Question 639Steam Plants - Assistant Engineer

The correct answer is B) centrifugal force. The over speed tripping device on an auxiliary turbine is automatically actuated by centrifugal force. As the turbine's rotational speed increases, the centrifugal force acting on the tripping mechanism also increases. Once the speed reaches a pre-determined critical value, the centrifugal force overcomes the spring tension or other restraining forces, causing the tripping mechanism to activate and shut down the turbine to prevent damage from over-speeding. The other options are incorrect because hydraulic pressure (A), high back pressure (C), and pneumatic force (D) are not the primary actuation mechanisms for over speed tripping devices on auxiliary turbines. These mechanisms may be used in other turbine control systems, but not specifically for the over speed tripping function.