What happens first when a cascade system starts?

When a cascade system starts, the first action involves the high-stage compressor. This is because the cascade system typically operates to create a temperature gradient that allows the low stage to effectively utilize cooling from the high stage. Starting the high-stage compressor first is crucial for establishing the necessary pressure differential and flow conditions that enable the low-stage compressor to function optimally afterward.

This sequence allows for proper cooling and thermal management, ensuring that the system can effectively transfer heat from one stage to another. If the low-stage compressor were to start first, it might not have the required conditions established by the high stage, leading to inefficiencies or insufficient cooling performance. Other options do not reflect the operational protocol of a cascade system, as they either misrepresent the process or suggest an ineffective initial start-up condition.