FORM 2
The Patents Act, 1970
(39 of 1970)
&
The Patent Rules, 2003
COMPLETE
SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION
STEAM TURBINE AND METHOD FOR ADJUSTING THRUST
FORCES THEREOF
2. APPLICANT (S)
(a) NAME : MlTSUBlSHl HEAVY INDUSTRIES, LTD.
(b) NATIONALITY : A company incorporated in Japan
(c) ADDRESS : 16-5, Konan 2-chome, Minato-ku, Tokyo 1088215
Japan
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention
and the manner in which it is to be performed.

BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a steam turbine and a
method of adjusting a thrust force of the steam turbine, particularly
regarding a steam turbine and a method of adjusting a thrust force
of the steam turbine which are capable of balancing of a thrust force
acting on a rotor shaft of the steam turbine which includes at least a
high-pressure (HP) blade cascade, an intermediate-pressure (IP)
blade cascade and a plurality of dummy members t h a t a r e attached
to a common rotor shaft.
Background of the Invention
Since the rotor shaft is subjected to the thrust force acting
thereon, the steam turbine is provided with a thrust bearing. With
a limited load capacity of the bearing, it is necessary to design the
steam turbine in consideration of a thrust balance so that the thrust
force acting on the rotor shaft does not exceed the load capacity of
the bearing under any operating condition.
Hence, the dummy members (dummy pistons) and the blade
cascades are attached to the same rotor shaft, so a s t h r u s t forces in a
counter-thrust direction are generated by the dummy members to
balance the forces acting i n an axial direction of the entire rotor
shaft. In this manner, the thrust force acting on the rotor shaft
is kept within the scope of the load capacity of the bearing under any
operation condition.
FIG.13 shows an outline view regarding a conventional steam
turbine under a normal operating condition, the conventional steam
t urbine being provided with dummy members for ad justing the
thrust forces.
In a conventional steam t u r b i n e 1 depicted in FIG.13, a
turbine casing (not shown) is formed around a rotor shaft 10'. The
turbine casing includes an inlet part (not shown) for introducing
high-pressure (HP) main steam 22, an inlet p a r t (not shown) for
introducing reheat steam 24 and an inlet p a r t (not shown) for
introducing low-pressure (LP) main steam 26.
Further, a HP blade cascade 2 to which the HP main steam is
supplied, an IP blade cascade 4 to which t h e r e h e a t steam 24 is
supplied and a low-pressure (LP) blade cascade 6 to which the LP
main steam 26 is supplied are attached to the rotor shaft 10 in this
order. The IP blade cascade 4 and the LP blade cascade 6 have
steam i n l e t s t h a t are open to one side, whereas the HP blade cascade
2 has a steam inlet is open t o other side being opposite to the one
side. Between the steam inlet of the HP blade cascade 2 and the
steam inlet of the IP blade cascade 4, a high-pressure (HP) dummy
member 12 is provided. On a steam o u t l e t side of the HP blade
cascade 2, an intermediate-pressure (IP) dummy member 14 and a
low-pressure (LP) dummy member 16 are provided i n t h i s order.
Further, a thrust balance conduit 30 is provided so as to
communicate the outlet side of the IP dummy member 14 to a l a t t e r
half of the IP blade cascade 4.
I n t h e steam t u r b i n e 1 as described above, the HP main
steam 22 from a boiler and the l i k e (not shown) e n t e r s t h e HP blade
cascade 2. And, the HP main steam 22 gives a rotary force to the
rotor shaft 10 while the steam passes through the HP blade cascade
2. The steam t h a t has done the work through the HP blade cascade
2 drops the pressure and the temperature gradually and is
discharged out of the steam turbine 1 as a low-temperature reheat
steam 28. The low-temperature reheat steam 28 discharged out of
the steam turbine 1 is reheated by a reheat boiler (not shown) to be
the reheat steam 24.
The IP reheat steam 24 that is reheated by the reheat boiler
gives the rotary force to the rotor shaft 10 and gradually reduces the
pressure and the temperature while the reheat steam 24 passes
through the IP blade cascade 4. Further, the LP main steam 26
gives the rotary force to the rotor shaft 10 and gradually reduces the
pressure and the temperature while the LP main steam 26 passes
through the LP blade cascade 6.
Further, a part of the high-pressure (HP) main steam 22
passes by the high-pressure (HP) dummy member 12 and a part of
the low-temperature reheat steam 28 that has passed through the
HP blade cascade and has reduced the temperature and the pressure,
passes by the intermediate- pressure (IP) dummy member 14 and the
low-pressure (LP) dummy member 16.
Further, in FIG.13, the thrust forces acting on the rotor shaft
10 at the cascades and the dummy members on the rotor shaft are
represented by encircled numbers, 1 to 6 and an example regarding a
set of the pressure values between adjacent pair of each blade
cascade (dummy parts) are shown in FIG.13. In addition, the
thrust forces indicated by encircled numbers 1,2,3,4,5 and 6 denote
the thrust forces acting on the LP dummy member 16, the IP dummy
member 14, t h e HP blade cascade 2, the HP dummy member 12, th'e
IP blade cascade 4 and the LP blade cascade 6, respectively. The
thrust force acing on each of the blade cascades can be computed
based on the gas pressure force working on each blade cascade and
the t h r u s t force acting on each of the dummy members can be
computed based on a pressure difference between both sides of each
dummy member and a cross-sectional area of each dummy member.
As shown in FIG.13, the dummy members 12, 14 and 16, and
the t h r u s t balance conduit 30 are provided so as t o balance the
t h r u s t forces by the steam p r e s s u r e . In other words, t h e t h r u s t
force acting on the HP dummy member 12 roughly serves as a
counterbalance t o the t h r u s t force acting on the HP blade cascade 2,
the t h r u s t acting on the IP dummy member 14 roughly serving as a
counterbalance t o the t h r u s t force acting on the IP blade cascade 4,
the t h r u s t force acting on the LP dummy member 16 roughly serving
as a counterbalance t o t h e t h r u s t force acting on the LP blade
cascade 6. Thus, the r e s u l t a n t t h r u s t force acting on the whole
steam t u r b i n e 1 is balanced.
F u r t h e r , in the steam turbine, in order to prevent the t h r u s t
bearing from being damaged, the r e s u l t a n t t h r u s t force needs to be
brought into balance not only in a case where t h e s t e a m t u r b i n e i s
operated under a normal operating condition but also in a case
where either the HP main steam supply or the reheat steam supply
is stopped.
F i r s t , a t t e n t i o n i s paid t o a case where the flow of the HP
main steam 22 through t h e steam t u r b i n e 1 as shown in FIG.13 is
stopped due to a trouble, a tuning operation or the like. FIG.14
shows the outline of t h e s t a t e of the steam t u r b i n e provided with
conventional dummy parts for adjusting t h r u s t balance, when the
supply of the HP main steam 22 is stopped.
As shown in FIG.14, when the supply of the HP main steam
22 is stopped, the flow of the steam s t r e a m i n g t h r o u g h the HP blade
cascade 2 stops, causing the pressure difference of the HP blade
cascade to be 0. Accordingly, t h e t h r u s t force represented by the
encircled numeral 3 as depicted in FIG.14 also becomes 0. Further,
the pressure difference of the HP dummy member 12 becomes
infinitesimal and, t h e t h r u s t force represented by the encircled
numeral 4 becomes approximately 0. Therefore, as shown in FIG.14,
t h e r e s u l t a n t t h r u s t force developed i n t h e whole steam turbine 1 is
substantially balanced, even in a case where the supply of the HP
main steam 22 is stopped.
In the next place, attention is paid to a case in which the flow
of t h e r e h e a t steam 24 and the LP main steam 26 through the steam
turbine 1 as shown FIG.13 i s stopped due to a trouble, a tuning
operation or the like. FIG.15 shows the outline of the s t a t e of the
steam turbine provided with conventional dummy p a r t s for
adjusting t h r u s t balance, when the supply of t h e r e h e a t steam and
the LP main steam is stopped.
As shown in FIG.15, when the supply of t h e r e h e a t steam 24
a n d t h e LP main steam 26 is stopped, the flow of the steam
s t r e a m i n g t h r o u g h the IP blade cascade 4 a n d t h e LP blade cascade 6
ends. Each of the pressures on both sides of the IP blade cascade 4
a n d t h e pressures on both sides of the LP blade cascade 6 becomes
approximately a level of vacuum pressure. Further, due to tl!e
t h r u s t balance conduit 30 t h a t communicates the IP dummy member
14 to the l a t t e r half of the IP blade cascade 4, the pressure between
the IP dummy member 14 and the LP dummy member 16 also
becomes a level of vacuum pressure.
In such case, in an LP system (a low-pressure p a r t of the
steam turbine), the pressure difference between both sides of the LP
blade cascade 6 and t h e pressure difference between both sides of
the LP dummy member 16 become approximately 0, resulting in the
thrust force acting on the rotor shaft being 0.
Further, in relation to the IP system (theintermediate-pressure part of the steam turbine),
the pressure at the outlet of the IP dummy member 14 becomes a level of vacuum
pressure and i n response to the vacuum pressure level, the thrust
force represented by the encircled numeral 2 as shown in FIG.15
increases. In addition, the pressure difference between both sides
of the IP blade cascade 4 becomes approximately 0. In this manner,
the thrust force represented by the encircled numeral 5 becomes
approximately 0. As a r e s u l t , the resultant t h r u s t force acting
toward the direction of the IP dummy member side (leftward in
FIG.15) increases.
Further, in relation to a HP system (a high-pressure part of
the steam turbine), t h e t h r u s t force generated in the HP blade
cascade 2 represented by the encircled numeral 3 is approximately
the same a s that of a normal operation condition, whereas the thrust
force represented by the encircled numeral 2 generated i n the HP
dummy member 12 increases by an amount corresponding to the
vacuum pressure level at the outlet of the HP dummy member 12.
Thus, the t h r u s t force acting i n the direction of the HP dummy
member (rightward in FIG.15) increase.
Hereby, the increase of the thrust force generated i n the IP
system is greater than the increase of the thrust force generated in
the HP system. Accordingly, the resultant t h r u s t force generated
in the whole steam turbine 1 increases i n the leftward direction in
Thus, the rssultant t h r u s t force acting on the whole steam turbine is
not balanced.
In a case where the flow of t h e reheat steam 24 is stopped, it
may be considered t h a t the HP dummy member 12 is upsized so t h a t
t h r u s t force in the rightward direction increases and the resultant
thrust force is balanced. However, the upsizing of the HP dummy
member 12 spoils the balancing i n t h e normal operation and t h u s ,
this approach iS not appropriate.
Hence, in relation to each of FIG.13 to FIG.15, t h e I P dummy
member 14 is downsized and t h e LP dummy member 16 is upsized.
By this, the balance of the thrust force can he maintained under t h e
normal operating condition, even in a case where the supply of any
one of the HP main steam and t h e reheat steam i s stopped.
In addition, Patent Reference 1 discloses another technology;
according to this technology, thrust forces acting on t h e steam
turbine are evaluated based on the measured data such as bearing
temperatures. Based on t h e r e s u l t s of t h e measurements, t h e
t h r u s t forces acting on the dummy members can be adjusted i n a n
electronic control approach, and the resultant t h r u s t force developed
in the whole steam turbine is brought into balance
[ R e f e r e n c e s l
[Patent R e f e r e n c e s l
Patent Reference 1: JP1996-189302

SUMMARY OF THE INVENTION

Subjects to be solved
In the conventional technology as explained above in
reference to FIG.13 through FIG.15, it is necessary to downsize the
IP dummy member 14 and upsize the LP-dummy member 16 so as to
balance the resultant thrust force even when the supply of the
reheat steam in addition to the HP main steam is stopped i n the
normal operation. Upsizing of the LP dummy member 16
accompanies upsizing of the casing that is located a t the outer
periphery of the LP dummy member 16. Accordingly, the whole
steam turbine 1 is inevitably upsized and the manufacturing cost
increases. Moreover, when the diameter of the LP dummy member
16 is increased, the steam leakage from the LP dummy member 16
toward the gland increases. Inevitably, there arises a possibility
that the performance of the steam turbine 1 deteriorated. In recent
years, the LP blade cascade is becoming larger, accompanying
upsizing of the LP dummy member. However, it is not desirable to
upsize the LP dummy member to balance the thrust forces.

Further, in the technology as disclosed by Patent Reference 1
where the balancing of t h e t h r u s t forces is performed by use of an
electric codtrol, there is a possibility that the reliability of the
electric system may cause a problem.
In view of the above problems of the related art, it is an
object of the present invention to provide a steam turbine and a
method of adjusting a thrust force of the steam turbine acting on a
rotor shaft of the turbine in an entire operating range of the steam
turbine without upsizing a LP dummy member or without using an
electric control of a complicated system.

Means to solve the Subjects

To solve the above issues, the present invention provides a
steam turbine having a t least a high-pressure. (HP) blade cascade, an
intermediate-pressure (IP) blade cascade and a plurality of dummy
members t h a t are attached to a common rotor shaft. The steam
turbine may include, but is not limited to:
a detection unit that detects a steam flow into an
intermediate-pressure (IP) chamber;
a pressure reducing unit that reduces a pressure difference
between both sides of a target dummy member of said plurality of
the dummy members when the steam flow into the IP chamber stops,
the target dummy member having one side communicating with a
part of the IP chamber; and
a control unit that controls the pressure reducing unit based on a detection result obtained by the detection unit.
In this manner, the thrust force generated a t the IP dummy
member when the steam flow into the IP chamber stops can be
eliminated. Thus, it is no longer necessary to increase the
diameter of the LP dummy member which wa5 conventionally needed
to balance the t h r u s t force generated at the IP dummy member. As
a result, the diameter of the LP dummy member can be reduced and
the t h r u s t forces acting on the rotor of the steam turbine can be
balanced in the entire operation range of the steam turbine without
using the electric control of the complicated system.
The above pressure reducing unit may include, but is not
limited to, a first conduit that connects the both sides of the target
dummy member and a first valve t h a t is provided in the first conduit
to adjust the pressure difference between the both sides of the target
dummy member.
In this way. the thrust forces acting on the rotor shaft of the
steam turbine can be balanced, with a simple configuration.
The above steam turbine may further include:
a third conduit that connects the one side of the pressure
reducing u n i t t o an outlet of the IP chamber; and
a third valve that is provided i n the third conduit.
When the first valve opens while the steam flow into the EP
chamber is not stopped, the control unit may control the third valve
to open so as to generate the pressure difference between the both
sides of the target dummy member.
I n t h i s way, even when the first valve is out of order, the
t h r u s t forces generated i n the steam turbine can be balanced and,
the reliability of the steam turbine can be enhanced.
The above pressure reducing unit may include, but is not
limited to: a second conduit that connects the part of the IP
chamber and t h e one side of the target dummy member; and
a second valve that is provided i n the second conduit to
adjust the difference between the both sides of t h e t a r g e t dummy
member.
The second valve may be closed when the steam flow into the
IP chamber stops.
In relation to the above, the second conduit is often provided
even in the conventional steam turbines. Thus, i n remodeling or
modernizing the conventional existing steam turbine, the pressure
reducing unit can be provided by simply fitting the second valve to
the existing second conduit without newly installing a conduit to the
steam turbine. Thus, the remodeling can be easily accomplished.
The above steam turbine may further include:
a bypass conduit that is provided to bypass the second valve;
and
an orifice t h a t is provided in the bypass conduit.
In this way, the thrust forces generated in the steam turbine
can be easily balanced.
The above steam turbine may also include:
a third conduit that connects the one side of the pressure
reducing u ni t to an outlet of the IP chamber; and
a third valve that is provided i n the third conduit.
When the second valve closes while the steam flow into the IP
chamber is not stopped, the control unit may control the third valve
to open so as to generate the pressure difference between the both
sides of the target dummy member.
To achieve the object of the present invention, the present
invention provides a method of adjusting a thrust force of a steam
turbine having a t least a HP blade cascade, an IP blade cascade and
a plurality of dummy members t h a t are attached to a common rotor
shaft. The method may include, but is not limited to, the step of
reducing a pressure difference between both sides of a target dummy
member of said plurality of the dummy members when the steam
flow into the IP chamber stops, the target dummy member having
one side communicating with a part of the IP chamber.
Further, in the above method, the pressure difference
between the both sides of the target dummy member may be
reducible by use of a first valve provided in a first conduit that
connec.ts the both sides of the target dummy member.
Further, in the above method, when the first valve opens
while the steam flow into the IP chamber is not stopped, the
pressure difference may be generated between the both sides of the
target dummy member by opening a third valve which is provided in
a third conduit t h a t connects the one side of the target dummy
member to an outlet of the IP chamber.
[0030]
In the above method of adjusting the t h r u s t force of the
steam turbine, the pressure difference between the both sides of the
target dummy member may be reducible by use of a second valve
provided in a second conduit that connects the part of the IP
chamber and the one side of the target dummy member.
In the above method of adjusting the t h r u s t force of tl:e
steam turbine, when the second valve closes while the steam flow
into the IP chamber is stopped, the pressure difference may be
generated between the both sides of the target dummy member by
opening a third valve which is provided in a third conduit that
connects the one side of the target dummy member to an outlet of the
IP chamber.

Effects of the Invention

According to the present invention, the steam turbine and
the method of adjusting the t h r u s t force of the steam turbine can be
provided which are operable to balance the thrust forces in the
entire operation range of the steam turbine without upsizing the LP
dummy member, as well as, without using the electric control of a
complicated system.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG.l shows a configuration of a single-casing reheat steam
turbine provided with a plurality of dummy members for adjusting
t h r u s t forces, according to a first preferred embodiment of the
present invention.
FIG.2 shows an outline of a normal operating s t a t e of the
steam t u r b i n e provided with the dummy members for adjusting
t h r u s t forces, according to the f i r s t preferred embodiment of the
present invention.
FIG.3 shows an outline of a state of the steam turbine
provided with t h e dummy members for adjusting t h r u s t forces when
the supply of the HP main steam is stopped, according .to the first
preferred embodiment of t h e present invention.
FIG.4 shows an outline of a state of t h e steam t u r b i n e
provided with the dummy members for adjusting t h r u s t forces when
the supply of t h e r e h e a t steam and the LP main steam is stopped,
according to the first preferred embodiment of the present invention.
FIG.5 shows an outline of a s t a t e of the steam t u r b i n e
provided with the dummy members for adjusting t h r u s t forces in a
case where a valve i s i n an abnormal condition in the normal
operating s t a t e of the steam t u r b i n e , according to t h e f i r s t preferred
embodiment of the present invention.
FIG.6 shows an outline of a s t a t e of the steam t u r b i n e
provided with the dummy members for adjusting t h r u s t forces, after
taking a countermeasure a g a i n s t t h e malfunction of the valve in the
normal operating s t a t e of the steam turbine, according to the first
preferred embodiment of t h e present invention.
FIG.7 shows an outline of a state of the steam turbine
provided with t h e dummy members for adjusting t h r u s t forces in a
case where another valve i s i n an abnormal condition in the normal
operating s t a t e of the steam turbine, according to the first preferred
embodiment of the present invention.
FIG.8 shows an outline of a state of the steam turbine
provided with the dummy members for adjusting t h r u s t forces, after
taking a countermeasure a g a i n s t t h e malfunction of said another
valve in the normal operating state of the steam t u r b i n e , according
to t h e f i r s t preferred embodiment of the present invention.
FIG.9 shows an outline of a state of the steam turbine
provided with the dummy members for adjusting t h r u s t forces,
according to the first preferred embodiment of t h e present invention,
in a case where the function of a valve i s o u t of order while the
supply .of the reheat steam and the LP main steam is stopped.
FIG.10 shows an outline of a state of the steam turbine
provided with the dummy members for adjusting t h r u s t forces,
according to the first preferred embodiment of the present invention,
after taking a countermeasure a g a i n s t t h e malfunction of the valve
while the supply of t h e r e h e a t steam and the LP main steam is
stopped.
FIG.11 shows an outline of a HP-IP steam turbine provided
with the dummy members for adjusting t h r u s t forces, according to a
second preferred embodiment of t h e present invention.
FIG.12 shows an outline of a HP-IP steam turbine provided
with the dummy members for adjusting t h r u s t forces? according to a
third preferred embodiment of the present invention.
FIG.13 shows an outline of a normal operating state of the
steam t u r b i n e provided with conventional dummy members.
FIG.14 shows an outline of a s t a t e of the steam turbii'e
provided with conventional dummy parts for adjusting t h r u s t
balance, when the supply of the HP main steam is stopped.
FIG.15 shows an outline of a state of t h e steam turbine
provided with conventional dummy parts for adjusting thrust
balance, when the supply of t h e reheat steam and the LP main steam
i s stopped.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention will now be
described in detail with reference to the accompanying drawings.
I t i s intended, however, that unless particularly specified,
dimensions, materials, shape, its relative positions and the like
shall be interpreted as illustrative only and not limitative of the
scope of the present invention.

PREFERRED EMBODIMENTS

(First Preferred Embodiment)
FIG.l shows a configuration of a single-casing reheat steam
turbine provided with a plurality of dummy members for adjusting
t h r u s t forces, according to a first preferred embodiment of the
present invention. In a steam turbine shown in FIG.l, a
lowpressure (LP) casing 32 and a HP-IP casing 34 (a
high-intermediate-pressure casing) are formed around a rotor shaft
10. The HP-IP casing 34 is provided with a high-pressure (HP)
steam inlet 23 through which HP steam 22 is supplied to t h e steam
turbine and a reheat steam i n l e t 25 through which reheat steam 24
i s supplied t o t h e steam turbine. Further, the LP casing 32 is
provided with a low-pressure (LP) steam inlet 27 through which LP
steam 26 is supplied to the steam turbine.
To the rotor shaft 10, attached are a HP blade cascade 2 to
which the HP main steam is supplied, an intermediate-pressure (IP)
blade cascade 4 to which t h e r e h e a t steam 24 is supplied and a
low-pressure (LP) blade cascade 6 to which the LP main steam 26 is
supplied in this order.
In the steam t u r b i n e , steam i n l e t sides of the IP blade
cascade 4 a n d t h e LP blade cascade 6 are arranged such that the
steam streams through the IP blade cascade 4 and the LP blade
cascade 6 in the same direction, whereas a steam i n l e t side of t h e HP
blade cascade 2 is arranged such that t h e steam streams through the
HP blade cascade 2 in the opposite direction. Further, a HP
dummy member 12 i s provided between t h e steam inlet side of the
HP blade cascade 2 and the steam inlet side of the IP blade cascade 4
On the steam outlet side of the HP blade cascade 2, an IP dummy
member 14 and a LP dummy member 16 are provided i n t h i s order.
Furthermore, a t h r u s t balance conduit 30 is provided to
communicate the steam o u t l e t side of the IP dummy member 14 to a
part of the IP blade cascade 4.
FIG.2 shows an outline of a normal operating state of the
steam turbine provided with the dummy members for adjusting
t h r u s t forces. Hereby, the same components in FIG.2 as i n F I G . l ,
FIG.13 through FIG.15 are given common numerals and are not
explained further. Herein, a normal operating s t a t e means an
operating s t a t e of the steam t u r b i n e in which all of the HP steam 22,
t h e r e h e a t steam 24 and the LP steam 26 are supplied to t h e steam
turbine.
Differently from the conventional technology shown in
FIG.13, in the first preferred embodiment of t h e present invention
as shown in FIG.2, t h e diameter of the IP dummy member 14 is
upsized in comparison with the conventional dummy member 14,
whereas the diameter of the LP dummy member 16 is downsized in
comparison with the conventional dummy member 16. With the LP
dummy member 16 having larger diameter, the t h r u s t forces of the
steam t u r b i n e as a whole are prevented from being unbalanced.
Further, a conduit 42 is provided to communicate the steam
inlet side of the IP dummy member 14 to the steam o u t l e t side
thereof and a valve 43 is provided on the conduit 42. A conduit 44 is
connected to the conduit 42 on a side closer to the steam outlet side
of the IP dummy p a r t t h a n the valve 43 a n d i n communication to the
steam outlet side of the IP blade cascade 4. A valve 45 is provided
on the conduit 44. A valve 41 is provided on t h e t h r u s t balance
conduit 30.
Further, a control unit 52 is provided. The control unit 52
reads a detected value detected by a pressure sensor 54 which is
provided a t the reheat steam inlet 25 and controls opening and
closing of the valves 41, 43 and 45 based on the detected value. In
the normal operating state where t h e r e h e a t steam 24 is supplied to
the steam turbine 1 and the pressure detected by t h e pressure sensor
54 is within a normal pressure range of the reheat steam 24, the
control unit 52 controls the valve 41 to open and the valves 43 and 45
to close as shown in FIG.2. As for the open-close s t a t e of the valves
in the attached drawings, the valve mark filled in with black
indicates an opened s t a t e , whereas the valve mark filled in with
white indicates a closed state.
In FIG.2 through FIG.10 and FIG.13 through FIG.15, the
unit k denotes a pressure value in kgfl cm2 to show pressure values
as only example values at indicated places.
As shown in FIG.2, t h e steam t u r b i n e is provided with the
dummy members 12, 14 and 16, and the t h r u s t balance conduit 30.
In t h e normal operating s t a t e , the resultant t h r u s t force generated
by the steam pressures is balanced.
Next, a case where the supply of the HP main steam 22 is
stopped in the steam turbine 1 shown in FIG.2 is explained. FIG.3
shows an outline of a state of the steam t u r b i n e provided with the
dummy members for adjusting t h r u s t forces'of the present inventisn
when the supply of the HP main steam i s stopped. In FIG.3 through
FIG.15, the control unit 52 is omitted.
In FIG.3, when the supply of the HP main steam 22 is
stopped, no steam i s supplied to the HP blade cascade 2, and the
pressure difference a t the HP blade cascade 2 becomes 0. Thus, the
t h r u s t force represented by the encircled numeral 3 as depicted in
FIG.14 also becomes 0. Accordingly, t h e pressure difference at the
HP dummy member 12 becomes significantly small and t h e t h r u s t
force represented by the encircled numeral 4 becomes close to 0.
Therefore, as shown in FIG.3, even when the supply of the HP main
steam 22 is stopped, t h e r e s u l t a n t t h r u s t force acting on the whole
steam t u r b i n e I is balanced.
Next, a case where the supply of the reheat steam 24 and the
LP main steam 26 is stopped in t h e steam t u r b i n e 1 shown in FIG.2
is explained. FIG.4 shows an outline of a state of the steam t u r b i n e
provided with the dummy members for adjusting t h r u s t forces of the
present invention when the supply of the reheat steam a n d t h e LP
main steam. is stopped.
In FIG.4, when the supply of the r e h e a t steam 24 and the LP
main steam 26 is stopped, no steam is supplied t o the IP blade
cascade 4 and t h e LP blade cascade 6. This causes the pressures at
both sides of the IP blade cascade 4 and the LP blade cascade 6 to be
approximately a t vacuum level. In the HP system (the
high-pressure part of the steam turbine), t h e t h r u s t force
represented by the encircled numeral 3 generated at the HP blade
cascade 2 is almost the same as the t h r u s t force i n the normal
operating state of the steam turbine. However, the thrust force
represented by the encircled numeral 2 generated a t the HP dummy
member 12 increases i n response to the increase regarding the level
of the vacuum pressure a t the outlet of the HP dummy member 12.
By this, the t h r u s t force acting on the HP dummy member 12
increases in the direction of the steam flow along the HP dummy
member (in the rightward direction in FIG.4).
When the control unit 52 (not shown in FIG.4) determines
that the reheat steam 24 is not supplied based on the pressure value
detected by the pressure sensor 54 (not shown in FIG.4), the control
unit 52 opens the valve 43. By this? the pressure difference
between both sides of the IP dummy member 14 becomes
approximately 0. Specifically, in a case where the reheat steam 24
is not supplied to the steam turbine i n the conventional technology,
an excessive t h r u s t force is generated at the IP dummy member 14 in
the leftward direction. On the other hand, in this preferred
embodiment of the present invention, the thrust force can be
prevented from being generated at the IP dummy member 14.
Further, in the case of FIG.4, the diameter of the LP dummy
member 16 is designed so as to generate a counter thrust force
(leftward in FIG.4) approximately by an amount corresponding to
the ahove-described increased thrust force generated i n the HP
system. Thus, the thrust force generated in the whole steam
turbine 1 is balanced.
In addition, the diameter of the LP dummy member 16 is
designed in advance so as to balance t h e t h r u s t forces in a case
where the valves 41 and 43 are opened in the state where the supply
of t h e r e h e a t steam and the LP main steam is stopped and, the
diameter of the IP dummy member 14 is designed in advance so as to
balance the t h r u s t forces in the normal operating state and t h e state
where the supply of the HP main steam i s stopped. In this way,
t h e t h r u s t force is prevented from being generated at the IP dummy
member 14 when the supply of the reheat steam and t h e LP main
steam i s stopped, and it becomes unnecessary to upsize the diameter
of the LP dummy member 16, apart from the conventional technology
in which the diameter upsizing was inevitable. Hence, the
diameter of the LP dummy member 16 can be small and the steam
leakage to the gland can be reduced. As a result, the performance
of the steam turbine can be enhanced.
Next, the countermeasures against the possible abnormal conditions
that may be caused by providing the valves 41, 43 and 45
are explained.
First, abnormal conditions of the valve 43 are now explained.
FIG.5 shows an outline of a state of the steam turbine
provided with the dummy members for adjusting t h r u s t forces of the
present invention in a case where the valve 43 is in an abnormal
condition i n the normal operating state of the steam turbine.
In FIG.5, when the valve 43 becomes out of order due to a
fault and so on, the valve 43 is opened and then both sides of the IP
dummy member 14 are in communication with each other, and the
pressure a t the steam outlet side of the IP dummy member 14
increases. And, the pressure difference between both sides of the
IP dummy member 14 becomes almost 0. Thus, the thrust force
generated at the IP dummy member 14 becomes almost 0. As a
result, the resultant thrust force of the whole steam turbine 1
becomes unbalanced.
In the event as described above, the pressure detected by a
pressure sensor 56 provided in the thrust balance conduit 30
increases. When the detected pressure value exceeds a prescribed
value; t h e n t h e control unit 52 (not shown in FIG.5) determines that
the valve 43 or 41 is not working properly.
Once i t i s determined that the valve 43 or 41 is not working
properly, the control unit 52 opens the valve 45.
FIG.6 shows an outline of a state of the steam turbilge
provided with the dummy members for adjusting thrust forces of the
present invention, after taking a countermeasure against the
malfunction of the valve 43 i n the normal operating state of the
steam turbine.
When the control unit 52 opens the valve 45, the steam outlet
side of the IP dummy member 14 communicates with the steam
outlet side of the IP blade cascade 4 via the conduit 44. A part of
the steam a t the steam outlet side of the IP dummy member 14
streams to the steam outlet side of the IP blade cascade 4. This
causes the pressure at the steam outlet side of the IP dummy
member 14 to drop so that the pressure difference between both
sides of the IP dummy member 14 is generated, thereby generating
the t h r u s t force at the IP dummy member 14. As a r e s u l t , the
resultant t h r u s t force generated i n the whole steam turblne 1 is
-
balanced. In addition. it is necessary to design the conduits 44 and
the valve 45 in advance so t h a t the steam flow rate through the
conduit 44 is almost the same as t h e steam flow rate through the
valve 43 when t h e valve 45 is opened in a case when the valve 43 is
abnormally opened.
As described above, even when the valve 43 is i n t h e
abnormal condition, the resultant thrust force can be kept balanced;
thus, the reliability of the steam turbine 1 can be enhanced with
additionally provided simple-components.
Next, the abnormal-conditions of the valve 41 are explained.
FIG.7 shows an outline of a state of the steam turbine
provided with the dummy members for adjusting t h r u s t forces of the
present invention in a case where the valve 41 i s i n an abnormal
condition in the normal operating state of t h e steam turbine.
In FIG.7, when the valve 41 becomes out of order because of a
fault and so on and the valve 41 is closed, t h e n t h e steam at the
outlet side of the IP dummy member 14 is no longer able to stream
toward the IP blade cascade 4 through the t h r u s t balance conduit 30.
On the other hand, when t h e r e i s a pressure difference between both
sides of the IP dummy member 14, t h e steam in a labyrinth seal
provided a t an outer periphery of the IP dummy member 14 leaks
toward the steam outlet side thereof. Thus, t h e pressure difference
between both sides of the IP dummy member 14 becomes
approximately 0. Accordingly, the thrust force acting on the IP
dummy member 14 becomes approximately 0. As a result, the
resultant force is unbalanced.
In the event as described above, t h e pressure detected by the
pressure sensor 56 provided on the thrust balance conduit 30
increases. When the detected pressure exceeds a prescribed value,
then the control unit 52 (not shown in FIG.5) determines t h a t the
valve 43 or 41 is not working properly.
Once it is determined t h a t the valve 43 or 41 is not working
properly, the control unit 52 opens the valve 45.
FIG.8 shows an outline of a state of the steam turbine
provided with the dummy members for adjusting t h r u s t forces of the
present invention? a f t e r taking a countermeasure against t h e
malfunction of the valve 41 in the normal operating state of the
steam t u r b i n e .
When the control unit 52 opens the valve 45, the steam outlet
side of the IP dummy member 14 communicates with t h e steam
outlet side of the IP blade cascade 4 via the conduit 44. Then, a
part of the steam a t t h e steam outlet side of the IP dummy member
14 streams into the steam outlet side of the IP blade cascade 4.
Thus, the pressure at t h e steam outlet side of t h e I P dummy member
14 drops so t h a t the pressure difference between both sides of t h e I P
dummy member 14 is generated. Accordingly, the t h r u s t force i s
generated at the IP dummy member 14 so t h a t t h e r e s u l t a n t thrust
force generated in the whole steam turbine 1 is balanced.
As described above, even when t h e abnormal condition of the
valve 41 happens. the resultant thrust force i s kept balanced. Thus,
the reliability of t h e steam turbine can be enhanced with additional
simple-components.
Next, abnormal-conditions t h a t may occur on the valve 41 in
a case where the supply of t h e reheat steam and the LP main steam
i s stopped are explained.
FIG.9 shows an outline of a state of the steam turbine
provided with the dummy members for adjusting t h r u s t forces of the
present invention, in a case where the function of the valve 43 is out
of order while the supply of the reheat steam and the LP main steam
is stopped
As described already based on &I€&-i t, i s necessary to
open the valve 43 i n the case where the supply of the reheat steam
.and the LP main steam is stopped. However, FIG.9 shows the case
where the valve 43 stays closed.
In FIG.9; with the valve 43 being closed, both sides of the IP
dummy member 14 are not in communication with each other. Thus,
the pressure difference between both sides of the IP dummy member
14 is generated so that the thrust force is generated a t the dummy
member 14. The thrust force generated at the dummy member 14
causes the resultant thrust force generated in the whole steam
turbine 1 to be unbalanced. In the present invention, the diameter
of the IP dummy member 14 is greater than that of the conventional
IP dummy member. For a corresponding amount, the unbalance (i.e.
being out of balance) regarding the developed resultant thrust force
increases.
In the event as described above, the pressure detected by the
pressure sensor 56 provided on t h e t h r u s t balance conduit 30 drops.
When the detected pressure value below a
prescribed value, then the control unit 52 (not shown in FIG.9)
determines t h a t the valve 43 is not working properly.
Once it is determined by the control unit 52 t h a t the valve 43
is not working properly, the control unit 52 closes the valve 41.
FIG.10 shows an outline of a state of the steam turbine
provided with the dummy members for adjusting thrust forces of the
present invention, a f t e r taking a countermeasure against t h e
malfunction of the valve 43 while the supply of t h e r e h e a t steam and
t h e LP main steam i s stopped.
With the valve 41 being closed, the pressure difference
between both sides of the IP dummy member 14 becomes
approximately 0 due to t h e steam leakage from the IP dummy
member 14. Accordingly, the thrust force acting on the IF dummy
member 14 becomes almost 0.
In this manner, t h e r e s u l t a n t t h r u s t force is balanced as is
the case with FIG.4 in which there is no abnormal condition
regarding the valve 43.
Specifically, the resultant force is kept balanced, even when
the abnormal condition regarding the valve 43 takes place.

(Second Preferred embodiment)

The disclosed technology of the present invention is also
applicable to HP-IP steam turbines.
F I G . l l shows an outline of a HP-IP steam turbine provided
with the dummy members for adjusting t h r u s t forces according to a
second preferred embodiment of the present invention.
The HP-IP steam turbine 101 depicted in F I G . l l is provided
with a turbine casing (not shown) is formed around a rotor shaft (not
shown). The turbine casing encloses the inlet parts (not shown) for
introducing HP steam and IP steam.
Further, a high-pressure (HP) chamber blade cascade 102 to
which the HP steam i s supplied and an intermediate-pressure (IP)
chamber blade cascade 104 to which the IP steam i s supplied are
attached t o t h e rotor shaft such t h a t steam inlets of the HP chamber
blade cascade 102 and t h e IP chamber blade cascade 104 are
disposed facing each other. Further, between the steam inlet of the
HP chamber blade cascade 8102 and the steam i n l e t the IP chamber
blade cascade 104, a first dummy member 111 and a second dummy
member 112 are provided. Further, a third dummy member 113 is
provided a t a steam outlet of the HP chamber blade cascade 102.
Further, a balance conduit 121 is provided to communicate a location
between the first dummy member 111 and the second dummy
member 112 to both sides of the third dummy member 113.
Furthermore, a balance conduit 122 is provided to communicate the
steam outlet of the third dummy member 113 to the steam outlet of
the IP chamber blade cascade 104. In addition, a valve 141 i s
provided on the balance conduit 121 between both sides of the third
dummy member 113 and the downstream side of the third dummy
member 113 and a valve 142 is provided on the balance conduit 122.
In relation to the HP-IP steam turbine as described above,
the table in F I G . l l summarizes a balance of the thrust forces of the
cases, when the turbine is operated normally, the supply of the HP
steam is stopped (the HP system is closed), and the IP steam is
stopped (the IP system is closed). The figures of the t h r u s t forces in
the table of FIG.%-U show not the absolute values b u t t h e relative
ratios among thrust forces appearing in design calculations.
As shown in FIG.=%==, in the normal operation state, the
resultant thrust force is substantially balanced when the HP system
is closed. In contrast, when the IP system is closed, the resultant
thrust force becomes unbalanced because of the t h r u s t force acting
on the third dummy member 113 and the resultant thrust force
increases rightward. I n t h i s event, when the valve 44 U ( C V 1 ) is
opened, the pressure difference between both sides of the third
dummy member 113 is reduced and thus, the resultant thrust force
generated i n the whole steam turbine can be balanced. In addition,
when the IP system is closed, the pressure difference between both
sides of the third dummy member 113 can be also reduced via the
steam leakage through the dummy member 113, by appropriately
closing the valve 142 instead of opening the valve 141. As a result,
the resultant thrust force generated in the whole steam turbine can
be balanced.

(Third Preferred embodiment)

FIG.12 shows an outline of the HP-IP steam turbine provided
with the dummy members for adjusting thrust forces according to a
third preferred embodiment of the present invention.
The same components in FIG.12 as in F I G . l l are givin
common numerals and are not explained further.
In FIG.12, a first dummy member 111'is provided. The first
dummy member 111' is formed by integrating the f i r s t dummy
member 111 and the second dummy member 112 (shown in FIG.111,
whose diameter is as same as the diameter of the f i r s t dummy
member 111. Hereby, the steam turbine in FIG.12 is not provided
with the balance conduit 121. Instead, the balance conduit 122 is
provided with a bypass conduit 123 that bypasses the valve 142.
Further, an orifice 124 is provided on the bypass conduit 123.
In a manner similar to the second preferred embodiment, the
resultant thrust force can be balanced, except when the IP system is
closed. When the IP system is closed, the resultant thrust force can
be balanced by adjusting the opening of the valve 142.
In the above event, when it is difficult to adjust the opening
of the valve such as setting the opening of the valve 142 at a minimal
level. it is recommendable to close the valve 142 and use the
orifice 124. In relation to this event, it is necessary to set the
size of the orifice in advance so that with the valve 142 being
full-closed, the steam pressure at a back side of the third dummy
member 113 is appropriate.
In other words, in a case where the IP system is closed, the
valve 142 is closed and the steam streams through the orifice 124.
Thus, the steam pressure a t the hack side of the third dummy
member 113 is appropriately maintained. Hence, the resultant
thrust force can he balanced.

Industrial Applicability

According to the present invention, it is possible to provide a
steam turbine and a method of adjusting a t h r u s t force of the steam
turbine acting on a rotor shaft of the turbine i n an entire operating
range of the steam turbine without upsizing a LP dummy member or
without using an electric control of a complicated system.

WE CLAIMS
1. A steam turbine having a t least a high-pressure blade
cascade, an intermediate-pressure blade cascade and a plurality 'of
dummy members that are attached to a common rotor shaft, the
steam turbine comprising:
a detection unit that detects a steam flow into an
intermediate-pressure chamber;
a pressure reducing unit that reduces a pressure difference
between both sides of a target dummy member of said plurality of
the dummy members when the steam flow into the
intermediate-pressure chamber stops, the target dummy member
having one side communicating with a part of the
intermediate-pressure chamber; and
a control unit that controls the pressure reducing unit based
on a detection result obtained by the detection unit.
2. The steam turbine according to claim 1,
wherein the pressure reducing unit comprises:
a first conduit that connects the both sides of the target
dummy member; and
a first valve that is provided i n the f i r s t conduit to adjust the
pressure difference between the both sides of the target dummy
member.
3. The steam turbine according to claim 2, further comprising:
a third conduit that connects the one side of the pressure
reducing u n i t t o an outlet of the intermediate-pressure chamber; and
a third valve that is provided i n the third conduit,
wherein, when the f i r s t valve opens while the steam flow into
the intermediate-pressure chamber is not stopped, the control unit
controls the third valve to open so as to generate the pressure
difference between the both sides of the target dummy member.
4. The steam turbine according to any one of claims 1 to 3,
wherein the pressure reducing unit comprises:
a second conduit that connects the part of the
intermediate-pressure chamber and the one side of the target
dummy member; and
a second valve that is provided in the second conduit to
adjust the difference between the both sides of the target dummy
member,
wherein the second valve is closed when the steam flow into
the intermediate- pressure chamber stops.
5. The steam turbine according to claim 4, further comprising:
a bypass conduit that is provided to bypass the second valve;
and
an orifice that is provided i n the bypass conduit.
6. The steam turbine according to claim 4, further comprising:
a third conduit that connects the one side of the pressure
reducing u n i t t o an outlet of the intermediate-pressure chamber; and
a third valve that is provided in the third conduit,
wherein, when the second valve closes while the steam flow
into the intermediate-pressure chamber is not stopped, the control
unit controls the third valve to open so as to generate the pressure
difference between the both sides of the target dummy member.
7 A method of adjusting a thrust force of a steam turbine
having a t least a high-pressure blade cascade, an
intermediate-pressure blade cascade and a plurality of dummy
members t h a t are attached to a common rotor shaft, the method
comprising the step of:
reducing a pressure difference between both sides of a target
dummy member of said plurality of the dummy members when the
steam flow into the intermediate-pressure chamber stops, the target
dummy member having one side communicating with a part of the
intermediate-pressure chamber.
8. The method of adjusting the thrust force of the steam turbine
according to claim 7,
wherein the pressure difference between the both sides of the
target dummy member is reducible by use of a first valve provided in
a first conduit t h a t connects the both sides of t h e t a r g e t dummy
member.
9. The method of adjusting the thrust force of the steam turbine
according to claim 8,
wherein, when the f i r s t valve opens while the steam flow into
the intermediate. pressure chamber is not stopped, the pressure
difference is generated between the both sides of the target dummy
member by opening a third valve which is provided in a third conduit
that connects the one side of the target dummy member to an outlet
of the intermediate-pressure chamber.
10. The method of adjusting the thrust force of the steam turbine
according to any one of claims 7 to 9,
wherein the pressure difference between the both sides of the
target dummy member is reducible by use of a second valve provided
in a second conduit that connects the ,part of the
intermediate-pressure chamber and the one side of the target
dummy member.
11. The method of adjusting the thrust force of the steam turbine
according to claim 10,
wherein, when the second valve closes while the steam flow
into the intermediate-pressure chamber is stopped, the pressure
difference is generated between the both sides of the target dummy
member by opening a third valve which is provided in a third conduit
that connects the one side of the target dummy member to an outlet
of the intermediate-pressure chamber.