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The fault clearing time of a circuit breaker is usually
Few minutes
Few seconds
One seconds
Few cycle of supply voltage
Few cycle of supply voltage
The fault clearing time of a circuit breaker is defined as the interval between the instant the fault current reaches the trip coil and the instant the arc is completely extinguished. For modern high-speed circuit breakers, this duration is typically between 2 to 8 cycles of the supply frequency (e.g., 40-160 ms for a 50 Hz system).
The fault clearing time of a circuit breaker is defined as the interval between the instant the fault current reaches the trip coil and the instant the arc is completely extinguished. For modern high-speed circuit breakers, this duration is typically between 2 to 8 cycles of the supply frequency (e.g., 40-160 ms for a 50 Hz system).
TtotalтАЛ=TrelayтАЛ+TbreakerтАЛ+TarcтАЛ тАФ Total clearing time decomposition
The total fault clearing time is the sum of the relay operating time, the mechanism opening time (breaker contact travel), and the arc extinction time. Efficient grid protection requires minimizing this time to maintain system stability, prevent equipment damage from thermal stress, and limit fault propagation. The arc extinction process is rapid, occurring naturally at the current zero crossing of the supply cycle.
Fault clearing time must be minimized to maintain transient stability of the power system.
A cycle at 50 Hz corresponds to 20 ms, meaning 5 cycles equal 100 ms.
Modern HV circuit breakers are designed for ultra-fast operation to prevent fault escalation.
Prevents structural damage to transformers and conductors.
Maintains generator synchronism during transient faults.
Higher speed breakers require complex arc-quenching media like SF6тАЛ.
High operating speed may increase mechanical stress on components.
Power transmission systems
Substation switchgear protection
Option A (Few minutes) is incorrect as it would lead to catastrophic equipment failure.
Option B (Few seconds) is used for delayed relay coordination, not the clearing time of the breaker itself.
Standard values in Indian grid codes often specify clearing times as T<100 ms for EHV systems.
D is correct тАФ The fault clearing time is designed to be extremely short, typically measured in cycles, to ensure the grid remains stable during transient disturbances.
Always remember that 1 cycle in a 50 Hz system is exactly 20 ms; competitive exams often ask for conversion between cycles and milliseconds.