What is the percentage at which a steam turbine should trip or shut down when normal operating speed is exceeded?

The percentage at which a steam turbine should trip or shut down when normal operating speed is exceeded is typically set between 10-15%. This range serves as a critical safety measure to protect the turbine and its components from potential damage caused by overspeed conditions. When a turbine exceeds its rated speed, it can lead to excessive centrifugal forces that may compromise structural integrity, causing catastrophic failures.

Operating speed limits are determined during the design and testing phases and are based on the materials used and the intended application of the turbine. By setting the trip limit within this 10-15% range, operators can ensure a proactive approach to safety, allowing for a sufficient buffer before the turbine reaches a dangerously high speed. This helps prevent mechanical failure and enhances the longevity and reliability of the turbine system.

The other ranges provided would generally be considered too lenient from a safety perspective, as they would allow the turbine to operate at speeds that could significantly risk damage or failure before initiating a shutdown. Thus, the 10-15% range is an industry-standard practice for the safe operation of steam turbines.