Short Answer:

An earthing switch is a safety device used in electrical substations and switchgear to connect electrical equipment or conductors directly to the earth (ground). This helps to discharge any residual or trapped voltage after disconnection and ensures a safe environment for maintenance work.

It is operated only when the circuit is already de-energized. Its main purpose is to protect personnel from accidental electric shock by providing a visible and reliable connection between the equipment and earth during maintenance or isolation procedures.

Detailed Explanation:

Earthing switch

In power systems, even after isolating a line or equipment, there may still be induced voltage, capacitive charges, or leakage currents present. This can be dangerous for workers carrying out maintenance. To make the area completely safe, an earthing switch is used to create a direct path for such unwanted electrical charges to flow safely into the ground.

An earthing switch is commonly installed in substations, switchyards, and high-voltage systems. It does not break current like a circuit breaker but only provides a secure earthing connection when the circuit is already switched off.

Function and working

1. Post-isolation grounding:
   • After disconnecting the equipment using a circuit breaker or isolator, the earthing switch is closed.
   • This provides a low-resistance path to earth for any remaining voltage or current.
2. Visible safety assurance:
   • A mechanical indication ensures that the circuit is visibly grounded.
   • This gives workers confidence that the system is safe to handle.
3. Mechanical or motor operation:
   • Can be manually operated using a handle or motor-operated in automated systems.
   • Often includes interlocks to prevent incorrect operation.
4. Installed with isolators:
   • Usually mounted along with isolators in a three-position switch (ON, OFF, EARTH).
   • This allows convenient switching between service, isolation, and earthing.

Types of earthing switches

• High-speed earthing switch:
  Designed to discharge trapped charges or induced voltages in transmission lines quickly.
• Maintenance earthing switch:
  Provides grounding during routine maintenance; operated manually or remotely.
• Disconnector with earthing feature:
  Combines isolator and earthing function in a compact design.

Applications

• Substations (AIS and GIS): To safely ground transformers, lines, or busbars.
• Switchgear panels: For earthing internal components during service.
• Transmission lines: To ground overhead lines during repair.
• Industrial plants: Ensures safety of large motors, generators, and equipment during shutdowns.

Safety importance

• Prevents electric shock or injury during inspection.
• Ensures no accidental energization of equipment under repair.
• Helps comply with safety regulations and maintenance procedures.

Conclusion:

An earthing switch is a vital safety device used to ground electrical equipment after it has been isolated. It helps remove any residual or induced voltages, protecting workers during maintenance. Though it does not interrupt load current, it plays a key role in ensuring safety by providing a visible and secure connection to earth in substations and high-voltage systems.