In a cascade system with large air-gap circuit-breakers, how many cascade steps should there be at most?

In a cascade system featuring large air-gap circuit breakers, the recommended maximum number of cascade steps is two. This is primarily due to several considerations related to system stability, reliability, and operational effectiveness.

Having only two cascade steps helps in minimizing the total fault current that the system has to manage, thereby reducing the stress on circuit breakers and enhancing their lifespan. In a cascade system, if too many steps are introduced, it may result in complexity in coordination, which can lead to difficulties in troubleshooting and potential failure in adequately isolating fault conditions.

Moreover, a maximum of two steps allows for better control of cascading failures. If a fault occurs, the first circuit breaker can trip, and if it fails to clear the fault, the second can act as a backup. Beyond two steps, the likelihood of unintended tripping due to various operational conditions increases, which could compromise the system's overall effectiveness and safety.

Therefore, the choice of two cascade steps in such systems aligns with the best practices in electrical engineering to promote reliability and maintain a manageable level of complexity within the network.