What Is a Shunt Reactor and Why Is It Used?

Published 27 Aug 2026Updated 27 Aug 20266 min readIntermediateGrid
Quick answer — A shunt reactor is an inductive device connected phase-to-ground (shunt) to absorb reactive power and reduce the system voltage, counteracting the excess capacitive effect of lightly loaded transmission lines and underground cables. It helps keep the voltage within limits, especially on long EHV/UHV lines.
Contents
What is a shunt reactor and what does it do?

The problem it solves

Long high-voltage lines and cables generate reactive power (capacitance). When lightly loaded, this raises the voltage above acceptable limits; a shunt reactor absorbs that reactive power to hold the voltage down.

Types

Shunt reactors can be fixed (switched at a substation) or variable (with a tap or thyristor control). They are common at EHV/UHV substations and large cable connections.

Why it matters

Without the reactor, excessive voltage can overload insulation, cause ferroresonance or trip the line. The reactor also supports system stability and reactive-power balance.

Worked example

A lightly loaded 400 kV line may over-volt by several per cent; installing a shunt reactor (typically rated in MVAr at the system voltage) absorbs the excess reactive power and restores the voltage to target.

References & standards

Related

Book seriesAcademy

Related manufacturers

Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Virginia Transformer Corp · Pennsylvania Transformer Technology

Related components

Protection, monitoring & diagnostics On-load tap changers
Technical content is prepared from engineering references, standards frameworks, manufacturer documentation and industry sources. Contractual or compliance decisions should refer to current official standards. TransformerPath Technical Editorial.
Source transformers for this application

Submit an RFQ or browse manufacturers and components.

Submit an RFQ Get Verified