# Thyristor-switched capacitor

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

A capacitor bank switched in or out at current zero by anti-parallel thyristors, giving fast stepwise reactive support.

## In plain English

### What does Thyristor-switched capacitor mean?

A thyristor-switched capacitor connects a capacitor bank through anti-parallel thyristors, usually with a small series reactor to limit inrush. The thyristors switch the capacitor in at the instant when the network voltage equals the capacitor voltage, avoiding transients, and switch it out at current zero. It is either fully on or fully off.

### A simple example

Single-line diagrams show a capacitor, a series reactor and the thyristor pair stacked on a shunt branch. Several TSC branches may be drawn to give multiple steps of capacitive output in a static var compensator or a fast power factor correction system.

### What the drawings help you do

Because it switches in discrete steps, fine control comes from combining TSC branches with a TCR. The symbol does not show discharge resistors or the valve voltage rating, which must withstand twice the peak voltage when the capacitor is charged and the network reverses.

### This particular reference

A capacitor bank switched in or out at current zero by anti-parallel thyristors, giving fast stepwise reactive support. A TSC switches capacitors in steps without transients; a mechanically switched capacitor uses a breaker and is much slower.

### Terms

- Signal: Electrical information passed between devices, rather than necessarily the main power supply.
- 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.

- [Static Var Compensators (SVC)](https://www.hitachienergy.com/products-and-solutions/facts/static-var-compensation-svc)
- [Capacitive component symbols](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-74580D46-0731-41A6-918D-2DB419114207.htm)


## What it represents

A thyristor-switched capacitor connects a capacitor bank through anti-parallel thyristors, usually with a small series reactor to limit inrush. The thyristors switch the capacitor in at the instant when the network voltage equals the capacitor voltage, avoiding transients, and switch it out at current zero. It is either fully on or fully off.
Single-line diagrams show a capacitor, a series reactor and the thyristor pair stacked on a shunt branch. Several TSC branches may be drawn to give multiple steps of capacitive output in a static var compensator or a fast power factor correction system.
Because it switches in discrete steps, fine control comes from combining TSC branches with a TCR. The symbol does not show discharge resistors or the valve voltage rating, which must withstand twice the peak voltage when the capacitor is charged and the network reverses.

## How to read it

- A small series reactor is part of the branch, not a separate filter.
- Count branches to find available steps.

## Information to show or reference

- State capacitor Mvar per step.
- Show series reactor and valve.
- Reference switching logic.

## Important distinction

A TSC switches capacitors in steps without transients; a mechanically switched capacitor uses a breaker and is much slower.

## Facts

- Switching: At voltage match, out at current zero
- Output: Stepwise capacitive Mvar
- Series element: Inrush-limiting reactor
- Preview: Independent educational illustration; consult the applicable standard and project legend for the exact graphic

## Public references

- [Static Var Compensators (SVC)](https://www.hitachienergy.com/products-and-solutions/facts/static-var-compensation-svc) — Hitachi Energy. Public SVC page naming the thyristor-switched capacitor branch.
- [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.