of 0.5pu to the bus. If the prime-mover torque is increased by 1%, by how much will the reactive power, Q change?

A synchronous generator is operating with a Ef=1.40pu. This machine having Xs of 1.2pu, is delivering a synchronous power of 0.5pu to the bus. If the prime-mover torque is increased by 1%, by how much will the synchronous power P change?

A

1%

B

10%

C

-1%

D

4%

Each of the question below consists of a question and three statements number I, II and III given below it. You have to decide whether the data provided in the statement are sufficient to answer the question. If the bus is travelling from Surat to Ahmadabad and a car is travelling from Ahmadabad to Surat, then what is the distance between Surat and Ahmadabad? I. The speed of a car is 40% less than the speed of bus. Bus started at 9 am and car started at 10 am and they meet at 3 pm of the same day. II. After travelling for 1 hour, because of traffic average speed of bus is decreased by 20% and covers distance between Surat to Ahmadabad in 11 hours. Original speed of car is 20% less than original speed of bus and before crossing bus it covered 200 km if starts 1 hour later than bus. After crossing car, bus covers remaining distance in 5 hours. III. Speed of bus is 10 km/hr more than the speed of car and before crossing car ratio of distances covered bus and car in same time was 5 : 4. Time taken by car to cover the distance between Ahmadabad and Surat is 2 hours 15 minutes more than time taken by bus to cover the same distance.

A

The data in statement II alone is sufficient to answer the question, while the data in neither statement I nor III alone are sufficient to answer the question.

B

The data in either statement II or in Statement III alone is sufficient to answer the question, while the data in statement I alone is not sufficient to answer the question.

C

The data is only statement III alone or in Statement I and II together are sufficient to answer the question.

D

The data in all Statement I, II and III together are not sufficient to answer the question.

E

If the data in all the Statement I, II and III together are necessary to answer the question.

Transient stability of the generator is dependent on (a) generator reactance; lower reactance decreases peak power and increases initial rotor angle. (b) how heavily the generator is loaded. (c) generator inertia; higher the inertia, slower the rate of the change of angle. (d) generator output during fault Which of the above is incorrect?

A

a

B

b

C

c

D

None of the above

If Xl is leakage reactance, Xf is reactance due to field winding, Xdw is reactance due to damper winding and Xa is armature winding reactance then reactance of synchronous generator in subtransient state is due to which of the following?

A

Xl ,Xdw and Xa

B

Xl and Xa

C

Xl , Xf ,Xdw and Xa

D

Xl and Xdw

A three-phase cylindrical rotor synchronous generator has a synchronous reactance Xs and a negligible armature resistance. The magnitude of per phase terminal voltage is VA and the magnitude of per phase induced emf is EA. Considering the following two statements, P and Q, P: For any three-phase balanced leading load connected across the terminals of this synchronous generator, VA is always more than EA Q: For any three-phase balanced lagging load connected across the terminals of this synchronous generator, VA is always less than EA Which of the following options is correct?

A

P is false and Q is true

B

P is true and Q is false

C

P is false and Q is false

D

P is true and Q is true

Consider the following statements regarding synchronous machines: 1. When a synchronous motor is over-excited, its back emf is greater than the supply voltage 2. When a synchronous motor is over-excited, its power factor is leading 3. Synchronous motor is used as capacitor where load is so large that construction of a static capacitor is impractical Which of these statements are correct?

A

1 and 2

B

1 and 3

C

2 and 3

D

1, 2 and 3

If Xa is the armature reactance of a synchronous machine and Xl is the leakage reactance of the same machine, then the synchronous reactance is ____________

A

Xa+Xl c) 1/2(Xa+Xl) d) None of the mentioned View Answer]

B

½(Xa)

C

1/2(Xa+Xl)

D

None of the mentioned

A bus and a truck are available to cross a jungle. The speed of the truck is thrice that of the bus. The capacity of the truck is 50 persons and that of bus is 30 persons. The average occupancy of the bus is twice that of the truck. The tickets for the bus and the truck cost Rs 1 and Rs 1.50 respectively. What is the ratio of the average rupee collection of the truck to that of the bus in a day? Assume there is no wastage time between trips and the occupancy of the bus / truck is defined as the ratio of the actual number of persons boarding it and its capacity.

A

15 : 4

B

15 : 2

C

15 : 8

D

15 : 7

Two identical synchronous machines A and B running at same speed are connected to each other through an inductor. Machine A is supplying an active power to Machine B and Machine B is supplying reactive power to Machine A, then which among the following is correct?

A

|V_a| > |V_b|

B

|V_a| < |V_b|

C

|V_a| = |V_b|

D

None of the above

When load on an over-excited or under excited synchronous motor is increased, rate of change of its armature current as compared with that of power factor is

A

more

B

less

C

equal

D

twice

A synchronous generator is running over excited with a Ef=1.40pu. This machine, with a synchronous reactance of 1.2pu, is delivering a synchronous power of 0.5pu to the bus. If the prime-mover torque is increased by 1%, by how much will the reactive power, Q change?

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