Reactors are available in various types, including air-core reactors, iron-core reactors, dry-type reactors, and oil-immersed reactors, each designed for specific operating conditions and applications.

Structurally, a reactor mainly consists of windings and insulating materials. The windings are typically made of copper or aluminum conductors, while the insulation system ensures reliable operation under high-voltage conditions.

In modern power systems, reactors are widely used to limit capacitive reactive power during power transmission, maintain reactive power balance, suppress harmonics, and prevent self-excited overvoltage caused by line capacitance. They play a vital role in ensuring the safe, stable, and efficient operation of the power grid.

What is a Reactor?

Simple Definition

A reactor is an electrical device that provides inductive impedance in a circuit.

Professional Definition

A reactor is a static electromagnetic device with inductive characteristics, mainly used to control current, limit fault current, filter harmonics, and compensate reactive power in power systems.

Why Are Reactors Used?

Modern power systems widely use nonlinear electrical equipment containing semiconductor components, such as industrial rectifiers, high-power frequency converters, AC/DC converters, and other power electronic equipment.

In addition, equipment involving electric arcs and ferromagnetic materials, such as electric arc furnaces, transformers, and generators, also generate large amounts of harmonic currents.

These harmonics can seriously affect power quality and system stability, leading to problems such as:

• Overheating of equipment
• Capacitor damage
• Increased power losses
• Voltage distortion
• Failure of compensation systems

When harmonic content is relatively low, harmonic suppressors may be sufficient. However, when harmonic levels become high, series reactors are required to effectively suppress harmonic currents and protect electrical equipment.

Classification of Reactors

1. Classification by Structure

By Phase Number

Single-phase reactor

Three-phase reactor

By Cooling Method

Dry-type reactor

Oil-immersed reactor

By Core Structure

Air-core reactor

Iron-core reactor

By Installation Location

Indoor reactor

Outdoor reactor

Classification by Application

Series Reactor

Installed in capacitor circuits to limit inrush current during capacitor switching operations. It also works together with capacitor banks to suppress specific harmonics.

Shunt Reactor

Commonly connected to transformer tertiary windings in EHV transmission systems. It compensates for capacitive charging current, limits voltage rise and switching overvoltage, reduces insulation requirements, and improves transmission reliability.

Current-Limiting Reactor

Used to limit short-circuit current to a safe level for electrical equipment and switchgear.

Filter Reactor

Connected in series with capacitor banks to form harmonic filtering circuits, providing a low-impedance path for specific harmonic frequencies.

Split Reactor

Installed in power systems to limit fault current. It presents low impedance during normal operation and high impedance under fault conditions.

Static Reactive Compensation Reactor

Used in thyristor-controlled dynamic reactive power compensation systems.

Starting Reactor

Applied for reduced-voltage starting of large AC motors to reduce starting current.

Smoothing Reactor

Widely used in HVDC transmission systems and DC drive equipment to reduce ripple current and stabilize DC output.

Classification by Voltage Level

High-Voltage Reactors

Suitable for voltage levels of 6kV, 10kV, 20kV, 35kV, and above.

Common types include:

• High-voltage series reactors
• Current-limiting reactors
• Filter reactors
• Shunt reactors
• Starting reactors
• Smoothing reactors
• Balancing reactors

Low-Voltage Reactors

Designed for systems rated at 380V, 400V, 450V, 480V, 600V, and 690V.

Common applications include:

• Capacitor series reactors
• Harmonic filter reactors
• Frequency converter input/output reactors
• Smoothing reactors

Main Functions of Reactors

Functions of Series Reactors

1. Limiting Inrush Current

Series reactors reduce switching surge current during capacitor bank energization, protecting capacitors and switching devices.

2. Suppressing Harmonics

They suppress high-order harmonics in the power system and prevent harmonic amplification, thereby protecting capacitors and improving power quality.

Functions of Current-Limiting Reactors

Current-limiting reactors are mainly used to restrict short-circuit current in power systems.

When a fault occurs, the reactor uses its inductive reactance to limit fault current within an allowable range, enabling circuit breakers and switchgear to safely interrupt the fault current.

Most current-limiting reactors adopt an air-core structure because of its excellent linear reactance characteristics and stable performance.

Applications of Filter Reactors

Filter reactors are connected in series with capacitor banks to form series resonant circuits for filtering specified harmonic frequencies.

At the fundamental frequency, the filter branch behaves capacitively and can simultaneously provide reactive power compensation.

A typical AC filter branch consists of:

• AC filter capacitor
• AC filter reactor
• To meet different harmonic filtering requirements, the inductance of the filter reactor is often adjustable through:
• Tap changers
• Adjustable winding spacing
• Multiple winding structures

Conclusion

Reactors are indispensable components in modern electrical power systems. They are widely used for harmonic suppression, reactive power compensation, voltage stabilization, and short-circuit current limitation.

With the rapid development of power electronics, renewable energy systems, and industrial automation, reactors have become increasingly important in improving power quality, enhancing equipment protection, and ensuring the reliable operation of modern power grids.