If only 11th order harmonic is required to be eliminated then which of the following filter is preferred?

Question

Examoogle · Accepted Answer

Option A: Tuned Filter

Explanation & Concepts:
A tuned filter, also known as a single-tuned passive filter, is specifically designed to provide a low-impedance path to a single targeted harmonic frequency, such as the 11th harmonic. It consists of a series combination of an inductor and a capacitor tuned to the frequency of the harmonic to be eliminated, effectively bypassing the harmonic current from the transmission system.

Working Principle: The principle relies on the resonant condition where the inductive reactance ($X_L$) equals the capacitive reactance ($X_C$) at the target harmonic frequency $h$. By setting $h \cdot 2\pi f L = \frac{1}{h \cdot 2\pi f C}$, the filter creates a short circuit for the harmonic component $h$, resulting in a very low impedance path that sinks the harmonic current to the ground.

Key Formulas: $f_h = h \cdot f = \frac{1}{2\pi \sqrt{LC}}$ — Resonant frequency condition for harmonic order $h$; $Z = R + j(h\omega L - \frac{1}{h\omega C})$ — Total impedance of the tuned filter

Key Points: Tuned filters are highly efficient for eliminating specific characteristic harmonics in HVDC systems.; The 11th and 13th harmonics are primary characteristic harmonics generated by 12-pulse HVDC converters.; A tuned filter provides minimal impedance at the resonant frequency $f_h$.

Advantages: Provides very low impedance at the target harmonic frequency; Economical for removing a specific, dominant harmonic; Provides reactive power support at the fundamental frequency

Disadvantages: Ineffective for filtering a wide range of frequencies; Performance is sensitive to component tolerances and temperature variations; Risk of resonance with system impedance

Applications: HVDC converter stations; Large industrial variable frequency drives; Electric arc furnace power systems

Additional Info: Damped filters (high-pass filters) are preferred when multiple harmonics over a wide frequency range need to be suppressed simultaneously.. In HVDC systems, 11th and 13th harmonic filters are commonly installed as independent tuned branches.

Answer: A is correct — Tuned filters are ideal for targeting a specific harmonic frequency like the 11th, whereas damped filters are used for broad-spectrum harmonic suppression.

Exam Tip: Always remember that characteristic harmonics for a p-pulse converter are defined by $h = np \pm 1$; for a 12-pulse converter, $n=1$ gives 11th and 13th harmonics.

Examoogle · Answer

Option B: Damped Filter

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