A 3-phase synchronous alternator is connected to the infinite bus is over excited, that corresponds to ______________

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.

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

Before an alternator can be connected to an infinite bus, which of the following must be the same for the alternator and the infinite bus?

A

Only frequency

B

Voltage, frequency and phase sequence; and the phase difference between the alternator and infinite voltages must be zero

C

Only voltage

D

Only phase sequence

In case of synchronous motor, which of the following are true? a. Synchronous motor is not self-starting b. If the rotor poles are excited by field current and the stator terminals are connected to AC supply, motor vibrates. c. Variable frequency supply is used to start synchronous motor. d. By using frequency converter, a synchronous motor can be brought from standstill to its desired speed.

A

Only a and b are true

B

Only b and c are true

C

All are true

D

None of the above

The operating point for an over excited alternator working near zpf lagging power factor gives ‘A’ as the operating point. Then if the same machine is working as an over excited synchronous motor will give same operating point at __________

A

zpf leading

B

zpf lagging

C

upf

D

there will never be the same operating point for the machine as motor as well as generator

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

Which of the following statements are correct for synchronous motors? 1. Synchronous motors are well-suited for direct connection top reciprocating compressors. 2. Over-excited synchronous motors are most commonly used for power factor improvement. 3. Synchronous motors are generally used for current regulation of long transmission lines Select the correct answer using the code given below.

A

1, 2 and 3

B

1 and 3 only

C

1 and 2 only

D

2 and 3 only

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

-0.475 %

B

0.475%

C

4.75%

D

-4.75%

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

The active power delivered by an alternator will _______ when the prime mover input is increased for the alternator connected to infinite bus bar.

A

increases

B

decreases

C

remains constant

D

no relation exists between the power and prime mover droop characteristic

A 3-phase synchronous alternator is connected to the infinite bus is over excited, that corresponds to ______________

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