Kaplan turbine
The Kaplan turbine is a propeller-type water turbine which has adjustable blades. It was developed in 1913 by the Austrian professor Viktor Kaplan, who combined automatically - adjusted propeller blades with automatically-adjusted wicket gates to achieve efficiency over a wide range of flow and water level. The Kaplan turbine was an evolution of the Francis turbine. Its invention allowed efficient power production in low- head applications that was not possible with Francis turbines.
Kaplan turbines are now widely used throughout the world in high-flow, low-head power production. The Kaplan turbine is an inward flow reaction turbine, which means that the working fluid changes pressure as it moves through the turbine and gives up its energy. The design combines radial and axial features.
The inlet is a scroll-shaped tube that wraps around the turbine's wicket gate. Water is directed tangentially through the wicket gate and spirals on to a propeller shaped runner, causing it to The outlet is a specially shaped draft tube that helps decelerate the water and recover kinetic energy.
The turbine does not need to be at the lowest point of water flow as long as the draft tube remains full SCEofwater. A higher the draft tube. The resulting pressure drop may lead to cavitation. Variable geometry of the wicket gate and turbine blades allow efficient operation f or a range of flow conditions. Kaplan turbine efficie ncies are typically over 90%, but may be lower i n very low head applications. Current areas of research include CFD driven efficiency improvements and new de signs that raise survival rates of fish passin g through.
Applications
Kaplan turbines are widely used throughout the world for electrical power prod uction. They cover the lowest head hydro sites and are especially suited for high flow conditions. Inexpensive micro turbines are manufactured for individual power production with as little as two feet of head.Kaplan turbine is low head turbine. Large Kaplan turbines are individually designed for each site to operate at th e highest possible efficiency, typically over 90%. They are very expensive to design, manufacture and install, but operate for decades.
Problem: A Kaplan turbine works under a head of 26.5 m, the flow rate of water being 1 70 m3/s. The overall efficiency is 90%. Determine the po wer and specific speed. The turbine speed is 150 rpm.
Solution:
Power developed = 0.9 � 170 � 10 3 � 9.81 � 26.5
W = 39.77 � 106 W or 39.77 MW
Dimensionless specific speed
Problem : A Kaplan turbine plant d evelops 3000 kW under a head of 10 m. While runni ng at 62.5 rpm. The discharge is 350 m3/s. The tip diameter of the runner is 7.5 m and the hub to tip ratio is 0.43. Calculate the specific speed, turbine efficiency, the speed ratio and flow ratio.
Speed ratio is based on tip speed. Hub diameter = 0.43 � 7.5 = 3.225 m Turbine efficiency = P / ? Q H g
Variations
The Kaplan turbine is the most widely used of the propeller-type turbines, but several other variations
exist:
Propeller Turbines
Propeller Turbines have non-adjustable propeller vanes. They are used in where the range ofhead is not large. Commercial products exist for producing several hundred watts from only a few feet of head. Larger propeller turbines produce more than 100 MW.
Bulb or Tubular turbines
Bulb or Tubular turbines are designed into the water delivery tube. A large bulb is centered inthe water pipe which holds the generator, wicket gate and runner. Tubular turbines are a fully axial design, whereas Kaplan turbines have a radial wicket gate.
Pit turbines
Pit turbines are bulb turbines with a gear box. This allows for a smaller generator and bulb. Straflo turbines are axial turbines with the generator outside of the water channel, con nected tothe periphery of the runner.
S- turbines
S- turbines eliminate the need for a bulb housing by placing the generator outside of the waterchannel. This is accomplished with a jog in the water channel and a shaft connecting the runner and generator.
Tyson turbines
Tyson turbines are a fixed propeller turbine designed to be immersed in a fast flowing river,either permanently anchored in the river bed, or attached to a boat or barge.
