Circuit breaker protection encompasses several key functions, including failure protection, automatic reclosing, charging protection, dead zone protection, three-phase inconsistency protection, and instantaneous follow-up. This article focuses specifically on circuit breaker protection in 3/2 wiring configurations, which are commonly used in high-voltage substations for enhanced reliability and system stability.
In traditional double busbar or single busbar wiring schemes, when a line protection system issues a trip command, only the local circuit breaker at the line end is tripped. In such cases, the automatic reclosing function typically operates on that single circuit breaker, aligning with the protection configuration. However, in 3/2 wiring mode, multiple protection functions—such as failure protection, automatic reclosing, three-phase inconsistency, dead zone protection, and charging protection—are integrated into a single device known as the circuit breaker protection unit.
Breaker failure protection is a critical component designed to address situations where a circuit breaker fails to operate after a relay protection signal is issued. If a fault occurs and the circuit breaker does not trip, the failure protection system detects this condition by analyzing the protection action information and the current status of the circuit breaker. It then triggers the tripping of other related breakers within the same substation, minimizing the impact of the fault and preventing potential damage to critical equipment like generators and transformers.
In 3/2 wiring, if a short circuit occurs on a line, both the adjacent and middle breakers are tripped. For example, if a fault happens on Line 2, both breakers (5021 and 5022) are tripped. If one of them, say 5021, fails to open, the failure protection mechanism will activate, causing all breakers on the 500kV I bus (e.g., 5011 and 5031) to trip, effectively isolating the faulty section. Similarly, if a fault occurs on the 500kV I bus itself, all connected breakers are tripped, and if a specific breaker fails, remote trip commands are sent to the opposite side of the line to ensure complete isolation.
Automatic reclosing is another essential feature in 3/2 wiring. When a fault is cleared, the system attempts to re-energize the line. The sequence of reclosing is crucial to avoid unnecessary stress on the system. Typically, the front-end breaker is reclosed first, followed by the middle breaker, ensuring that the system remains stable even if a permanent fault exists. The reclosing process can be initiated either through position mismatch or external trip signals, and it offers various modes, such as single-phase, three-phase, or integrated reclosing.
Charging protection is applied during the charging of components like buses or transformers. It uses overcurrent elements to detect faults during the initial charging phase. Once activated, it trips the circuit breaker, initiating failure protection if necessary. Dead zone protection is also vital, as it addresses faults that occur between the circuit breaker and the current transformer, which might otherwise go undetected. This protection is faster than failure protection to minimize damage.
Three-phase inconsistency protection is used to handle situations where a circuit breaker does not fully trip, leading to an unbalanced system. This protection ensures that the system is isolated quickly to prevent harm to equipment and maintain stability. Instantaneous follow-up refers to additional tripping actions that occur after the initial trip, depending on the type of fault detected.
Finally, AC voltage disconnection detection and trip position abnormal alarms help monitor the health of the system, ensuring that any anomalies are promptly addressed. These features collectively contribute to the reliable operation of power systems using 3/2 wiring configurations.
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