Shunt Reactor-Types, Construction & Applications

In an electrical power system, a shunt reactor stabilizes the transmission line voltage during load fluctuation conditions. A typical shunt reactor is basically a power inductor used to compensate for the reactive power in transmission systems.

In this article, we will discuss the definition, construction, types, and uses of shunt reactors.

What is a Shunt Reactor?

A shunt reactor is an electrical device that is used to absorb or compensate for the reactive power in the transmission systems. It is similar to a power transformer, but it has only a single winding, whereas a power transformer has three windings.

Shunt reactors are crucial in improving the power and energy efficiency of the electrical power system. The primary function of this reactor is to absorb and compensate the reactive power in long-distance high-voltage transmission lines and cables. These types of reactors are directly connected in parallel to the power lines.

A shunt reactor operates to stabilize line voltage under load fluctuations. Therefore, these reactors act as a crucial component within high-voltage power transmission systems.

In a traditional power system, a fixed-rating shunt reactor is either continuously connected to the transmission line or switched based on the varying load conditions.

In practice, a three-phase shunt reactor is connected to the electrical power systems. Its primary purpose is to compensate for the capacitive reactive power in the power system and regulate overvoltages occurring from load disconnections.

A shunt reactor must withstand the maximum continuous operating system voltage to ensure optimal performance of the power transmission. For example, in a 440 kV power system, the line voltage should be maintained 5% above the rated value.

Construction of Shunt Reactor

The construction of a typical shunt reactor is similar to a power transformer, but it has only one winding, as shown in the following figure.


The construction of a shunt reactor involves the following major components:

(1). Core – The core of a shunt reactor is designed from cold-rolled grain-oriented silicon steel sheets. This effectively minimizes the hysteresis losses in the reactor. The silicon steel sheets are laminated to reduce the eddy current losses in the core of the reactor.

(2). Winding – The winding of a reactor consists of copper conductors covered with paper insulation.

(3). Cooling System – A typical shunt reactor is so designed that it handles only low currents. Therefore, the Oil Natural Air Natural (ONAN) cooling system is best suited for these types of reactors. Along with the ONAN cooling system, a radiator bank is also integrated with the main tank of the reactor to improve the overall cooling efficiency.

(4). Main Tank – The main tank of the reactor has a typical bell tank-type design. The bell tank of the reactor is designed from steel sheets with an appropriate thickness. The steel sheets are tightly welded together to create the reactor tank to ensure a complete vacuum inside the tank.

Types of Shunt Reactors

On the basis of construction, these reactors can be classified into the following two types:

  • Dry Type Shunt Reactor
  • Oil Immersed Type Shunt Reactor

Let us now discuss these types of reactors in detail.

(1). Dry Type:

A dry-type reactor is mainly designed to operate within a voltage range of up to 34.5 kV. The dry-type reactor is basically an air-core-type reactor whose major parts are directly exposed to the environment. This type of reactor is commonly used on the tertiary winding of a transformer, where it is connected to the transmission line to compensate for the reactive power.

The dry-type reactors can be used for both indoor and outdoor applications. These reactors are so designed that they provide an arrangement of windings that allows airflow between turns and layers for natural air cooling.

The dry-type reactors have several advantages, such as light weight, low cost, low losses, and easy and less maintenance. These shunt reactors can be used in a limited voltage range.

(2). Oil Immersed Type:

The oil-immersed shunt reactors have core and winding assemblies immersed in oil filled in a tank just like a power transformer. The oil serves two functions, i.e., insulation and cooling of the reactor windings.

Oil-immersed shunt reactors can be designed in both single-phase and three-phase units. These types of reactors are provided with forced cooling along with self-cooling mechanisms to ensure maximum operational performance.

The oil-immered type reactors are mainly used in medium and high-voltage applications.


These reactors are widely used in electrical power systems. Some major applications are listed as follows:

  • They are used to absorb and compensate reactive power in transmission lines, which provides a regulated stable voltage at the load end.
  • They are also used in electrical substations to improve the system power factor by controlling reactive power.
  • By controlling the reactive power, they also reduce the line losses and improve transmission efficiency.
  • They are used in substations to regulate voltage to provide a constant voltage during low load conditions.
  • They are also used in industrial facilities in electric motor drives to improve power factor and efficiency.
  • Sometimes, it is also used to reduce electromagnetic interference produced by high-voltage transmission lines.

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