# FACTS Questions and Answers – SSSC and Immunity to SSR

This set of FACTS Multiple Choice Questions & Answers (MCQs) focuses on “SSSC and Immunity to SSR”.

1. SSSC is an acronym for ________
a) Static Shunt Synchronous Compensator
b) Sub synchronous Series Compensator
c) Static Series Synchronous Compensator
d) Sub Synchronous Series Compensator

Explanation: SSSC is an acronym for static synchronous series compensator. It employs advanced technique of power control series compensation. Functionally it injects voltage in quadrature to the line current to control the overall reactive voltage drop across the line. It has the property to induce inductive or capacitive voltage in series with the line connected.

2. SSSC is an example of VIT FACTS controller.
a) True
b) False

Explanation: Static synchronous series compensator is an example of voltage source FACTS controller. It is not a variable impedance type FACTS controller. As the name suggests, SSSC is basically a series connected controller and not a shunt-connected one.

3. The operation of the SSSC is analogous to those compensation characterizing ideal synchronous machines.
a) True
b) False

Explanation: The operation of the SSSC is analogous to those compensation characterizing ideal synchronous machines. It also performs analogous to compensating ideal synchronous machines. Both of them provide approximately instantaneous speed of response and control features independent of system voltage during shunt operation and current during series operation.

4. SSSC employs ________ switching converters.
a) self-commutated, voltage-sourced
b) self-commutated, current-sourced
c) forced-commutated, voltage-sourced
d) voltage-commutated, current-sourced

Explanation: SSSC employs self-commutated, voltage-sourced switching converters. In doing so, it realizes rapidly controllable, static synchronous voltage sources. Thus it becomes an important FACTS Controller.

5. The SSSC provides reactive compensation without ac capacitors or reactors.
a) True
b) False

Explanation: The SSSC provides reactive compensation without ac capacitors or reactors. It automatically produces or takes in the reactive power exchanged with the system because of its intrinsic capability to exchange both real and reactive power with the ac system, just like a synchronous machine does. However, the real power exchanged must be supplied to it, or absorbed from it, by the ac system.

6. If you have two capacitors C1 = 10F and C2 = 5F. What would be the equivalent capacitance to provide series compensation in power system.
a) 15F
b) 1/15 F
c) 10/3 F
d) 3/10 F

Explanation: A series capacitor is also used to provide series compensation in power system. Therefore we shall use series connection and the equivalent capacitance
= 1/(1/C1+1/C2)
= 1/(1/10+1/5)
= 1/(3/10)=10/3 F

7. Reactive shunt compensation cannot maintain the desired voltage profile along the transmission line in spite of changing real power demand.
a) True
b) False

Explanation: Reactive shunt compensation aims at maintaining the desired voltage profile along the transmission line in spite of changing real power demand. It is highly effective method to control the in voltage variation along the transmission line. Thus specified voltage level is maintained at the load end of a sub-transmission or distribution system.

8. Without proper reactive shunt compensation techniques, an increase in real power transmission will certainly result in an increase of reactive power demand at the end-voltage generators.
a) True
b) False

Explanation: Without proper reactive shunt compensation techniques, an increase in real power transmission will certainly result in an increase of reactive power demand at the end-voltage generators. This will, in turn, lead to an increase in voltage variation along the transmission line. Thus adequate reactive shunt compensation is required for proper flow of reactive and real power and maintaining a desired voltage profile at load end.

9. The function of the static VAR compensator (SVC) is to control ________
a) only injection of reactive power
b) only absorption of reactive power
c) either injection or absorption of reactive power
d) neither injection nor absorption of reactive power

Explanation: Static VAR compensator (SVC) a shunt device that regulates the voltage at its terminals by controlling the amount of reactive power either being injected into or absorbed from the associated power system. Location of SVC strongly affects controllability of swing modes. Generally the best location for an SVC is at a point where voltage swings most. Normally, the midpoint of a transmission line between any two given locations is a good location.

10. In a TSR, a thyristor exhibits a maximum average current 1000A for a conduction angle of 180°. Assuming the current waveform to be half cycle sine wave, find the corresponding maximum average current corresponding to conduction angle 60°.
a) 200A
b) 565A
c) 5.65A
d) 1000A

Explanation: By definition, the form factor (F.F) of half cycle sine wave for any conduction angle Φ is given by
F.F = IRMS / IAVG ………………………………………………………….(i)
=> F.F = √[(1/2)∏0Φ sin2Θ dΘ]/ [(1/2)∏0Φ sinΘdΘ
=> F.F = √[∏{Φ – (1/2) sin2Φ}]/(1-cosΦ)……………………..…(ii)
Putting Φ = 180° in equation (ii), F.F = ∏/2…………..………….(ii)
In the problem it is given that IAVG = 1000A
Therefore, from equation (i) RMS current rating of the thyristor,
IRMS = 1000*(∏/2) = 1570A
When Φ = 60°, from equation (ii), F.F = 2√[∏{(∏/3) – (√3/4)}] = 2.78
Since RMS current rating of the thyristor [corresponding to maximum average current at conduction angle 180°] cannot be exceeded,
Therefore, IAVG = 1570/2.78 = 565A (approx)

11. In a power system where the voltage-control is done by Static VAR Compensator (SVC), if the power system is modeled as an equivalent voltage source VS and its equivalent system impedance XS, the SVC bus voltage VSVC and SVC current ISVC is given by the relation _______
a) VS = VSVC + ISVCXS
b) VS = VSVC – ISVCXS
c) VSVC = VS + ISVCXS
d) VS = VSVC ± ISVCXS

Explanation: In a power system where the voltage-control is done by Static VAR Compensator (SVC), if the power system is modeled as an equivalent voltage source VS and its equivalent system impedance XS as viewed from the SVC terminals; the SVC bus voltage VSVC and SVC current ISVC is given by the relation: VS = VSVC ± ISVCXS Here the voltage drop of ISVC. XS is due to the SVC current ISVC and it in phase with the system voltage VS. The SVC bus voltage decreases with the inductive SVC current and increases with the capacitive current. That is why ISVC is positive if inductive and ISVC is negative if capacitive.

12. What is the location for a static VAR compensator decided normally?
a) midpoint in the transmission line
b) receiving end in the transmission line
c) sending end in the transmission line
d) anywhere in the transmission line

Explanation: Location of SVC strongly affects controllability of swing modes. In FACTS, the SVC is a shunt device that regulates the voltage at its terminals by controlling the amount of reactive power either being injected into or absorbed from the associated power system. Generally the best location for an SVC is at a point where voltage swings most. Normally, the midpoint of a transmission line between any two given locations is a good location.

13. The circuit configuration of TCPAR is similar to that of breaker-switched capacitors, reactors and mechanical tap-changing transformers.
a) True
b) False

Explanation: The circuit configuration of TCPAR is similar to that of breaker-switched capacitors, reactors and mechanical tap-changing transformers. It appears so because TCPAR employs reactive impedances and tap-changing transformers with conventional thyristor valves (switches) as controlled elements. However, TCPAR exhibits much faster response and sophisticated operation controls than the later.

14. TCPAR can provide reactive compensation.
a) True
b) False

Explanation: TCPAR cannot provide reactive compensation. This is because it is unable to generate reactive power. However, TCPAR can exchange both real and reactive) power.

15. In TCPAR, the voltage regulation is obtained by injecting voltage in ________
a) phase with the system current
b) phase quadrature with the system voltage
c) phase with the system voltage
d) phase quadrature with the system voltage

Explanation: In TCPAR, the voltage regulation is obtained by injecting voltage in phase quadrature with the system voltage. As the name indicates, the thyristor switches are employed to control the phase angle of the injected voltage. This is achieved by controlling the value of the delay angle of thyristors incorporated.

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