Current Limiting Reactor

When a plant expands, the fault level rises with it, and one day it passes what the existing switchgear can interrupt. A series reactor puts the impedance back so the breakers you already own stay inside their rating.

TypeSeries current limiting reactor
FunctionReduce prospective short circuit current
Secondary functionLimit motor starting and inrush current
Selection basisPercentage impedance added to the system

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Product Overview

In electrical engineering, current limiting reactors can reduce short circuit currents, which result from plant expansions and power source additions, to levels that can be adequately handled by existing distribution equipment. They can also be used in high voltage electric power transmission grids for a similar purpose. In the control of electric motors, current limiting reactors can be used to restrict starting current or as part of a speed control system.

How it works: a current limiting reactor is used when the prospective short circuit current in a distribution or transmission system is calculated to exceed the interrupting rating of the associated switchgear. The inductive reactance is chosen to be low enough for an acceptable voltage drop during normal operation, but high enough to restrict a short circuit to the rating of the switchgear. The amount of protection a current limiting reactor offers depends upon the percentage increase in impedance that it provides for the system.

The main motive of using current limiting reactors is to reduce short circuit currents so that circuit breakers with lower short circuit breaking capacity can be used. They can also be used to protect other system components from high current levels and to limit the inrush current when starting a large motor.

Application Scenarios

Distribution systems after plant expansion or added generation
High voltage transmission grids
Large motor starting and speed control systems
Protecting system components from high current levels

Technical Features

Reduces fault current to within the interrupting rating of existing switchgear
Inductive reactance chosen for acceptable normal running voltage drop
Also used to restrict large motor starting current
Allows circuit breakers with lower breaking capacity to remain in service

Specification available on request.

FAQ

Questions Buyers Ask

How is the reactance chosen?

It is a compromise. Low enough that the volt drop at normal load is acceptable, high enough that the prospective fault current falls below the switchgear rating. Send the system fault level, the breaker rating and the load and an engineer will work through it.

Can a reactor replace a switchgear upgrade?

Often yes, and that is why it exists: adding impedance is usually far cheaper than replacing a whole switchboard because the fault level crept up.

Does it help with motor starting?

Yes. In motor control a series reactor restricts starting current, and can form part of a speed control scheme.