Capacitors for power factor correction are rated in

Question

Examoogle · Accepted Answer

kVAR

Explanation: Capacitors used for power factor correction are rated in kVAR (kilovolt-ampere reactive) because they supply reactive power to the electrical system to compensate for the lagging reactive power consumed by inductive loads.

Working Principle: Inductive loads like motors and transformers draw lagging reactive power from the supply, lowering the power factor. A capacitor bank connected in parallel acts as a source of leading reactive power, which cancels out the lagging reactive power component, thereby reducing the total current drawn from the source and improving the power factor toward unity.

Key Formulas: $Q_c = P(	an\phi_1 - 	an\phi_2)$ — where $Q_c$ is the required capacitor rating in kVAR; $PF = \cos\phi = \frac{P}{S}$ — definition of power factor where $P$ is active power and $S$ is apparent power

Key Points: Capacitors provide leading reactive power (kVAR).; Power factor correction minimizes line losses ($I^2R$).; Improving PF increases the usable capacity of transformers and cables.; kVAR rating determines the magnitude of reactive compensation.

Advantages: Reduces electricity bills by avoiding low PF penalties.; Decreases thermal stress on cables and transformers.

Disadvantages: Risk of over-correction leading to leading power factor.; Harmonic resonance issues in non-linear load environments.

Applications: Industrial motor installations.; Power distribution grids.; Large commercial lighting systems.

Additional Info: kW measures real power consumed by resistive loads.. kVA is the unit for apparent power, representing the total capacity of an electrical system.. kV is the unit for potential difference.. Option D is the only unit representing reactive power.

Answer: D is correct — Capacitors are rated in kVAR as they specifically provide reactive power compensation to improve the system power factor.

Exam Tip: Always remember the 'Triangle of Power': $S^2 = P^2 + Q^2$. Capacitors directly reduce the 'Q' component, effectively shrinking the 'S' (kVA) vector for a constant 'P' (kW) load.

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