CAP 3PH
Three-phase power-factor capacitor
A three-phase capacitor assembly provides a documented reactive-power function connected to the power circuit.
SLD / Schematic
Symbols · DCB
Detuned capacitor bank
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.
- 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.
Read the source: Capacitor and filter product offerings · Capacitive component symbols
SLD · DCB
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.
A distinction that matters
A detuned bank avoids resonance and absorbs little harmonic current; a tuned filter is designed to sink harmonic current.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Capacitor and filter product offerings
Public shunt compensation banks with and without reactors context.
Capacitive component symbols
Public capacitor symbol family context.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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