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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Earth switch is connected between
Line and earth
Two lines
Line and neutral
circuit breaker and isolators
Line and earth
An earth switch is a mechanical switching device used to connect a circuit to the ground for safety purposes. It is connected between a phase conductor (Line) and the ground (Earth) to discharge any residual charges and ensure the line is at zero potential before maintenance.
An earth switch is a mechanical switching device used to connect a circuit to the ground for safety purposes. It is connected between a phase conductor (Line) and the ground (Earth) to discharge any residual charges and ensure the line is at zero potential before maintenance.
Vearth=0 V — The target potential of the line after grounding
Idischarge=Rswitch+RgroundVresidual — The current flow during discharge
The primary mechanism involves creating a metallic, low-impedance path to earth. Once the main line is isolated from the power source using an isolator, the earth switch is closed. This prevents accidental energization and discharges trapped capacitive energy, ensuring the safety of personnel working on the equipment.
Used during maintenance to ensure electrical safety.
Must have a high short-circuit current carrying capacity for a specified duration.
Interlocked with the main isolator to prevent operation while the line is live.
Does not interrupt load current; it only closes when the circuit is already de-energized.
Provides safe working environment for personnel.
Discharges stored electrical energy (capacitance) from lines.
Protects equipment from accidental re-energization.
Requires additional interlock mechanisms.
Adds complexity and space requirements in substation bay design.
High-voltage transmission line maintenance.
Transformer and busbar section maintenance.
Gas Insulated Substations (GIS) and Air Insulated Substations (AIS).
An earth switch must be rated for the full fault current of the system at that point.
Option D is incorrect because circuit breakers and isolators are primary switching components, whereas the earth switch is an auxiliary safety device.
A is correct — An earth switch provides a low-resistance path between the electrical line and the earth to ensure zero potential for maintenance.
Always remember that an Earth Switch is an auxiliary device. It should never be closed while the circuit is live, which is why mechanical interlocks are mandatory in all substation designs.