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What is the use of earthing transformer ?

An earthing transformer, also known as a grounding transformer, plays a crucial role in power distribution systems by providing a path for fault currents to safely dissipate into the ground. Its primary function is to create a low-impedance connection to the earth, ensuring the effective grounding of electrical systems. Here’s a detailed explanation of the use and importance of an earthing transformer:

Purpose of Earthing Transformer:

  1. Grounding of Power Systems:
    • The primary purpose of an earthing transformer is to facilitate the proper grounding of power systems. Grounding is essential for various reasons, including safety, system stability, and the effective operation of protective devices.
  2. Fault Current Path:
    • In the event of a fault, such as a short circuit or ground fault, fault currents need a low-impedance path to flow safely to the ground. The earthing transformer provides this path, preventing excessive voltages and minimizing the risk of electrical shock and damage to equipment.
  3. Neutral Grounding:
    • Power systems often use neutral grounding to improve system stability and limit fault currents. The earthing transformer is a key component in creating a neutral grounding connection, helping to maintain the system’s voltage levels and protect equipment.

Construction and Configuration:

  1. Winding Arrangement:
    • An earthing transformer typically consists of three windings: primary, secondary, and tertiary. The primary winding is connected to the power system, the secondary winding is connected to the ground, and the tertiary winding is used to create a magnetic flux that helps control the earthing transformer’s impedance.
  2. Impedance Control:
    • The tertiary winding allows control over the impedance of the earthing transformer. By adjusting the connections or the number of turns in the tertiary winding, the impedance can be controlled to ensure a desired level of fault current flowing through the transformer during a fault.

Applications and Types:

  1. Solidly Grounded Systems:
    • In power systems with solid grounding, the earthing transformer helps limit the fault current magnitude and provides a controlled grounding path. This is crucial for minimizing equipment damage and ensuring the safety of personnel.
  2. Resistance Grounding:
    • In systems with resistance grounding, the earthing transformer may be used in conjunction with grounding resistors to limit the fault current and control the system’s grounding characteristics. This is common in industrial settings.
  3. Reactance Grounding:
    • Some power systems use reactance grounding, where the earthing transformer provides the necessary reactance to limit fault currents. This approach is often used in systems where a higher level of system stability is required.
  4. Low-, Medium-, and High-Voltage Systems:
    • Earthing transformers are employed in a wide range of voltage levels, from low-voltage systems to high-voltage transmission networks. The design and configuration of the earthing transformer vary based on the specific application and system requirements.

Benefits of Earthing Transformers:

  1. Safety:
    • The primary benefit of an earthing transformer is enhanced safety. It helps prevent high voltages during fault conditions, reducing the risk of electrical shock and protecting both personnel and equipment.
  2. Equipment Protection:
    • By providing a controlled grounding path, an earthing transformer protects sensitive equipment from damage that can result from excessive fault currents.
  3. System Stability:
    • Proper grounding, facilitated by the earthing transformer, contributes to the stability of the power system. It helps maintain voltage levels and prevents cascading failures during fault conditions.
  4. Compliance with Standards:
    • Earthing transformers are designed to comply with relevant electrical standards and codes, ensuring that power systems meet safety and performance requirements.
  5. Fault Location and Detection:
    • The presence of an earthing transformer aids in locating faults within the power system. Monitoring fault currents and voltages can help detect and isolate faults for timely intervention.


In conclusion, the use of an earthing transformer is fundamental to the safe and reliable operation of power distribution systems. By providing a controlled path for fault currents to dissipate into the ground, the earthing transformer enhances safety, protects equipment, and contributes to the stability of power systems across various voltage levels and applications.

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