The present invention relates to a device for remote engagement and
disengagement of barring gear for turning the turbine rotor slowly during shutdown
prior to starting the turbine to ensure evenly heating or cooling of rotor. More
particularly the present invention replaces/overcomes the limitation of now obsolete
technology of remote operation of barring gear of Steam Turbines using the invented
device as claimed in this application.
The device for remote operation of steam turbine barring gear using solenoid
valve shall hereinafter referred as 'device'.
Turbines used in coal or nuclear fuel based thermal power plants shall
hereinafter referred as 'turbine’.
BACKGROUND OF THE INVENTION
High capital expenditure related to new capacity augmentation, poor financial
health of the utilities and emerging fuel constraints necessitate efficiency improvement
of the existing power stations in the country. Renovation and Modernization (R&M) of
thermal power plants plays a critical role in restoring the power station's rated capacity
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and reducing coal consumption, and is one of the most cost effective options to
achieve additional generation in a short gestation period.
Critical operational plant parameters viz. Heat rate, Auxiliary power
consumption, plant availability and force outage for coal plants in India which
emphatically indicates the need of R&M in order to tap the huge potential for energy
efficiency improvement and reducing emission of Greenhouse gases.
The heat rate is an important parameter that impacts the efficiency of the plant.
Lower heat rate of plants imply lower specific coal consumption and in turn lower fuel
cost and Green House Gas emissions thereby reducing pollution associated with these
sets.
Presently many LMW (Leningrad Metal Works, Russia) make sets that were
manufactured and supplied by BHEL India are operating at different power stations in
the country have completed more than 25 years and are on verge of end of their
service life.
With Renovation and Modernization (R&M) of older in-service thermal sets, large
populations of whom have completed more than 25 years and are on verge of end of
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their service life, being considered a more cost effective way of augmenting power
generation capacity than installing new, their technology dates back to early 1950's
thereby providing admirable scope of improving the efficiency and increasing the output
by R&M of these sets.
A thermal power station is a power plant in which heat energy is converted to
electric power. Thermal power plants use water as working fluid. Nuclear and coal
based power plants fall under this category. The way energy from fuel gets
transformed into electricity forms the working of a power plant.
In a thermal power plant a steam turbine is rotated with help of high pressure
and high temperature steam and this rotation is transferred to a generator to produce
electricity. (Refer fig. 1)
When turbine blades get rotated by high pressure high temperature steam, the
steam loses its energy. This in turn will result in a low pressure and low temperature
steam at the outlet of the turbine. Here steam is expanded till saturation point is
reached. Since there is no heat addition or removal from the steam, ideally entropy
of the steam remains same. This change is depicted in the p-v and T-s diagrams
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(Refer fig. 2). If we can bring this low pressure, low temperature steam back to its
original state, then we can produce electricity continuously.
Barring gear (or "turning gear") is the mechanism provided to rotate the
turbine generator shaft at a very low speed after unit stoppages. Once the unit is
"tripped" (i.e., the steam inlet valve is closed), the turbine coasts down towards
standstill. When it stops completely, there is a tendency for the turbine shaft to
deflect or bend if allowed to remain in one position too long. This is because the heat
inside the turbine casing tends to concentrate in the top half of the casing, making
the top half portion of the shaft hotter than the bottom half. The shaft therefore
could warp or bend by millionths of inches. The turning gear turns the turbine rotor
slowly, about 3-7 rpm, during shutdown, prior to starting the turbine, or when the
turbine is hot. Turning the rotor slowly ensures that it is heated or cooled evenly.
If the rotor is allowed to come to a rest when hot, temporary bowing and
excessive vibration can result. Distortion of the turbine casing also results because the
hotter steam rises to the top of the casing.
The same phenomenon is also observed during starting up of the turbine when
steam is supplied to the sealing to create the vacuum. If the rotor is stationary there
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would be non-uniform heating of the rotor which will result in distortion of rotors. The
barring gear during starting of turbine, would slowly rotate the turbine-generator rotor
and thereby resulting in the uniform heating of rotor. Thus any distortion in the rotor
would be avoided.
During starting period, operation of barring gear eliminates the necessity of
'breaking away' the turbine-generator rotors from stand still and thereby provides
for a more uniform smooth and controlled starting. If the shutdown is for an indefinite
period, it is advisable to continue to roll the rotor until the turbine has thoroughly
cooled.
In general, switching 'ON' of the barring gear can be done either by remote
manual control from Unit Control Panel (UCP) or from with the help of a selector in
UCP, selection to operate the barring gear can be done either from local panel or
from remote switch in UCP.
In manual operation, the driving gear is shifted to its extreme right position up
to the collar on worm wheel shaft and in that position it meshes with the gear on
turbine rotor and the external lever presses the limit switch. The electric motor is
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switched on and thereby its rotation is transmitted to turbine rotor through worm and
spur gears.
For switching off the barring gear, when the speed of turbine rotor increases,
due to action of the steam, the barring gear automatically switches off. The electric
motor gets switched off by the release of the limit switch. The manual operation of
bringing the driving gear out of the mesh or switching 'OFF' the barring gear is done
through opening the cover wheel and rotate it in anticlockwise direction till the driving
gear and also the external lever comes back to its initial position.
One example of a decoupling turning gear arrangement is that disclosed in U.S.
Patent 3,919,894 wherein the turning gear drives the turbine rotor through a bull
gear attached to the rotor shaft. Whenever the turbine rotor is at an elevated speed
(e.g., above the turning gear speed), the turning gear is automatically disengaged or
decoupled from the rotor bull gear. A low speed signal is used to reengage the turning
gear on shutdown as the rotor coasts down to zero speed. This is carried out by
actuating a pressurized cylinder which moves a gear carriage and which thereby
causes the gears to reengage. However, the turning gear may also be manually
engaged.
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Presently in 200/210 MW sets that have to undergo R&M, the general method
of engaging turning gears on steam turbines is to manually displace the turning gear
to bring it into engagement with a co-acting rotor gear. Barring gear has to be latched
with the electric motor using a hand lever installed at the cover due to unoperational
/ obsolete remote mechanism.
The original arrangement was based upon a Russian design 440 V AC operated
electromagnet. The design and availability of the electromagnet has become obsolete
and presently unavailable. For incorporating the automatic operation of turbine through
Automatic Turbine Run-Up System (ATRS) for enhanced customer satisfaction and
better operator safety, barring gear engagement mechanism also needs to be
automated for remote operation of engaging the motor with turbine rotor. Hence, for
retrofitting and modernisation of barring gear engagement process under this
development, the 400V AC-operated electromagnet has been replaced with 24V DCoperated
3/2 solenoid valve. Solenoid valve can be operated from control system with
24V DC Power Supply. New Logics are developed for the operation of solenoid valve
for engaging the barring gear motor and this logic has been incorporated in ATRS.
This design for remote engagement process of barring gear eliminates human error
and provides maximum protection against malfunctions. It enables safe, smooth and
make Operator's task less arduous.
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This invention relates to remote engagement and disengagement of barring
gear, with the general purpose of this invention to provide an improved device and a
technology along with an improved fixture for remote engagement and disengagement
of barring gear, which will be more efficient, and provide more functions than
previously known arrangement for the same purpose.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a device for remote
engagement and disengagement of barring gear for turning the turbine rotor slowly
during shutdown prior to starting the turbine to ensure evenly heating or cooling of
rotor, which is capable of automatic operation of turbine through barring gear
engagement mechanism.
Another object of the invention is to propose a device for remote engagement
and disengagement of barring gear for turning the turbine rotor slowly during shutdown
prior to starting the turbine to ensure evenly heating or cooling of rotor, which
eliminates human errors and provides maximum protection against malfunction.
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A further object of the invention is to propose a device for remote engagement
and disengagement of barring gear for turning the turbine rotor slowly during shutdown
prior to starting the turbine to ensure evenly heating or cooling of rotor, which is able
to restrict the rotor to come to a rest preventing temporary bowing, excessive vibration
and distortion of the turbine casing.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
These together with other objects and advantages which will become
subsequently apparent reside in the details of construction and operation as more fully
hereinafter described and claimed, reference being had to the accompanying
drawings forming a part hereof, wherein like numerals refer to like parts throughout,
and in which:
Figure 1 is a diagrammatic representation of power production in thermal power
plants by rotating steam turbine;
Figure 2 is a diagrammatic representation of steam pressure and temperature drop
when turbine absorbs energy from it;
Figure 3 is the line diagram of the assembled invented device for remote engagement
and disengagement of barring gear;
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Figure 4 is the 3-dimensional isometric view of the invented device;
Figure 5 is the side 3-dimensional view of invented device showing location of oil
connections;
Figure 6 is the line diagram of gasket (1) used in invented device;
Figure 7 is the line diagram of intermediate piece (2) used in invented device;
Figure 8 is the line diagram of Screw hexagonal – M10 (3) used in invented device;
Figure 9 is the line diagram of Pipe union (4) used in invented device;
Figure 10 is the line diagram of threaded union (6) used in invented device;
Figure 11 is the line diagram of Stud M10 (7) used in invented device;
Figure 12 is the line diagram of Nut M10 (8) used in invented device;
Figure 13 is the line diagram of Pin (9) used in invented device;
Figure 14 is the line diagram of Support Plate (10) used in invented device;
Figure 15 is the line diagram of Screw Hex M6 (11) used in invented device;
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Figure 16 is the line diagram of Nut Hex M6 (12) used in invented device;
Figure 17 is the representation of Solenoid Valve (13) used in invented device.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Figure 4 shows Isometric view and Figure-5 shows Side view of invented device
showing location of oil connections and all the major components have been marked in
the above referred figures.
Details of major components of Invented arrangement and their functions are
described below:
Barring gear Servomotor (14): The existing servomotor consists of a
piston and a compression spring installed below the piston. On the upside of the piston
an oil inlet port has been provided from where oil of 0.6 bar (g) is supplied; this oil
pushes the piston in downward direction. The downward movement of the piston in
turns push the lever and latches the barring gear.
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Solenoid Valve (13): 3/2 way valve has been used to control the supply of oil
to servomotor. The inlet supply is connected to port-3 of the solenoid valve. When
the valve is energized, the oil supply at port-3 gets connected to port-2, which pushes
the piston of barring gear in downward direction and barring gear gets latched. When
the solenoid valve is De-energized, Port-2 gets connected to Port-1, which is
connected to drain. This allows the piston to move to upward position by spring force.
Intermediate Piece (2): This acts as a manifold to connect the servomotor
to solenoid valve.
Support Assembly (10): Support assembly has been designed to mount the
solenoid valve with the servomotor.
Pipe Connection (4 and 6): 3 nos. item no. 4 of Dnom 12 has been used to
connect the solenoid valve with the manifold for supply and drain of oil. Item no. 6 is
designed as a threaded connection to connect supply line with the solenoid valve port.
Assembly and description of the developed device is as per below:
The arrangement basically consists of Existing servomotor consisting of a piston
which needs to be pushed down against the spring force to latch the barring gear.
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A manifold called as Intermediate piece (2) has been designed to connect the
ports of servomotor with the solenoid valve (13). The intermediate piece (2) is fixed in
the location using 6 nos. M10 (3) screws with the servomotor. A gasket (1) is installed
between the intermediate piece (2) and Servomotor (14) to avoid any leakage from the
connection. The Pipe union (4) has been welded with the intermediate piece (2) at the
supply port. Another pipe union (4) has been fastened with the Intermediate piece (2)
at the Threaded location. The solenoid valve (13) has been installed with the
servomotor (14) top cover using 3 nos. of M10 Stud (7) and Nut (8). 2 nos. cylindrical
pins (9) are used to locate the Support plate (10) with the Servomotor cover. The
solenoid valve (13) has been fixed with the support plate using 2 nos. M6 screws (11)
and nuts (12). The holes (15) to fix the solenoid valve (13) with the support plate (10)
has been made elliptical to allow adjustment to suit the assembly. At the supply port of
the solenoid valve (13) a threaded connection (6) has been installed with Pipe union (4)
at other end to connect supply pipeline with the solenoid valve (13). The drain
connection to the valve using Pipe union (4). The pipe from valve to the manifold has to
be site routed as per ease to work.
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It is further important to note that in addition to providing solutions for remote
engagement and disengagement of barring gear, the same device is adaptable for
different ratings of steam turbines, providing an even further versatile scope of use.
With assembly of the device and its use in remote operation of barring gear, it
is apparent that the embodiment of the invention, as described hereinabove, will
provide an extremely critical device for engagement and disengagement of barring
gear.
The foregoing is considered as illustrative only of the principles of the invention.
Further, since numerous modifications and changes will readily occur by those skilled in
the art, it is not desired to limit the invention to the exact construction and operation
shown and described, and accordingly all suitable modifications and equivalents may
be resorted to, falling within the scope of the invention as claimed.
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WE CLAIM
1. A device for remote engagement and disengagement of barring gear for turning
the turbine rotor slowly during shutdown prior to starting the turbine to ensure evenly
heating or cooling of rotor, the said device comprising;
an intermediate piece (2) acting as manifold disposed to connect ports of a
servomotor (14) with a solenoid valve (13);
a gasket (1) installed between the intermediate piece (2) and servomotor (14)
for avoiding any oil leakage from the connection;
a pipe union (4) welded with the intermediate piece (2) at supply port of
servomotor (14) for connecting the solenoid valve with the manifold (2) for supply and
drain of oil;
another pipe union (4) fastened with the intermediate piece (2) as a threaded
connection for connecting supply line with the solenoid valve port;
a support (10) fixed at the servomotor (14) top cover with plurality of studs (7)
and nuts (8),
characterized in that,
the solenoid valve (13) is installed with the servomotor (14) being supportably
fixed with the support plate (10) with plurality of screws (11) and nuts (12) wherein the
location of the support plate is configured with the servomotor cover (14) with plurality
of cylindrical pins (9), wherein the solenoid valve (13) is disposed for controlling supply of oil to servomotor (14).
2. The device as claimed in claim 1, wherein the support plate (10) is fixed to servomotor top cover with M10 studs (7) and nuts (8) and with the solenoid with M6 screws (11) and nuts (12).
3. The device as claimed in claim 1, wherein the holes (15) of support plate (10) is made elliptical to accommodate adjustment in assembly.