Subject : Power Plant Engineering

Topic: Chap 4- Combined Cycles

Difficulty: Medium

5M

A Kaplan turbine has adjustments in both guide vanes and runner vanes. Generally, double regulators are provided in a Kaplan turbine. The governor regulates the guide blade opening as well as the runner vane angles simultaneously. The adjustment of guide vanes is similar to that of a Francis turbine. The runner vanes are regulated by a separate Servomotor. The control valves for both the runner and guide vanes are interconnected to ensure a define runner vane angle for the given vane opening. The runner vane angles may be adjusted while the turbine is in motion. The piston rod of the servomotor (of the runner vanes) pass through the hollow turbine shaft as shown in figure.

The movement of the piston is transmitted to the runner of the piston is transmitted to the runner vane by a small crank connected to cross head. The servomotor acts as the coupling between the turbines shaft and the generator shaft. Oil from the governor is admitted to the upper or lower side of the servomotor piston through pipes.

This will reduce or increase the blade angle. The governor actuates simultaneously both the guide vane and the runner vane. Thus for all loads, the turbine is able to maintain high efficiency.