Why Series Reactor is Used in Capacitor Bank

Views: Author: Time: 2019-02-18

A reactor is a coil which has large number of turns and whose ohmic resistance value is much greater. Reactors are used to limit the short circuit currents which can cause damage to the equipment of the power system. The additional reactance added in series with the system for protection are called reactors.


A current limiting reactor is a kind of reactor which limits the heavy flow of current through other sectors of the system. In this case, we don’t have to shut down the whole system, we can just isolate the faulty section.

Reactors are also used to protect the circuit breakers of different ratings. They are used to limit the short circuit currents according to the capacity of circuit breakers. Thus, while doing changes in the system, we don’t have to replace the circuit breakers, due to which, time and money, both can be saved.

Types of Reactors

On the basis of construction, the reactors are of two types:

1. Dry type or air core or open type or Unshielded type reactors

2. Oil immersed or magnetically shielded or iron core reactors.

Air core reactors: The reactors in which no iron core or steel core is used are called air core reactors. These reactors are only used up to 33kv. These reactors are larger in size. Concrete slabs are arranged in the form of a circle and stranded copper coil conductors are embedded in it. These slabs provide good mechanical strength during short circuit currents.

Post insulators made of porcelain support these reactors. These are also called cast concrete type reactors. Insulated conductors are used for winding so as to provide insulation between turns, glass or porcelain material used.


These are simple, have constant current and reactance as well as greater mechanical strength.


Not suitable for outdoor services and takes much space due to their large size, difficult to provide cooling and can only be used up to 33kv.

Iron core reactor: The reactors consisting of iron core are called iron core reactors. A coil is placed inside a standard transformer tank and oil is filled for cooling and insulation purposes. Shielding is provided to prevent losses. This would also prevent stray magnetic fields; the core is laminated. Shields are made in the form of short-circuited rings and are earthed via end plates. The mmf produced in the rings due to short-circuit current, keeps the flux inside the shield.

These reactors are also called oil immersed type reactors and can be used for any voltage level.


These reactors provide greater protection against short-circuit currents, have high thermal capacity suitable for both indoor and outdoor services and can be operated at any voltage level.


They are costly, complex and difficult to repair.

Having understand what reactor is and the various types available, it is crucial to know why the series type is used in capacitor bank.

· For a multi-step banks in close proximity to each other, series reactors will be part of each separate bank for the purpose of limiting inrush current during back to back switching.

· In applications where harmonic current distortion is high due to the use of nonlinear loads, series reactors are used to detune the capacitor bank parallel resonant point.

· They are also used in series to tune the series resonant point of the capacitor to act as a harmonic filter.

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