# Shunt Reactors: Types, Working and Design

- Link: https://studyelectrical.com/2024/09/shunt-reactors-types-working-and-design.html
- Published: 2024-09-20T03:56:59+00:00
- Author: Tesla

Shunt reactors are specialized devices utilized in electrical power systems to **
manage reactive power**, particularly in **high voltage transmission lines** and**
underground cable networks**.

As power systems expand, issues such as excessive voltage arise, leading to the 
need for compensation mechanisms. Shunt reactors are introduced to address these
issues by counteracting the** leading reactive power**, ensuring **system stability
and efficiency**.

This article provides an in-depth exploration of shunt reactors, their types, operations,
and the technology behind them.

## **The Need for Shunt Reactor**

The expansion of very high voltage (VHV) transmission systems and [underground cable](https://studyelectrical.com/2018/12/types-of-underground-cables.html)
networks leads to** unwanted reactive power**, specifically leading reactive power.
This can **cause over-voltage situations**, especially during **low load conditions**
often called as **[Ferranti effect](https://en.wikipedia.org/wiki/Ferranti_effect)**.

Shunt reactors, primarily switched in during periods of low demand, provide the 
necessary compensation by **absorbing the excess reactive power**. The main function
of shunt reactor is **reactive power compensation**.

[**Series reactors**](https://studyelectrical.com/2023/09/current-limiting-reactor-series.html)
on the other hand are used to **limit short-circuit currents** and **manage power
flow**.

## Shunt Reactor Connection

The image below demonstrates how shunt reactors are integrated into the power system
to enhance voltage stability and protect against transients, contributing to the
overall reliability of the electrical network.

![Shunt reactor connection diagram](https://studyelectrical.com/wp-content/uploads/
2024/09/Shunt-reactor-connection-diagram.webp)

Shunt reactor connection diagram

**Types of Connections:**

 1. **Direct Connection to Transmission Line:**
 2.  * Shunt reactors can be directly connected in parallel with the transmission line.
     * This allows them to absorb reactive power directly from the line, stabilizing
       voltage levels.
 3. **Connection to Tertiary Winding of Transformer:**
 4.  * Alternatively, shunt reactors can be connected to the tertiary winding of a 
       transformer.
     * This configuration allows for reactive power absorption from the transformer,
       helping to manage voltage levels without direct interference with the main transmission
       line.

 * **RC Snubber Filter:**
    - Often used in conjunction with directly connected shunt reactors.
    - The filter helps to protect the power system by damping transients and reducing
      oscillations.
 * By absorbing excess reactive power, shunt reactors prevent overvoltage conditions
   in the power system.
 * They ensure stable and efficient operation of the power network, particularly
   during low load conditions or over long transmission lines.

## **Types of Shunt Reactors**

Shunt reactors are generally classified into two principal types based on their 
core structure and design:

### **1. Air Core Shunt Reactors**

Air core, or coreless reactors, **do not have a magnetic core**. Instead, the magnetic
flux generated circulates within the winding itself and passes through **air or 
another medium of unit permeability, like mineral oil. **

![air core shunt reactor](https://studyelectrical.com/wp-content/uploads/2024/09/
air-core-shunt-reactor.jpg)

Air core shunt reactor

This design is typically **used at lower voltages** due to its simplicity and _**
effectiveness in environments with fewer external magnetic constraints.**_

### **2. Gapped Core Shunt Reactors**

Gapped core shunt reactors, on the other hand, feature a** magnetic core inside**
and **concentric with the winding. **

![Basic components of gapped core shunt reactors](https://studyelectrical.com/wp-
content/uploads/2024/09/Basic-components-of-gapped-core-shunt-reactors-active-part-
1.webp)

Basic components of gapped core shunt reactors

This core is constructed from **radially disposed laminated steel discs**, separated
by **gaps **filled with an **insulating fluid**. These gaps help maintain the desired**
voltage-current characteristic**, making this design suitable for **higher voltage
applications.**

## **Working Principles of Shunt Reactors**

The functionality of shunt reactors relies heavily on their core design and the 
magnetic properties of their components.

### **1. Air Core Reactors**

In air core reactors, the magnetic flux circulates within the winding and through
a medium of low permeability.

These reactors feature a **linear magnetization characteristic**, meaning their 
reactance remains relatively constant until the magnetic shield saturates. This **
saturation point** usually lies well **above the reactor’s rated voltage**, ensuring
stable performance across a wide range of operational conditions.

![Magnetization characteristics of Shunt reactor](https://studyelectrical.com/wp-
content/uploads/2024/09/Magnetization-characteristics-of-Shunt-reactor.webp)

_**A – Theoretical (Constant Impedance)
B – Air core reactor with shield saturation
at knee point voltageC – Gapped core reactorThe above characteristic is important
for the operation of the reactor duringvoltage transition

### **2. Gapped Core Reactors**

The windings in gapped core reactors are generally of** disc or layer type**, featuring**
small conductors** that **minimize eddy current losses** and **local hot spots**.

![Single phase gapped core shunt reactor](https://studyelectrical.com/wp-content/
uploads/2024/09/Single-phase-gapped-core-shunt-reactor.webp)

Single phase gapped core shunt reactor

![Three phase gapped core shunt reactor](https://studyelectrical.com/wp-content/
uploads/2024/09/Three-phase-gapped-core-shunt-reactor.webp)

Three phase gapped core shunt reactor

The magnetic core consists of **silicon steel discs** arranged radially, with the**
air gaps** forming a critical part of the **reactor’s impedance control mechanism**.

## **Air Core Reactor Design and Characteristics**

Air core reactors, often used in **lower voltage applications**, have a straightforward
design. The [cylindrical winding](https://studyelectrical.com/2022/11/transformer-windings-types-and-design.html)
is typically housed within an external magnetic shield, which is designed to channel
the return flux and prevent excessive heating in nearby metallic structures. The
external shield can vary in shape, as long as it effectively contains the magnetic
flux.

![Air Core Reactor](https://studyelectrical.com/wp-content/uploads/2024/09/Air-Core-
Reactor.webp)

Cutaway View of Magnetically Shielded Air Core Reactor

## **Gapped Core Reactor Design and Characteristics**

### **Magnetic Core Structure**

The core of a gapped core reactor is made up of **silicon steel discs**, each **
encapsulated in epoxy resin** to **reduce vibrations and noise**. The discs are 
separated by **ceramic or slate spacers**, which form the critical air gaps. These
air gaps play a vital role in stabilizing the magnetic flux within the reactor and
maintaining a consistent impedance across different operating conditions.

![A Magnetic Disc with Gap Supporting Discs](https://studyelectrical.com/wp-content/
uploads/2024/09/A-Magnetic-Disc-with-Gap-Supporting-Discs.webp)

A Magnetic Disc with Gap Supporting Discs

### **Air Gaps in Gapped Core Reactors**

The presence of air gaps in these reactors serves several purposes:

 * They **prevent large radial flux components** in the coil.
 * They help **maintain a consistent magnetic flux** across the reactor’s height.
 * They allow for **impedance adjustments** within specified tolerances.

The magnetic forces acting across these air gaps can cause vibrations and noise,
necessitating the use of strong axial pressure to maintain alignment. This pressure
is usually applied using tie rods that either pass through the core’s center or 
are positioned outside the windings, depending on the design.

The magnetic force between the different elements of the core is given by:
$$F=\
frac{B^2_{\max}\cdot S_{ag}}{2\mu_o}$$

Where $B_\mathrm{max}=$induction in air gap[Tesla]
$S_{ag}=$cross sectional area
of the air gap[m’]$\mu_o=4\pi\cdot10^{-7}$

## **Operational Considerations for Shunt Reactors**

 * The effective operation of shunt reactors involves carefully balancing the magnetic
   and electrical properties of the components.
 * For instance, in gapped core reactors, the primary impedance is determined by
   the air gaps. When the core reaches saturation, the impedance increases, a characteristic
   that differentiates gapped core designs from air core reactors.

## **Single Phase and Three Phase Shunt Reactors**

### **1. Single Phase Shunt Reactors**

Single phase reactors typically feature a magnetic frame with yokes and return legs.
The tank housing these reactors is usually cylindrical, with attached radiators 
to manage the cooling requirements.

![Single phase shunt reactor](https://studyelectrical.com/wp-content/uploads/2024/
09/Single-phase-shunt-reactor.webp)

Single phase shunt reactor

### **2. Three Phase Shunt Reactors**

In three-phase reactors, the **fluxes in each phase are displaced by 120°**, resulting
in zero vector sum in the yoke. This unique arrangement allows for designs both 
with and without return legs.

![Three phase shunt reactor](https://studyelectrical.com/wp-content/uploads/2024/
09/Three-phase-shunt-reactor.webp)

Three-phase shunt reactor

The choice between these designs depends on the customer’s impedance requirements,
with reactors lacking return legs exhibiting lower zero sequence impedance due to
the high reluctance in the air gap between yokes.

## **Cooling Mechanisms in Shunt Reactors**

 * The cooling system for shunt reactors varies **based on their phase configuration**.
    - **Single phase** reactors might have **cylindrical tanks with attached radiators**.
    - **Three-phase** reactors often feature **rectangular tanks**.
 * Proper cooling is critical for preventing overheating and maintaining the reactor’s
   longevity.

## **Applications and Benefits of Shunt Reactors**

 * Shunt reactors are essential in **maintaining the stability** of power systems**
   by managing reactive power**, thus **preventing over-voltage conditions**.
 * They are particularly useful in **long-distance high-voltage transmission lines**
   and **extensive cable networks**, where reactive power compensation is a significant
   concern.

## **Common Challenges in Shunt Reactor Operation**

 * Challenges include **managing the noise and vibrations** caused by magnetic forces
   in gapped core reactors and **ensuring effective cooling** in high voltage applications.
 * Additionally, **maintaining alignment** and **minimizing eddy current losses**
   in the windings are critical for optimal performance.

## **Design Innovations in Shunt Reactors**

 * Recent innovations focus on **enhancing the magnetic shielding of air core reactors**
   and **improving the material composition of core discs** in gapped core reactors.
 * Advances in **insulation fluids** and **materials for gap spacers** also contribute
   to better performance and reduced operational noise.

## **Future Trends in Shunt Reactor Technology**

 * Future developments are likely to include further** optimization of core materials**,
   more **compact designs for high-voltage reactors**, and** improved cooling systems.**
 * The **integration of digital monitoring and control systems** for real-time performance
   assessment is another anticipated trend.

## **Frequently Asked Questions (FAQs)**

### **1. What is the primary function of a shunt reactor?**

Shunt reactors are used to manage reactive power and control voltage levels in power
transmission systems, especially in high voltage applications.

### **2. What is the difference between air core and gapped core reactors?**

Air core reactors lack a magnetic core and rely on the surrounding medium for flux
circulation, while gapped core reactors feature a magnetic core with gaps for precise
impedance control.

### **3. Why are air gaps important in gapped core reactors?**

Air gaps help stabilize magnetic flux, maintain consistent impedance, and reduce
radial flux components within the winding.

### **4. How does cooling work in shunt reactors?**

Cooling is typically achieved using radiators attached to the reactor’s tank, with
designs varying between single-phase and three-phase configurations.

### **5. Are shunt reactors used only in high voltage applications?**

Primarily, yes. They are crucial in managing reactive power in high voltage transmission
lines and extensive cable networks.

### **6. What are the future trends in shunt reactor technology?**

Trends include advancements in core materials, compact designs, and the integration
of digital monitoring systems.

## **Conclusion**

Shunt reactors play a critical role in stabilizing power transmission systems by
controlling reactive power and maintaining appropriate voltage levels. Whether through
air core or gapped core designs, these devices are essential in ensuring the efficiency
and reliability of modern electrical grids. As technology advances, further innovations
in shunt reactor design and operation will continue to support the growing demands
of global power networks.

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