High voltage circuit breaker performance

(2) Rated current: This refers to the maximum continuous current that the circuit breaker can carry without overheating or sustaining damage. It indicates the device’s capacity to handle long-term load conditions in an electrical system.

(3) Rated breaking current: This is the maximum current the circuit breaker can safely interrupt under its rated voltage. It is expressed in kiloamperes, representing the effective value of the short-circuit current's symmetrical component. When the circuit breaker operates below its rated voltage, its breaking capacity may increase. However, due to mechanical limitations in the arc quenching chamber, there is a maximum limit called the ultimate breaking current.

(4) Dynamic steady current: Also known as the "symmetrical breaking current," this parameter measures the circuit breaker's ability to withstand the electrodynamic forces caused by short-circuit currents. It is the peak current that the breaker can endure while in the closed position, without being damaged by the electromagnetic forces involved.

(5) Closing current: This parameter defines the circuit breaker's ability to close under fault conditions. When closing into a short circuit, the breaker may have to handle large currents, which can cause contact welding if not properly managed. The rated closing current is the maximum peak current the breaker can reliably close without damage. It is generally equal to 2.55 times the rated breaking current.

(6) Thermal stability current: This refers to the maximum current the circuit breaker can withstand for a specified time without thermal damage. It reflects the device's ability to handle the heat generated by short-circuit currents. The rated thermal stability current is typically equal to the rated breaking current and is allowed for 2 seconds, though longer durations (such as 4 seconds) may be recommended for higher capacities.

(7) Closing and opening time: These are performance parameters that define how quickly the circuit breaker can respond to commands. The closing time is the duration from the start of the closing mechanism to when the main contacts make contact. The opening time includes the inherent opening time (from the release of the trip coil to contact separation) and the arc extinction time (from contact separation to arc extinction). Together, they form the full opening time.

(8) Operating cycle: This describes the sequence of operations a circuit breaker can perform within a specific time frame. Since many faults in overhead lines are temporary, the circuit breaker must be able to open and reclose quickly to restore power efficiently. An operating cycle involves multiple opening and closing actions at set intervals, ensuring reliable operation and system stability.