# Detuned capacitor bank

Canonical URL: https://eloragrid.ai/symbols/detuned-capacitor-bank
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: DCB
Drawing use: SLD
Reference families: IEC, IEEE / ANSI

Power factor correction capacitors with series reactors that tune each step below the lowest significant harmonic.

## In plain English

### What does Detuned capacitor bank mean?

A detuned capacitor bank places a reactor in series with each capacitor step so that the step resonates at a frequency below the lowest significant harmonic, commonly expressed as a detuning factor such as 7 per cent, which tunes near 189 Hz on a 50 Hz network. This prevents the bank from forming a parallel resonance that would amplify 5th harmonic currents from converters.

### A simple example

Single-line diagrams show several capacitor steps, each with a series reactor and a switching contactor or thyristor switch, controlled by a power factor regulator using a current transformer on the incoming supply. The detuning factor is noted on the bank.

### What the drawings help you do

The series reactor raises the voltage across the capacitors above network voltage, so the capacitors must be rated accordingly. The symbol does not show that voltage rise, the reactor thermal rating or the regulator settings.

### This particular reference

Power factor correction capacitors with series reactors that tune each step below the lowest significant harmonic. A detuned bank avoids resonance and absorbs little harmonic current; a tuned filter is designed to sink harmonic current.

### Terms

- Winding: A coil of conductor inside an electrical machine or transformer.
- Normally open / normally closed: The contact state in the normal condition defined for the drawing.
- Coil: A wound conductor that can produce a magnetic field when energised.

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)
- [Capacitive component symbols](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-74580D46-0731-41A6-918D-2DB419114207.htm)


## What it represents

A detuned capacitor bank places a reactor in series with each capacitor step so that the step resonates at a frequency below the lowest significant harmonic, commonly expressed as a detuning factor such as 7 per cent, which tunes near 189 Hz on a 50 Hz network. This prevents the bank from forming a parallel resonance that would amplify 5th harmonic currents from converters.
Single-line diagrams show several capacitor steps, each with a series reactor and a switching contactor or thyristor switch, controlled by a power factor regulator using a current transformer on the incoming supply. The detuning factor is noted on the bank.
The series reactor raises the voltage across the capacitors above network voltage, so the capacitors must be rated accordingly. The symbol does not show that voltage rise, the reactor thermal rating or the regulator settings.

## How to read it

- Read the detuning factor, usually given as a percentage.
- Capacitor voltage rating should exceed network voltage.

## Information to show or reference

- State kvar per step and detuning factor.
- Show reactors, switching and regulator CT.
- Reference capacitor voltage rating.

## Important distinction

A detuned bank avoids resonance and absorbs little harmonic current; a tuned filter is designed to sink harmonic current.

## Facts

- Elements: Capacitor steps with series reactors
- Detuning factor: Commonly 5.67, 7 or 14 per cent
- Purpose: Power factor correction without resonance
- 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 shunt compensation banks with and without reactors context.
- [Capacitive component symbols](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-74580D46-0731-41A6-918D-2DB419114207.htm) — Autodesk. Public capacitor 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.