This set of FACTS Multiple Choice Questions & Answers (MCQs) focuses on “Stability Factors of AC Transmission System – 2”.
1. Varying the ________ of voltage injected in series with a transmission network, the active and reactive current flow in it can be influenced.
a) amplitude and phase angle
b) amplitude
c) phase angle
d) sequence
View Answer
Explanation: Varying the amplitude and phase angle of voltage injected in series with a transmission network, the active and reactive current flow in it can be influenced. Thus, power flow, reactive and active, in any transmission system can be changed with this change of current flow. So voltage injection methods aptly find their incorporation FACTS controllers.
2. Handling of real power in a transmission system through a series FACTS controller requires ________ relationship between its voltage and the line current.
a) quadrature
b) any angle other than 900
c) zero angle
d) opposite angle
View Answer
Explanation: Handling of real power in a transmission system through a series FACTS controller requires any angle other than quadrature (900) relationship between its voltage and the line current. This is because with quadrature (900) relationship between its voltage and the line current, a series FACTS controller can only supply or consume variable reactive power only. Under this quadrature condition, active power cannot be controlled by a series FACTS controller.
3. To handle real power in a transmission system, a shunt FACTS controller requires quadrature relationship between its current and the line voltage.
a) True
b) False
View Answer
Explanation: To handle real power in a transmission system, a shunt FACTS controller requires any angle other than quadrature (900) relationship between its current and the line voltage. This is because with quadrature (900) relationship between its current and the line voltage, a shunt FACTS controller can only supply or consume variable reactive power only. Under this quadrature condition, active power cannot be controlled by a shunt FACTS controller.
4. A transmission network can incorporate the connection of a combined series-series FACTS controller to it for its stability of power flow.
a) True
b) False
View Answer
Explanation: A transmission network can incorporate the connection of a combined series-series FACTS controller to it. Technically this method of combined series-series compensation is employed in a multiline transmission system where separate series controllers are connected to different transmission lines. These separate series controllers are controlled in a co-ordinated way to provide independent series compensation for each connected line.
5. What kind of power does a unified series-series FACTS controller transfer via the dc power link?
a) Active
b) Reactive
c) Capacitive
d) Inductive
View Answer
Explanation: Being connected to a multiline transmission system, a unified series-series FACTS controller transfers active power among the lines via the dc power link. It provides independent series reactive compensation for each connected transmission line as it is controlled in a co-ordinated manner. Here the dc terminals of the individual units connected to each line of the multiline transmission system are all connected together for real power transfer.
6. The constraints that a power transmission system may face are ________
a) no constraints at all
b) equipment constraints only
c) system constraints only
d) both equipment and system constraints
View Answer
Explanation: The constraints that a power transmission system may face are both equipment and system constraints. Equipment constraints are defined by their specified ratings which are to be maintained for their normal operating conditions with defined time limits of working parameters in abnormal conditions above which they may result in damage. System constraints are due to the basic physical characteristics which define the behavior of the power system under transient conditions like dynamic load change, tripping of any generation unit, etc.
7. Equipment constraints of a power transmission system are ________
a) only thermal limitations
b) only dielectric limitations
c) both thermal and dielectric limitations
d) not present
View Answer
Explanation: Equipment constraints of a power transmission system are both thermal and dielectric limitations. Depending on the thermal time constants, equipments are subjected to produce excessive heat operating under abnormal conditions above specified time limits, especially in those having short time thermal ratings. Excessive heat produced by current carrying conductors, results in unacceptable sags in transmission lines and degradation of insulation of other associated equipments likewise.
8. Steady state thermal specifications of conductors dictate the ampacity of transmission lines.
a) True
b) False
View Answer
Explanation: Steady state thermal specifications of conductors dictate the ampacity of transmission lines. For a given ambient temperature, each transmission line exhibits its characteristic maximum temperature depending on its conductor material. It dictates the amount of current flow through the line without rise in its temperature as excessive current flow will increase the temperature of the line beyond its specified limit and degrade the same.
9. Overloading can damage a transmission line.
a) True
b) False
View Answer
Explanation: Overloading, especially over specified time limit, can damage a transmission line. This is because overloading means a larger amount of current flowing through it. This implies excessive loss in the form of heat, the result of which is increase in temperature of the transmission line.
10. Voltages and reactive power demand of transmission lines are affected by line parameters.
a) True
b) False
View Answer
Explanation: Voltages and reactive power demand of transmission lines are affected by line parameters. This is because the line parameters are defined by conductor dimensions and exhibit different characteristic behaviors towards voltage, current and power flow (reactive and active).
11. Voltages and reactive power demand of transmission lines are affected by length of line.
a) True
b) False
View Answer
Explanation: Voltages and reactive power demand of transmission lines are affected by length of line. This is because length of line determines the values of line parameters. This in turn dictates the modeling of transmission lines and, hence, considerations of the line parameters based on their relative placement. This modeling throws light on the handling capacity of voltage and reactive power demand of transmission lines.
12. Voltages and reactive power demand of transmission lines are affected by power transfer.
a) True
b) False
View Answer
Explanation: Voltages and reactive power demand of transmission lines are affected by power transfer. This is because a transmission line is characterized by the sending end voltage at its power source end and the receiving end voltage at its load end, depending on its loading condition. This in turn regulates the overall power flow through it. Again the line parameters by their characteristic features handle the voltages and powers required by them differently.
13. Lossless line approximation is valid for EHV transmission lines.
a) True
b) False
View Answer
Explanation: Lossless line approximation is valid for EHV transmission lines. This is because extra high voltage transmission lines have low resistance or negligible resistance with respect to other line parameters. The loss is generally denoted as heat which is produced due to the inherent resistive property of the line.
14. What does SIL stand for?
a) Surge Impedance Loading
b) Severe Impedance Loading
c) Surge Inductive Loading
d) Surplus Impedance Loading
View Answer
Explanation: SIL stands for Surge Impedance Loading. SIL determines the direction of power flow for a given condition of the transmission line. It determines whether the reactive power will be absorbed or generated by the system or network concerned.
15. Cables of lengths exceeding 30-40km are rarely used for ac transmission.
a) True
b) False
View Answer
Explanation: Cables of lengths exceeding 30-40km are rarely used for ac transmission. The reason is that cables generate reactive power because of their inherent capacitive property and so voltages can be very high at low loading levels, especially for long lengths. Cables are more “unforgiving” towards overloads.
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