What is a Shunt Reactor : Construction & Its Working

In energy systems, renewable energy sources & cables are becoming more common. But, in cases, irregular active power or reactive power has negative side effects. So, the shunt reactor plays an essential role to balance these changes. In the year 1990, shunt reactors were supplied by Hyosung Industries up to 345kV voltage level and 200MVAr range of reactive power. This can be extended to distribute with the highest voltage level like 765kV and reactive power of 250MVAr. These reactors are used to compensate for reactive power in underground cables otherwise connecting renewable energy sources. Hyosung Industries also supply customized solutions like reactors including auxiliary windings & variable shunt reactors. This article discusses an overview of shunt reactor, types and it’s working.

What is Shunt Reactor?

A shunt reactor is one kind of electrical device, used to stabilize the voltage throughout load differences in high voltage power transmission systems. The rating of a normal shunt reactor is fixed and all the time it is connected to the transmission line based on the load.

Shunt Reactor
Shunt Reactor

The shunt reactor working principle is, in an energy system, a shunt reactor works like an absorber for reactive power, so it increases the efficiency of the energy system. It is a compact device used to compensate for reactive power in high voltage transmission lines as well as in cable systems. The connection of this can be done with the power line directly otherwise to a 3-winding transformers tertiary winding. To connect or switch this shunt reactor permanently, a circuit breaker is used.

It must be capable of the highest continuous operating voltage. For example, For the 400 KV system, 5% higher than the rated voltage in normal power frequency difference without surpassing the 150oC of temperature at any element of the shunt reactor. When the reactor operates at normal conditions, then core losses may occur. So care must be taken for reducing these losses while designing.

Shunt reactors are extensively used for controlling the voltage throughout load differences in high voltage energy transmission systems. Based on the requirements of voltage, these reactors will operate to provide compensation of reactive power.


This reactor is mainly used for compensating capacitive reactive power for the transmission line. The construction of the shunt reactor may change from one designer to another.

Shunt Reactor Circuit Diagram
Shunt Reactor Circuit Diagram

Both the shunt reactors as well as power transformers are the same, however, they have simply a single winding for each phase. The windings of these can be connected in the star model by accessing the neutral point (YN). The connection of neutral point can be done toward the installation of an earthing system throughout the power transformer’s tertiary winding. These reactors are available in two types like conservator/dry type otherwise oil-immersed.

The protections, as well as accessories that are used in this reactor, are the same as used in power transformers. Especially in an oil-immersed type reactor, where must be stressed the pressure of oil in the relief valve as well as the air breather.

Types of Shunt Reactor

These are classified into two types based on the construction like dry-type as well as oil-immersed.

Dry Type

Generally, a Dry-type shunt reactor is limited to 34.5 kV of voltage. Generally, it is applied on the third winding (tertiary) of a transformer and connected to the transmission line being compensated. These reactors are air-core type, open to environment & appropriate for indoor otherwise outdoor application. Generally, ambient air’s natural convection is used for cooling the unit through windings arrangement to allow the airflow among turns as well as layers.

These turns & layers are mechanically supported with bracing members otherwise supports are made from different materials like glass polyester, concrete & ceramics. The construction of reactors can be done like single-phase units and placed over insulating pedestals/ base insulators to give the insulation to the ground for supporting the reactor.

This kind of reactor has no shielding but generates an external magnetic field with high-intensity once the reactor is enabled. It requires care while denoting the clearances as well as reactor unit arrangement, station structure, a mounting pad, and any metal area in the region of the reactor.

A closed metallic loop in the surrounding area of the reactor will generate heat, losses & arcing at joints; so, it is significant to keep away from these loops to keep adequate distances. It requires shielding once it is not achievable to assemble dry-type units within an equilateral-triangle pattern that is isolated from exterior magnetic influences.

As compared with oil-immersed types, the dry type reactors have some benefits like less weight, low cost, low losses, less maintenance, etc. The main drawbacks are limits on voltage ratings as well as the high-intensity exterior magnetic field. When the reactor is activated then it does not have an iron core and there is no magnetizing inrush current.


These reactors have two design configurations like coreless type as well as gapped iron-core type. These two configurations have longtime constant currents with low-frequency throughout de-energizing, determined through the parallel arrangement of the inductance of the reactor as well as line capacitance. But, the design of the gapped iron-core has a more severe energizing inrush as compared with the coreless type.

Most of the designs of coreless shunt reactors have a magnetic shield that surrounds the loop to hold the flux in the reactor tank. Generally, the steel core leg gives a magnetic flux lane using the loop of a power transformer which is arranged through insulating support structures. So this kind of design will result in an inductor that is linear for voltage.

These types of reactors are designed like a 1-phase otherwise 3-phase units & are extremely related in outside look to that of usual power transformers. They are mainly designed for either forced cooling or self-cooling.

Difference between Shunt Reactor & Power Transformer

The construction of both the shunt reactor well as power transformer is similar but there are some main differences between them based on their characteristics. The main difference between shunt reactor and power transformer are discussed below.

Shunt Reactor Power Transformer
Shunt reactor includes single winding Power transformer includes three windings
This type of reactor consumes reactive power to enhance the efficiency of the system The power transformer is used to change voltage like step up otherwise step down.
In this reactor, the main ampere-turns like AT are equivalent to minor ampere-turns because of the lack of other windings In the power transformer, the main ampere turn like AT is the sum of moving AT as well as minor AT.
The designing of a shunt reactor can be done without an iron core to avoid the hysteresis loss The designing of a power transformer can be done with an iron core
Shunt reactors are two types like dry-type & oil-immersed Power transformers are available in different types like autotransformer, polyphase, leakage & resonant.
Shunt reactor has a large amount of magnetizing current As compared to a shunt reactor, it has a less magnetizing current
Shunt reactor is rated in MVAr The power transformer is rated in kVA
Shunt reactor is used in cables network & high voltage systems. The power transformer is used to transmit the voltage level.

Measurement of Losses in Shunt Reactor

The shunt reactor losses should be measured at rated voltage as well as frequency. However, for a shunt reactor with an extremely high voltage type, it may be complex to assemble a high test voltage throughout the measurement of losses. So complexity can be defeat by measuring the measurement losses of the shunt reactor at any voltage lesser as compared with the reactor’s system voltage.

After that, the loss which is measured can be multiplied through the square of the fraction of rated current & the reactor current to attain the loss at rated voltage & applied reduced test voltage.
When the power factor of the shunt reactor is less, then the loss measurement through conventional wattmeter cannot be dependable, as an alternative of bridge technique for measurement may be accepted for better precision.

This test cannot separate the measurement losses in different elements of the shunt reactor. To keep away from, the test correction can consequence for a reference temperature and it is preferable to obtain the measurement once the normal temperature of the winding turns into equivalent to the reference temperature.


The applications of shunt reactors include the following.

  • It is used to enhance the efficiency of power as well as energy system because it absorbs as well as compensate the reactive power in transmission lines as well as cables.
  • It works as an absorber for reactive power, so it increases the system’s energy efficiency.
  • It is applicable for different systems like HV as well as EHV.
  • The variable shunt reactor is used for optimizing the existing network condition dynamically and also the voltage within the network.
  • It is used to enhance the stability of the network as well as for continuous voltage regulation in low-load operation or no-load operation of the lines.
  • These are used for enhancing power quality as well as voltage stability.

Thus, this is all about an overview of the shunt reactor, construction, working & its applications. It is similar to a power transformer which includes simply one winding for each phase than the power transformer. These reactors are mainly used for increasing the power as well as the efficiency of the system because it absorbs as well as balances the reactive power within as well as transmission lines with high voltage. The connection of shunt reactor can be done directly with tertiary winding or the power line of 3- winding transformer. Here is a question for you, what are the advantages of shunt reactor?