A METHOD FOR EASY REPLACEMENT OF RUNNER ENVELOPE OF
HYDROTURBINE (KAPLAN TURBINE)
FIELD OF INVENTION
The invention relates to a method for easy replacement of runner envelope (2) of
hydro turbine. More particularly, the invention relates to constructing a novel
cylindrical foundation (12) in the form of well, a modified stayring bottom flange (16)
and a modified make-up piece (8) which facilitates easy replacement of runner
envelope (2) worn out by cavitation and erosion.
BACKGROUND OF THE INVENTION
In Kaplan turbines, the runner rotates in a metallic chamber called runner envelope.
The runner blade tips (1) maintain a fine clearance with runner envelope so as to
avoid leakage loss and maximize the power produced by the runner. Water escapes
through the blade tip clearances leading to a phenomenon called slit cavitation which
eats away material of both runner blades and runner envelope. With high silt content
in the water, erosion accelerates the wear of both blades and envelope. The worn
out blades are replaced by taking out the runner. The worn out runner envelope is
salvaged to some extent by carrying out in-situ weld repair and grinding. In some
projects the wear of runner envelope is so high that it is no longer possible to
salvage by in-situ repair.
In such a case the runner envelope is cut-off by flame cutting and removed from
concrete using pneumatic chisels/drills. Removing the worm out runner envelope is a
very long and tedious process. Installing a new runner envelope is again a
challenging and herculean task. Anchoring the runner envelope with the primary
concrete has to be done by improvised methods. The whole process of removing a
worn-out runner envelope and installing a new one is so long that it leads to huge
generation loss.

It is in the background of these difficulties that the cylindrical foundation (12) with
special features in the stay ring (3) and make-up piece (8) have been developed to
address the burning problem.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method which facilitates a easy
replacement of runner envelope (2) of a hydro turbine worn out by cavitation and
erosion.
Another object of the invention is to propose a method for easy erection of runner
envelope of hydro-turbine which delinks the erection and embedment of runner
envelope (2) from the erection of stay ring (3), spiral casing (4) and concreting of
the turbine pit and generator barrel (27) above stay ring (3).
A further object of the invention is to propose a method for easy erection of runner
envelope (2) of a hydro-turbine which reduces the project execution cycle by
facilitating adoption of site fabricated spiral casing (4), un-machined stay ring (3) and
concreting of turbine pit and generator barrel (27) while the runner envelope (2)
gets fabricated and machined at works.
DETAILED DESCRIPTION OF THE INVENTION
Runner envelopes (2) of the Kaplan turbines get worn-out by slit cavitation due to
water escaping at high velocities through the clearance between blade tip and the
envelope. This problem gets further aggravated if the silt content in the water is
high. Removing a worn-out runner labyrinth and replacing it, is a very tedious
operation leading to long shut down and consequent generation loss. Looking into
the difficulties faced and the huge generation loss during replacement of a worn-out
runner envelope (2), an ingenious well type foundation has been developed with

special features in stay ring (3) and make-up piece (8) for quick and easy
replacement of runner envelope (2).
The novelty of the invention lies creating a well type cylindrical foundation in which
the runner envelope (2) is installed and packed with sand. For replacement of worn-
out runner envelope (2), make-up piece (8) at the bottom of runner envelope (2) is
cut-off and sand around runner envelope is removed. A new runner envelope (2) is
installed in position and again packed with sand. This novel development is now
explained in detail.
The foundation for spiral casing, stay ring and runner envelope as per prior art
consisted of radial concrete piers on which they were supported and tightly held to.
After proper alignment and holding, concrete is poured around runner envelope and
below stay ring and spiral casing. Thus the runner envelope was embedded in
concrete and therefore removing a worn-out envelope from concrete was a tedious
task.
Foundation as per the novel development consists of a well type structure. Top of
the well is used for supporting the stay ring. Inside of the well is used for installing
the runner envelope. There are horizontal radial screws jacks (6) and tie rods (7) for
firmly positioning the runner envelope. Radial piers (17) emanating from the outer
diameter of the well are for supporting the spiral casing segments. Spiral casing
segments are held in concrete as per the prior art practice by pouring concrete
around spiral segments. Sand is packed in the radial gap (18) between outer
diameter (14) of runner envelope (2) and inner diameter (15) of cylindrical well (12).
For this purpose a manhole (9) is provided in the stayring bottom flange(16) for
bigger turbines and ramming holes (13) in the case of smaller turbines. Dry sand
poured through holes (26) in stay ring (16) could form heaps; therefore an ingenious
method of pouring sand water mixture would be used so that sand packs properly
around runner envelope (2). For draining out the water, but allowing the sand to
remain in position a baffle (10) is provided at bottom in the make-up piece (8) with
drain holes (19). The baffles would prevent sand from going out but would allow
water to drain-off. After all the water is drained out, the

drain holes would be plugged (11) and seal welded. Additionally small slits (20)
would be left at the weld of make-up piece (8) to draft tube cone (21) allowing water
below drain holes to be totally removed. These slits would be subsequently welded.
In the case of bigger turbines, erection personnel can get into the well foundation
through manhole (9) in the stay ring bottom flange (16) for proper ramming as
shown in fig.05 i.e. proper compacting of sand around runner envelope. In the case
of small turbines where enough space cannot be provided for erection people to get
in to the well, holes (13) would be provided in the stay ring bottom flange (16)
through which ramming / compacting of sand can be done. For pouring sand water
mixture, a funnel type arrangement (22) would be used into which sand would be
fed in and water jets (23) would force in the sand in the form of sand water mixture.
For removing the worn-out runner envelope (2), first the make-up (8) is cut-off by
flame cutting. Then packed sand (25) at the bottom of runner envelope and around
runner envelope is removed by high pressure water jets (24). After removing the
worn-out envelope, a new one (2) is installed and packed with sand as already
discussed above.
SUMMARY OF THE INVENTION
Runner envelopes (2) of Kaplan turbines operating in areas like the Himalayan region
with high silt content in the river water get eroded and need replacement.
Replacement of runner envelopes as per the conventional design is a very tedious
process and leads to huge generation loss. This invention is about a novel well type
foundation along with a modified stay ring (3), stayring bottom flange (16) and
make-up piece of runner envelope which permit erection of runner envelope (2) after
the erection of stay ring (3), spiral casing (4) and concreting of turbine pit and
generator barrel (27). Unlike conventional runner envelopes (2), concrete is not
poured around runner envelope but a mixture of sand and water.

Water is drained-off from holes in the bottom allowing sand to pack around runner
envelope. Worn-out runner envelope is removed by cutting-off the make-up piece at
bottom of envelope and removing sand packed around runner envelope by high
pressure water jets or other suitable means. A new runner envelope is put in position
and again packed with sand.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1 - Installation of Runner envelope, stay ring and spiral casing as per prior art.
Fig.2 - Isometric view of pier type foundation for stay ring, spiral casing, & runner
envelope as per prior art.
Fig.3 - Installation of Runner envelope, stay ring and spiral casing in the novel well
type foundation.
Fig.3A - Installation of runner envelope, stay ring, spiral casing and runner in the
novel well type foundation where few details have been shown in magnified
scale.
Fig.4 - Isometric view of novel well type foundation for runner envelope & stay ring
and radial pier type foundation for spiral casing.
Fig.5 - Procedure for pouring sand water mixture and packing sand around runner
envelope (in large turbine).
Fig.5A - Procedure for pouring sand water mixture and packing sand around Runner
Envelope (in small turbine).
Fig.6 - Procedure for removing worn out runner envelope.
Fig.7 - Selection thru of a typical power house showing generator barrel.

LIST OF ITEMS
1. Kaplan runner blades
2. Runner envelope
3. Stay ring
4. Spiral casing
5. Radial pier type foundation as per prior art for stay ring, spiral casing and
runner envelope.
6. Screw Jacks
7. Tie rods
8. Make-up piece as per prior art
9. Man hole in stay ring bottom flange of large turbines as per innovative design.
10. Baffle plate in make-up piece as per innovative design.
11. Water drain plug as per innovative design.
12. Well type foundation as per innovative design.
13. Hole in stay ring bottom flange for compacting sand.
14. Outer diameter of runner envelope.
15. Inner diameter of cylindrical well.
16. Stay ring bottom flange.
17. Radial piers.
18. Radial gap around runner envelope where sand and water is packed

19. Hole in the make up piece for draining water.
20. Small slits at the lower end junction of make-up-place.
21. Draft tube cone.
22. Funnel type arrangement for pouring sand and water.
23. Water jet used after pouring sand.
24. High pressure water jet for removing sand.
25. Packed sand around runner envelope.
26. Holes for pouring sand and water.
27. Generator Barrel

WE CLAIM
1. A method for easy replacement of runner envelope (2) of a Kaplan type hydro turbine
comprising;
cutting of the make up piece (8) to facilitate easy removal of runner envelope (2);
removing the packed sand (25) by high pressure water jet (24);
removing the worn out runner envelope (2);
replacing by a new runner envelope (2);
positioning the runner envelope (2) with the help of screw jacks (6) and tie rods (7);
fixing the new runner envelope (2) with the make up piece (8) by welding;
providing a hole (26) for pouring sand and water in the annular space between outer
diameter (14) of runner envelope (2) and inner diameter (15) of the cylindrical
structure (12) of the well;
providing a manhole (9) for large turbine and a hole (13) for small turbine to
facilitate ramming and compacting of the sand in the annular space (18);
providing a baffle (10) at the make up piece with drain hole (19) to allow water to
drain out while retaining the sand by the baffle;
plugging the drain hole (19) by welding after draining out water;
providing small slits (20) at the junction of the make up piece (8) and draft tube cone
(21) to totally drain out water;
closing the slits (20) by welding;
wherein the sand water mixture disposed around the runner envelope (2) in the
annular space (18) is rammed to have compact sand around the runner envelope (2);

ABSTRACT
The invention is about the method for easy replacement of runner envelope (2) of
Kaplan type hydro turbine comprising; cutting the make up piece (8) to facilitate
easy removal of the runner envelope (2); removing the packed sand (25) by high
pressure water jets (24); removing the worn out runner envelope (2); replacing by a
new runner envelope (2); positioning the runner envelope (2) firmly with the help of
screw jacks (6) and tie roads (7); fixing the runner envelope (2) with the make up
piece (8) by welding;
Pouring the sand and water mixture through the hole (26) in the stayring bottom
flange (16) in the annular space (18) between the outer diameter (14) of runner
envelope (2) and the inner diameter (15) of cylindrical structure (12);
Providing a manhole (9) in the stayring bottom flange (16) for large turbine and hole
(13) in the case of smaller turbines for ramming and compacting sand in the annular
space (18) around the runner envelope (2);
Providing a baffle plate (10) at the make up piece with a hole (19) for draining out
the water while retaining the sand by the baffle plate (10);
Plugging the drain hole (19) by welding after bulk of the water is drained out;
providing small slits (20) at the junction of make up piece (8) and draft tube cone
(21) to totally drain out water; closing the slits (20) by welding; wherein the sand
water mixture is disposed around the runner envelope (2) and rammed to have a
compact sand around the runner envelope (2);