Power factor of choke is

Question

Examoogle · Accepted Answer

zero lagging

Explanation: An ideal choke is a pure inductor which offers only reactance without resistance. In a pure inductive circuit, the current lags the voltage by exactly $90^\circ$, resulting in a power factor of $\cos(90^\circ) = 0$ (lagging).

Working Principle: In an inductor, the magnetic field storage mechanism causes the current to reach its peak value after the voltage peak occurs. The phase angle $\phi$ is defined as $90^\circ$ for an ideal coil, leading to a lagging power factor. Practically, real-world chokes have small winding resistance ($R$), making the power factor slightly greater than zero, but theoretically, it is considered zero lagging.

Key Formulas: $pf = \cos(\phi)$ — Definition of power factor where $\phi$ is the phase angle; $\phi = 	an^{-1}(\frac{X_L}{R})$ — Phase angle calculation for an inductive load

Key Points: A pure inductor does not consume active power ($P = 0$ Watts).; The current lags the voltage by $90^\circ$ in a purely inductive circuit.; Real chokes have a very low, non-zero power factor due to internal copper resistance.; Power factor is always lagging for inductive loads.

Advantages: Useful for limiting fault current in electrical circuits.; Prevents rapid changes in current due to the property of self-induction.

Disadvantages: Lowers the overall power factor of the system when used as a ballast.; Requires reactive power (VAR) support from the supply.

Applications: Ballast in fluorescent lighting circuits.; Current limiting in industrial motor starters and distribution systems.

Additional Info: The term 'choke' specifically implies an inductive coil designed to block higher-frequency alternating current while allowing direct current or lower-frequency AC to pass.. Option C (zero leading) is incorrect because leading power factor is characteristic of capacitive circuits.

Answer: B is correct — An ideal choke acts as a pure inductor, causing the current to lag the voltage by $90^\circ$, resulting in a zero lagging power factor.

Exam Tip: Remember the mnemonic 'ELI' for inductive circuits: Voltage (E) Leads Current (I) in an inductor (L). Consequently, power factor is always lagging.

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