Neutral Grounding Reactor (NGR): Working and Advantages

In electrical power systems, safety is of utmost importance to prevent accidents, equipment damage, and ensure the reliability of the entire network. One crucial component used to maintain system stability and protect equipment is the Neutral Grounding Reactor (NGR). In this article, we will discuss the concept of the Neutral Grounding Reactor, its purpose, and its significance in power systems.

Neutral Grounding Reactor (NGR)

Understanding Neutral Grounding

Before we dive into the specifics of Neutral Grounding Reactors, let’s briefly understand the concept of neutral grounding. In an electrical power system, the power is generated in three phases – typically referred to as A, B, and C phases. These phases are balanced and symmetrical. In a three-phase system, a neutral point is created as a reference potential for the three phases.

Traditionally, there are three types of neutral grounding: solid grounding, ungrounding (floating), and low-resistance grounding. However, each method has its pros and cons, which led to the development of a fourth option known as neutral grounding through the use of Neutral Grounding Reactors.

What is a Neutral Grounding Reactor (NGR)?

A Neutral Grounding Reactor (NGR) is a specialized electrical device that is used to control and limit fault currents in a power system by introducing a controlled impedance into the neutral path. It is essentially a high-impedance device placed in series with the neutral line of the power transformer or generator.

The primary function of the NGR is to limit the ground fault current during a fault condition. When a fault occurs, such as a short circuit between a phase conductor and ground, a massive amount of fault current can flow through the neutral path. This high fault current can be highly destructive, leading to severe equipment damage, hazards to personnel, and service interruptions.

Working Principle

During normal system operation, the Neutral Grounding Reactor allows a small amount of current to flow through the neutral path, balancing the system and maintaining a reference point for phase voltages. However, in the event of a fault, the NGR acts as an impedance that significantly restricts the fault current flow.

By limiting the fault current, the Neutral Grounding Reactor helps prevent excessive damage, making it an essential component in modern power systems. The impedance offered by the NGR is carefully chosen to strike a balance between protecting the system and avoiding maloperations during transient conditions.

Advantages of Neutral Grounding Reactors or (NGR):

  1. Fault Current Limitation: The primary advantage of NGRs is their ability to limit the magnitude of fault currents during short circuits. This feature helps safeguard sensitive equipment from damage and reduces the risk of electrical fires.
  2. Personnel Safety: By reducing fault currents, NGRs enhance the safety of maintenance personnel by mitigating the potential for high-risk electrical shocks during fault conditions.
  3. Equipment Protection: NGRs play a crucial role in protecting transformers, generators, and other electrical equipment from excessive mechanical and thermal stresses during faults.
  4. System Stability: Neutral Grounding Reactors contribute to maintaining system stability by preventing overvoltages and minimizing voltage dips during fault conditions.

Neutral grounding reactor vs Resistor

Neutral Grounding Reactors (NGRs) and Neutral Grounding Resistors (NGRs) are both devices used in electrical power systems to control and limit fault currents in the neutral path. While they serve similar purposes, they differ in their design, functionality, and applications. Let’s explore the main differences between Neutral Grounding Reactors and Neutral Grounding Resistors:

Design and Construction:

  • Neutral Grounding Reactor (NGR): An NGR is an inductive device that consists of a coil wound around a magnetic core. It introduces impedance into the neutral path, limiting the fault current by offering inductance. NGRs are typically larger and heavier than Neutral Grounding Resistors due to the presence of the magnetic core.
  • Neutral Grounding Resistor (NGR): An NGR, on the other hand, is a resistive device designed to provide impedance in the neutral circuit by utilizing resistive elements. It is constructed using resistive material such as metal alloys, and the resistance value is chosen based on the required fault current limitation.

Impedance Characteristics:

  • NGR: The impedance provided by an NGR is primarily inductive in nature. Inductive impedance causes a phase shift between voltage and current during a fault, which can be beneficial in certain applications like arc suppression and fault current limitation.
  • NGR: In contrast, the impedance offered by an NGR is purely resistive. Resistive impedance does not introduce any phase shift and simply limits the current flow during a fault condition.


  • NGR: Neutral Grounding Reactors are often used in high-voltage systems, such as power transformers and generators. They are suitable for applications where transient overvoltages need to be suppressed, as the inductive impedance can absorb and dampen voltage spikes during faults.
  • NGR: Neutral Grounding Resistors are commonly used in low to medium-voltage systems. They are typically applied in industrial settings where fault currents need to be limited to protect equipment and ensure personnel safety.

Transient Behavior:

  • NGR: Due to the inductive nature, Neutral Grounding Reactors can produce a temporary overvoltage, known as ferroresonance, during certain fault scenarios. Special precautions and design considerations are required to mitigate this phenomenon.
  • NGR: Neutral Grounding Resistors do not exhibit ferroresonance, as their resistive nature does not cause the same transient effects.


Neutral Grounding Reactors (NGRs) are indispensable components of modern electrical power systems, providing essential protection against ground faults and contributing to overall system stability. Their ability to limit fault currents ensures the safety of personnel, protects equipment, and reduces costly downtime. As technology continues to advance, NGRs will remain a critical element in maintaining the reliability and security of electrical power networks across the world.

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