When the power factor in the transmission line is leading, which device is employed at substation to

Question

When the power factor in the transmission line is leading, which device is employed at substation to reduce the power factor:

Examoogle · Accepted Answer

Reactor

Explanation: When a transmission line operates under leading power factor conditions (often caused by the Ferranti effect in lightly loaded or capacitive lines), shunt reactors are employed. These devices provide inductive reactive power (VAR absorption) to neutralize the excess capacitive reactive power, thereby maintaining voltage stability and bringing the power factor closer to unity.

Working Principle: A shunt reactor consists of a large inductive winding that draws lagging current from the system. By drawing lagging VARs, it compensates for the surplus capacitive VARs generated by the long transmission line capacitance $C_{line}$, effectively preventing the voltage rise at the receiving end of the line.

Key Formulas: $Q_{L} = \frac{V^2}{\omega L}$ — reactive power absorbed by a shunt reactor; $Q_{C} = V^2 \omega C$ — reactive power generated by line capacitance

Key Points: Leading power factor is common in long transmission lines at light loads due to line shunt capacitance.; Shunt reactors are used to prevent voltage rise at the receiving end of the transmission line.; They help in regulating voltage by absorbing excess reactive power generated by the transmission line itself.; Synchronous condensers are primarily used for generating reactive power to improve lagging power factor.

Advantages: Prevents overvoltage due to Ferranti effect; Improves voltage regulation in long transmission lines; Increases the power transfer capability of the line by controlling voltage

Disadvantages: Increases active power loss in the system; Requires significant physical space at the substation; Cannot provide dynamic voltage control as effectively as a STATCOM

Applications: EHV and UHV long distance transmission lines; Substations connected to underground cable networks; Light load operational scenarios

Additional Info: The Ferranti effect refers to the phenomenon where the receiving end voltage is higher than the sending end voltage at light loads or no-load conditions.. CVT (Capacitive Voltage Transformer) is a measuring device for voltage sensing and is not used for power factor correction.. Synchronous condensers are over-excited synchronous motors used to supply leading reactive power, used when the power factor is lagging.

Answer: B is correct — Shunt reactors are inductive devices used to compensate for excess capacitive reactive power in transmission lines, effectively reducing the power factor from leading towards unity.

Exam Tip: Always remember: Leading PF leads to voltage rise; use Inductive compensation (Reactors). Lagging PF leads to voltage drop; use Capacitive compensation (Capacitors/Synchronous Condensers).

Related Questions

Discussion (0)