This set of FACTS Multiple Choice Questions & Answers (MCQs) focuses on “Combined Compensators – UPFC”.
1. UPFC is an acronym for ________
a) United Power Flow Controller
b) Unity Power Factor Controller
c) Unified Power Factor Controller
d) Unified Power Flow Controller
View Answer
Explanation: UPFC is an acronym for Unified Power Flow Controller. It is made by back to back connection of converters with common DC link. It exhibits multi-functional capability in controlling of power flow in a multiline transmission network.
2. UPFC is actually a ________ compensator.
a) series
b) parallel
c) non-parallel
d) series-parallel combination
View Answer
Explanation: UPFC is actually a series-parallel combination compensator. No single conventional compensating equipment is present like UPFC, which has multi-functional capability in controlling of power flow in a transmission network. It is different from IPFC
3. UPFC is an example of VIT FACTS controller.
a) True
b) False
View Answer
Explanation: Unified Power Flow Controller is an example of voltage source FACTS controller. It is not a variable impedance type FACTS controller. IPFC is a combined series shunt FACTS controller.
4. ______ exhibits multi-functional capability in controlling of power flow in a transmission network.
a) UPFC
b) DSTATCOM
c) DVR
d) UPQC
View Answer
Explanation: UPFC exhibits multi-functional capability in controlling of power flow in a transmission network. These include simultaneous terminal voltage regulation, phase shifting and series capacitive line compensation. The FACTS devices DSTATCOM, DVR and UPQC are used to mitigate multiple power quality problems.
5. UPFC displays ________ quadrant operations.
a) only one
b) one or two
c) only three
d) all four
View Answer
Explanation: UPFC displays all the four quadrant operations. Fundamentally UPFC functions as an ideal ac-to-ac power converter. It is capable of achieving free power flow in either direction between the ac terminals of its constituent two converters.
6. UPFC is an interconnected FACTS device, consisting of ________
a) STATCOM and SSSC
b) STATCOM and SVC
c) SVC and SSSC
d) STATCOM and TCSC
View Answer
Explanation: UPFC is an interconnected FACTS device, consisting of STATCOM and SSSC. Hence it constitutes of two voltage sourced converters. These back-to-back connected converters are operated through a common dc link.
7. UPFC is an interconnected FACTS device, encapsulating ________
a) a shunt converter and a series converter
b) two shunt converters
c) two series converters
d) either two shunt or two series converters
View Answer
Explanation: UPFC is an interconnected FACTS device, encapsulating a shunt converter and a series converter in it. These two converters are back-to-back and marked as Converter 1 and Converter 2. A dc storage capacitor forms the dc link between these converters.
8. The UPFC is capable of controlling, ________, all the parameters that affects transmission power flow.
a) not simultaneously
b) simultaneously or selectively
c) not selectively
d) neither simultaneously nor selectively
View Answer
Explanation: The UPFC is capable of controlling, simultaneously or selectively, all the parameters that affects transmission power flow. These include voltage, impedance and phase angle. It is devised to work for four quadrant operation.
9. The UPFC can independently control ________ power flow in the transmission line.
a) reactive and real
b) only reactive
c) only real
d) neither reactive nor real
View Answer
Explanation: The UPFC can independently control reactive and real power flow in the transmission line. This is so because the transmission line current flows through the voltage source series converter of the UPFC. This results in reactive and active power exchange between the converter and the system connected.
10. Both the Converters of the UPFC are capable of independent generation or absorption of reactive power.
a) True
b) False
View Answer
Explanation: Both the Converters (Converter1 and Converter2) of the UPFC are capable of independent generation or absorption of reactive power at its own ac terminal. The constituent shunt converter can be utilized to operate for reactive power exchange (absorption or generation of controllable reactive power) with the transmission line connected. This can be done independent of the reactive power exchange performed by the series converter.
11. There can be reactive power flow through the DC link of the UPFC.
a) True
b) False
View Answer
Explanation: There CANNOT be reactive power flow through the DC link of the UPFC. The DC link of the UPFC allows the real power flow. The real power demanded at the common DC link by the series converter of the UPFC is supplied or absorbed by the shunt converter of the UPFC.
12. The UPFC ________ the injected series compensating voltage when connected to a transmission power network.
a) can keep constant or vary
b) can keep constant only
c) can vary only
d) has no control on
View Answer
Explanation: The UPFC can keep constant or vary the injected series compensating voltage when connected to a transmission power network. Basically it can keep the injected series compensating voltage independent of the line current variation and hence, can maintain constant injected series compensating voltage. Also the UPFC can vary the injected series compensating voltage proportionately with the line current variation.
13. The control of UPFC is based on the vector control approach.
a) True
b) False
View Answer
Explanation: The control of UPFC is based on the vector control approach. The term vector is used instead of the word ‘phasor’ or ‘phase’ This is so because this control approach encapsulates the reference to the set of three instantaneous phase variables like, currents or voltages, which sum-up to zero.
14. The UPFC control system can be classified as __________
a) internal control and transmission control
b) internal control and external control
c) functional and non-functional control
d)series control and shunt control
View Answer
Explanation: The UPFC control system can be classified as internal control and external control. Internal control is basically the converter control, which includes providing gating signals to the converters so that their output parameters properly respond to the internal reference variables. External control refers to the functional operation control which defines the operating modes of the UPFC and the generation of the internal references.
15. In the reactive power control mode of the shunt converter of the UPFC, the reference input is ________
a) Inductive VAR request
b) Capacitive VAR request
c) Inductive VAR request or Capacitive VAR request
d) Inductive current request or capacitive current request
View Answer
Explanation: In the reactive power control mode of the shunt converter of the UPFC, the reference input is inductive VAR request or capacitive VAR request. The shunt converter of the UPFC translates the VAR reference into a corresponding shunt current request. It then adjusts the gating of the converter to establish the required current.
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