Sunday, April 24, 2016

Kaplan turbine

Axial Flow Turbine Kaplan Hydro Turbine / Kaplan Water Turbine for Water Head 2m - 70m Hydropower Project

The Kaplan (axial-flow) turbine for low head from 2m to 70m. This type of turbine is mostly suitable for hydropower stations with low water head and big flow.
lts feature is that the water flow passes through the runner axially. The axial-flow turbine can be classified into two forms according to the runner construction: one is fixed blades (Propeller) for small variation of head and power, the other is movable blades (Kaplan) for large variation of head and power.
The kaplan turbine with vertical shaft arrangement , with three types as open flume, pressure flume, and seal off (concrete spiral case).
Generally, Kaplan turbine is composed of distributor, guide vane, runner, draft tube etc. 

Main Structure of Kaplan Water Turbine

This hydraulic turbine is axial flow turbine with a vertical shaft. And its spiral case is made of metal or concrete.
The water flows through the channeling pipe, and then into the spiral case, which ensure that the water enter the turbine circumferentially and symmetrically, forming certain circumfluence quantum.
The water flows through the stay ring into the distributor, whose guide vanes can regulate the turbine discharge and the flow direction and thus make the water flow into the runner circumferentially and symmetrically. Consequently, the runner revolves and converts hydraulic energy into mechanical energy and then drives the rotor of the generator revolve by the force of the main shaft of the hydraulic turbine, thus converting the mechanical energy into electrical energy. The water, which has gotten out of the runner, flows to the downstream of river through the draft tube.
Because of the restoration of the draft tube, the energy of the water flowing out of the outlet, is partly reused, thus loss is reduced and efficiency is improved.

Main structures of the hydraulic turbine are described in the following.

Draft tube assembly

It includes draft tube straight cone and metal bend tube. Because of the restoration of the draft tube, the energy of the water flowing out of the outlet is partly reused, thus loss is reduced and efficiency is improved.

Rotating parts assembly

Rotating department is mainly composed of a runner, main shaft, radial turbine bearing and seals of main shaft. Runner with the blades of stainless steel of 06Cr13Ni4Mo assembled and welded. After having been mould into shape, all the  blades must be processed to the required degree of roughness and precision.
To ensure the stable operation of runner, a test for still balance is performed in the manufactory. Shared by the hydraulic turbine and hydro generator, the vertical main shaft, connects the runner with pins. The main shaft seal is of the type with soft graphite packing
The radial turbine bearing is water-lubricating elastic metal-plastics bearing,clean water,0.15~0.2Mpa.
kaplan turbine runner

Distributor assembly

Distributor consists of head cover, bottom ring, guide vanes, the regulating ring, transmission departments and any other parts. They are divided into two parts. One part includes guide vanes and supporters of three parts of shaft sleeves, namely bottom ring and head cover. The other part includes guide vane arm, conjunction rod, regulating ring, and pull-push rod of transmission departments.

a. Guide vane and its supporting parts.

There are  guide vanes spreading in a circle equally.

Guide vane is standard blade-shaped with positive curvature This enables the guide vanes to have the virtues of little hydraulic loss and high degree of strength as guide vanes opening varies. The Guide vanes are made of 20SiMn.On the bottom of guide vane, shaft sleeves are fixed with the bottom ring and they are self-lubricating bearings of thin plates of Fluon. In the head cover, shaft sleeves are fixed with the bottom ring and they are self-lubricating bearings of thin plates of Fluon.
Guide vanes

b. Transmission department.

Control ring is welded with steel plates, supported by head cover. On the joint surface are anti-grinding plates of nylon, which are used for guide in direction. There is pressing plate so that control ring wont go up. On the top, control ring are connected with two connecting rods. Below, there are 24 holes to pins, spreading in a circle equally. Control ring is connected with guide vanes through pins, connecting plates and guide vane arms.

The shear pins between the guide vane arms and connecting plates are the weakest part in the transmission department of guide vane. If guide vanes close with great difficulty, the shear pins are immediately sheared to protect other parts. Consequently the signaling equipment is sheared, and signal is sent.

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