High voltage circuit breaker performance

(2) Rated Current: This parameter indicates the circuit breaker's ability to carry continuous current over time. It represents the maximum current that the device can handle without overheating or sustaining damage during long-term operation.

(3) Rated Breaking Current: This refers to the circuit breaker’s capacity to interrupt fault currents safely. Under the rated voltage, it is the highest current that the circuit breaker can reliably disconnect. The unit is expressed in kiloamperes (kA), representing the effective value of the short-circuit current’s symmetrical component. In lower voltage grids, the breaking current can be increased, but due to mechanical limitations in the arc chamber, there is a maximum limit called the limiting breaking current.

(4) Dynamic Stability Current: This parameter measures the circuit breaker’s ability to withstand the electrodynamic forces caused by short-circuit currents. It refers to the peak current that the circuit breaker can endure while in the closed position without being damaged by the electromagnetic forces generated during a short circuit.

(5) Closing Current: This is the parameter that describes the circuit breaker’s ability to close under fault conditions. When closing into a short circuit, the breaker must handle a large inrush current. The closing current is the maximum peak current the circuit breaker can reliably close without damage. The rated closing current is usually equal to the dynamic stability current, which is about 2.55 times the rated breaking current.

(6) Thermal Stability Current and Duration: This parameter reflects the circuit breaker’s ability to withstand the thermal effects of short-circuit currents. The thermal stability current is the effective value of the maximum symmetrical short-circuit current that the circuit breaker can carry for a specified period without damage. According to national standards, the rated thermal stability current is equal to the rated breaking current, with a standard duration of 2 seconds. For longer durations, 4 seconds is commonly recommended.

(7) Closing Time and Opening Time: These parameters define the operational speed of the circuit breaker. The closing time is the interval from when the closing mechanism is activated until the contacts make contact. The opening time includes two parts: the inherent opening time (from the moment the trip coil is energized to when the contacts separate) and the arc extinction time (the time required for the arc to fully extinguish after separation). Together, these make up the full opening time.

(8) Operating Cycle: This refers to the circuit breaker’s ability to perform multiple operations—such as closing and opening—within a short time frame. Since many faults on overhead lines are temporary, the circuit breaker must be capable of quickly restoring service after a fault is cleared. An operating cycle involves a sequence of opening and closing actions within a specific time interval, ensuring reliable and stable system performance.