# FACTS Questions and Answers – Controllable Parameters – Set 3

This set of FACTS Multiple Choice Questions & Answers (MCQs) focuses on “Controllable Parameters of AC Transmission System – 3”.

1. A symmetric circuit with two sets of ‘IGBT with anti-parallel diode’ in series exhibits ________
a) single quadrant operation
b) two quadrant operations (voltage bidirectional)
c) two quadrant operations (current bidirectional)
d) four quadrant operations

Explanation: A symmetric circuit with two sets of ‘IGBT with anti-parallel diode’ in series exhibits four quadrant operations. Here each individual set of ‘IGBT with anti-parallel diode’ principally functions as a SPDT switch. Thus such a symmetric circuit, in fact, is realized by two SPDT switches in series.

2. A transistor and a diode when connected in anti-parallel exhibits ________
a) bidirectional current conduction
b) bidirectional voltage blocking
c) unidirectional current conduction
d) unidirectional voltage blocking

Explanation: A transistor and a diode when connected in anti-parallel exhibits bidirectional current conduction. This anti-parallel combination of transistor and diode finds its application in realizing different switches designed for bidirectional current conduction. The resultant circuit may exhibit unidirectional or bidirectional voltage blocking as per the requirement of switch-designs.

3. A transistor and a diode when connected in series exhibits ________
a) bidirectional current conduction
b) bidirectional voltage blocking
c) unidirectional current conduction
d) unidirectional voltage blocking

Explanation: A transistor and a diode when connected in series exhibits bidirectional voltage blocking. This series combination of transistor and diode finds its application in realizing different switches designed for bidirectional voltage blocking. The resultant circuit may exhibit unidirectional or bidirectional current conduction as per the requirement of switch-designs.

4. An asymmetric circuit with two sets of ‘IGBT with anti-parallel diode’ in series exhibits ________
a) single quadrant operation
b) two quadrant operations (voltage bidirectional)
c) two quadrant operations (current bidirectional)
d) four quadrant operations

Explanation: An asymmetric circuit with two sets of ‘IGBT with anti-parallel diode’ in series exhibits four quadrant operations. Here ‘IGBT of each individual set along with anti-parallel diode of other set’ principally functions as a SPST switch. Thus such an asymmetric circuit, in fact, is realized by two SPST switches in parallel.

5. What does PAR stand for?
a) Phase Angle Regulator
b) Power Angle Regulator
c) Pulse Angle Regulator
d) Parity Angle Regulator

Explanation: PAR stands for Phase Angle Regulator. They exhibit voltage injection in series with the line. In ideal condition, the output voltage of PAR is equal in magnitude with the input voltage but with a phase difference of ±Φ.

6. What does TCPAR stand for?
a) Thyristor Controlled Phase Angle Regulator
b) Thyristor Controlled Power Angle Regulator
c) Thyristor Controlled Pulse Angle Regulator
d) Thyristor Controlled Parity Angle Regulator

Explanation: TCPAR stands for Thyristor Controlled Phase Angle Regulator. Also synchronous voltage source PARs are available. Both of them are ideally able to vary the phase angle between the voltages at the two ends of the insertion transformer by ±Φ without changing the magnitude.

7. PARs can control the reactive power flow independently of the real power in a power transmission network.
a) True
b) False

Explanation: PARs CANNOT control the reactive power flow independently of the real power in a power transmission network. Also PARs cannot increase the maximum transmittable power for a given value of real power. PARs can vary the transmitted power at the given transmission angle ∂.

8. ________ has/have a wide range for real power control.
a) UPFC
b) PAR
c) TCPAR
d) UPFC and PAR

Explanation: UPFC has a wide range for real power control. PAR does not possess this trait. Also UPFC facilitates the broad-range independent control of the reactive power demanded at the receiving end.

9. The compensating voltage of the ________ can be controlled totally independent of the line current.
a) SSSC
b) TSSC and GCSC
c) TSSC
d) GCSC

Explanation: The compensating voltage of the SSSC can be controlled totally independent of the line current. TSSC and GCSC do not possess this trait. SSSC basically exhibits continuously variable series voltage compensation in quadrature with the line current.

10. Choose the right option among the alternatives – The SSSC/TCSC/TSSC/GCSC displays/display a considerably wider control range at low transmission angles than the SSSC/TCSC/TSSC/GCSC.
a) SSSC and TCSC, TSSC and GCSC
b) SSSC and GCSC, TCSC and TSSC
c) SSSC and TSSC, TCSC and GCSC
d) GCSC, TCSC and SSSC

Explanation: The SSSC and the TCSC display a considerably wider control range at low transmission angles than the TSSC and the GCSC. This is because the SSSC and the TCSC are capable to inject compensating voltage with both 90°0 lagging (or capacitive) and 90°0 leading (or reactive) relationship with respect to the line current. Thus they can both increase and decrease the transmitted power.

11. UPFC has superior power flow control characteristics as compared with SSSC, TCSC, TSSC and GCSC
a) True
b) False

Explanation: UPFC has superior power flow control characteristics as compared with SSSC, TCSC, TSSC and GCSC. This is evident from the fact that UPFC can control both real and reactive power independently over a broad range. These controls are independent of the transmission angle as well.

12. The series controller can be power electronics based variable source of __________
a) main frequency
b) sub-synchronous frequency
c) harmonic frequency
d) main frequency, sub-synchronous frequency, harmonic frequency or their combination

Explanation: The series controller can be power electronics based variable source of main frequency, sub-synchronous frequency, harmonic frequency or their combination. It can also a variable capacitive or inductive impedance. Their basic principle is to inject voltage in series with the line.

13. The purpose of a switch is to ________
a) close a circuit
b) open a circuit
c) open and close a circuit
d) protect from overcurrent

Explanation: The purpose of a switch is to open and close a circuit. Unlike a circuit breaker, it is not an interrupting device. A switch is not intended to protect a circuit from any abnormal or fault conditions; it is used for switching purpose only.

14. A fuse is similar to a switch.
a) True
b) False

Explanation: A fuse is NOT similar to a switch. A fuse with the right configuration when connected to a circuit protects it from overcurrent. It cannot be used for switching on and off any circuit which a switch can. Also a switch CANNOT protect a circuit from any abnormal or fault conditions

15. The aim of a healthy transmission system is to provide power at________
a) rated frequency only
b) rated voltage only
c) specified waveform only
d) rated frequency, rated voltage and specified waveform

Explanation: The aim of a healthy transmission system is to provide power at rated frequency, rated voltage and specified waveform. It should also ensure the quality, continuity and safety of the power available at the receiving end. Therefore, at the prevailing or dynamic load changes the transmission system with greater controllability, improved transferability is required to save the system from transients due to abnormal conditions.

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

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