Why Reactors are used in Power Systems and their Types

A reactor is a coil with a large number of turns and high ohmic resistance. Its primary purpose is to limit the short circuit currents that can potentially damage power system equipment. Reactors are added in series with the system to provide additional reactance for protection.

Current Limiting Reactors

A current limiting reactor is a specific type of reactor that restricts the flow of heavy currents through other sections of the system. By isolating the faulty section, it allows the rest of the system to remain operational without the need for a complete shutdown.

Current limiting reactors also play a crucial role in protecting circuit breakers of different ratings. They are used to control the short circuit currents based on the capacity of the circuit breakers. This eliminates the need for replacing circuit breakers when making changes to the system, resulting in significant savings in time and cost.

Working Principle of Current Limiting Reactors

The short circuit current (Isc) can be calculated using the formula Isc = E/X, where X is the reactance of the circuit during a fault and E is the voltage given. The reactance and current are inversely proportional – as X increases, Isc decreases, and vice versa. Short circuit currents depend on factors such as generating capacity, fault point voltage, and circuit reactance.


Additional Uses of Reactors

  1. Arc Suppression: Reactors are employed for suppressing arcs.
  2. Harmonic Filtering: They can filter out harmonics.
  3. In Auto Transformers: Reactors can be used in series with low reactance auto transformers.
  4. In Induction Regulators: Reactors can be utilized in series with low reactance induction regulators.
  5. Surge and Lightning Protection: Reactors provide protection against high voltage waves, surges, and lightning.
  6. Motor Starting Current Control: Reactors can help control the starting currents of motors.

Why Reactors are Used?

Reactors are used in power systems for several important reasons, primarily related to maintaining stable and efficient operation of the electrical grid. A reactor is a type of passive electrical device that is used to control the flow of electric current in a circuit. There are two main types of reactors: inductive reactors and capacitive reactors. Here’s why reactors are used in power systems:

  1. Voltage Regulation: Reactors are often used to regulate voltage levels within the power system. Inductive reactors can help to raise the voltage by introducing a voltage drop in the circuit, which can be useful in cases where the voltage is too high. Conversely, capacitive reactors can lower the voltage by absorbing reactive power and reducing the voltage levels.
  2. Reactive Power Compensation: Power systems consist of both active power (real power) and reactive power. Reactive power doesn’t perform useful work, but it’s necessary for maintaining voltage levels and ensuring the proper functioning of the power system. Reactors can be used to provide reactive power support by either absorbing (capacitive reactors) or generating (inductive reactors) reactive power as needed to maintain the power factor and voltage stability.
  3. Line Impedance: Reactors are used to control the impedance of transmission lines. This can help limit fault currents and provide better fault tolerance by reducing the stress on circuit breakers and other protective devices during faults.
  4. Transient Stability: During sudden changes in the power system, such as faults or disturbances, reactors can help improve the transient stability of the system. By limiting the rate of change of current, reactors prevent rapid fluctuations that could destabilize the system.
  5. Harmonic Filtering: Reactors are sometimes used for harmonic filtering. In systems where nonlinear loads (like computers, electronic devices, etc.) introduce harmonics into the power system, reactors can be used to mitigate these harmonics and improve power quality.
  6. Damping Oscillations: Reactors can dampen power oscillations that can occur in the power system due to various factors. These oscillations can lead to instability and affect the overall performance of the grid.
  7. Series Compensation: In some cases, reactors can be used for series compensation in transmission lines. By inserting reactors in series with transmission lines, the effective impedance can be adjusted, which helps to increase the transmission capacity and reduce line losses.
  8. Transformer Inrush Current Limitation: Inductive reactors are used to limit the inrush current that occurs when transformers are energized. This helps prevent excessive stress on the transformers and associated equipment.

Overall, reactors play a crucial role in maintaining the reliability, stability, and efficiency of power systems by managing voltage levels, reactive power flow, impedance, and other important parameters.

Types of Reactors

Air Core Reactors

Air core reactors, as the name suggests, do not use an iron or steel core. They are primarily used up to 33kV. These reactors have a larger size, with copper coil conductors embedded in concrete slabs arranged in a circular form. Post insulators made of porcelain support these reactors. Glass or porcelain material is used to provide insulation between turns.


  • Simple construction
  • Constant current and reactance
  • Greater mechanical strength


  • Not suitable for outdoor services
  • Occupies more space due to the large size
  • Difficult to provide cooling
  • Limited usage up to 33kV

Iron Core Reactors

Iron core reactors consist of an iron core and are known as oil-immersed type reactors. A coil is placed inside a standard transformer tank and filled with oil for insulation and cooling purposes. Shields are provided to prevent losses and stray magnetic fields, and the core is laminated to maintain magnetic flux. Short-circuited rings act as shields and are earthed through end plates.

Iron core reactors, also known as oil-immersed reactors, can be utilized at any voltage level.


  • Greater protection against short-circuit currents
  • High thermal capacity
  • Suitable for both indoor and outdoor services
  • Operable at any voltage level


  • Costly and complex
  • Difficult to repair

Reactors Types According to Usage

Reactors are passive electrical components used in various applications within power systems and other fields. They come in several types, each designed to fulfill specific functions. The main types of reactors are:

  1. Inductive Reactors:
    • Iron Core Reactors: These reactors have a core made of magnetic material (usually iron) and are used for applications such as voltage regulation, current limiting, and harmonic filtering. They provide inductive reactance and can be used for both steady-state and transient stability enhancement.
    • Air Core Reactors: These reactors have no magnetic core and are primarily used for high-frequency applications and in situations where magnetic saturation is a concern. They are also used in applications like power factor correction and voltage regulation.
  2. Capacitive Reactors:
    • Capacitor-Bank Reactors: These reactors are used in combination with capacitor banks for power factor correction. They help control the flow of reactive power and maintain a desired power factor in the system.
    • Thyristor-Controlled Reactors (TCRs): TCRs are used to dynamically adjust the amount of reactive power injected into the system. They are often used in applications where the reactive power requirements vary frequently.
  3. Line Tuning Reactors:
    • These reactors are used to adjust the impedance of transmission lines. They help control line characteristics, such as impedance and voltage regulation, to optimize power transmission.
  4. Neutral Grounding Reactors:
    • These reactors are connected to the neutral point of a power system to limit fault currents and provide grounding in systems with ungrounded or low-resistance grounded systems.
  5. Current-Limiting Reactors:
    • These reactors are designed to limit fault currents in the event of a short circuit or other fault conditions. They help protect equipment and reduce stress on circuit breakers.
  6. Smoothing Reactors:
    • Smoothing reactors are used in applications involving direct current (DC) systems to reduce ripple and smooth out the DC voltage.
  7. Arc Suppression Reactors:
    • These reactors are used in high-voltage applications to suppress or extinguish arcs that can occur during switching operations or faults.
  8. Shunt Reactors:
    • Shunt reactors are connected in parallel with capacitors to limit the overvoltage that can occur due to the resonance between the reactive power sources. They help maintain the stability of the system.
  9. Series Reactors:
    • Series reactors are inserted in series with transmission lines to limit the current and control the impedance, which can help increase transmission capacity and reduce fault currents.
  10. Transformer Inrush Current Limiting Reactors:
  • These reactors are connected in series with transformers during startup to limit the inrush current that occurs due to the magnetization of the transformer core.

The choice of reactor type depends on the specific requirements of the application, such as voltage control, reactive power compensation, fault current limiting, and harmonic filtering. Each reactor type serves a unique purpose in maintaining the reliability and stability of power systems and other electrical installations.

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