construction and working of Kaplan turbine
A Kaplan turbine is hydraulically similar to a propeller turbine except for its variable-pitch characteristies. Further, the hub is large to Accommodate the mechanism for blade-angle changes. In regulating the blades is located either in the hub or in hub cone. The normal range of specific speed, Ns, of the Kaplan turbine is 260 to 900. The range of Ns from 260 to 450 is the overlap region with the Francis turbine. The characteristic feature of a Kaplan turbine is the presence of adjustable propeller blades. A Kaplan turbine having adjustable blades and adjustable guide vanes are fixed and the blades are adjustable, such turbines are to be described as single-regulated and this kind of turbine is commonly termed semi-Kaplan to distinguish them from the double regulated turbines. most designs, the servomotor Axial flow turbines with fixed runner blades are called propeller turbines.
main five components of kaplan turbine
1. Scroll Casing and Stay Vanes:
Scroll casings, in general, are similar to those used in a Francis turbine. For lower heads, 1.e., up to 30 m head, concrete scroll cases are the general choice. The semi spiral type concrete casings are highly preferred. For higher head (30 to 60 m), where pressure heads are too high for concrete, steel plates are used in forming the scroll case. The cross section is normally circular. Stay rings with stay vanes anchored to concrete are provided in the scroll cąse. These stay vanes are generally of steel plates with infilling of reinforced concrete and conduct the water to guide vanes. They also act as structural members.
2. Guide Vanes:
Guide vane cascade that receives the water directed by stay vanes is similar to that of Francis turbine. The control of all the guide vanes is through is regulating ring actuated by a servomotor.
3. Whirl Chamber:
The space between the guide vane outlet and inlet of the runner is known as whirl chamber. In this chamber, the flow changes from radial orientation to axial direction. The lower portion of this chamber that is in the immediate vicinity of the blades is known as chamber.) runner The guide vanes impart a whirl component to the flow coming into the whirl chamber. This flow in the chamber could be approximated to a free vortex with whirl velocity (Vu) being inversely proportional to the radius. The product of Vu and radius r, called circulation, is a constant in the whirl chamber. Thus, we have maximum whirl velocity at the hub and minimum whirl velocity at the cylindrical boundary of the chamber. On the other hand, the rotating blade causes peripheral velocity u to vary directly with the radius, with minimum at the hub and maximum at the tip of the blade. The result is a complex velocity distribution in the blade passages.
Further, to accommodate the comnplex velocity pattern all along the blade, the blades will have a twisted shape with airfoil cross section. Design of the shape of the blades is a very challenging task and the current practice relies heavily on advanced computation methods using CFD (Computational Fluid Dynamics) procedures. The clearance between the outer blade ends and the runner chamber ring should be as small as possible for all possible blade angles of runner. Generally, the gap is about 0.1% of the D1. possibility in the region of the gap, the runner chamber is made of cast/welded stainless chromium-nickel steel. The ratio of hub diameter to blade diameter varies in the range 0.35 to 0.65 with higher values at lower specific speed. runner diameter Cavitation being.
4.Propeller-Shaped Adjustable Blades):
Runner (With The runner is Kaplan turbine is a set of the specially designed blades appearance of a ship's propeller. There is no shroud covering the tips of the blades. The blades are connected to the drive shaft at the hub as shown in figure 1.10. The hub itself is a small bulge in the shaft and has blades attached to it. In a Kaplan turbine, the pitch of the blades are adjustable and link mechanism is housed inside the hub. In some models, servomotors are also housed in the hub. In propeller turbines, the blades are fixed rigidly to the hub. that give.
A nose cone projects from the hub below the fixture location of the blades to the hub. In Kaplan turbine, the hollow of the nose cone and Ke bub is filled with oil under pressure to provide lubrication to moving parts of control mechanism packed in that portion. The outside of the hub has a spherical bulge to keep small clearance between the blades at all angles. The number of blades varies from 3 to 8 and the blades are made of structural steel, stainless steel. The hub is made of structural steel like carbon steel/high strength micro alloy/heat stainless steel. Generally, four blades are used for heads up to 30 m and for every additional head slab of 10 m, an additional blade is needed. Very rarely eight, blades are used. For heads less than about 15 m, sometimes three blades are used.
5. Draft Tube:
A draft tube is an essential, integral part of a reaction turbine and plays a significant part in the installation of the turbine unit relative to the tail water level. Kaplan turbines are generally associated with low heads and high discharges and the draft tube plays a very substantial role in the operation of the unit. In a low-head, high- discharge unit, the largest distribution of head loss is from the draft tube. Thus, the height and geometry of the draft-tube has considerable influence on the efficiency and power output of a Kaplan turbine. Efficient elbow-type draft-tubes are of common choice.
Cavitation in the draft tube is another point of concern in draft tube design. In view of these, dimensions of a draft tube for an axial flow turbine in a project receives extensive attention and study. the design of optimal shape and .
6. Governor Mechanism:
The governor is an essential, integral component of the Kaplan turbine. It does two functions. Control the guide-vane openings and thereby regulates the discharge into the turbine. Regulates through servo control mechanism, the disposition of the blades to the flow and achieves high efficiencies at part loads. The aspect of blade control is absent in fixed-blade propeller turbines.
A Kaplan turbine is hydraulically similar to a propeller turbine except for its variable-pitch characteristies. Further, the hub is large to Accommodate the mechanism for blade-angle changes. In regulating the blades is located either in the hub or in hub cone. The normal range of specific speed, Ns, of the Kaplan turbine is 260 to 900. The range of Ns from 260 to 450 is the overlap region with the Francis turbine. The characteristic feature of a Kaplan turbine is the presence of adjustable propeller blades. A Kaplan turbine having adjustable blades and adjustable guide vanes are fixed and the blades are adjustable, such turbines are to be described as single-regulated and this kind of turbine is commonly termed semi-Kaplan to distinguish them from the double regulated turbines. most designs, the servomotor Axial flow turbines with fixed runner blades are called propeller turbines.
1. Scroll Casing and Stay Vanes:
Scroll casings, in general, are similar to those used in a Francis turbine. For lower heads, 1.e., up to 30 m head, concrete scroll cases are the general choice. The semi spiral type concrete casings are highly preferred. For higher head (30 to 60 m), where pressure heads are too high for concrete, steel plates are used in forming the scroll case. The cross section is normally circular. Stay rings with stay vanes anchored to concrete are provided in the scroll cąse. These stay vanes are generally of steel plates with infilling of reinforced concrete and conduct the water to guide vanes. They also act as structural members.
2. Guide Vanes:
Guide vane cascade that receives the water directed by stay vanes is similar to that of Francis turbine. The control of all the guide vanes is through is regulating ring actuated by a servomotor.
3. Whirl Chamber:
The space between the guide vane outlet and inlet of the runner is known as whirl chamber. In this chamber, the flow changes from radial orientation to axial direction. The lower portion of this chamber that is in the immediate vicinity of the blades is known as chamber.) runner The guide vanes impart a whirl component to the flow coming into the whirl chamber. This flow in the chamber could be approximated to a free vortex with whirl velocity (Vu) being inversely proportional to the radius. The product of Vu and radius r, called circulation, is a constant in the whirl chamber. Thus, we have maximum whirl velocity at the hub and minimum whirl velocity at the cylindrical boundary of the chamber. On the other hand, the rotating blade causes peripheral velocity u to vary directly with the radius, with minimum at the hub and maximum at the tip of the blade. The result is a complex velocity distribution in the blade passages.
Further, to accommodate the comnplex velocity pattern all along the blade, the blades will have a twisted shape with airfoil cross section. Design of the shape of the blades is a very challenging task and the current practice relies heavily on advanced computation methods using CFD (Computational Fluid Dynamics) procedures. The clearance between the outer blade ends and the runner chamber ring should be as small as possible for all possible blade angles of runner. Generally, the gap is about 0.1% of the D1. possibility in the region of the gap, the runner chamber is made of cast/welded stainless chromium-nickel steel. The ratio of hub diameter to blade diameter varies in the range 0.35 to 0.65 with higher values at lower specific speed. runner diameter Cavitation being.
4.Propeller-Shaped Adjustable Blades):
Runner (With The runner is Kaplan turbine is a set of the specially designed blades appearance of a ship's propeller. There is no shroud covering the tips of the blades. The blades are connected to the drive shaft at the hub as shown in figure 1.10. The hub itself is a small bulge in the shaft and has blades attached to it. In a Kaplan turbine, the pitch of the blades are adjustable and link mechanism is housed inside the hub. In some models, servomotors are also housed in the hub. In propeller turbines, the blades are fixed rigidly to the hub. that give.
A nose cone projects from the hub below the fixture location of the blades to the hub. In Kaplan turbine, the hollow of the nose cone and Ke bub is filled with oil under pressure to provide lubrication to moving parts of control mechanism packed in that portion. The outside of the hub has a spherical bulge to keep small clearance between the blades at all angles. The number of blades varies from 3 to 8 and the blades are made of structural steel, stainless steel. The hub is made of structural steel like carbon steel/high strength micro alloy/heat stainless steel. Generally, four blades are used for heads up to 30 m and for every additional head slab of 10 m, an additional blade is needed. Very rarely eight, blades are used. For heads less than about 15 m, sometimes three blades are used.
5. Draft Tube:
A draft tube is an essential, integral part of a reaction turbine and plays a significant part in the installation of the turbine unit relative to the tail water level. Kaplan turbines are generally associated with low heads and high discharges and the draft tube plays a very substantial role in the operation of the unit. In a low-head, high- discharge unit, the largest distribution of head loss is from the draft tube. Thus, the height and geometry of the draft-tube has considerable influence on the efficiency and power output of a Kaplan turbine. Efficient elbow-type draft-tubes are of common choice.
Cavitation in the draft tube is another point of concern in draft tube design. In view of these, dimensions of a draft tube for an axial flow turbine in a project receives extensive attention and study. the design of optimal shape and .
6. Governor Mechanism:
The governor is an essential, integral component of the Kaplan turbine. It does two functions. Control the guide-vane openings and thereby regulates the discharge into the turbine. Regulates through servo control mechanism, the disposition of the blades to the flow and achieves high efficiencies at part loads. The aspect of blade control is absent in fixed-blade propeller turbines.
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