U.S. patent number 3,718,837 [Application Number 05/244,796] was granted by the patent office on 1973-02-27 for control system for an extraction turbine system.
This patent grant is currently assigned to Tokyo Shibaura Electric Company Limited. Invention is credited to Hiroya Sato, Mitsuhisa Yokota.
United States Patent |
3,718,837 |
Yokota , et al. |
February 27, 1973 |
CONTROL SYSTEM FOR AN EXTRACTION TURBINE SYSTEM
Abstract
A control system for an elastic fluid turbine having a high
pressure turbine stage and a motive fluid flow thereto regulated by
a main control valve, and a low pressure turbine stage to which the
flow of motive fluid is controlled by an interstage control valve.
A speed/load control arrangement controls the main and interstage
control valves in the same directions responsive to rotational
speed of the turbine and a pressure control arrangement controls
the valves respectively in opposite directions responsive to the
pressure of extracted motive fluid. The control of the main control
valve by the pressure control arrangement is interrupted when the
load of the turbine system is lost, to prevent overspeed upon such
occurrence.
Inventors: |
Yokota; Mitsuhisa (Asahi-ku,
Yokohama-shi, Kanagawa-ken, JA), Sato; Hiroya
(Isogo-ku, Yokohama-shi, Kanagawa-ken, JA) |
Assignee: |
Tokyo Shibaura Electric Company
Limited (Kawasaki-shi, JA)
|
Family
ID: |
12157449 |
Appl.
No.: |
05/244,796 |
Filed: |
April 17, 1972 |
Foreign Application Priority Data
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|
|
|
|
Apr 19, 1971 [JA] |
|
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46/25133 |
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Current U.S.
Class: |
361/20; 60/646;
290/2; 361/51 |
Current CPC
Class: |
F01D
21/02 (20130101); F01K 7/345 (20130101) |
Current International
Class: |
F01D
21/02 (20060101); F01D 21/00 (20060101); F01K
7/34 (20060101); F01K 7/00 (20060101); H02h
007/06 () |
Field of
Search: |
;290/2,40 ;60/105
;307/86 ;317/13R,19 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Trammell; James D.
Claims
Accordingly what is claimed as new and desired to be secured by
letters patent of the United States is:
1. A control system for an extraction turbine system having a high
and low pressure turbine stages and driving a mechanical load
comprising:
main control valve means for regulating the flow rate of a motive
fluid from a motive fluid generator to said high pressure turbine
stage;
interstage control valve means for regulating the flow rate of the
motive fluid from said high pressure turbine stage to said low
pressure turbine stage;
a speed/load control arrangement for controlling said main and said
interstage control valve means in the same direction to each other
in response to the rotational speed of said turbine;
a pressure control arrangement for controlling said main and said
interstage control valve means in opposite directions to each other
in response to a pressure of the extracted steam; and
means for interrupting the control of said main control valve means
by said pressure control arrangement when said mechanical load of
the turbine is removed.
2. A control system as claimed in claim 1 wherein:
said mechanical load is an electric generator; and
said interrupting means is actuated when a circuit breaker which
connects said electric generator to an electric load thereof is
opened.
Description
BACKGROUND OF THE INVENTION
1. Field Of The Invention:
This invention relates generally to a control system for an elastic
fluid turbine and more particularly to a control system for a
turbine having at least one extraction stage.
2. Description Of The Prior Art:
In turbine control systems for elastic fluid turbines of the types
such as, for example, extraction noncondensing, extraction
condensing, two-stage extraction condensing, and the like, there
are provided speed/load control arrangements and extraction
pressure control arrangements. These control arrangements regulate
a main control valve unit and an interstage or integral control
valve unit, the main control valve unit controlling the flow rate
of the motive fluid from a motive fluid generator to a high
pressure turbine, and the interstage control valve unit controlling
the flow rate of the motive fluid from the high pressure turbine to
a low pressure turbine. Increasing or decreasing the opening of the
main control valve unit results in the output power of the turbine,
and also the pressure or quantity of the extracted fluid in the
extraction stage, being increased or decreased, whereas increasing
and decreasing the opening of the interstage control valve unit
results in the output power of the turbine being respectively
increased and decreased, while the pressure or quantity of the
extracted fluid is in turn decreased and increased.
Accordingly, the speed/load control arrangement is adapted to
regulate the main control valve unit and the interstage control
valve unit so as to control the turbine speed without adverse
effect on the extraction stage and the extraction pressure control
arrangement is adapted to regulate the main control valve unit and
the interstage control valve unit in a reverse direction of each
other so as to control the extraction of fluid without causing a
variation of the output power of the turbine. Also, the speed/load
control and the extraction control arrangements are adapted to
operate independently of each other, so that the desired speed of
the turbine and the desired pressure of the extracted fluid may be
achieved under a turbine operation having a load larger than a
predetermined value such as, for example, a half-load.
Under the condition where there is no variation in the desired
quantity of extracted fluid, the main control valve unit is
generally adapted to be operated to open and close against a speed
variation of the turbine at such a rate that the main control valve
unit is closed from the full load opening thereof to an opening
thereof at which the turbine operates at the rated speed under no
load, hereinafter referred to as the "no-load opening", when the
turbine speed rises above its rated speed by a predetermined value
such as, for example, 5 percent of its rated speed, thus
characterized as 5 percent speed regulation. In other words, the
output power of the turbine is caused to change from its rated
value to null when the speed reaches 105 percent of the rated
speed. Where a turbine system operated as described above drives an
electric generator, it is necessary to rapidly close the main
control valve unit to the "no-load opening" in order to prevent an
undesirable or dangerous speed rise when the generator load is lost
due to a fault in the electric power system to which the output of
the generator is supplied. However, the decrease in the opening of
the main control valve unit caused by the speed/load control
arrangement also tends to cause the quantity of the extracted fluid
to decrease, whereby the pressure control arrangement tends to
cause the main control valve to open. The turbine speed is then
liable to rise a relatively large amount.
In a turbine system wherein the quantity of the extracted fluid is
relatively large when compared with the total flow quantity of the
motive fluid being supplied to the turbine, the opening of the main
control valve is largely affected by the pressure control
arrangement. In these turbine systems, there is not only a fear
that the speed of the turbine is liable to reach 108 to 109 percent
of the rated speed but also a most perplexing problem of the speed
reaching a set speed, in Japan being usually 110 percent of the
rated speed, at which an over-speed trip device operates to stop
the operation of the turbine system. It is desirable to make the
over-speed as low as possible, and yet, once the over-speed trip
device operates to halt the operation of the system, it is
troublesome and time consuming to re-start the turbine system.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention is to provide a
turbine control system for a turbine system having one or more
extraction stages capable of preventing dangerous or undesirable
over-speed upon loss of load.
Briefly stated, according to this invention, the foregoing object
is attained by a control system for an extraction turbine system
having a high pressure turbine stage and a motive fluid flowing
thereto being regulated by a main control valve means, and a low
pressure turbine stage, the flow to which of a motive fluid is
controlled by an interstage control valve means. There are provided
a speed/load control arrangement and a pressure control
arrangement, the former controlling the main and interstage control
valve means in the same directions in response to rotational speed
of the turbine and the latter controlling the main and interstage
control/valves in opposite directions of each other in response to
the pressure of the extracted motive fluid. Additionally, means are
incorporated for interrupting control of the main control valve
means by the pressure control arrangement when the load of the
turbine system is removed, thereby to prevent an undesirable
over-speed from occurring upon loss of the turbine load.
BRIEF DESCRIPTION OF THE DRAWING
Various other objects, features and attendant advantages of the
present invention will be more fully appreciated as the same
becomes better understood from the following detailed description
when considered in connection with the accompanying drawing,
wherein:
FIG. 1 shows a schematic circuit diagram of one embodiment
according to this invention; and
FIG. 2 is a diagram to explain the operation of the embodiment
shown in FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, the embodiment shown therein is a control
system adapted for use with a turbine system which, generally being
indicated by the reference numeral 10, comprises a high pressure
turbine 11 and a low pressure turbine 12, which drive an electric
generator 13. A motive fluid, such as a steam generated by a motive
fluid generator, as for example, a steam boiler 14, flows through a
main control valve 15 to the high pressure turbine and expands
therein, whereupon one part of the steam flows through an
interstage or integral extraction control valve 16 to the low
pressure turbine 12 and the residual part of the steam flows out to
an extraction line 17. The steam flowing to the low pressure
turbine 12 expands therein, then finally flows to a condenser 18.
The main control valve 15 regulates the flow rate of the steam from
the steam generator 14 to the high pressure turbine 11, while the
interstage control valve 16 regulates the flow rate of the steam
from the high pressure turbine 11 to the low pressure turbine 12.
Although the actual system usually employs a plurality of main
control valves and a plurality of interstage control valves, as is
well known to those skilled in the art, for the sake of brevity,
only one control valve and one interstage valve are shown. The
extraction line is connected to a thermal load, not shown. Electric
power generated by the generator 13 is supplied through a main
circuit breaker 19 to electric loads 20, or supplied to an electric
power system 21 through a circuit breaker 22.
In order to detect the turbine speed, a pair of electro-magnetic
pick-up devices 23 and 24 are provided, and the output signals of
each are applied to speed detectors 25 and 26, respectively. The
speed signals from the detectors 25 and 26 are supplied to a high
value gate 27, which is arranged to transmit the higher speed
signal of the two speed signals applied thereto, whereby a speed
signal of fail safe is obtained at an output terminal thereof. A
sensor 28 and a pressure detecting device 29 are disposed in the
extraction line 17, whereby to provide an electric signal
representing the pressure of the extracted steam.
There is provided a speed/load controller, generally indicated by
the reference numeral 30, comprising a main device 31 and a speed
regulation setting device 32. The main S/L control device 31
compares the actual speed represented by the speed signal from the
high value gate 27 with a reference speed represented by a
reference signal from a speed setting device 33 to produce an
output signal. The maximum value of the output signal of the device
31 is limited in accordance with a reference signal from a load
setting device 34, thereby to limit the maximum load which the
turbine 10 can share. The output of the device 31 is treated in a
speed regulation setting device 32 for providing a speed control
signal. The speed regulation setting device 32 may be an
operational amplifying device having an input resistor, a high gain
amplifier and a feedback resistor. The amount of the speed
regulation can be adjusted by variation of the ratio between the
input and feedback resistors. The speed control signal is
responsively operable for opening of the main control valve 15 to
obtain the desired speed of the turbine 10 under the condition that
the turbine 10 has a load equal to or lower than that set by the
load setting device 34.
The speed control signal is applied to an adder 35 which may
comprise an operational amplifier 36, a pair of input resistors 37
and 38 and a feedback resistor 39. Also applied to the adder 35 is
a pressure control signal through the resistor 38, hereinafter
described. An output of the adder 35 is amplified by a power
amplifier 40, then applied to an electric-mechanical convertor 41.
A hydraulic servo mechanism 42 is provided to actuate the main
control valve 15 in accordance with the mechanical output of the
convertor 41.
The pressure signal from the pressure detector 29 is supplied to a
pressure controller, generally indicated by the reference numeral
43, to obtain a pressure control signal in a similar manner to the
treatment of the speed/load controller 30. The pressure controller
comprises a main device 44 and a pressure regulation setting device
45. The main pressure control device 44 compares the actual
pressure of the extracted steam represented by the pressure signal
from the detector 29 with a desired pressure represented by a
reference signal from a pressure setting device 46 to produce an
output signal, the maximum value thereof being limited by a signal
being applied from a setting device 47 of a limiter. The output
signal of the device 44 is applied to the pressure regulation
setting device 45 which may be an operational amplifier having
input and feedback resistors, to thereby provide a pressure control
signal. The amount of the pressure regulation can be adjusted by
adjustment of the ratio between the input and output resistors.
This pressure control signal is applied to an inverter or polarity
changer 48, which may also be an operational amplifier, and is
further applied to an adder 49. The adder 49 comprises a high gain
amplifier 50, a pair of input resistors 51 and 52, and a feedback
resistor 53. The output of the adder 49 is amplified by a power
amplifier 54 and is then supplied to an electric-mechanical
convertor 55, and the mechanical output thereof in turn is given to
a hydraulic servo mechanism 56 to drive the interstage control
valve 16.
The pressure control signal from the pressure controller 43 is also
supplied through a contact 57b of a relay 57 to the adder 35
through the input resistor 38 thereof, while the speed control
signal from the speed/load controller 30 is applied to the adder 49
through the input resistor 52 thereof.
In order to detect any loss of load of the generator 13, there is
provided a relay 58 which is connected in series with a contact 19b
which takes a closed position when the main circuit breaker 19 is
open and which takes an open position when the circuit breaker 19
is closed. The contact 19b may be an auxiliary contact associated
with the main circuit breaker 19. Thus, when the main circuit
breaker 19 is opened, the relay 58 is energized by power supply
busses P and N for the control operation, whereby the normally open
contract 58a of the relay 58 is operated to close. One terminal of
a relay 57 is connected to the control supply bus P while the other
terminal thereof is connected through a diode 59 of indicated
polarity and the contact 58a to the control supply bus N. There is
further provided a relay 60 connected in parallel with the relay
57. Provided across the lower terminal of the relay 60 and the bus
N are a normally open contact 60a of the relay 60 and a contact 61
in series relation. The contact 61 is an output contact of a
detector 62 which operates in response to the pressure control
signal from the pressure controller 43 in such a manner that the
contact 61 is open only when the pressure control signal takes a
value which represents that the pressure or the quantity of the
extracted steam is at a zero level. Thus when the main circuit
breaker 19 is open, and the contact 19b is closed, the relay 58 is
energized to cause the contact 58a thereof to close, whereby the
relays 57 and 60 are energized to cause the contacts 57b and 60a
respectively open and close. If the contact 58a becomes open, the
closure of the contact 60a keeps the energization of the relays 57
and 60 under a condition such that the contact 61 remains
closed.
There is further provided a contact 57a which is also one of the
related contacts of the relay 57 and takes a closed position only
when the relay 57 is energized. One terminal of the contact 57a is
connected to the lower input terminal in the drawing of the adder
35, and the other terminal is connected to an appropriate potential
supply P.sub.o which corresponds to a value of the pressure control
signal representing that the pressure of the extracted steam is
zero. In other words, the level P.sub.O is equal to that at which
the detector 62 operates to open the contact 61 thereof.
As is well known by those skilled in the art, in an actual system
many other devices are provided, such as, for example, control
means for partial arc operation, an over-speed trip device, and so
on, such devices being omitted herein because the description of
such devices is not essential for an understanding of this
invention.
The operation of this embodiment will now be explained with
reference to FIG. 1.
In the normal operation, the turbine 10 or the generator 13 bears a
load over the predetermined value, such as a half-load, which is
determined by the design of the system, and the desired quantity of
the steam is extracted from the high pressure turbine 11.
The main circuit breaker 19 is closed, so that the contact 19b is
open, and in turn, the relay 58 is de-energized so that the contact
58a is open, and the detector 62 detects the pressure control
signal to make the contact 61 thereof open, hence the relay 57 and
60 are in the de-energized state, whereby the contacts 57b and 57a
are closed and opened, respectively.
When the rotational speed of the turbine 10 tends to decrease as is
the case when there is no variation in the quantity of the
extracted steam, the speed control signal from the speed/load
controller 30 increases so that the main and interstage control
valves 15 and 16 are actuated toward more open positions until the
speed of the turbine 10 becomes consistent with the desired speed
set by the setter 33. Thus, the load which the turbine 10 bears
increases. The ratio between the shift quantities of the main and
interstage control valves 15 and 16 is adjusted to cause no adverse
affection to the pressure of the extracted steam line 17. This
adjustment is achieved by adjusting the ratio between input and
feedback resistors 37 and 39 of the adder 35 and adjusting the
ratio between input and feedback resistors 52 and 53 of the adder
49.
In the above description, if the speed control signal is restricted
by the load limitation set by the load setting device 34, the
actual rotational speed of the turbine 10 can not increase up to
the desired speed, while the limitation of the load which the
turbine 10 bears can be obtained. This feature is also obtained
where the generator 13 is connected to the electric power system
which is also supplied with electric power by one other or more
generators. That is, the load which the turbine 10 bears is
controllable by adjusting the set value of the load limiting setter
34 although the generator 13 rotates in synchronism with the
frequency of the power system.
When the speed of the turbine 10 increases, the speed/load control
arrangement operates to compensate for the speed rise. The
operation in such case will be easily understood and the further
description is omitted.
When the pressure of the extracted steam decreases under the
condition that no variation in the speed of the turbine 10 exists,
the pressure control signal increases in response thereto. This
pressure control signal is transmitted through the contact 57b of
closed state to the adder 35, then the main control valve 15 is
actuated towards an open state. On the other hand, an inverted
pressure control signal from the inverter 48 is supplied to the
adder 49, then the interstage control valve 16 is actuated towards
a closed state. Thus the pressure of the extracted steam increases
until the same reaches the desired value set by the pressure setter
46. It is noted that the appropriate adjustment of the ratio of the
input and feedback resistors 38 and 39 and of the ratio of the
input and feedback resistors 51 and 53 is required in order to
cause the turbine speed to have no variation.
In the above pressure control operation, there is also achieved a
limiting function for the quantity of the extracted steam by
adjusting the setting device 47, whereby the amount of the
extracted steam can be restricted below the rated value, which is
defined by the design of the turbine system.
Next, the operation upon the removal of a load will be
explained.
When the main circuit breaker 19 is tripped due to a fault in the
loads 20, or in the power system 21 or the like, the contact 19b is
closed to energize the relay 58 and in turn to close the contact
58a. The relays 57 and 60 are thus energized so that the contact
57b is opened and contacts 57a and 60a are closed. As the contact
61 of the detector 62 keeps a closed state because the pressure
control signal exists, the relays 57 and 60 are in a self-hold
state. Together with the above behavior, the speed of the turbine
10 increases because of the loss of its load.
The speed control signal from the speed/load controller 30
decreases rapidly to the value corresponding to the "no-load
opening" of the main control valve 15, thus the main control valve
15 is operated toward its no-load opening. Accordingly, the
pressure of the extracted steam decreases so that the pressure
control signal increases. However, the contact 57b has already been
opened while the contact 57a has been closed substantially
simultaneously with the trip of the main circuit breaker 19 to
supply the zero level signal P.sub.O to the adder 35 with the
result that the output signal from the adder 35 has been suddenly
decreased thereby. Hence, the main control valve is operated in
response only to the speed control signal from the speed/load
controller 30. On the other hand, the inverted pressure control
signal from the inverter 48 is supplied to the adder 49 and this
signal promotes the closing operation of the interstage control
valve 16. Thus, the speed of the turbine which has been increasing
due to the loss of load decreases rapidly.
The system is reset by adjusting the set value of the setting
device 46 to zero level, when the pressure control signal from the
circuit 45 is also brought to zero and contacts 61 of detector 62
open. Relays 57 and 60 then become de-energized, assuming that
circuit breaker 19 has been reset and the contacts 19b re-opened,
and the contacts 57b, 57a returned to their closed and open
positions, respectively.
Referring now to FIG. 2, in the graph shown therein, the ordinate
represents the opening of the main control valve, and the abscissa
the speed control signal and the percentage of speed rise of the
turbine.
Assume at first that the contact 57b is always closed. When the
turbine speed rises over 100 percent of the rated speed thereof due
to the tripping of the main circuit breaker 19, the opening of the
main control valve 15 takes a value along the line A if the
quantity of the extracted steam is zero. In this case, the main
control valve is actuated towards a "no-load" condition opening
when the turbine speed reaches 105 percent of its rated speed.
However, if the quantity of the extracted steam is a maximum value,
the main control valve is operated in accordance with the line B.
Then the main control valve cannot take its "no-load" opening
unless the speed of the turbine reaches a value more than b percent
of the rated speed. Accordingly, it becomes difficult to restrict
the speed rise of the turbine less than 10 percent. As is easily
understood, if the quantity of the extracted steam takes a value
between the maximum and zero, the main control valve is controlled
along a line parallel to the line A and B existing therebetween,
such as shown as a dotted line C in FIG. 2.
According to this embodiment, the contact 57b is opened upon the
tripping of the main circuit breaker 19 and also the contact 57a is
closed, and the main control valve 15 is controlled along the line
A whenever the load of the turbine is lost. Further, the closure of
the contact 57a serves to suddenly decrease the output of the adder
35 by a value corresponding to the pressure control signal from the
device 45, whereby the main control valve 15 is operated towards
its closed direction by such decrease in the output of the adder
35. The inverted pressure control signal from the inverter 48
serves to make the interstage control valve 16 to take the opening
smaller than that of the case where the pressure control signal
from the pressure controller 43 is made at a zero level.
Thus, the speed rise upon the removal of the turbine load is
effectively restricted and the usual fears involving the operation
of an over-speed trip device are eliminated.
While there is shown what is considered to be the preferred
embodiment of the invention, it is, of course, understood that
various other modifications, such as, for example, employing
transisterized circuitry instead of the relay 57, 58 and 60, are
possible, and it is understood therefore, that within the scope of
the appended claims, the invention may be practiced otherwise than
as specifically described herein.
* * * * *