Question 384Steam Plants - 1st Asst/Chief

The correct answer is C. Explanation: The main propulsion turbine overspeed relay is designed to automatically close the throttle valve in the event of excessive turbine speed. This is typically achieved through a mechanical-hydraulic system, where excessive turbine speed causes an increase in oil pressure that opens a spring-loaded relay valve, which in turn tends to close the steam control valve and reduce the turbine speed. This is the mechanism described in option C, making it the correct answer. The other options are incorrect because they do not accurately describe the functioning of the main propulsion turbine overspeed relay. Option A describes a centrifugal force-based mechanism, which is not the typical design for this type of system. Option B involves a temperature-based mechanism, which is not the primary method for turbine overspeed protection. Option D describes a weight-based mechanism, which is also not the standard design for a turbine overspeed relay.