FIELD OF INVENTION
The present invention generally relates to testing of hydro turbine models. More
particularly, the invention relates to guide apparatus of vertical axis model Francis
turbines for model testing in specialized test rigs.
BACKGROUND OF THE INVENTION
Francis turbines are designed afresh for every hydro power plant owing to the
uniqueness of every site in terms of the head, discharge & speed, more specifically
specific speed which is a mathematical combination of these quantities. This calls for
detailed experimental tests to be conducted on the new hydraulic design to ascertain its
suitability and acceptance based on the performance parameters. These tests are
conducted on homologous small scale models in specialized Laboratories wherein
homologous hydraulic conditions as existing at actual site are created and the small
scale turbine made to operate under these conditions and performance parameters are
measured. The Francis turbines operate in a wide range of specific speed and the
hydraulic design is strongly dependent on the specific speed. Since every Project / site
of Hydro turbine is unique in terms of specific speed and consequently the hydraulic
design is unique. There is a huge variation in design to design and hence a new small
scale working model has to be manufactured for every project for the experimental
tests to be conducted for design verification and performance validation. Consequently
all components of the small scale model including guide apparatus have to be
manufactured afresh. The mechanism for turning and control of opening of guide vanes
is one of the most complicated sub-assemblies of a Francis turbine model. Design,
manufacturing and assembly of this 'Guide Apparatus' is a complex and expensive
process. As per the prior art, a new guide apparatus consisting of guide vane levers and
links dependent on guide vane PCD is designed and manufactured for every project.

This method is not only un-economical, but also leads to unequal distribution of
stresses on the guide vanes and associated levers. The present invention aims at a
'Universal guide apparatus' for the entire range of Francis turbine specific speed and
known parameters of experimental test-bed including the complete range of applicable
runner discharge diameters. The Universal guide apparatus can be used for Francis
turbine models of all specific speeds, irrespective of the value of Guide Vane PCD (Pitch
Circle Diameter), and a method of application of the same such that the same
components of Guide apparatus like regulating ring, guide vane levers and pins can be
used considering a particular number of guide vanes.
PRIOR ART
A new Guide apparatus is designed and manufactured for every project
A detailed web-search of prior-art in related subject has yielded the following patents:
Patent no. 252295 ("A compact single piece / jointless regulating ring for Francis type
hydro turbine with external regulation of guide apparatus"),
Patent no. 245801 ("A two pieces bottom ring device having a separate curved plate
unit of guide apparatus for a Francis turbine")
Patent no. 194320 ("A guide apparatus linkage for hydro turbines")
Above patents use some features of guide apparatus for Francis turbines.
But the above patents are not directly related to experimental model testing ot Francis
turbine models. However, the features of guide apparatus mechanisms described in the
above patents are referred to in the following description of prior art.

Since the PCD (Pitch Circle Diameter) of guide vanes and the design of structural
components of Francis turbine models vary from project to project, a new guide
apparatus is designed and manufactured for every project. The guide apparatus
consists of non-standard links and levers transmitting the movement of regulating
mechanism to rotation of individual guide vanes about their axes. The design of the link
and lever needs to be changed for every project and hence, is manufactured afresh for
every project.
As the PCD of guide vanes changes, the pitch of the adjacent guide vanes changes. In
order to ensure that all guide vanes are rotated with the same angle, it is essential that
the length of the link is equal to the pitch of the guide vanes. This enables movement
of the four-bar linkage in a parallelogram ensuring equal rotation of all guide vanes
(Figure 2 & Figure 3). This leads to a non-standard design of the links and
corresponding levers as these are derived from the varying values of guide vane PCD.
Hence, a disadvantage of the prior art is that a new mechanism needs to be designed
and manufactured for every project, which is rather uneconomical.
Another disadvantage of the prior art is that torque is provided to a single 'regulating'
lever and it is subsequently transmitted to the other levers. This leads to an unequal
distribution of stresses in the system.
OBJECTS OF THE INVENTION
1. It is therefore the object of the invention to provide an universal design of guide
apparatus for experimental testing of Francis type Hydro Turbine models and a
method of application of the same.
2. Another object of the invention is to provide a guide apparatus for experimental
testing of Francis type Hydro Turbine models which can be applied to all types of

Francis turbine models irrespective of specific speeds and consequently varying
guide vane PCD (Pitch Circle Diameter).
3. A further object of the invention is to provide guide apparatus for experimental
testing of Francis type Hydro Turbine models such that the same components
can be used in different settings to accommodate models with different guide
vane PCD for the complete range of operation of Francis Turbine models.
SUMMARY OF THE INVENTION
In case of Francis Turbines, guide vanes are provided to control the flow into the
runner where a set of moveable row of blades with each guide vane moving about
its axis from completely closed condition to maximum possible opening as per
requirement of power generation. The guide vanes are moved by an elaborate
mechanism known as guide apparatus. The function of the guide apparatus is to
ensure accurate and equal rotation of all guide vanes for the complete cange of
operation from fully closed position to full open position.
The present invention provides for a universal design of guide apparatus for
experimental testing of Francis type Hydro Turbine models and a method of
application of the same such that the guide apparatus can be used for experimental
testing of Francis type Hydro Turbine models which can be applied to all types of
Francis turbine models irrespective of specific speeds and consequently varying
guide vane PCD (Pitch Circle Diameter).

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: Components of Guide Apparatus (Prior Art)
Figure 2: Links & Levers of Guide Apparatus (Prior Art)
Figure 3: Equivalent 4-bar Chain (Prior Art)
Figure 4: Regulating Ring type guide apparatus (Present Invention)
Figure 5: Regulating Ring (Present Invention)
Figure 6: Standard Guide Vane Lever (Present Invention)
Figure 7a: Method of Application (Standard Orientation)
Figure 7b: Method of Application (Reversed Orientation)
DESCEIPTION OF THE INVENTION
For the purpose of controlling the discharge through a Francis turbine, movable guide
vanes are provided at the inlet of the runner. These guide vanes can be rotated about
their axes such that they allow different quantities of water per unit time at different
openings and hence, can be used to regulate the power output from the turbine.
Since the design of Francis turbines changes for every project depending upon the
hydraulic conditions of head, discharge and geography of the project site, model tests
are performed on scaled homologous models of turbines in specialized test rigs in order
to validate the performance parameters of the turbine. These models are in similitude
with the full scale turbine so that the model test results can be used to predict the
hydraulic performance of the full scale turbine. These models consist of all components
of the turbine including the guide apparatus which is one of the most typical sub-
assemblies of the model. Design and manufacturing of this guide apparatus is a time-
taking, cumbersome process & costly affair. An objective of this invention is to design a
universal guide apparatus which is capable of accommodating Francis turbine models

with particular number of guide vanes for all specific speeds of Francis turbine range
irrespective of the value of Guide Vane PCD.
The novel guide apparatus consists of a regulating ring (3), standard levers (2) and
standard pins (4), guide vane lever (1).
A number of novel features have been incorporated in the present art in order to
achieve universality of application.
In an embodiment of this invention, the 4 turning joints of the prior art have been
replaced with a combination of 3 turning joints and one sliding joint. In order to ensure
that all the guide vanes rotate by the same angle, the fourth turning joint has been
replaced with a sliding joint wherein standard pins slide inside equidistant radial slots
cut out on a standard annular plate known as regulating ring (3). By doing so, the
conditions of a parallelogram type 4-bar mechanism are satisfied irrespective of the
value of the Guide vane PCD, thus ensuring that all guide vanes are rotated by the
same angle of different models.
As another embodiment of this invention, the standard guide vane lever (1) has been
designed such that it allows the regulating ring (3) to be positioned at a distance above
the top cover of the model rather resting it on the top cover itself. The standard guide
vane lever (1) has been designed in a Z-shape such that it allows the regulating ring (3)
to be positioned at a distance above the top cover. This allows for the flexibility of using
the lever in different orientations in order to incorporate a variety of models with
different Guide vane PCD or runner discharge diameters.
As another aspect of this invention, for achieving universality of guide apparatus design,
the length of the radial slot has been evolved using the following criteria:
(Slot OD-slot ID) / L1 = 2.72
(Slot OD- slot ID) / L2 = 4.08

For the purpose of accommodating different runners (having different discharge
diameters) and different guide vane PCD, two holes have been provided in the guide
vane lever (1) effectively providing two lengths (L1 & L2) in the same component
(Figure 6). The above formulation allows the regulating mechanism to accommodate
different models having varying guide vane PCD and runner discharge diameters
ranging from 350 mm to 450 mm, which is the most probable range of values for
runner discharge diameters to cover the complete range of Francis turbine models as
per requirement of experimental test bed.
Another advantage of the present invention is a high level of durability of the standard
mechanism since the pin which is the only sliding member in the mechanism is easily
replaceable in case it wears out.
Another advantage of the present invention is that it provides for an even distribution of
stresses during operation since the torque is transmitted to the annular disc viz.
regulating ring and subsequently the regulating ring (3) transmits the torque to
individual guide vane levers (1). Hence, the stresses are distributed evenly throughout
the mechanism overcoming the concentration of stresses in some particular members
resulting in uneven deformation leading to inaccuracy. Also, as a result of the above,
the errors (if any) in the system are not transmitted or propagated from one guide vane
to another and hence, the accuracy of the system increases.
The other advantage of this invention is to provide a method of application of the
standard guide apparatus such that the standard components like guide vane lever and
pin can be used for all Francis turbine models. This is achieved by reversing the
orientation of guide vane lever in case it is not possible to accommodate the model
using the standard orientation. The Z-shape of the guide vane lever makes it possible to
reverse the orientation since it not only allows to position the regulating ring at some
distance above the top cover, but also to transmit turning torque to the guide vane in
reversed orientation. This has been explained in Fig. 7a and 7b in greater detail.

WE CLAIM
1. A universal guide apparatus for experimental testing of Francis type Hydro
turbine models comprising:
a standard regulating ring (3);
a Z-shaped guide vane lever (1);
a pin (4);
a regulating lever (2);
wherein the regulating lever (2) drives the regulating ring (3), the arrangement
providing a mechanism consisting of combination of turnings and sliding joints,
characterized in that the regulating ring (3) is having equally spaced slots in which the
pin (4) moves to and fro thus giving rotational movement to the Z-shaped guide lever
(1) and in turn to the guide vanes, as well as accommodating the variation of PCD.
2. The universal guide apparatus as claimed in claim 1 where the guide vane is held
by guide vane lever (1).
3.The universal guide apparatus as claimed in claim 1 wherein each slot of the
regulating ring (3) is having a slot length so that different models having runner
discharge diameter ranging from 350mm to 450mm can be accommodated.

4. The universal guide apparatus as claimed in claim 1 wherein the Z-shaped guide
vane lever (2) has 2 holes at L1 and L2 length from the guide vane axis for
reversing the orientation of guide vane lever in case it is not possible to
accommodate the model of standard orientation.

ABSTRACT

The invention relates to a novel design of the guide apparatus including the mechanism
for controlling the movement of guide varies of model Francis turbines such that the
said mechanism can be universally used for testing Francis turbines models of all
specific speeds for the complete working range of model runner discharge diameters as
per requirement of the experimental test-bed set up.
The novel guide apparatus replaces the conventional one consisting of only turning
joints with a combination of turning joints and a sliding joint in conjunction with a
number of newly designed features such that the universal mechanism can be applied
for testing Francis turbine models of all specific speeds with equal number of guide
vanes irrespective of the value of Guide Vane Pitch Circle Diameter (PCD).