A power factor of a circuit can be improved by placing which, among the following, in a circuit?
A
Inductor
B
Capacitor
C
Resistor
D
Switch

Question

A power factor of a circuit can be improved by placing which, among the following, in a circuit?

Examoogle · Accepted Answer

Capacitor

Explanation: Power factor improvement is achieved by connecting a capacitor in parallel with an inductive load. The capacitor provides leading reactive power (VARs) that neutralizes the lagging reactive power consumed by inductive loads like motors or transformers, bringing the net power factor closer to unity.

Working Principle: Most industrial loads are inductive, requiring lagging reactive power for magnetic field excitation, which decreases the power factor. A capacitor draws a leading current, supplying the required reactive power locally to the inductive load. By reducing the magnitude of the reactive current supplied by the source, the phase angle between voltage and current decreases, and $\cos\phi$ increases toward 1.

Key Formulas: $PF = \cos\phi = \frac{P}{S}$ — Definition of power factor as the ratio of real power to apparent power; $Q_C = P(	an\phi_1 - 	an\phi_2)$ — Required capacitor rating to improve power factor from $\cos\phi_1$ to $\cos\phi_2$

Key Points: Most electrical loads (motors, fluorescent ballasts) are inductive and have a lagging power factor.; A low power factor leads to higher current for the same real power, causing increased copper losses ($I^2R$).; Power factor improvement reduces line losses and improves voltage regulation.; Improving power factor avoids penalties imposed by electricity distribution companies.

Advantages: Reduction in electricity bills due to penalty avoidance; Increased capacity of existing distribution system; Reduced $I^2R$ losses in transmission lines; Improved voltage profile at the load end

Disadvantages: Risk of over-correction leading to leading power factor; Potential for voltage rise at light load conditions due to capacitive effect; Requires periodic maintenance of capacitor banks

Applications: Industrial motor installations; Commercial buildings with heavy HVAC usage; Electrical substations and distribution grids; Power supply units in electronics

Additional Info: Unity power factor ($\cos\phi = 1$) is ideal, meaning the load is purely resistive.. Option A (Inductor) would decrease the power factor of an inductive load even further.. Option C (Resistor) increases active power consumption but does not help in compensating reactive power.. Option D (Switch) is a control device and does not affect the reactive power balance.

Answer: B is correct — A capacitor placed in parallel with an inductive load provides leading reactive power, which cancels out the lagging reactive power, thereby improving the overall power factor of the circuit.

Exam Tip: Always remember that for power factor improvement, capacitors are connected in parallel, whereas for series resonance, they are connected in series.

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