This set of FACTS Multiple Choice Questions & Answers (MCQs) focuses on “Special Purpose Controllers – TCBR”.
1. TCBR is the abbreviation of ________
a) Thyristor-Controlled Braking Resistor
b) Thyristor-Controlled Braking Regulator
c) Thyristor-Controlled Braking Receiver
d) Thyristor-Commuted Braking Resistor
View Answer
Explanation: TCBR is the abbreviation of Thyristor-Controlled Braking Resistor. It incorporates the switching of a resistor to help stabilization of a power system. Basically the thyristor is employed to control the switching of resistor.
2. TCBR incorporates ________
a) linear resistor
b) non- linear resistor
c) either linear resistor or non-linear resistor
d) neither linear resistor nor non-linear resistor
View Answer
Explanation: TCBR usually incorporates linear resistor. The resistor is controlled to make it use in minimizing the power acceleration of a system like a generating unit, during occurrence of disturbances. It also helps in stabilizing the power system.
3. TCBR exhibits ________ switching of the resistor.
a) cycle by cycle
b) continuous
c) non-cyclic
d) asymmetric
View Answer
Explanation: TCBR exhibits cycle by cycle switching of the resistor. This is achieved by firing angle control of the thyristor based ac switch. Also half- cycle by half-cycle firing control can be achieved through it.
4. In TCBR, ________ firing control is used to damp low-frequency oscillations selectively.
a) cycle by cycle
b) continuous
c) half-cycle by half-cycle
d) non-cyclic
View Answer
Explanation: In TCBR, half-cycle by half-cycle firing control is used to damp low-frequency oscillations selectively. However, to minimize the cost TCBR is sometimes thyristor switched but without firing angle control.
5. TCBR incorporates ________ thyristor-switched resistor.
a) series-connected
b) either series-connected or shunt-connected
c) neither series-connected nor shunt-connected
d) shunt-connected
View Answer
Explanation: TCBR incorporates shunt-connected thyristor-switched resistor. TCBR is utilized to achieve both transient and dynamic stability. It can satisfactorily damp oscillations.
6. TCBR is referred to as ________ Brake.
a) Static
b) Synchronous
c) Dynamic
d) Non-Synchronous
View Answer
Explanation: TCBR is referred to as Dynamic Brake. This is because with proper firing angle control it poses itself dynamically as an oscillation damper, transient stabilizer, etc. Thus it acts as an efficient brake for the component that needs braking during various transients and oscillations.
7. TCBR can efficiently aid to ________ a turbine-generator.
a) synchronize
b) sub-synchronize
c) super-synchronize
d) de-synchronize
View Answer
Explanation: TCBR can efficiently aid to synchronize a turbine-generator. This is done by a TCBR as it can lessen and swiftly damp sub-synchronous shaft torques. Out-of-phase synchronizing of a turbine-generator can create shaft torques harsher than a thunder-struck three-phase fault at the generator.
8. TCBR can damp ________
a) super-synchronous resonance
b) synchronous resonance
c) asynchronous resonance
d) sub-synchronous resonance
View Answer
Explanation: TCBR can damp sub-synchronous resonance. SSR may result from series capacitor compensation. This problem of detrimental sub-synchronous shaft torques may be further aggravated by series capacitor compensators leaving a power plant.
9. TCBR ________ damping to prevent dynamic instability.
a) cannot enhance
b) can enhance
c) is never designed for
d) allows ineffective
View Answer
Explanation: TCBR can enhance damping to prevent dynamic instability. Dynamic instability is caused by low frequency oscillations between interconnected ac systems. TCBR with proper firing control is used to damp these low-frequency oscillations.
10. How does TCBR prevent transient instability during the first swing cycle in power system?
a) By immediately taking the power caused by power swing, away from the generator
b) Without affecting the power caused by power swing
c) By allowing the power caused by power swing to reach generator
d) By marginally taking the power caused by power swing, away from the generator
View Answer
Explanation: TCBR prevents transient instability during the first swing cycle in the power system by immediately taking the power caused by power swing, away from the generator. Otherwise the power caused by power swing during the first swing cycle can adversely accelerate the generator. A TCBR often at the lowest possible cost proves itself to be a highly reliable FACTS Controller.
11. TCBR stabilizes power system transients and ________
a) super-synchronous oscillations
b) synchronous oscillations
c) asynchronous oscillations
d) sub-synchronous oscillations
View Answer
Explanation: TCBR stabilizes power system transients and sub-synchronous oscillations. TCBR efficiently does it by reducing the net available energy for acceleration of the generating unit during power swings. Thus it reduces speed deviation of the generating unit during any disturbance.
12. The best location for a TCBR is ________
a) near a generator
b) away from the generator
c) in the middle of transmission lines
d) near transmission lines
View Answer
Explanation: The best location for a TCBR is near a generator. This is because a TCBR being near to the generator can damp and prevent transient instability conditions reaching the generator. Thus the generator is kept safe from any undesirable oscillations arising from low frequency disturbances and power swings.
13. TCBR is NOT employed in three phase power system.
a) True
b) False
View Answer
Explanation: TCBR is employed in three phase power system. Each leg of a three-phase TCBR is controlled to make it useful as a reliable FACTS Controller. Given appropriate rating, if a large bank of TCBR is employed; to achieve redundancy, it may be divided into two or required number of banks.
14. A three-phase TCBR is ________ connected.
a) wye or delta
b) always wye
c) always delta
d) always zig-zag
View Answer
Explanation: A three-phase TCBR is wye or delta connected. Though both wye and delta connection are possible for TCBR, delta connection is preferred for TCBR. This is because delta connection does not require the grounded path.
15. TCBR can allow safe high-speed reclosing of lines near a power plant.
a) True
b) False
View Answer
Explanation: TCBR can allow safe high-speed reclosing of lines near a power plant. It does so without feeding high-torsional torques on the shaft system. Its preferred approach is made available to first save the turbine-generator from the first transient swing and then to assist in damping of the undesirable oscillations.
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