# Single-tuned harmonic filter

Canonical URL: https://eloragrid.ai/symbols/single-tuned-harmonic-filter
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: HF
Drawing use: SLD, Schematic
Reference families: IEC, IEEE / ANSI

A shunt series-LC branch tuned near one harmonic order to sink that harmonic current from the network.

## In plain English

### What does Single-tuned harmonic filter mean?

A single-tuned filter is a capacitor and reactor in series, connected in shunt and tuned to resonate near one harmonic frequency, often slightly below the 5th, 7th or 11th. At that frequency it presents a low impedance and draws harmonic current away from the network, while at fundamental frequency it supplies capacitive reactive power.

### A simple example

Drawings show a capacitor and reactor in series on a shunt branch, labelled with the tuned order, and often several such branches for different orders. Unbalance protection for the capacitor bank and a dedicated breaker are normally shown.

### What the drawings help you do

A tuned filter creates a parallel resonance with the network at a frequency just below its tuning, which can amplify other harmonics. The symbol does not show the network impedance scan or detuning tolerance, so the harmonic study must accompany it.

### This particular reference

A shunt series-LC branch tuned near one harmonic order to sink that harmonic current from the network. A single-tuned filter targets one harmonic order; a damped high-pass filter attenuates a broad band above its corner frequency.

### Terms

- Rating: A value stating the conditions for which equipment is specified.
- Schematic: A drawing showing function and connections rather than physical appearance.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [Capacitor and filter product offerings](https://www.hitachienergy.com/products-and-solutions/capacitors-and-filters)
- [AutoCAD Electrical: Reactors and inductors](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-BAD50DBF-0951-44A0-BB4C-A57B4A4ED895.htm)


## What it represents

A single-tuned filter is a capacitor and reactor in series, connected in shunt and tuned to resonate near one harmonic frequency, often slightly below the 5th, 7th or 11th. At that frequency it presents a low impedance and draws harmonic current away from the network, while at fundamental frequency it supplies capacitive reactive power.
Drawings show a capacitor and reactor in series on a shunt branch, labelled with the tuned order, and often several such branches for different orders. Unbalance protection for the capacitor bank and a dedicated breaker are normally shown.
A tuned filter creates a parallel resonance with the network at a frequency just below its tuning, which can amplify other harmonics. The symbol does not show the network impedance scan or detuning tolerance, so the harmonic study must accompany it.

## How to read it

- Read the harmonic order label on each branch.
- The filter also supplies fundamental reactive power.

## Information to show or reference

- State tuned order, Mvar and quality factor.
- Show breaker and unbalance protection.
- Reference harmonic study.

## Important distinction

A single-tuned filter targets one harmonic order; a damped high-pass filter attenuates a broad band above its corner frequency.

## Facts

- Elements: Series capacitor and reactor
- Behaviour at tuning: Low impedance sink
- Fundamental output: Capacitive Mvar
- Preview: Independent educational illustration; consult the applicable standard and project legend for the exact graphic

## Public references

- [Capacitor and filter product offerings](https://www.hitachienergy.com/products-and-solutions/capacitors-and-filters) — Hitachi Energy. Public passive and harmonic filter product context.
- [AutoCAD Electrical: Reactors and inductors](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-BAD50DBF-0951-44A0-BB4C-A57B4A4ED895.htm) — Autodesk. Public reactor symbol family context.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.