FIELD OF THE INVENTION
The present invention relates to a dual purpose device to enhance the life of
shaft seals and to improve the evacuation of turbine leakages of Francis turbines.
BACKGROUND OF THE INVENTION
In a hydro turbine, as shown in figure-1, a shaft seal assembly (1)
prevents/minimizes water leakages between a rotating shaft (2) and a top cover
(3) through which the shaft (2) of the turbine passes.
In a shaft seal (1), clean cooling water is fed to a plurality of sealing elements
(4). This cooling water is fed at a pressure higher than the pressure of water
maintained in the top-cover (3) below the shaft seal (1). The cooling water
forces it's way down through an interface between a lower sealing element (4b)
of said sealing elements (4), and a shaft sleeve (5) provides the necessary
sealing, lubrication and cooling. The water film passing down prevents silt
particles in the dirty river water below the shaft seal (1) to enter into the shaft
seal (1) and thus prevent damage to both the shaft sleeve (5) and the lower
sealing elements (4b). The shaft seals (1) perform satisfactorily in the beginning;
however as the runner labyrinths (14) get worn out due to silt in the river water,
the pressure of water in the top cover (3) below the shaft seal (1) keeps on
increasing. When the water pressure on the top cover (3) due to wear of the
labyrinth (14) exceeds the pressure of cooling water being fed into the shaft seal
(1), a flow reversal takes place. Due to the flow reversal, silt particles enter the
shaft seal (14) and ultimately damage both the shaft sleeve (5) and the lower
sealing elements (4b) of the shaft seal (1). A pre-emptive situation of this
problem could be avoided by replacement of the runner labyrinth (14) when the
pressure on the top-cover starts increasing. This however, entails a long shut

down of the turbine generator set, leading to generation loss.
The inventors of the present invention recognized that a device to decrease the
pressure below the shaft seal may enhance the performance of the shaft seals
(I) and frequent replacement of the runner labyrinths (14) can be eliminated.
In the top cover of a reaction turbine, water leakages from the shaft seals as
well as from the seals of guide vane trunnions, generally takes place. All these
leakages lead to accumulation of water in the top cover and the water level
starts rising. According to the prior art, an elaborate arrangement is made to
evacuate these water leakages so that the rising water does not enter into the
turbine guide bearing (6).
The elaborate leakage evacuation system of prior art consists of the following:-
1. drilling several gravity drain holes (11) in two or three stay vanes (7) of a
plurality of vanes of a stayring (8) for draining out in excess water by
gravity;
2. providing two numbers electric motor operated pumps (9); and
3. provision of an ejector (10) operable by high pressure water form
penstock / cooling water system or compressed air system.
Thus, according to the prior art arrangement, the water leakages of the shaft
seal, that of the guide vane stem seals, and that from the bush housings of the
guide vanes, is led through the gravity drain holes (11) in the stay vanes (7).
When the rate of above leakages increases beyond what the gravity drain holes
(II) can discharge, the water level in the top cover rises. This rising water level
is sensed by a first level electrode mounted in the top cover and a first electric
motor pump (9) is activated which is stopped once the level goes down below a
threshold level, as sensed by said first level electrode.

If however the leakage exceeds the evacuation capability of a single electric
pump (9), then the level of water in the top cover is sensed by a second level
electrode; which would start the second electric pump. With the two pumps in
operation, the water level in the top cover starts receding and the reduced water
level is sensed by a third electrode and based on a transmitted signal, the
second electric pump and/or both the pumps is de-activated. In case there is an
A.C. supply failure, both the electric pump (9) would stop, and level of water in
the top cover would rise to a level which is below the guide bearing. However, to
pre-empt this situation, said a least one ejector (10) is operated to evacuate the
rising leakage water, which is hydraulically operated.
Operation (start/stopping) of the pumps and the ejector is controlled by said
level electrodes mounted in the top cover.
The prior art arrangement has the ejector (10) installed at a convenient point in
the turbine pit. The ejector (10) is energized by taking pressure tapping from the
penstock or compressed air supply. The leakage water is sucked in through a
suction pipe with a strainer installed at its bottom end. The drawback of the
existing ejector system is that before the leakage water is sucked out, air in
suction line has to be sucked out, which takes sufficient time. Also since the
ejector (10) is installed at a position quite above the position from which the
leakage water to be sucked; sufficient energy is lost in the suction, thereby
reducing the total discharging capacity of the ejector.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a dual purpose device to
enhance the life of shaft seals and to improve the evacuation of turbine leakages
of Francis turbines.

Another object of the invention is to propose a dual purpose device to
enhance the life of shaft seals and to improve the evacuation of turbine
leakages of Francis turbines, which increases the reliability and rate of
evacuation of turbine leakages of Francis type hydro turbines.
SUMMARY OF THE INVENTION
According to the invention, there is provided a dual purpose device to
enhance performance of in shaft seals disposed between the rotating shaft
and top cover of Francis type hydro turbines, comprising at least one shaft
seal assembly (1) to prevent water leakage between the rotating turbine
shaft (2) and the top cover (3) through which the shaft (2) passes, the
shaft seal assembly (1) having at least one each lower and upper sealing
elements (4b, 4a), the shaft (2) having one each end sleeve (5), a plurality
of runner labyrinth (14) provided to prevent damage of the shaft sleeves
(5); one stay ring (8) having a plurality of stay vanes (7), the stay vanes (7)
having drain holes (11) at least three stay vanes receiving the leakage
water from the shaft seal (1), and guide vane stem seals having housing of
the guide vanes, characterized by comprising an ejector means having a
nozzle (19) connected to the pressurized water line from below the shaft
seal (1), at least one diffuser (24) cum protection sleeve (22); an ejector
housing cum strainer (23) to house the ejector nozzle (19) and the diffuser
(24), the ejector housing (23) having a plurality of holes in its body (25),
and screwed to the stay ring (8) on the gravity drain holes (11) through
which the leakage water is sucked in and drained down, the diffuser (24)
cum protection sleeve (22) protecting the holes in the stay vane (7) of the
turbine against erosion damage due to silt in the water.
According to the present invention the performance of the shaft seals of
Francis turbines is enhanced by relieving the top cover water pressure
below shaft seals, and by allowing this water to flow through gravity drains

in the stay vanes. Maintaining a low pressure below the shaft seal enables
feeding of high pressure clean filtered water to the shaft seal elements for
lubrication and cooling by virtue of greater pressure difference.
Further, the invention adapts an ejector installed at the top of the gravity
drain. This ejector is energized by high pressure water from the top cover
below the shaft seal. The ejector sucks the surrounding leakage water of
the turbine. With the provision of the ejector, the rate of evacuation of
turbine leakages is increased multifold.
Since releasing water below the shaft seal to the ejector on top of the
gravity drain is a continuous process, the reliability of evacuation of the
turbine leakages is greatly enhanced.
In the pipe line, for energizing the ejector, is installed a solenoid operated
valve to stop the water flowing through the ejector once the turbine is
stopped. This solenoid valve allows admission of the high pressure water to
the ejector on starting of the turbine.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1: Prior art arrangement of evacuating turbine leakages.
Fig. 2: Device for evacuating turbine leakages according to the invention.
Fig. 3: Arrangement of shaft seal as per prior art.
Fig. 4: Disposition of the shaft seal according to the invention.
Fig. 5: Evacuation of turbine leakages by a gravity drain as per prior art.
Fig. 6: Evacuation of turbine leakages by an ejector by taking high
pressure tapping from penstock as per prior art.
Fig. 7 Evacuation of turbine leakages by an ejector by taking pressure
tapping from compressed air supply as per prior art.
Fig. 8: Configuration and disposition of an ejector enhanced gravity drain

by taking pressure tapping from top cover below shaft seal, according to
the invention.
Fig. 9: Enlarged view of an ejector enhanced gravity drain of fig.8.
Fig. 10: Exploded view of the innovated ejector enhanced gravity drain
showing assembly sequence of Fig.8.
Fig.ll: Details of major components of the innovative ejector enhanced
gravity drain of Fig.8.
Fig. 12: Shows the ejector enhanced gravity drain of Fig.8, by taking
pressure tapping from compressed air supply.
Reference numerals of the features of the invention
1. Shaft seal
2. Shaft
3. Top cover
4a. Upper sealing elements of shaft seal
4b. Lower sealing element of shaft seal
5 Shaft sleeve
6. Turbine guide bearing
7. Stay vanes
8. Stay ring
9. Electric motor pump set
10. Ejector as per prior art
11. Gravity drain hole in stay vanes
12. Solenoid operated valve
13. Ejector as per innovative
arrangement
14. Runner labyrinths

Additional labyrinths on shaft flange O.D. for protection of shaft seal.
Booster pump ring below shaft seal
Strainer above gravity drain to prevent choking of hole
Strainer in the suction line of ejector
Nozzle of ejector
Housing of ejector as per prior art
Diffuser of ejector assembly as per prior art
Protection, sleeve / pipe
Ejector housing cum strainer of innovative design
Diffuser of ejector assembly of innovative design
Grub Screws
DETAIL DESCRIPTION OF THE INVENTION
As shown in Fig. 2, shaft seals (1) of hydro turbines function satisfactorily
on commissioning. For satisfactory functioning of the turbine, filtered
cooling water at a pressure higher than the pressure of water in the top
cover (3) below the shaft seal (1), is fed into the shaft seal. This high
pressure water forces its way down in the interface between the lower
rubber sealing element (4b) and the rotating shaft sleeve (5). Thus this film
provides the necessary lubrication, and cooling, and prevents ingress of silt
particles present in the river water in the top cover (3). For turbines
operated by water with high silt content, the shaft seals (1) fail quite fast
and the turbines have to be frequently stopped for replacement of the
runner labyrinths (14) including the shaft seal elements (4a and 4b). Detail
study by the present inventors reveals that due to high silt in the river
water, the runner labyrinths (14) get worn-out fast. Due to excess wear of
the runner labyrinths (14), water pressure in the top cover (3) after the
runner labyrinths (14) and below the shaft seal (1) increases. When the
water pressure in the top cover (3) below the shaft seal (1) increases to
such an extent, that cooling water fed between the upper sealing element

4a) and the lower sealing element (4b) cannot force it's way down through
the interface between the lower sealing element (4b) and the shaft sleeve
(5), the lower rubber sealing element (4b) gets pressed against the shaft
sleeve (5) by the high pressure water of the top cover (3).
After this stage, the lower sealing element (4b) gets damaged very fast and
the water from the top cover (3) below the shaft seal (1) pushes its way up
into the shaft seal (1). Very soon, the upper sealing elements (4a) also gets
damaged. At this stage, the turbine is to be stopped to prevent flooding. In
the process, the shaft seal elements (4a, 4b), and the shaft sleeve (5) also
gets damaged by the silt particles trapped between the sealing element
(4a, 4b) and the shaft sleeve (5).
After stoppage of the turbine for replacement of shaft seal elements (4a
and 4b), the runner labyrinths (14) are also replaced.
According to the inventive concept, a configuration is envisaged such that
the pressure below the shaft seal (5) should be less than the cooling water
fed to the shaft seal (1).
Accordingly, the invention teaches an innovative device to restrict the
pressure in the top cover (3) below the shaft seal (1). This water is
generally allowed to let out through a plurality of gravity drain holes (11),
configured in stay vanes (7) of the stay ring (8). Since the water pressure
below the shaft seal (1) would be about 2 kg/cm2 for low head turbines
and about 4 to 5 kg/cm2 for medium head turbines, the velocity of water
escaping through the gravity drain (11) would be high.
Thus, the high pressure water from the top cover (3) escaping through the
gravity drain holes (11) are at a high velocity. Second part of the inventive
concept is about utilizing the high velocity energy.

As shown in Fig. 8, the high pressure water from the top cover (3) below
the shaft seal (1) is connected to a convergent nozzle (19). The high
velocity jet is directed into a diffuser (24). Below the convergent nozzle
(19) i.e. at the vena-contracta, a low pressure zone is created on account
of which any fluid in the vicinity of the convergent nozzle (19) and the
diffuser (24) is sucked in. Thus, an ejector assembly (13) is installed above
the gravity drain hole (11) in the stay vanes (7), which sucks in the
accumulated leakage water.
Thus, this ejector system (13, 23, 19, 24) serves the dual purpose of
reliving pressure below the shaft seal (1) for improving its life and
simultaneously evacuates accumulated leakage water.
As shown in Fig. 9, an ejector housing (23) with holes on its outer diameter
serves as a strainer as well as a housing for the ejector (13) to
accommodate the convergent nozzle (19) and the diffuser (24). Since the
water in the top cover (3) below the shaft seal (1) would contain silt,
therefore the holes (11) in the stay vane (7) would get eroded. In order to
protect the holes (11) in the stay vane (7), a sleeve / pipe (22) is screwed
to the bottom end of the diffuser (24).
To utilize the annular space between the holes (11) in the stay vane (7)
and outer diameter of the pipe (22), the diffuser (24) along with the
protection pipe (22) is suspended from the ejector housing (23) by at least
four grub screws (25) (see Fig. 10). In the water line from the top cover (3)
below the shaft seal (1) to the ejector (13) is installed (see Fig.2), a
solenoid operated valve (12) which admits water on starting of the turbine.
In comparison to the prior art ejector (10) system, the device of the
invention allows acceleration of the evacuation of leakage water which
according to the prior art flows down by natural gravitational effect only.

Therefore, the rate of evacuation of the leakage water with the innovated
ejector is much faster than that of the prior art. Also the present invention
eliminates the sucking out of air and the consequential time loss. Since
operation of the inventive ejector is continuous, the frequent operation of
the solenoid valve (12) is reduced, and operation of the valves (12)
including the level sensing electrode does not arise. Therefore, reliability of
the evacuation of turbine leakages is greatly enhanced. The solenoid
operated valve (12) is installed in the pressure line / relieving the pressure
below the shaft seal (1) to energize the ejector (13). This solenoid valve
(12) is interlocked with the starting and stopping of the turbine. This
solenoid valve (12) opens the ejector line (13) before start of the turbine
and stops the ejector (13), a little while after stopping of the turbine.
For the sake of contingency the innovated device is provided with an
ejector enhanced gravity drain energized by compressed air supply and a
conventional electric pump.

WE CLAIM
1. A dual purpose device to enhance performance of in shaft seals
disposed between the rotating shaft and top cover of Francis type hydro
turbines, comprising:
at least one shaft seal assembly (1) to prevent water leakage between
the rotating turbine shaft (2) and the top cover (3) through which the
shaft (2) passes, the shaft seal assembly (1) having at least one each
lower and upper sealing elements (4b, 4a), the shaft (2) having one
each end sleeve (5), a plurality of runner labyrinth (14) provided to
prevent damage of the shaft sleeves (5);
one stay ring (8) having a plurality of stay vanes (7), the stay vanes (7)
having drain holes (11) at least three stay vanes receiving the leakage
water from the shaft seal (1), and guide vane stem seals having
housing of the guide vanes, characterized by comprising:
an ejector means having a nozzle (19) connected to the pressurized
water line from below the shaft seal (1), at least one diffuser (24) cum
protection sleeve (22); an ejector housing cum strainer (23) to house
the ejector nozzle (19) and the diffuser (24), the ejector housing (23)
having a plurality of holes in its body (25), and screwed to the stay ring
(8) on the gravity drain holes (11) through which the leakage water is
sucked in and drained down, the diffuser (24) cum protection sleeve
(22) protecting the holes in the stay vane (7) of the turbine against
erosion damage due to silt in the water.
2. The device as claimed in claim 1, wherein the diffuser (24) cum
protection sleeve (22) is suspended inside the ejector body (23) by a
plurality of screws so as to allow leakage water to partially escape

through an annular clearance between the diffuser (24) and the holes
(11) in the stay vane (7), and wherein a pipe (22) is screwed at the
bottom end of the diffuser (24).
3. The device as claimed in claim 1, wherein in the pipeline extending to
the ejector (13) from the shaft seal (1), a solenoid operated valve (12)
is installed to open the valve (12) when the turbine is started and close
the valve (12) when the turbine is stopped.
4. A dual purpose device to enhance performance of in shaft seals
disposed between the rotating shaft and top cover of Francis type hydro
turbines, as substantially herein described and illustrated with reference
to the accompanying drawings.

ABSTRACT

The invention relates to a dual purpose device to enhance performance of in
shaft seals disposed between the rotating shaft and top cover of Francis type
hydro turbines, comprising at least one shaft seal assembly (1) to prevent water
leakage between the rotating turbine shaft (2) and the top cover (3) through
which the shaft (2) passes, the shaft seal assembly (1) having at least one each
lower and upper sealing elements (4b, 4a), the shaft (2) having one each end
sleeve (5), a plurality of runner labyrinth (14) provided to prevent damage of the
shaft sleeves (5); one stay ring (8) having a plurality of stay vanes (7), the stay
vanes (7) having drain holes (11) at least three stay vanes receiving the leakage
water from the shaft seal (1), and guide vane stem seals having housing of the
guide vanes, characterized by comprising an ejector means having a nozzle (19)
connected to the pressurized water line from below the shaft seal (1), at least
one diffuser (24) cum protection sleeve (22); an ejector housing cum strainer
(23) to house the ejector nozzle (19) and the diffuser (24), the ejector housing
(23) having a plurality of holes in its body (25), and screwed to the stay ring (8)
on the gravity drain holes (11) through which the leakage water is sucked in and
drained down, the diffuser (24) cum protection sleeve (22) protecting the holes
in the stay vane (7) of the turbine against erosion damage due to silt in the
water.