U.S. patent number 3,757,130 [Application Number 05/098,568] was granted by the patent office on 1973-09-04 for overspeed preventive apparatus for engines.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Ryosuke Arie, Mamoru Huzieda, Takashi Kishigami, Katsumi Takemura, Yoshihiro Uchiyama, Akihiro Yasumoto.
United States Patent |
3,757,130 |
Uchiyama , et al. |
September 4, 1973 |
OVERSPEED PREVENTIVE APPARATUS FOR ENGINES
Abstract
An electro-hydraulic overspeed preventive apparatus for an
engine in which two overspeed preventive control systems are
provided in addition to a speed control system including a working
fluid flow regulating valve disposed at the inlet of the engine and
means for controlling the opening of the working fluid flow
regulating valve in response to an error signal representative of
the deviation of the actual speed from the desired speed. The two
overspeed preventive control systems respectively are operated to
close the working fluid flow regulating valve prior to the
operation of the speed control system when the acceleration signal
representative of the actual acceleration exceeds a predetermined
limit and when the difference between two signals respectively
representative of the state of flow of the working fluid and the
electrical output of the load exceeds a predetermined limit.
Inventors: |
Uchiyama; Yoshihiro (Hitachi,
JA), Yasumoto; Akihiro (Hitachi, JA),
Takemura; Katsumi (Hitachi, JA), Kishigami;
Takashi (Hitachi, JA), Huzieda; Mamoru
(Ibaraki-ken, JA), Arie; Ryosuke (Hitachi,
JA) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JA)
|
Family
ID: |
27298439 |
Appl.
No.: |
05/098,568 |
Filed: |
December 16, 1970 |
Foreign Application Priority Data
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|
|
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Dec 19, 1969 [JA] |
|
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44/101646 |
Dec 19, 1969 [JA] |
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44/101647 |
Jul 24, 1970 [JA] |
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45/64306 |
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Current U.S.
Class: |
290/40R; 415/17;
361/239 |
Current CPC
Class: |
H02P
23/16 (20160201) |
Current International
Class: |
H02P
23/00 (20060101); H02p 009/04 () |
Field of
Search: |
;317/5,19,21 ;415/17,10
;60/105,39.2,39.25 ;290/40 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Simmons; G. R.
Claims
What is claimed is:
1. An apparatus for preventing an engine from overspeed
comprising:
a working fluid flow regulating valve disposed at the inlet of the
engine;
first means, responsive to the speed of the engine, for detecting a
deviation between the actual speed of the engine and a
predetermined speed, and for selectively controlling the opening
and closing of said working fluid flow regulating valve in response
to said deviation;
second means, responsive to the rate of change of the speed of the
engine, for detecting a deviation between the actual acceleration
of the engine and a predetermined acceleration and for generating a
first electrical signal representative of said deviation;
third means, responsive to the state of flow of the working fluid
passing through said engine, for generating a second electrical
signal representative thereof;
fourth means, responsive to the output load of said engine for
generating a third electrical signal representative thereof;
fifth means, coupled to the outputs of said third and fourth means,
for combining said second and third electrical signals and for
generating a fourth electrical signal when said combined second and
third electrical signals exceed a predetermined fixed value;
and
sixth means, coupled to said second and fifth means, for
controlling the rapid opening and closing of said working fluid
flow regulating valve, in response at least one of said first and
fourth electrical signals, independently of the control of the
opening and closing of said working fluid flow regulating valve by
said first means.
2. An apparatus according to claim 1, wherein said first means
includes a hydraulic servo valve means, coupled to said working
fluid flow regulating valve, for controlling the opening of said
working fluid flow regulating valve, and wherein said sixth means
includes a dumping valve, coupled to said hydraulic servo valve
means, for draining hydraulic fluid from said hydraulic servo valve
means, in response to at least one of said first and fourth
electrical signals.
3. An apparatus according to claim 1, wherein said first means
includes valve actuator means, coupled to said working fluid flow
regulating valve, for controlling the actuating thereof in response
to an electrical signal applied thereto, and further including
seventh means coupled to said first means, for generating a fifth
electrical signal to be supplied to said valve actuator means, in
response to the rate of change of said deviation exceeding a
preselected amount.
4. An apparatus according to claim 1, wherein said second and fifth
means include means for enabling the generation of said first and
fourth electrical signals prior to the selective control by said
first means in response to the cut-off of a high load from said
engine, while preventing the generation of said first and fourth
electrical signals in response to the cut-off of a relatively lower
load from said engine, to thereby permit said first means to
control the opening and closing of said working fluid flow
regulating valve at a cut-off of a relatively lower load.
5. An apparatus according to claim 2, wherein said second and fifth
means include means for enabling the generation of said first and
fourth electrical signals prior to the selective control by said
first means in response to the cut-off of a high load from said
engine, while preventing the generation of said first and fourth
electrical signals in response to the cut-off of a relatively lower
load from said engine, to thereby permit said first means to
control the opening and closing of said working fluid flow
regulating valve at a cut-off of a relatively lower load.
6. An apparatus according to claim 5, wherein said first means
includes valve actuator means, coupled to said working fluid flow
regulating valve, for controlling the actuating thereof in response
to an electrical signal applied thereto, and further including
seventh means coupled to said first means, for generating a fifth
electrical signal to be supplied to said valve actuator means, in
response to the rate of change of said deviation exceeding a
preselected amount.
7. An apparatus according to claim 2, wherein said first means
includes valve actuator means, coupled to said working fluid flow
regulating valve, for controlling the actuating thereof in response
to an electrical signal applied thereto, and further including
seventh means coupled to said first means, for generating a fifth
electrical signal to be supplied to said valve actuator means, in
response to the rate of change of said deviation exceeding a
preselected amount.
8. An apparatus according to claim 7, further including delay
means, coupled between at least one of said second and fifth means
and said sixth means, for continuing the actuation of said dumping
valve until a sufficiently large signal for closing said working
fluid flow regulating valve is supplied from said first means
through said servo valve means.
9. An apparatus according to claim 8, wherein said delay means is
coupled between each of said second and fifth means and said sixth
means.
10. An apparatus according to claim 8, wherein said fifth means
comprises a first summing amplifier to which said second and third
signals are applied, a first comparator circuit for comparing the
output of said first summing amplifier with a first reference
voltage and a first solenoid switch coupled to the output of said
first comparator circuit for enabling the coupling of said fourth
electrical signal to said sixth means.
11. An apparatus according to claim 10, wherein said second means
comprises a first differentiator circuit to which a signal
representative of the actual speed of the engine is applied, a
second comparator circuit for comparing the output of said first
differentiator circuit with a second reference voltage and a second
solenoid switch coupled to the output of said second comparator
circuit for enabling the coupling of said first electrical signal
to said sixth means.
12. An apparatus according to claim 11, wherein said seventh means
comprises a second differentiator circuit to which a signal
representative of said speed deviation is applied and a voltage
threshold responsive amplifier circuit for enabling the generation
of said fifth signal to be supplied to said valve actuator means
when the load of the engine has been cut off.
13. An apparatus according to claim 12, wherein each of said delay
means comprises a pair of solenoid switches the windings of which
are connected in parallel with a slow release contact responsive to
one of said windings, coupled to the supply line therefor, while
the output of the other winding is connected to said sixth means.
Description
This invention relates to an apparatus for preventing engines such
as steam turbines from an overspeed.
The increase in the unit output of engines such as steam is
followed by a general tendency toward reduction in the weight of
the turbine rotor compared with the turbine output, and the turbine
rotor tends to be more easily accelerated than heretofore. A fairly
rapid response to speed is therefore required for the speed
governing system for the steam turbine. However, conventional
mechanical speed governors employing levers as a component thereof
have had a certain limit in the ability to respond to speed due to
various factors including mechanical friction, play and
inertia.
Further, the increase in the turbine output results in a complex
structure of the plant including the turbine equipment and it is
necessary to monitor and control the operation of the whole plant
by the transfer of signals between it and an electronic computer
combined therewith. It is apparent that a speed governor consisting
of mechanical elements is not fit for this kind of control. An
electro-hydraulic speed governing apparatus has appeared to meet
various demands, including the ability to rapidly respond to speed,
the complexity of the structure of the control mechanism and the
ease of transfer of signals, which are required for the speed
governing apparatus for the steam turbine.
It is an object of the present invention to provide an apparatus
for preventing an engine such as a steam turbine from an overspeed,
which includes two overspeed preventive systems of different
characters thereby to positively protect the steam turbine against
damage.
Another object of the present invention is to provide an apparatus
of the kind above described which is capable of quickly closing a
fluid flow regulating valve in response to a signal indicative of
the cut-off of a load.
Still another object of the present invention is to provide an
apparatus of the kind above described in which a dumping valve is
provided for draining hydraulic fluid from the servo valve disposed
in the speed control system so as thereby to reduce the size of the
servo valve.
A further object of the present invention is to provide an
apparatus of the kind above described in which the overspeed
preventive systems have valve closing means of different kinds
responsive to the cut-off of a high load and a low load
respectively so that the overspeed preventive systems are operable
within a narrow range.
The above and other objects, features and advantages of the present
invention will be apparent from the following detailed description
taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a block diagram of an electro-hydraulic speed governor
system adapted to be used with a reheating steam turbine having a
reheater;
FIG. 2 is a block diagram of an apparatus according to the present
invention;
FIG. 3 is a diagrammatic view showing the structure of the
apparatus of the present invention in more detail; and
FIG. 4 is a graph showing a maximum value of the rotor speed
relative to a load when the load is cut off in a reheating steam
turbine equipped with the overspeed preventive apparatus according
to the present invention.
Quick closure of a steam flow regulating valve is always
encountered with two problems. One of the problems is how fast an
abrupt increase in the speed due to, for example, cut-off of a load
is detected, while the other problem is how fast the valve is
closed in response to the signal indicative of the abrupt increase
in the speed.
Consider now a case in which a load of a steam turbine generator
operating in the steady state while driving the load is momentarily
cut off. The phenomenon which takes place in such a condition will
be discussed in detail hereunder. During the steady operation of
the steam turbine generator, there is an exact balance between the
power given by the steam for rotating the turbine rotor and the
power transmitted to an associated power system from the generator
connected to the turbine for consumption by the electric power
system. Cut-off of the load represents a transient state in which
the power consumed by the latter is removed momentarily from the
state of equilibrium resulting in a great unbalance and steam in a
quantity more than is required is supplied to the turbine rotor.
The turbine rotor is accelerated due to the unbalance between the
power applied thereto and the power consumed by the load, and the
speed of the turbine rotor is subject to a variation until the
unbalance is eliminated. This power unbalance appears necessarily
before the turbine rotor is accelerated. The unbalance corresponds
to the deviation of the actual speed of the turbine rotor from the
desired speed. Therefore, if it is possible to detect the
occurrence of the unbalance and to close the steam flow regulating
valve before the turbine rotor is subject to acceleration, an
undesirable overspeed can be more effectively prevented than with
the speed control system in which control operation is not started
until the speed is increased and a signal indicative of the
increase in the speed is fed back to the input side.
The load imparted to the rotor of the turbine driving the generator
can be quantitatively known by detecting the load of the generator,
that is, the output (wattage) of the generator determined by the
generated current and voltage, or by detecting the current when the
voltage is constant. On the other hand, the power imparted to the
turbine rotor can be quantitatively known by detecting whether the
working fluid acting upon the turbine rotor has a sufficient
potential to flow and the flow occurs actually. In other words, the
power imparted to the turbine rotor can be quantitatively known by
detecting whether the working fluid flowing downstream of the steam
flow regulating valve has a pressure and seeking the value of the
fluid pressure if the fluid has a pressure. In the case of a
reheating steam turbine especially, the power developed by the
intermediate and low pressure turbine disposed downstream of the
reheater occupies about 70 percent of the total power, and the
steam in the reheater flows into the intermediate and low pressure
turbine to transmit the power to the turbine rotor even when the
first valve disposed at the inlet of the high pressure turbine is
closed. Therefore, the opening of the second valve disposed
downstream of the reheater or fluid pressure at the outlet of this
valve should be detected in order to know the power imparted to the
turbine rotor. Repeating again, the occurrence of an unbalance as
described above results in the acceleration of the turbine rotor.
The greater the unbalance and the lighter the weight of the turbine
rotor, the turbine rotor is accelerated to a greater degree.
Further, the greatest acceleration of the turbine rotor is seen
immediately after the unbalance occurs. Thus, if this acceleration
could be detected, the tendency and degree of the turbine rotor
toward rotation at an overspeed can be known.
In order that the fluid flow regulating valve can be quickly
closed, it is necessary to quickly discharge the hydraulic pressure
having been imparted to the piston in the hydraulic cylinder for
maintaining the valve in the open position. The discharge of
hydraulic fluid or oil can be done by the use of the servo valve
disposed in the speed control system. However, the servo valve must
have a considerably large capacity in order that the turbine valve
can be closed at an actually required high speed by the servo
valve.
The intermediate flow restricting valve in the reheating steam
turbine is maintained in a substantially full opened position
during the normal operation of the turbine, and therefore a servo
valve of a small capacity may be satisfactorily used in conjunction
with the intermediate flow restricting valve. However, when a valve
of a large capacity is required for the quick closure of the fluid
flow regulating restricting valve in the case of an emergency only,
it is economical to provide a second dumping valve to serve for
quick closure of the flow restricting valve beside the servo valve.
That is, a dumping valve adapted to serve solely for the purpose of
the quick closure of the fluid flow regulating valve (adjusting
valve or intermediate flow restricting valve) is preferably
provided in addition to the servo valve.
The action of the dumping valve for the quick closure of the fluid
flow regulating valve is applied from the system external to the
speed control system as described above, and it is, as it were, a
sort of external disturbance applied to the speed control system
when considered from the side of the speed control system.
Therefore, there is a need for switch-over from the external system
to the speed control system for continuously maintaining the
turbine at a controlled speed after the load has been cut off and
the turbine has started to run steadily at no load. There is also
an interference between the two systems on the same valve. It is
therefore desirable that the dumping valve may not be operated
except for the quick closure of the fluid flow regulating valve,
and the fluid flow regulating valve may normally be closed by the
operation of the speed control system, hence by the servo valve.
The operation of the dumping valve does not vary depending on the
degree of the load cut off, and the designing of the dumping valve
so as to respond to a too small unbalance in the upper load is
undesirable from the viewpoint of satisfactory operation of the
turbine in that the dumping valve operates incessantly in response
to a small transient variation in the load. It is therefore
desirable to limit the operating range of the dumping valve to a
minimum and to arrange so that the fluid flow regulating valve be
quickly closed by the speed control system in the case of the
cut-off of a low load.
One of the problems inherent in the electrohydraulic speed governor
is the reduction of reliability due to the increase in the number
of component parts. In other words, the electronic circuit of the
electrohydraulic speed governor includes a very large number of
transistors, resistors, condencers, etc., and it is quite probable
that even carefully selected parts may fail to properly function.
Accordingly, the unbalance detecting and valve actuating system
should be provided in duplex for improving the safety taking into
consideration possible failure of the safeguard means.
Referring now to the drawings wherein like parts are indicated by
like reference numerals throughout the figures and referring
particularly to FIG. 1, a high pressure steam turbine 1 and an
intermediate and low pressure steam turbine 2 are connected to an
electric generator 3. Steam is supplied through a first steam flow
regulating valve 4 into the high pressure turbine 1 to impart a
portion of its effective energy to the turbine rotor. The exhaust
from the high pressure turbine 1 is reheated by a reheater 5, and
the reheated steam is supplied through a second steam flow
regulating valve 6 into the intermediate and low pressure turbine 2
to be finally exhausted therefrom.
A contact-less electromagnetic pickup 8 disposed adjacent to a gear
7 mounted on the rotary shaft of the generator 3 detects the
rotational speed of the turbine rotor and delivers a pulse signal
which is proportional to the speed of the turbine rotor. A
digital-analog converter 9 converts the pulse signal into a d.c.
voltage which is proportional to the rotational speed of the
turbine rotor. The d.c. voltage signal indicative of the actual
speed N is compared in an adder 10 with a desired speed N.sub.O,
and the difference is amplified by an amplifier 11. The deviation
or error signal thus amplified is applied to a servo valve 12 in
which the electrical signal is converted into a corresponding
displacement of the valve spool for actuating the piston in a
hydraulic cylinder 13 which actuates the valve 4. The motion or
stroke of the piston is converted into an electrical signal by a
stroke detector 14 and the electrical signal is fed back through an
operational amplifier 15 to the input side of the servo valve 12 to
set the position of the valve 4 relative to the actuating
signal.
In the meantime, the speed deviation or error signal is amplified
by an amplifier 16 to be applied to a servo valve 18 in which the
electrical signal is converted into a corresponding displacement of
the valve spool for actuating the piston in a hydraulic cylinder 17
which actuates the valve 6. The motion or stroke of the piston is
converted into an electrical signal by a stroke detector 20 and the
electrical signal is fed back through an operational amplifier 21
to the input side of the servo valve 18 to set the position of the
valve 6 relative to the actuating signal. During the normal
operation, the flow rate of the fluid is regulated by the valve 4,
while the valve 6 which has a greater opening than the valve 4 is
opened fully and does not requlate the fluid flow. The amplifier 16
acts to establish such a static relationship between the valves 4
and 6 relative to the speed error signal.
It will be seen that, when the rotational speed of the turbine
rotor is increased to bring a large deviation of the actual speed
from the desired speed due to an unbalance between the fluid
supplied to the turbine and the load resulting from the cut-off of
the load, the valve 4 is first closed and the valve 6 is
subsequently closed in response to the error signal appearing in
such a basic control system. However, with the recent general
tendency toward a higher unit output of the turbine and a larger
capacity of the reheater, it has become the absolutely essential
condition that the valves 4 and 6, especially the valve 6 be closed
more quickly. More precisely, it has become the essential condition
that the valve 6 be transiently quickly closed, or in some cases,
closed earlier than the valve 4 to quickly shut off the flow of
working fluid in the event of an unusual state such as an abrupt
increase in the speed of the turbine rotor, while the static
relationship between the valves 4 and 6 is maintained by the basic
speed control system in the manner described above during the
normal operation.
An apparatus according to the present invention which meets the
above requirement is diagrammatically shown in FIG. 2. Referring to
FIG. 2, the apparatus comprises a basic speed control system which
includes an electronic circuit group 24 and a valve actuating means
28. The electronic circuit group 24 generates a valve actuating
signal 74 in response to the application of a signal 22
representative of the speed setting, a signal 23 representative of
the load demand and a signal 25 representative of the actual speed
of the turbine rotor. The valve actuating means 28 actuates a steam
valve means 29 in response to the valve actuating signal 74.
In addition to the basic speed control system described above, the
apparatus comprises an overspeed preventive control system which
includes means 36 and a relay means 37. A signal 34 representative
of the fluid pressure downstream of the steam valve means 29 or a
signal 34' representative of the opening of the steam valve means
29 and a signal 35 representative of the power or current at the
load are applied to the means 36 to be compared with each other in
the means 36. When the difference or unbalance between the signal
34 or 34' and the signal 35 is greater than a predetermined setting
33 which is also applied to the means 36 in the form of a signal,
the means 36 energizes the relay means 37 for quickly urging the
steam valve means 29 into the fully closed position. That is, this
system monitors the operation of the turbine by detecting any
unbalance between the power input and power output to and from the
turbine rotor on the basis of the signals 34 or 34' and 35, and
actuates immediately the relay means 37 and a rapid valve-closing
means to quickly close the steam valve means 29 when the unbalance
exceeds the predetermined setting 33 resulting in the danger of
rotation of the turbine rotor at an overspeed. Thus, this system
acts to quickly close the steam valve means 29 independently of the
basic speed control system. By virtue of the provision of such a
system, a servo valve of a relatively small capacity can be used
for the speed control during the normal operation in which the
quick control described above is not required, while the steam
valve means 29 can be quickly closed in the case of an overspeed
which occurs quite rarely. Another overspeed prevention control
system in the apparatus includes an acceleration comparing means 31
and a relay means 32. The speed signal 25 is applied to the
acceleration comparing means 31 in which the speed signal 25 is
differentiated to obtain the acceleration and this acceleration is
compared with an acceleration setting 30. In the event that the
acceleration exceeds the fixed value resulting in the possibility
of overspeed, the acceleration comparing means 31 actuates the
relay means 32 and the rapid valve-closing means 80 to close the
steam valve means 29 independently of the basic speed control
system. The two systems for energizing the respective relay means
32 and 37 are provided for the purpose of improving the safety of
the electro-hydraulic speed governor which includes a large number
of parts. That is, the provision of the two unbalance detecting and
valve actuating systems is advantageous in that the operation of
any one of these two systems can safely prevent an undesirable
overspeed and the safety can be ensured even in the event of
failure of either system.
The relay means 32 and 37 are restored to the original de-energized
state after the overspeed is eliminated and the basic speed control
system including the electronic circuit group 24, the valve
actuating means 28 and the steam valve means 29 is now ready to
carry out the normal speed control.
The systems for externally closing the steam valve means 29 operate
whenever the respective operating conditions are satisfied and make
on-off operation to close the valve means 29 at a maximum speed
regardless of the magnitude of the load cut off. The operation of
these external systems may provide a sort of external disturbance
when considered from the side of the basic control system, and
there may be an interference between the basic speed control system
and the external systems. It is therefore desirable to prevent the
external systems from operation as much as possible except the case
in which quick closure of the valve means 29 is required and to
close the valve means 29 by the basic control system in the case in
which the load is low. It is therefore preferred that the setting
33 of unbalance may have a greatest possible value and any
unbalance smaller than this value may be dealt with by a load
cut-off signal generator 27. The operation of the load cut-off
signal generator 27 may be such that it differentiates the valve
actuating signal 74, and after suitable amplification of the
differentiated value, delivers a signal which has such a polarity
as to work in the valve closing direction. This signal is applied
to an adder 26 to be added to the valve actuating signal 74. More
precisely, the load cut-off signal generator 27 does not deliver
any signal during the normal operation, but delivers a valve
closing signal which is dependent upon the magnitude of
acceleration when a large unbalance occurs resulting in the
acceleration. This valve closing signal is added by the adder 26 to
the valve actuating signal 74 representative of the speed deviation
and a signal of great magnitude is transiently applied to the valve
actuating means 28 to quickly close the valve means 29. By this
arrangement, the function of the basic speed control system can be
improved more effectively than when it is responsive solely to the
speed deviation or error signal thereby to close the valve means
29.
In FIG. 3, there is shown an embodiment of the present invention in
which the the present invention is applied especially to the quick
closure of steam flow regulating valve 6 provided in a steam valve
means.
A speed detector 38 detects the speed of the turbine rotor and
applies a signal 25 proportional to the actual speed of the turbine
rotor to an electronic circuit group 24. The electronic circuit
group 24 compares the signal 25 with a signal 22 representative of
the speed setting and a signal 23 representative of the load demand
to provide the valve actuating signal 74, in the same manner as
described with respect to FIG. 2. The valve actuating signal 74 is
applied to valve actuating circuits 44 and 45 for actuating the
respective steam flow regulating valves 4 and 6. The valve
actuating circuit 45 and a servo valve 18 constitute a valve
actuating means 28. The means 38, 24, 44 and 45 constitute a basic
speed control system similar to a prior art system which operates
in response to the speed deviation.
According to the present invention, a system including a load
cut-off signal generator 27 having means 40, 41 and 42 is
associated with the basic speed control system. The valve actuating
signal 74 for actuating the valve 6 is applied to a differentiator
40 to be differentiated thereby. The greater the variation in the
valve actuating signal 74, that is, the higher the speed with which
the valve 6 is closed in response to the increase in the speed of
the turbine rotor due to the cut-off of the load, the output signal
delivered from the differentiator 40 has a correspondingly greater
magnitude. A slide resistor 41 acts as a selective circuit which
does not allow the passage of the output signal of the
differentiator 40 until the valve closing signal delivered from the
differentiator 40 exceeds a fixed value which is set up on the
basis of the value when the load has been cut off. Thus, no signal
is delivered from the selective circuit 41 during the normal
operation in which the rate of speed variation is small, while the
valve closing signal which is dependent upon the rate of speed
increase is delivered transiently from the selective circuit 41
only when the rate of speed increase exceeds a fixed value to an
extent that the valve 6 must be quickly closed, namely, when the
load has been cut off. An amplifier 42 maintains the transiently
generated signal until it disappears gradually so as not to urge
the valve 6 into an open position due to an abrupt reduction in the
magnitude of the signal resulting from a reduction in the rate of
speed increase. The signal delivered from the system described
above is applied to an adder 26 provided in the speed control
system. The output signal of the adder 26 is amplified by an
amplifier 39 and then applied to the valve actuating circuit 45. By
virtue of the provision of the system described above, the
function, for actuating the valve 6, of the basic speed control
system responsive solely to the speed deviation can be effectively
improved.
The valve actuating signal delivered from the valve actuating
circuit 45 is applied to the servo valve 18 to control the position
of a piston 76 in a hydraulic cylinder 73, which is provided in the
steam valve means 29, against the force of a spring 75 thereby to
actuate the valve 6. Meanwhile, in a rapid valve-closing means 80,
a dumping valve 72 is normally kept in the closed position, but
when it is required to quickly close the valve 6, the dumping valve
72 is urged into the open position to drain hydraulic fluid or oil
from a drain port 77 so that the valve 6 can be closed quicker than
when it is closed by the servo valve 18. It will thus be seen that
the dumping valve 72 operates in the case in which the operation of
the servo valve 18 cannot prevent an overspeed higher than an
allowable value, thereby protecting the turbine from damage. The
dumping valve 72 is actuated by a solenoid 71 which is energized
when one of relay contacts 57 and 70 is in the on state.
A transmitter 58 for detecting the state of flow of the working
fluid passing through the engine thereby producing an electrical
output signal, for example, for converting the steam pressure at
the outlet of the valve 6 into an electrical output signal 34, and
a transmitter 59, for converting the electrical output of the load
or the output current of the generator, into an electrical output
signal 35, apply the respective output signals 34 and 35 to a
summing amplifier 60, which constitutes a comparing means 36
together with a comparator 61, a contact 63 and a solenoid 64. In
the summer amplifier 60, one of the signals 34 and 35 is subtracted
from the other and the difference signal is applied to the
comparator 61. The comparator 61 compares the difference signal
with a reference voltage and the contact 63 is closed when the
difference between the difference signal and the reference voltage
exceeds a fixed value. The closure of the contact 63 energizes the
solenoid 64 to thereby close a contact 65. The reference voltage is
set up to be larger than the difference signal produced by the
summing amplifier 60 in response to the cut-off of a predetermined
load. Thus, this overspeed preventive control system, including the
comparing means 36, is capable of operating in response to the
cut-off of a high load which is higher than the predetermined load.
However, when a low load, which is lower than the predetermined
load, is cut-off, this overspeed preventive control system is not
operative, and the signal delivered from the load cut-off signal
generator 27 is applied to the adder 26, to thereby rapidly close
the valve 6, through the valve actuating means 28 short of a
tripping of the machine. The closure of the contact 65 energizes
solenoids 67 and 68 of a relay means 37, and a contact 66 is closed
to establish a self-holding circuit so that the solenoids 67 and 68
are kept energized even when the contact 63 is opened due to the
disappearance of the operating condition which has appeared before.
The energization of the solenoid 67 closes the contact 70 resulting
in the energization of the solenoid 71. A timer relay disposed in
the relay means 37 is energized in response to the energization of
the solenoid 68, and its contact 69 is opened after a predetermined
length of time to cut off the energizing current supplied to the
solenoids 67 and 68 with the result that the contact 70 is urged
into the original open position. The length of time ranging from
the actuation of the contact 70 to the restoration thereof is so
determined that the dumping valve 72 may not be restored to the
original closed position until a sufficiently large signal for
closing the valve 6 is applied to the piston 73 from the basic
speed control system through the servo valve 18 due to the increase
in the speed of the turbine rotor. After the restoration of the
dumping valve 72 to the original closed position, the valve 6 is
actuated under the control of the basic speed control system.
The speed signal 25 is also applied to a limiter 43 disposed in a
comparing means 31 which includes a potentiometer 46, an amplifier
47, an element 48, a summing amplifier 49, a solenoid 51 and a
contact 62. The limiter 43 is connected to the potentiometer 46 so
that a signal is delivered from the limiter 43 only when the speed
exceeds the rated speed. This signal is applied to the amplifier 47
for giving a time lag of first order and to the element 48. The
amplifier 47 and element 48 apply their output signals to the
summing amplifier 49 in which one of the signals is subtracted from
the other so that the summing amplifier 49 delivers a signal which
is representative of the acceleration obtained by differentiating
the speed signal 25 and has a higher voltage level at a greater
rate of speed increase. This signal representative of the
acceleration is compared in the comparator 50 with a reference
voltage, to thereby produce a difference signal. The contact 62 is
closed to energize a solenoid 51 thereby to close a contact 52 when
the difference signal which indicates a danger due to the
acceleration exceeds predetermined setting. Thus, this overspeed
preventive control system, including comparing means 31, is capable
of operating in response to the cut-off of a high load, which is
higher than a predetermined load. However, when a low load which is
relatively lower than the predetermined load, is cut-off, this
overspeed preventive control system is not operative, but the
signal delivered from the load cut-off signal generator 27 is
applied to the adder 26, to thereby rapidly close the vlave 6
through the valve actuating means 28, in the same manner as
discussed in connection with the above overspeed preventive control
system including comparing means 36. The closure of the contact 52
energizes solenoids 53 and 55 of a relay means 32, and a contact 54
is closed to establish a self-holding circuit, so that the
solenoids 53 and 55 remain energized even when the contact 62 is
opened due to the disappearance of the operating condition which
has previously appeared. The energization of the solenoid 53 closes
the contact 57, so as to actuate the rapid valve-closing means 80,
to thereby rapidly close the valve 6 in the same manner as
previously discussed in connection with the above-mentioned
overspeed preventive control system. A timer, having a contact 56,
disposed in the relay means 32, also functions in the same manner
as the timer in the relay means 37. It will thus be seen that the
apparatus according to the present invention ensures an increased
reliability and can protect the turbine from damage in a more
positive manner than heretofore by virtue of the provision of the
two independent unbalance detection and signal transmission systems
for energizing the solenoid 71.
Referring to FIG. 4, the dumping valve 72 is actuated when the load
exceeds a point A, and in the range in which the load is lower than
that shown by the point A, the speed control by means of feedback
is solely carried out. It will be seen from FIG. 4 that the speed
can be maintained at a value lower than the maximum allowable speed
.phi..sub.a over the entire range of the load.
* * * * *