Question 398Steam Plants - 1st Asst/Chief

A) centrifugal force is the correct answer. The over speed tripping device installed on an auxiliary turbine is automatically actuated by centrifugal force. As the turbine's rotational speed increases beyond a safe limit, the resulting centrifugal force acts on a mechanism within the device, causing it to trip and shut down the turbine to prevent damage. The other options are incorrect because: B) Pneumatic force is not the primary mechanism for over speed tripping. C) High back pressure may be a consequence of over speed, but does not directly actuate the tripping device. D) Hydraulic pressure is not the main force that triggers the over speed tripping mechanism.