This set of Transformers test focuses on “Tap Changing Transformers – 2”.
1. Face plate carrying suitable studs is mounted on _____________
a) lower yoke
b) upper yoke
c) away from tapped positions
d) anywhere
View Answer
Explanation: The face plate carrying the suitable studs can be mounted at a convenient place on the transformer such as upper yoke or located near the tapped positions on the windings. The movable contact arm A may be rotated by handwheel mounted externally on the tank.
2. Why microswitch is provided to open the circuit breaker?
a) To prevent inadvertent operation
b) To make circuit energized again
c) To avoid unauthorised operation
d) For various other purposes
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Explanation: To prevent inadvertent operation, an electromagnetic latching device or microswitch is provided to open the circuit breaker so as to deenergize the transformer as soon as the tap changer handle is moved; well before the contact of the arm with the stud (with which it was in contact) opens.
3. With the introduction of on-load tap changers, operating efficiency ___________
a) improves
b) decreases
c) depends on the application
d) stays constant
View Answer
Explanation: On-load tap changers are used to change the turn ratio of transformer to regulate system voltage while the transformer is delivering load. With the introduction of on-load tap changer, the operating efficiency of electrical system gets considerably improved.
4. During the operation of on-load tap changer main circuit ______________
a) can be opened
b) always closed
c) depends on application type
d) depends on the construction
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Explanation: During the operation of an on-load tap changer the main circuit should not be opened to prevent (dangerous) sparking and no part of the tapped winding should get short-circuited. All forms of on-load tap changing circuits are provided with an impedance, which is introduced to limit short circuit current during the tap changing operation.
5. On-load tap changers are generally _______________
a) resistor type
b) reactor type
c) can be resistor type or reactor type
d) can’t say
View Answer
Explanation: All forms of on-load tap changing circuits are provided with an impedance, which is introduced to limit short circuit current during the tap changing operation. The impedance can either be a resistor type or centre-tapped reactor can also be used. The on-load tap changers can in general be classified as resistor or reactor type.
6. In modern type, all tap-changers are made of _____________
a) resistor type
b) reactor type
c) can be either resistor or reactor type
d) can’t say
View Answer
Explanation: The impedance can either be a resistor or centre-tapped reactor. The on-load tap changers can in general be classified as two types- resistor or reactor type. In modern designs the current limiting is almost invariably carried out by a pair of resistors.
7. Why an energy storage device is provided on on-load tap changing transformers?
a) To ensure transition is started
b) To store additional energy
c) To ensure that transition once started is completed
d) To check the extra energy produced due to transition
View Answer
Explanation: To ensure that the transition once started gets completed, an energy storage (usually a spring device) is provided which acts even if the auxiliary power supply happens to fail. It thus, serves an important role.
8. Highest tap changers available as on today are ___________
a) 1475 kV impulse
b) 2000 kV impulse
c) 575 kV impulse
d) 955 kV impulse
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Explanation: At present tap changers are available for the highest insulation level of 1475 kV (peak) impulse and 630 kV power frequency voltage. Efforts are underway to develop tap changers suitable for still higher insulation levels.
9. Which of the following is/are part/s of tap changing circuit?
a) Automatic voltage regulator
b) A time delay relay
c) Compounding elements
d) AVR, time delay relay, compounding elements
View Answer
Explanation: The main components are an automatic voltage regulator, a time delay relay, and compounding elements. The time delay here, prevents unwanted initiation of a tap change by a small transient voltage fluctuation. It may be set for a delay upto 1 min.
10. Compact tap changers are made of _____________
a) thyristorized tap changers
b) vacuum switches in diverter switch
c) metallic tap changers
d) rubbered tap changers
View Answer
Explanation: More compact tap changers with high reliability and performance are being made by employing vacuum switches in the diverter switch. Also, now thyristorized tap changers are available widely in market for special applications where a large number of operations are desired.
Sanfoundry Global Education & Learning Series – Transformers.
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