In SR, the biasing shunt capacitor is equipped with small tuning inductors to provide

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The correct answer is Option C: filtering of the remnant harmonics. In Static Reactors (SR) or SVCs, shunt capacitors are used to provide reactive power compensation. Small tuning inductors (detuning reactors) are placed in series with these capacitors to prevent resonance with the power system impedance at specific harmonic frequencies, effectively filtering out remnant harmonics.

Step-by-Step Solution & Concepts:
In Static Reactors (SR) or SVCs, shunt capacitors are used to provide reactive power compensation. Small tuning inductors (detuning reactors) are placed in series with these capacitors to prevent resonance with the power system impedance at specific harmonic frequencies, effectively filtering out remnant harmonics.

Working Principle: The combination of the shunt capacitor ($C$) and a small tuning inductor ($L$) creates a series resonant circuit tuned to a specific harmonic frequency (typically the 5th or 7th harmonic). By setting the resonant frequency $f_r = \frac{1}{2\pi\sqrt{LC}}$ slightly below the target harmonic, the filter offers a low-impedance path to the ground for those frequencies, thereby preventing them from circulating in the main power system.

Key Formulas: $f_r = \frac{1}{2\pi\sqrt{LC}}$ — Resonant frequency of the tuned filter; $Z_n = j(n\omega L - \frac{1}{n\omega C})$ — Impedance at the n-th harmonic

Key Points: Tuning reactors prevent parallel resonance between the capacitor bank and the system transformer reactance.; These filters are essential in HVDC and FACTS installations to improve Power Quality.; The 'small' size of the inductor ensures the fundamental frequency ($50Hz$) impedance remains capacitive for VAR compensation.

Advantages: Improved voltage profile; Mitigation of harmonic distortion; Reduced system resonance risks

Disadvantages: Increased installation footprint; Additional costs due to reactor insulation requirements

Applications: HVDC converter stations; Large industrial loads with non-linear characteristics; SVC (Static VAR Compensator) installations

Additional Info: Sub-harmonic oscillations (Option A) are typically controlled by damping circuits or controller adjustments, not simple shunt passive components.. Slope correction (Option B) refers to the $V-I$ characteristic adjustment in SVCs, usually handled by software or transformer settings.

Answer: C is correct — The tuning inductors convert the shunt capacitor into a series resonant filter designed to shunt unwanted harmonic currents to ground.

Exam Tip: Always remember that in power systems, a capacitor alone is a harmonic sink that might cause parallel resonance; adding an inductor makes it a frequency-selective filter.

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Option A: sub harmonic oscillations

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Option B: slope correction

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Option D: lagging power factor range operation

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