Which one following devices is not responsible for lagging power factor?

Question

Examoogle · Accepted Answer

Capacitor

Explanation: A capacitor is a leading power factor device because the current leads the voltage by $90^\circ$ in an ideal pure capacitor. In contrast, inductive devices like motors, furnaces, and transformers require reactive power to establish magnetic fields, resulting in a lagging power factor where current lags voltage.

Working Principle: In an inductive circuit, the coil stores energy in a magnetic field, causing the current to lag behind the applied voltage. A capacitor stores energy in an electric field, which forces the current to lead the voltage. By placing a capacitor in parallel with an inductive load, the leading reactive current compensates for the lagging reactive current, thereby improving the overall power factor of the system.

Key Formulas: $Q_L = V I \sin \phi$ — Reactive power of an inductive load; $Q_C = -V^2 \omega C$ — Reactive power provided by a capacitor

Key Points: Inductive loads (motors, transformers, furnaces) consume reactive power ($VAR$).; Capacitive loads generate reactive power, acting as a source of reactive power ($VAR$).; Lagging power factor indicates an inductive dominant circuit.; Leading power factor indicates a capacitive dominant circuit.

Advantages: Capacitors are used for power factor correction.; Reduces the kVA rating of electrical equipment.

Disadvantages: Excessive capacitance can lead to over-voltage conditions.; May lead to resonance issues in circuits with harmonic content.

Applications: Power factor correction banks in industrial plants.; Voltage support in transmission lines (STATCOM/SVCs).

Additional Info: Induction furnaces use high-frequency magnetic fields to heat metals, which are inherently inductive.. Transformers require magnetizing current, contributing to lagging power factor.. Induction motors consume reactive power for the excitation of the magnetic circuit.

Answer: C is correct — A capacitor is a leading power factor device because current leads voltage by $90^\circ$ in an ideal capacitive circuit.

Exam Tip: Always remember the mnemonic 'ELI the ICE man': In an Inductor (L), E (Voltage) leads I (Current); in a Capacitor (C), I (Current) leads E (Voltage).

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