FIELD OF INVENTION
The present invention is about the new construction of bottom ring of guide
apparatus for Francis Turbines operating in water containing hard and abrasive
slit particles. The basic concept of this project is to facilitate easy replacement of
eroded curved plate of bottom ring of guide apparatus for those Francis type
turbines, which operate in water containing hard slit particles. In flow path, the
curved plate is located after guide vanes and before the runner. The bottom ring
houses the lower journal of guide vanes and in conventional design, the curved
plate forms an integral part of the bottom ring, which guides the water to runner
skirt with a smooth transition. The dynamic velocity just after the vanes jumps to
a very high value because of change in direction of flow path from guide vanes
to runner blades, as a result of which, the abrasive slit particles in water severely
erode the curved plate surface. After sometime, the curved plate requires in-situ
repair or complete replacement of the bottom ring may be necessitated.
Replacement of bottom ring calls for complete dismantling of turbine and
generator causing long shutdown of machine and loss of power generation.
Since erosion may not be avoided but complete replacement of bottom ring
could be avoided and this forms the basic idea of invention. To minimize
dismantling of turbine and cutting down shutdown period drastically, a new
development of bottom ring has been evolved in which, the curved plate is made
bolted to the bottom ring so that only the curved plate can be replaced without
much hassle. In this design, dismantling of guide apparatus assembly is avoided.

BACKGROUND OF THE INVENTION
Bottom ring (6) is a component of guide apparatus (8) assembly of hydro turbine (see
Fig. 1) which houses the lower journal of guide vanes (2). In a conventional design,
the curved plate (5) forms an integral part of bottom ring (6) (see Fig. 2) and guides
the water to the runner skirt in a smooth transition from radial to axial direction. The
dynamic velocity of water in the zone is very high because of sudden change in
direction of flow path. Now in case of the hydro turbines operation in water having
good amount of hard and abrasive silt particle, erosion of under-water parts is a
perennial problem. These slit particles erode the surface of the curved plate (5) and
since the velocity in the zone is very high, the large impact of slit particles causes
servere damage to the curved plate (5). Ultimately, the bottom ring (6) needs to be
replaced which calls for complete dismantling of both turbine and generator.
The deficiency of the bottom ring arrangement was thoroughly and to minimize the
downtime of the power generating equipment, a new design of bottom ring (6) was
developed by using bolted curved plate (5) in place of the integral one adopted earlier.
The detailed design of the new bottom ring is described below.

SUMMARY OF THE INVENTION
Accordingly, there is provided an improved bottom ring (6) system of guide apparatus
for Francis Turbines operating in silty water consisting of a bottom ring and a curved
plate (5) wherein the said bottom ring is a component of the guide apparatus assembly
of the hydro turbine when separately made bottom ring (6) and curved plate (5) are
bolted together so that when required one can be separated from the other.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 a typical section through turbine.
Fig. 2 bottom ring (Conventional Design).
Fig. 3 bottom ring (New Design).
Figure 1 - Section through turbine:
A typical sectional arrangement of a Francis type hydro turbine showing the location of
bottom ring. The bottom ring is shown in enlarged view in subsequent figures.

Figure 2 - Bottom ring (Conventional Design)
The conventional design of bottom ring is shown in Figure 2. This shows the housing
for guide vane journal and the integral curved plate.
Figure 3 - Bottom ring (New Design).
The new design of bottom ring is shown in Figure 3 with bolted arrangement of curved
plate.
DETAILED DESCRIPTION OF THE INVENTION
In the new invention, the bottom ring (6) and the curved plate (5) are made separately
and the later is bolted to the former (see Fig. 3). Now in case of the component
needing replacement as a result of erosion damage, only the curved plate (5) can be
changed, while retaining the main body of the lower ring. If the machine is designed
for runner removal from bottom then even dismantling of generator is also eliminated.
Thus this design facility in quick replacement of the component and reduction in
downtime of the machine there are saving in electricity generation loss.

EXAMPLES/PREFERRED EMBODIMENTS
The inventors on experimental basis installed the new bottom ring arrangement
in the turbines of larji HEP installed with three generating units of 42 MW each.
The hydro power station is located in Himachal Pradesh state of India and
harness the hydro potential of river Beas, which originates from the Himalayas.
The river water contains very high amount of slit with good amount of quartz
particles. Other power utilities have also shown keen interest in the new design
of bottom ring for their forthcoming projects.
Advantages of the present invention
The advantages of this present invention over the prior art are:
(l)Only two operators can complete this work of replacement instead of five
operators usually engaged in the conventional design.
(2) About 70% saving of the downtime of the machine in terms of electricity
generation loss. This is a huge economical benefit.

WE CLAIM
1. A two pieces bottom ring (6) device having a separate curved plate unit
(5) of guide apparatus for Francis turbine comprising:
a bottom ring (6) without a curved plate (5) in a guide apparatus;
a separate removable curved plate (5);
characterized in that,
the said bottom ring (6) and the curved plate (5) are separately and
removable joined together by bolts (3) so that the said curved plate when
damaged can be easily replaced by removing it from the bottom ring (6)
without dismantling the bottom ring (6) or any parts of the turbine.
2. The device as claimed in claim 1, wherein the bottom ring (6) has a seat
to accommodate the curved plate (5) and the curved plate (5) and the
bottom ring (6) have a plurality of holes and threaded holes respectively
to accommodate the bolts (3) for fixing.

A two pieces bottom ring (6) device having a separate curved plate unit (5) of
guide apparatus for Francis turbine operating in silty water, consists of a bottom
ring (6) without a curved plate (5) in a guide apparatus and a separate
removable curved plate (5) joined together by bolts so that the curved plate (5)
when damaged can be easily replaced by removing it from the bottom ring (6)
without dismantling the bottom ring (6) or any other parts of the turbine.