2nd Class Power Engineering (2B1) Practice Exam

In a bypass governing turbine, throttle valves play a crucial role in controlling the flow of steam to the turbine's blading. The correct answer indicates that these valves are positioned both at the inlet and downstream of the blading. This setup allows for more precise control over steam flow as it can adjust not only the initial steam conditions entering the turbine but also the flow after the steam has passed through the initial stages of the turbine blading.

By having throttle valves at both locations, the governing system can effectively manage the turbine's speed and power output under varying load conditions. This design allows for a more responsive operation when adjustments are necessary, leading to enhanced efficiency and stability in turbine performance.

In contrast, the other choices suggest more limited placements of the throttle valves. For example, having them only at the steam chest or just at the inlet would not provide the necessary control over the subsequent stages of steam expansion, potentially leading to inefficiencies. Similarly, placing them exclusively downstream of the first stage would ignore the critical need for initial flow regulation at the very start of the steam path. Therefore, the comprehensive placement of throttle valves at both the inlet and downstream of the blading is essential for the optimal functioning of a bypass governing turbine.