The core mechanism of a primary and secondary deep fusion circuit breaker in achieving current-limiting protection during short-circuit interruption is achieved through the synergistic effect of its unique structural design, electromagnetic tripping characteristics, and current-limiting technology. This allows it to rapidly disconnect the circuit before the short-circuit current reaches its peak value, thus limiting the impact of the short-circuit current on equipment and the power grid.
The structural design of the primary and secondary deep fusion circuit breaker is the foundation of its current-limiting protection. Its primary circuit employs a multi-stage series or parallel conductive structure, while the secondary circuit works in conjunction with the primary circuit through a specially designed contact system. When a short circuit occurs, the current preferentially flows through the primary circuit, which has superior conductivity. The secondary circuit's contact system, through a unique U-shaped structure or point contact design, reverses the current direction between the moving and stationary contacts, generating a repulsive force. This repulsive force reduces the pressure between the contacts and increases the contact resistance, thereby limiting further current increase. Simultaneously, the synergistic effect of the primary and secondary circuits ensures the formation of multiple parallel current paths at the moment of short circuit, reducing the current density of any single path through current shunting, further suppressing the rise of the short-circuit current.
The rapid response of the electromagnetic trip unit is crucial for achieving current-limiting protection in primary and secondary deep fusion circuit breakers. When the short-circuit current exceeds the trip unit's setting, the electromagnetic trip unit generates a sufficiently large suction force within a very short time, driving the operating mechanism to actuate and rapidly separate the contacts. This process is typically completed within milliseconds, much faster than the time it takes for the short-circuit current to reach its peak. For example, some circuit breaker models can complete the tripping action within 10 milliseconds after a short circuit occurs, while the peak of the short-circuit current usually occurs 10 to 20 milliseconds after the short circuit. Therefore, the rapid response of the electromagnetic trip unit effectively avoids the impact of short-circuit current on equipment and the power grid.
The implementation of current-limiting technology also relies on the special arc-extinguishing device of the primary and secondary deep fusion circuit breaker. When the contacts separate, an electric arc is generated between them, and the presence of the arc prolongs the duration of the short-circuit current. To quickly extinguish the arc, primary and secondary deep fusion circuit breakers typically employ magnetic blowout arc extinguishing or vacuum arc extinguishing technology. Magnetic blowout arc extinguishing elongates the arc and blows it into the arc-extinguishing chamber through a magnetic field, causing it to cool and extinguish rapidly. Vacuum arc extinguishing utilizes the high insulation strength of the vacuum environment to extinguish the arc quickly after the contacts separate. These arc-extinguishing technologies can significantly shorten the arc duration, thereby limiting the energy accumulation of short-circuit current.
The synergistic effect of primary and secondary deep fusion circuit breakers is also reflected in their selective protection function. In power distribution systems, selective protection needs to be established between upstream and downstream circuit breakers; that is, when a short circuit occurs in the downstream circuit, the upstream circuit breaker should not trip to avoid escalation of the fault. Primary and secondary deep fusion circuit breakers achieve selective protection by adjusting the tripping characteristics of the primary and secondary circuits, making the tripping time of the upstream circuit breaker slightly longer than that of the downstream circuit breaker. This synergistic effect not only improves the reliability of the system but also optimizes the effect of current-limiting protection.
From the perspective of current-limiting effect, primary and secondary deep fusion circuit breakers can significantly reduce the peak value and energy of short-circuit current. By rapidly disconnecting the circuit and limiting current rise, circuit breakers can control the peak short-circuit current within the equipment's tolerance range, while reducing the thermal shock and mechanical stress on conductive parts such as cables and busbars. This current-limiting effect is crucial for protecting expensive equipment, preventing electrical fires, and maintaining stable power grid operation.
In practical applications, primary and secondary deep fusion circuit breakers are widely used in scenarios requiring high-reliability current-limiting protection, such as data centers, hospitals, and industrial production lines. These scenarios have extremely high requirements for power continuity and equipment safety; any short-circuit fault can lead to serious consequences. Primary and secondary deep fusion circuit breakers provide reliable power protection for these scenarios through their superior current-limiting protection performance.
To ensure the continued effectiveness of the current-limiting protection performance of primary and secondary deep fusion circuit breakers, regular maintenance and optimization are essential. Maintenance includes checking contact wear, cleaning arc-extinguishing devices, and testing the trip unit's operating characteristics. Simultaneously, the circuit breaker's settings and protection parameters should be adjusted in a timely manner according to changes in system load and short-circuit current levels to ensure it is always in optimal operating condition.
