Adjustable-Blade Hydroturbine

a reaction hydroturbine having a single adjustment in which the power is varied by rotating the runner blades. The flow is twisted before entering the runner by means of a spiral intake or guide vanes, the stator. This type of turbine is shut down either by means of specially shaped runner blades or by means of an auxiliary shutoff member, such as a cylindrical gate. Adjustable-blade turbines may have axial or diagonal flow. Outside the USSR they are sometimes called Toman turbines. Their use is advisable in hydroelectric power plants where abrasive wear is high, since they have fewer parts subject to wear than the Kaplan hydroturbine. They are not widely used.

a double-control reaction hydroturbine in which power is regulated by simultaneous rotation of the inlet guide vanes and runner blades. The design was patented by the Austrian engineer V. Kaplan in 1920.

In an adjustable-blade hydroturbine the runner blades may be perpendicular to the axis of the turbine (axial turbine), or they may form an acute angle with the axis (diagonal turbine). The rotatable blades of the runner have pivots that are mounted in the apertures of the runner hub. Inside the hub is a servomotor that rotates the runner blades. (The term “Kaplan turbine” is usually used outside the USSR; in the USSR such turbines are called adjustable-blade hydroturbines.)

A distinction is made between vertical and horizontal adjustable-blade hydroturbines. Vertical turbines are usually used in hydroelectric power plants for heads of 15-60 m. Horizontal turbines are used in flow-through units in hydroelectric power plants for heads of 15–30 m. In vertical adjustable-blade hydroturbines the stream of water from the intake tube is twisted in the scroll casing and strikes the stator, which imparts axial symmetry to the flow. From there it passes into the radial guide vanes of the turbine. The direction of flow is changed from radial to axial by means of a deflector before the runner.

In horizontal adjustable-blade turbines of the flow-through capsule type the scroll casing is replaced by diagonal inlet guide vanes.

The suction pipeline of a vertical adjustable-blade turbine is curved; that of a horizontal turbine is straight.

For given values of the power output and head of a hydroelectric power plant, an adjustable-blade hydroturbine has unambiguously definable values for the angles of rotation of the guide vanes and runner blades that provide maximum efficiency under those operating conditions. A hydroturbine combiner is mounted in the governor of an adjustable-blade turbine. Adjustable-blade turbines have flatter performance characteristics than mixed-flow turbines operating at the same head; the adjustable-blade design also has higher values for power and speed of rotation (for the same head and runner diameter). However, the structural strength and anticavitation properties of adjustable-blade turbines are inferior to those of the mixed-flow turbines. Therefore, adjustable-blade turbines cannot be used efficiently in hydroelectric power plants with heads greater than 60-70 m. The power ratings of adjustable-blade turbines can be as high as 200 megawatts.

As of 1974, the largest adjustable-blade turbines were operating in the USSR, in the Saratov Hydroelectric Power Plant, which had 21 vertical turbines with a runner diameter of 10.3 m and two horizontal turbines with a diameter of 7.5 m.