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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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Which of the following is closed after line is disconnected from the supply?
Isolator
Earth switch
Circuit breaker
Relay
Earth switch
An earth switch is a mechanical switching device used to connect a circuit to the ground. It is operated only after the circuit is disconnected from the high-voltage supply by an isolator to ensure personnel safety during maintenance.
An earth switch is a mechanical switching device used to connect a circuit to the ground. It is operated only after the circuit is disconnected from the high-voltage supply by an isolator to ensure personnel safety during maintenance.
Vearth=0 V — Ensures the conductor is at zero potential for safety.
Itrap=C⋅dtdV — Represents the discharge of trapped capacitive charge through the earth switch.
The switching sequence in a substation follows a strict protocol: 1. The Circuit Breaker (CB) opens to interrupt the load current. 2. The Isolator opens to provide a visible physical gap. 3. The Earth switch is closed to drain any trapped capacitive charge and bring the conductor to zero potential. This sequence prevents accidental short-circuiting of the live line.
Interlocking mechanisms prevent closing the earth switch if the isolator is closed.
Essential for discharging residual charges in long transmission lines.
Provides a visible and reliable ground for maintenance personnel.
Ensures maximum safety during maintenance
Discharges trapped static energy
Increases complexity of the switching bay
Requires mechanical interlocks
High Voltage Substations
Transmission Line Maintenance
Transformer Testing
Operating rule: Always isolate first, then earth.
Circuit breaker is for load interruption; Isolator is for no-load disconnection; Earth switch is for safety grounding.
B is correct — The earth switch is closed after the line is disconnected to ground the conductor and ensure safety for operators.
Remember the 'Live-to-Dead' sequence: Always open the Circuit Breaker first, then the Isolator, and only then close the Earth Switch to avoid hazardous arcing.