In a cascade system with large air-gap circuit-breakers, what is the maximum number of cascade steps allowed?

In a cascade system with large air-gap circuit-breakers, the maximum number of cascade steps allowed is two. This limitation is primarily due to several critical factors, including operational reliability and the management of electrical arcs during the interruption of high currents.

When circuit-breakers operate in series (or cascade), the overall system is designed to maintain effective interrupting capabilities while ensuring safety and minimizing the risk of system failure. If a cascade system were to have more than two steps, it would introduce complexities that could lead to unreliable performance. The interaction between multiple circuit-breakers could create challenges in synchronizing operations, increasing the risk of arcing and damaging the equipment.

Additionally, as the number of cascade steps increases beyond two, the potential for delays in trip signals and the time taken to clear faults could compromise the protection of the electrical system as a whole. Therefore, the design standards and operational practices typically stipulate a maximum of two cascade steps to ensure that the system remains manageable, efficient, and safe.

This design consideration reflects general practices in the electrical engineering field, aiming to maintain a balance between circuit protection and operational efficiency.