Reactors in PE Power

Reactors are the primary source of controlling and regulating voltage in power systems, making Reactors in PE Power a crucial exam topic. A Layman often confuses it with the reactors used in Nuclear power plants.

But here, this is not the case. To help you study and prepare for Reactors in PE Power, this detailed guide will assist you in covering all the critical aspects of power reactors and how the process of power monitoring in reactors is carried out.

Let’s start with the fundamentals of Reactors in PE Power.

What are Reactors?

Reactors in the PE Power and power engineering domain refer primarily to inductors used in electrical power systems to control current and improve the power factor.

These reactors fundamentally differ from nuclear reactors used in nuclear power plants to generate energy through nuclear fission. In power engineering, reactors are used in transmission and distribution systems and power generation facilities.

Working Principle

Reactors work on the principle of electromagnetic induction. They consist of a coil wound on a magnetic core and leverage the property of inductance. When alternating current (AC) flows through the coil, a magnetic field is generated around it.

This magnetic field induces a voltage (electromotive force) in the coil that opposes the change in current (according to Lenz’s Law). This property of opposing changes in current flow is termed inductance and is measured in henries (H).

Types of Reactors

Some commonly used and studied power reactors in PE Power include:

  1. Shunt Reactors: Connected in parallel with the system, they are primarily used to absorb reactive power, thereby reducing the voltage rise in the system, especially in high-voltage networks with low loads. They are essential for controlling voltage with significant capacitive effects in long transmission lines.
  2. Series Reactors: These are connected in series with power system elements. They are used to limit fault currents, improve stability, control load sharing in parallel lines, and mitigate the impact of short-circuit currents.
  3. Current-limiting Reactors: A subtype of series reactors specifically designed to limit the current in the event of a fault.
  4. Filter Reactors: Used with capacitors to form filter circuits that mitigate harmonic distortions in the system.

We will discuss these power reactors in detail in the upcoming sections.

Power Monitoring in the Reactors – Usecases and Application 

The power reactors are mainly used for:

  • Voltage Control: Reactors help maintain voltage within desired limits across the power system by absorbing or supplying reactive power.
  • Power Factor Correction: Reactive power compensation using shunt reactors can improve the system’s power factor, which is crucial for efficient energy delivery.
  • Limiting Fault Currents: Series reactors can limit the magnitude of fault currents, thereby protecting equipment from damage and improving system stability.
  • Harmonic Filtering: Combined with capacitors, they form filter circuits that reduce harmonic distortion in power systems, improving power quality.
  • Load Balancing: Series reactors can be used to balance loads in parallel lines, ensuring optimal transmission network operation.

Specifications and Size of the Reactor

  • Rating and Size of the Reactor: Reactors are rated based on their inductive reactance and current-carrying capacity. The system voltage and the intended application influence the size of the reactor.
  • Thermal Performance: Reactors generate heat and must be designed to dissipate this heat effectively. Cooling systems, either air or oil, are critical in reactor design.
  • Core Material: The magnetic core is typically made of high-grade steel laminations to minimize core losses and improve efficiency.
  • Insulation: High-quality insulation is essential to withstand the electrical stresses in high-voltage environments.
  • Acoustic Noise: Reactors can produce acoustic noise, which requires mitigation through design or installation techniques for smooth and silent operations.

Types and Classification of Reactors

The most common and widely used types of Reactos are listed below, along with their construction and working. At the end of this section, don’t go through a chart as a key to note differences between different types of Reactors.

Classification based on Construction and Design

Air-Core Reactors

Air-core reactors are constructed without any magnetic core. Instead, they consist of windings of conductive wire (like copper or aluminum) coiled around a non-magnetic form (such as a plastic or ceramic cylinder).

The absence of a magnetic core means these reactors rely on the air (or the non-magnetic medium) inside and around the coils to establish their magnetic field.

Working Mechanism
  • When alternating current flows through the windings, a magnetic field is generated in and around the coils. The inductance is due to this magnetic field.
  • Unlike iron-core reactors, air-core reactors do not exhibit magnetic saturation, as no core material can reach a saturation point. 
  • Their inductance is generally lower than that of iron-core reactors, and they are less susceptible to losses like hysteresis and eddy currents.

Primarily used in radio frequency and high-frequency applications, such as inductors in radio transmitters and receivers, filters in audio equipment, and in certain types of transformers where minimal core losses are essential.

Iron-Core Reactors

Iron-core reactors are based on coils wound around a magnetic core, typically made from high-permeability material like laminated silicon steel. The magnetic core concentrates the magnetic field lines, greatly increasing the reactor’s inductance.

Working Mechanism
  • The alternating current flowing through the coils generates a magnetic field amplified by the iron core. This results in higher inductance compared to an air-core design.
  • However, iron-core reactors can experience magnetic saturation, where increasing the current does not proportionally increase the magnetic field strength.
  • They are also subject to core losses, including hysteresis (energy loss due to the reversal of magnetization in the core) and eddy current losses (induced currents in the core that produce heat).

Widely used in power systems for voltage regulation, reactive power compensation, current limiting, and other applications where higher inductance is required.

Purpose-based Classification

Shunt Reactors

Shunt reactors are typically iron-core reactors connected in parallel with the power system.

Working Mechanism
  • They absorb the reactive power generated in high-voltage power systems, particularly under light load conditions.
  • During periods of low demand, transmission lines can act like capacitors and generate reactive power, increasing voltage. Shunt reactors absorb this excess reactive power, helping to maintain a stable voltage level in the system.

Commonly used in electrical power transmission systems to control the voltage during off-peak hours or when the load on the system is relatively low.

Series Reactors

Series reactors are also typically iron-core but are connected in series with the power system.

Working Mechanism
  • They add impedance to the line, which limits the current flow and can improve the system’s stability.
  • In the event of a short circuit or fault, series reactors help limit the fault current to a manageable level, protecting equipment and reducing the risk of damage.

Used in power transmission and distribution systems for current limiting, load balancing between parallel lines, and mitigating the impact of short-circuit currents.

Combined Reactors

Combined reactors incorporate elements of both shunt and series reactors in a single unit.

Working Mechanism
  • Depending on the system’s requirements, these reactors can function as shunt or series reactors.
  • In one mode, they can absorb reactive power (like a shunt reactor); in another mode, they can limit current (like a series reactor).

They offer flexibility in power systems where voltage regulation and current limitation are required. This makes them suitable for more complex or variable power system applications.

Further Types

There are some other types of special-purpose resistors, including:

  1. Tuning Reactors
  2. Current Limiting Reactors
  3. Smoothing Reactors

For further detail on this, don’t forget to see the table below to understand the differences between different types of Resistors in PE Power.

Feature/TypeAir-Core ReactorIron-Core ReactorShunt ReactorSeries ReactorCombined ReactorTuning ReactorCurrent Limiting ReactorSmoothing Reactor
Core MaterialNone (air or non-magnetic medium)Magnetic core (usually silicon steel)Magnetic coreMagnetic coreCombination of bothMagnetic or Air-coreMagnetic coreMagnetic or Air-core
Primary FunctionHigh-frequency applicationsHigh-inductance applicationsVoltage control, reactive power compensationCurrent limiting, load balancingDual function of shunt and seriesHarmonic filtering, impedance matchingLimiting fault currentsSmoothing DC current
Susceptibility to SaturationNot applicableYes (prone to magnetic saturation)Limited by designLimited by designBased on designSpecific to the designLimited by designSpecific to the design
LossesMinimal hysteresis and eddy current lossesHysteresis and eddy current lossesDependent on designDependent on designDependent on designDependent on designDependent on designDependent on design
Inductive ReactanceLower compared to iron-coreHigher due to core concentrationHigh for voltage controlHigh for current limitationVariable depending on modeTuned to specific frequenciesHigh for effective limitationLow pass filter characteristics
ApplicationsRadio frequency, high-frequencyPower systems, high-inductive needsPower transmission systemsPower transmission systemsVersatile power system applicationsPower quality improvement, communicationsPower transmission systemsDC power systems

This is it for Reactors in PE Power. Remember to check other helpful study guides for PE Power exam preparation at Study for FE.


Now, you have a rich idea about how reactors play a crucial role in electrical power systems’ stability, efficiency, and safety. Their design and application require a deep understanding of electromagnetic principles, power system dynamics, and material science, making reactors in PE Power a complex but essential exam topic.

Don’t forget to read our detailed blog on Electrical Machines Theory in PE Power to understand the laws and principles associated with the functionality and operations of different electrical systems.

For an effective PE Power Exam Preparation, don’t forget to consult valuable resources, guides, and tips & tricks at Study for FE – Your go-to Platform for all things FE-related.


Licensed Professional Engineer in Texas (PE), Florida (PE) and Ontario (P. Eng) with consulting experience in design, commissioning and plant engineering for clients in Energy, Mining and Infrastructure.