This set of FACTS Multiple Choice Questions & Answers (MCQs) focuses on “Power Semiconductor Devices – Thyristor, GTO and MTO – Set 3”.
1. Fast thyristors can be ________
a) only symmetric
b) only asymmetric
c) either symmetric or asymmetric
d) neither symmetric nor asymmetric
View Answer
Explanation: Fast thyristors can be either symmetric or asymmetric. They can be reverse conducting also. Their mode of operation depends on the choice of the operator and its design for the specific application.
2. GTO can be ________
a) only symmetric
b) only asymmetric
c) either symmetric or asymmetric
d) neither symmetric nor asymmetric
View Answer
Explanation: GTO can be either symmetric or asymmetric. They can be reverse conducting also. Their mode of operation depends on the choice of the operator and its design for the specific application.
3. IGBT can be ________
a) only symmetric
b) only asymmetric
c) either symmetric or asymmetric
d) neither symmetric nor asymmetric
View Answer
Explanation: IGBT can be only asymmetric. They cannot be symmetric. However, they can be reverse conducting also. Their mode of operation depends on the choice of the operator and its design for the specific application.
4. Which of the following is essential for high frequency switching?
a) General purpose diodes
b) High speed power diodes
c) Either general purpose diodes or high speed power diodes
d) Neither general purpose diodes nor high speed power diodes
View Answer
Explanation: High speed power diodes is essential for high frequency switching. It exhibits rating up to 6000v. Its reverse recovery time ranges from 0.1 to 5microsec.
5. Schottky power diodes have high recovery time.
a) True
b) False
View Answer
Explanation: Schottky power diodes do not have high recovery time. Rather they exhibit very small recovery time (in nano-seconds range). They have low on-state voltage.
6. In a thyristor, when a small current is passed through its________, it conducts.
a) gate terminal to its cathode
b) cathode to its anode terminal
c) gate terminal to its anode
d) anode to its gate terminal
View Answer
Explanation: In a thyristor, when a small current is passed through its gate terminal to its cathode it conducts. However, it conducts only when its anode terminal is at higher potential than that of its cathode. Conversely, it will not conduct when its cathode is at higher potential than that of its anode terminal.
7. The gate circuit controls a thyristor in its conduction mode.
a) True
b) False
View Answer
Explanation: The gate circuit cannot control a thyristor in its conduction mode. This is because, once thyristor reaches its conduction mode, the gate circuit has no affect and cannot change its operation mode. In conduction mode, its forward voltage is very low (typically ranges from 0.5 to 2 V).
8. Thyristors can be ________
a) line-commutated only
b) forced-commutated only
c) line-commutated or forced-commutated
d) neither line-commutated or forced-commutated
View Answer
Explanation: Thyristors can be line-commutated or forced–commutated. It depends on the type of commutation principle and design adopted for its turning-off. A thyristor can be turned off naturally or through additional commutation circuit.
9. Forced-commutated thyristors are designed to be turned off depending on the sinusoidal nature of its input voltage.
a) True
b) False
View Answer
Explanation: Forced-commutated thyristors are NOT designed to be turned off depending on the sinusoidal nature of its input voltage. An additional commutation circuitry is employed to turn it off. Line-commutated thyristors are designed to be turned off depending on the sinusoidal nature of its input voltage.
10. SIT stands for ________
a) Static Induction Thyristor
b) Silicon Induction Thyristor
c) Static Induction Transistor
d) Silicon Induction Transistor
View Answer
Explanation: SIT stands for Silicon Induction Transistor. SIT is a variety of power transistor. Other types of power transistors are BJTs, power MOSFETs, IGBTs.
11. Power BJTs cannot be used in power converters.
a) True
b) False
View Answer
Explanation: Power BJTs can be used in power converters. But the limitation is that frequency must be below 10kHz. Their power ratings range up to 1200V, 400A.
12. RCT is an acronym for ________
a) Reverse Conducting Thyristor
b) Repulsive Conducting Thyristor
c) Resistance Conducting Thyristor
d) Recovery Conducting Thyristor
View Answer
Explanation: RCT is an acronym for Reverse Conducting Thyristor. It exhibits bidirectional current capability. Also, TRIAC has Bidirectional current capability.
13. GATT is an acronym for ________
a) Gate-Assisted turn-off Thyristor
b) Gate-Assisted turn-on Thyristor
c) Gate-Active turn-off Thyristor
d) Gate-Actuated turn-on Thyristor
View Answer
Explanation: GATT is an acronym for Gate-Assisted turn-off Thyristor. It has an exclusive design feature including a shunted cathode, a dynamic gate and a bypass diode. The bypass diode is required to make possible the blend of both dynamic turn-on and gate-assisted turn-off in the same device.
14. Positive voltage pulse turns off BJT and zero voltage turns it on.
a) True
b) False
View Answer
Explanation: Positive voltage pulse DOES NOT turn off BJT and zero voltage DOES NOT turn it on. Actually positive voltage pulse turns on BJT and zero voltage turns it off. BJT exhibits unipolar voltage-withstanding capability.
15. Positive voltage pulse turns off GTO and negative voltage pulse turns GTO on.
a) True
b) False
View Answer
Explanation: Positive voltage pulse DOES NOT turn off GTO and negative voltage pulse DOES NOT turn GTO on. Positive voltage pulse turns on GTO and negative voltage pulse turns GTO off. GTO exhibits unipolar voltage-withstanding capability.
Sanfoundry Global Education & Learning Series – Flexible AC Transmission System (FACTS).
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