Which one of the following statements is NOT true regarding use of capacitor for power factor correc

Question

Which one of the following statements is NOT true regarding use of capacitor for power factor correction ?

Examoogle · Accepted Answer

Protection fuse should be connected in the line of the capacitor bank.

Explanation: The statement regarding the fuse is incorrect because, while capacitors need protection, they should be connected as close to the inductive load as possible, not the supply. Furthermore, capacitor circuits require specific current-limiting protection like MCCBs or HRC fuses, but the standard practice is to place them local to the motor/load to minimize line current.

Working Principle: Power factor correction capacitors supply reactive power ($Q_c$) to counteract the lagging reactive power ($Q_L$) demanded by inductive loads. By placing the capacitor near the load, the reactive current $I_q$ is neutralized at the source, reducing the total current drawn from the transmission line, which lowers $I^2R$ losses and voltage drops.

Key Formulas: $Q_c = P(	an\phi_1 - 	an\phi_2)$ — Reactive power required for correction; $I_{switch} = C \frac{dv}{dt}$ — High inrush current during capacitor switching

Key Points: Capacitors should be located near the load to reduce copper losses in the cables.; Switching a capacitor bank creates high inrush current due to low impedance at high frequencies.; Over-correction leads to leading power factor, which may cause over-voltages.; Automatic Power Factor Correction (APFC) panels are used for fluctuating loads.

Advantages: Reduces line losses ($I^2R$); Improves voltage regulation at load terminals; Increases active power capacity of existing distribution equipment

Disadvantages: Potential for harmonic resonance if system impedance is high; Susceptible to high inrush currents upon switching; Dielectric degradation over time

Applications: Industrial motor installations; Distribution transformers; HVAC and lighting systems

Additional Info: Option A is correct: Placing it near the load is the primary requirement for effective power factor improvement.. Option B is the correct answer to the 'NOT True' question because the fuse should be placed protecting the capacitor unit specifically, but the phrasing implies a general line connection issue; however, in technical exams, it is noted that capacitor banks should have their own switching/protective gear separate from main feeders.. Option C is correct: To prevent over-correction during low load, capacitors are switched off.. Option D is correct: Due to $i = C \frac{dv}{dt}$, capacitors cause transient high currents requiring heavy-duty contactors/cables.

Answer: B is correct — Protection fuse should be connected to the capacitor bank specifically, but the statement as written implies an incorrect general connection topology regarding power system hierarchy.

Exam Tip: Always remember that $Q_c = P(	an\phi_1 - 	an\phi_2)$ is the fundamental equation for calculating capacitor bank rating, where $\phi_1$ is the initial angle and $\phi_2$ is the target angle.

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