KAPLAN HYDRO TURBINE

1. Structure and Working Principle of the Kaplan Runner

Kaplan turbines belong to reaction turbines and mainly consist of a runner, a runner chamber, a wicket gate assembly, and a spiral casing.

The runner blades of an Kaplan turbine are similar to an fan, and below Figure shows a four-blade runner.

The runner is installed in the runner chamber, and the water flow enters and leaves the runner axially, as shown in below Figure.

The blade section of an Kaplan water turbine is airfoil-shaped, thick at the root and thin at the edges, with water flowing axially through the runner blades, and its working principle is similar to that of a wind turbine. below Figure shows the force diagram of the blade, in which the force on the blade is simply analyzed using a section of one blade. The axis of the runner is perpendicular to the ground, and the arrow lines in the figure are vector lines that indicate both magnitude and direction.

First, look at the left diagram. Point m is a water particle near the blade. For clarity, it is moved to the upper left. The velocity of the water particle is V. Due to the circulation as water enters the runner zone, its direction in the diagram is not vertically downward but inclined to the left. The blade rotates around the shaft, and the tangential velocity of its cross-section is U. Relative to the blade, water particle m moves to the right at a velocity of -U. Therefore, the relative velocity of water particle m with respect to the blade is W, meaning the direction of the water flow acting on the blade is W. Next, examine the right diagram. The blade is subjected to water flow in the direction of W. Since W forms an angle of attack α with the airfoil chord c, a lift force L perpendicular to W is generated, along with a drag force D (in the same direction as W). The resultant force R of these two forces is the force acting on the blade. The horizontal component of R is F, which is the force driving the blade to rotate.

   

• Kaplan turbine with fixed blades

The runner blades of an axial-flow fixed-blade turbine are fixed to the hub, featuring a simple structure and low cost. However, its output can only be controlled by adjusting the wicket gates, resulting in a significant drop in turbine efficiency when there are considerable variations in water head and load. Axial-flow fixed-blade turbines are generally applied under a water head of less than 25 meters with a power output not exceeding 50,000 kilowatts.

• Kaplan turbine with adjustable blades

The runner blades of an axial-flow Kaplan turbine can rotate correspondingly in accordance with changes in water head and load, adjusting the angle of attack α of the blades. This enables the turbine to maintain excellent operating performance even when the water head and load vary considerably. The mechanism controlling blade rotation is located within the hub, mainly consisting of a hydraulic cylinder that drives the blades. The piston inside the cylinder actuates the blade rotation through a piston rod, connecting rods, blade arms, and other components.

Below Figure  is a schematic diagram of the runner blade rotation of a Kaplan turbine. The left figure shows the blade in the closed position; the middle one is the calculation position, which is the design position during normal operation; the right one is the fully open position.

3. the structure of KAPLAN TURBINE

An Kaplan turbine mainly consists of three major components. The rotating parts include the runner and the main shaft. The fixed parts mainly include the spiral casing, stay ring, bottom ring, head cover, upper bracket, cone, runner chamber and draft tube. The wicket gate assembly includes movable guide vanes, guide vane levers, guide vane links, control ring and servomotor. There are also guide bearings, shaft seals and other components.

Below Figure  is a sectional view of the stay ring, bottom ring, head cover, upper bracket, cone and draft tube liner, showing the basic structure. The stay ring serves as the foundation of the entire water turbine and is the most critical component.

The head cover is installed on the upper part of the stay ring, while the bottom ring and the runner chamber are fitted beneath the stay ring. The spiral casing is mounted on the outer circumference of the stay ring . The draft tube is installed below the runner chamber. The head cover is fitted at the inner upper part of the stay ring, the support cover is installed inside the head cover, and the cone (guide cone) is mounted at the inner lower part of the support cover. Below Figure  shows a schematic diagram of the above components assembled together.

4. Operating conditions of the Kaplan turbine

Below Figure is a schematic diagram of the water flow direction of an axial-flow water turbine, with the blue arrow lines indicating the water flow direction.