# FACTS Questions and Answers – Controllable Parameters – Set 2

This set of FACTS Multiple Choice Questions & Answers (MCQs) focuses on “Controllable Parameters of AC Transmission System – 2”.

1. A passive switch is controlled exclusively by a third terminal.
a) True
b) False

Explanation: A switch generally, when switched on connects two points and disconnects those two points when switched-off. An active switch does have a third terminal exclusively for its own control. An active switch is controlled exclusively by the third terminal.

2. Which of the following can be used as a DPST switch?
a) Diode
b) BJT
c) MOSFET
d) P-N junction diode

Explanation: A DPST switch is characterized by its double quadrant operation. MOSFET does posses an integral body diode. Unlike the other given options, MOSFET exhibits defined bidirectional flow of currents during its different modes of operations because of its integral body diode. So MOSFET can be used as a DPST effectively.

3. What does DPST switch mean?
a) Double Pole Single Throw
b) Double Pole Single Thyristor
c) Double Pole Single Thermostat
d) Double Pole Single Transistor

Explanation: DPST switch means Double Pole Single Throw switch. Some specific semiconductor devices can behave in the configuration of DPST. It shows double quadrant operation.

4. In a BJT diode series realization, flow of current is controlled by ________
a) the control terminal of diode
b) the control terminal of both diode and BJT
c) the control terminal of BJT
d) neither diode nor BJT

Explanation: In a BJT diode series realization, flow of current is controlled by the control terminal of BJT. Basically diode does not possess any control terminal but BJT does. Thus in a BJT diode series realization, BJT performs its inherent property of controlling current by its third terminal.

5. Choose the right option among the alternatives – The inherent property of a MOSFET with body diode is to exhibit positive/negative, on-state/off-state conduction of current and positive off-state blocking of voltage.
a) Positive, off-state
b) Negative, on-state
c) Positive or negative, on-state
d) Positive or negative, off-state

Explanation: The inherent property of a MOSFET with body diode is to exhibit positive or negative, on-state conduction of current and positive off-state blocking of voltage. A diode individually can function as a SPST switch. But this diode when becomes an integral part of a MOSFET, enables two-quadrant operation as a switch.

6. Choose the right option among the alternatives – The inherent property of an IGBT is to exhibit positive/negative on-state conduction of current and positive/negative off-state blocking of voltage.
a) Positive, negative
b) Positive, negative
c) Negative, negative
d) Positive, positive

Explanation: The inherent property of an IGBT is to exhibit positive on-state conduction of current and positive off-state blocking of voltage. Both diode and BJT also show single-quadrant operation. But IGBT shares the same property of single-quadrant operation with BJT not diode.

7. What will be the mode of conduction of current in the following figure, if A is a BJT and B is a diode and they are used alternatively?

a) Positive, on-state
b) Negative, on-state
c) Positive or negative, on-state
d) Positive or negative, on-state

Explanation: If A is a BJT and B is a diode in the following figure, to make the circuit work, evidently if switch A works for TON part of the time period, switch B will operate for (1- TON) part of the time period. Therefore, both BJT and diode will make the current flow in the same direction through the circuit. Here the mode of conduction of current will be on-state positive.

8. What will be the mode of operation in the following figure, if A is a BJT and B is a diode and they are used alternatively?

a) on-state positive voltage blocking
b) on-state negative voltage blocking
c) positive or negative, on-state voltage blocking
d) positive or negative, off-state voltage blocking

Explanation: If A is a BJT and B is a diode in the following figure, to make the circuit work and they are used alternatively, evidently both BJT and diode will follow their inherent voltage blocking operation. Therefore, because of both BJT and diode operating alternatively, the circuit will exhibit the positive or negative, off-state voltage blocking mode of operation.

9. Bidirectional current conduction is the property of a ________
a) power source
b) SPST switch
c) DPST switch
d) diode

Explanation: A power source can be d.c or a.c. Hence specific inference cannot be drawn. Bidirectional property is the property of a DPST switch, not a single SPST. A diode is a SPST switch. Hence bidirectional current conduction is the property of a DPST switch.

10. A DPST switch can only exhibit bidirectional current conduction.
a) True
b) False

Explanation: A DPST switch can exhibit bidirectional current conduction. Also directional voltage blocking is the trait for a DPST switch. Some power electronic devices exhibit bidirectional current conduction while some do directional voltage blocking. Thus these power electronic devices show two-quadrant operations.

11. Choose the right option among the alternatives – The property of a BJT diode series realization is to exhibit positive on-state conduction of current and positive/negative off-state/on-state blocking of voltage.
a) On-state positive
b) On-state negative
c) Positive or negative, on-state
d) Positive or negative, off-state

Explanation: The property of BJT diode series realization is to exhibit positive on-state conduction of current and positive or negative off-state blocking of voltage. Both diode and BJT individually show single-quadrant operation but with different polarity of voltage blocking. Therefore, because of both BJT and diode being in series, the circuit will exhibit the positive or negative, off-state voltage blocking mode of operation.

12. A four-quadrant switch can be realized with ________
a) passive electronic switches only
b) active electronic switches only
c) both passive and active electronic switches
d) both mechanical and electronic switches

Explanation: A four-quadrant switch can be realized with active electronic switches only. This is because active switches do possess control terminal and the four quadrant applications of a switch requires four controllable modes of operation. They are positive or negative on-state conduction of current and positive or negative off-state blocking of voltage.

13. A four-quadrant electronic switch requires two control switches.
a) True
b) False

Explanation: A four-quadrant electronic switch may require one or two control switches or otherwise as per the underlying logic of circuitry. A four diode bridge configuration with a BJT as its diagonal element may be realized as a four-quadrant electronic switch. Here the switch is with one control terminal at the BJT section as the diodes have no control terminal.

14. A four-quadrant electronic switch may be realized with two control switches.
a) True
b) False

Explanation: A four-quadrant electronic switch may require one or two control switches or otherwise as per the underlying logic of circuitry. A circuit with two sets of ʻIGBT with anti-parallel diodeʼ is capable to implement a four-quadrant electronic switch. Here two IGBTs contribute to two control switches.

15. What does SPDT switch mean?
a) Single Pole Double Throw
b) Single Pole Double Thyristor
c) Single Pole Double Thermostat
d) Single Pole Double Transistor

Explanation: SPDT switch means Single Pole Double Throw switch. Some semiconductor power devices or their combinations can behave in the configuration of SPDT. Two SPDT switches can be utilized to realize four quadrant operations.

Sanfoundry Global Education & Learning Series – Flexible AC Transmission System (FACTS).

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