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A charging current is discharge through_____ after the line is disconnected from the main supply?
Earth switch
Circuit breaker
Isolator
Relay
Earth switch
An earth switch is a mechanical switching device used to ground a disconnected transmission line or equipment. When a high-voltage line is disconnected from the supply, the remaining charge due to line capacitance must be safely discharged to the ground to ensure safety for maintenance personnel.
An earth switch is a mechanical switching device used to ground a disconnected transmission line or equipment. When a high-voltage line is disconnected from the supply, the remaining charge due to line capacitance must be safely discharged to the ground to ensure safety for maintenance personnel.
Q=CтЛЕV тАФ The charge Q stored in a transmission line with capacitance C at voltage V
W=21тАЛCV2 тАФ The energy stored in the electric field of the line
Transmission lines behave as capacitors, storing a significant amount of electrical energy even after being disconnected from the supply. By operating the earth switch, the conductors are connected to the ground potential. This provides a low-impedance path for the trapped charge to dissipate, preventing the buildup of dangerous induced voltages or accidental electrocution during maintenance.
Transmission lines have significant shunt capacitance to ground.
Trapped charges cause dangerous voltages, known as 'capacitive residual voltage'.
Earth switches are interlocked with isolators for safety protocol.
Discharging is mandatory before personnel approach the equipment for maintenance.
Ensures safety of maintenance crew by eliminating stored energy.
Prevents accidental re-energization effects.
Provides a zero-potential reference for testing.
Requires high mechanical reliability.
Can be damaged if closed on a live line (requires interlocks).
HV and EHV Substation maintenance.
Transmission line end-points.
Transformer bushings and cable terminations.
The circuit breaker is designed to interrupt fault currents but does not provide visual isolation or grounding.
An isolator is a mechanical device used for separating equipment from the live source but lacks the capability to dissipate charge to ground.
A is correct тАФ An earth switch is specifically designed to ground a disconnected conductor, allowing the capacitive charging current to discharge safely to the earth.
Always remember that isolators provide physical separation, while earth switches provide a ground potential path. Never confuse their operational sequence: open the circuit breaker, then the isolator, then close the earth switch.