Ferranti effect can be reduced by which of the following method?

Question

Examoogle · Accepted Answer

Shunt Capacitor

Explanation: The Ferranti effect refers to the phenomenon where the receiving-end voltage of a long transmission line exceeds the sending-end voltage under light load or no-load conditions. Shunt reactors (connected at the receiving end) are the standard mitigation device because they compensate for the line's capacitance by absorbing reactive power.

Working Principle: In long transmission lines, the shunt capacitance ($C$) causes a leading charging current to flow even without load. This current flows through the series inductance ($L$) of the line, creating a voltage drop that adds vectorially to the sending voltage, resulting in a higher voltage at the load end. Shunt reactors provide an inductive current that cancels this capacitive charging current, thereby regulating the voltage profile.

Key Formulas: $V_R = V_S \sec(\beta l)$ — The receiving end voltage for a lossless line of length $l$; $Q_{comp} = V^2 \omega C$ — Reactive power compensation required to negate charging current

Key Points: Ferranti effect is predominant in long overhead transmission lines (typically > 250 km).; It is caused by the line capacitance effect under light-load or no-load conditions.; Shunt reactors are connected in parallel to the line to absorb excess reactive power.; The effect leads to insulation stress on equipment at the receiving end.

Advantages: Maintains voltage within operational limits under light load.; Prevents insulation failure at terminal equipment.

Disadvantages: Requires additional installation space for reactors.; Increases system capital cost.

Applications: Extra High Voltage (EHV) and Ultra High Voltage (UHV) transmission networks.; Long-distance long-line transmission systems.

Additional Info: Note: The original question statement says 'B) Shunt Capacitor' is the correct answer, but this is technically incorrect; the correct device for the Ferranti effect is a 'Shunt Reactor' (Option D).. Shunt capacitors are used to improve power factor in inductive loads, which would actually worsen the Ferranti effect by increasing the capacitive charging current.

Answer: D is correct — Shunt reactors are used to neutralize the capacitive charging current of the line.

Exam Tip: In exams, remember: Ferranti effect (Voltage rise) is countered by Shunt Reactors (Inductors), while Poor Power Factor (Voltage drop) is countered by Shunt Capacitors.

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