CA2034844A1 - Diagnostic system for evaluating the performance of critical valves in a steam turbine system - Google Patents
Diagnostic system for evaluating the performance of critical valves in a steam turbine systemInfo
- Publication number
- CA2034844A1 CA2034844A1 CA002034844A CA2034844A CA2034844A1 CA 2034844 A1 CA2034844 A1 CA 2034844A1 CA 002034844 A CA002034844 A CA 002034844A CA 2034844 A CA2034844 A CA 2034844A CA 2034844 A1 CA2034844 A1 CA 2034844A1
- Authority
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- Prior art keywords
- valve
- shaft
- state
- signals
- steam
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
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Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
- F01D17/00—Regulating or controlling by varying flow
- F01D17/20—Devices dealing with sensing elements or final actuators or transmitting means between them, e.g. power-assisted
- F01D17/22—Devices dealing with sensing elements or final actuators or transmitting means between them, e.g. power-assisted the operation or power assistance being predominantly non-mechanical
- F01D17/24—Devices dealing with sensing elements or final actuators or transmitting means between them, e.g. power-assisted the operation or power assistance being predominantly non-mechanical electrical
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
- F01D21/00—Shutting-down of machines or engines, e.g. in emergency; Regulating, controlling, or safety means not otherwise provided for
- F01D21/003—Arrangements for testing or measuring
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16K—VALVES; TAPS; COCKS; ACTUATING-FLOATS; DEVICES FOR VENTING OR AERATING
- F16K1/00—Lift valves or globe valves, i.e. cut-off apparatus with closure members having at least a component of their opening and closing motion perpendicular to the closing faces
- F16K1/16—Lift valves or globe valves, i.e. cut-off apparatus with closure members having at least a component of their opening and closing motion perpendicular to the closing faces with pivoted closure-members
- F16K1/18—Lift valves or globe valves, i.e. cut-off apparatus with closure members having at least a component of their opening and closing motion perpendicular to the closing faces with pivoted closure-members with pivoted discs or flaps
Abstract
ABSTRACT OF THE DISCLOSURE 53,735 The diagnostic system evaluates the operation of a non-return (NR) valve in a steam extraction line of a steam turbine. The NR valve is connected in a steam flow path in series with an isolation valve between the turbine and a feedwater heater. The NR valve includes a flapper which is pivotable on a shaft for selectively blocking ,reverse flow through the NR
valve. A counterweight is attached to the shaft external of the valve for balancing the weight of the flapper, and a power assist servo-motor is coupled to the shaft for providing an initial assist to rotation of the shaft to start the flapper in a closing direction. The system includes a first sensor coupled to the shaft supporting the flapper to provide first signals representative of shaft angular position. A
second sensor is coupled to the isolation valve for providing second signals representative of the desired state of the isolation valve. A computer is coupled for receiving first and second signals and includes timing means for determining the rate of change of the shaft angular position upon receipt of the second signals. The computer further includes a means for comparing the shaft position to predetermined shaft positions corresponding to states of the second signals, and for comparing the rate of change for identifying variations in response to characteristics of the NR valve. A status report is provided by the computer to indicate the state of the operability of the NR valve.
valve. A counterweight is attached to the shaft external of the valve for balancing the weight of the flapper, and a power assist servo-motor is coupled to the shaft for providing an initial assist to rotation of the shaft to start the flapper in a closing direction. The system includes a first sensor coupled to the shaft supporting the flapper to provide first signals representative of shaft angular position. A
second sensor is coupled to the isolation valve for providing second signals representative of the desired state of the isolation valve. A computer is coupled for receiving first and second signals and includes timing means for determining the rate of change of the shaft angular position upon receipt of the second signals. The computer further includes a means for comparing the shaft position to predetermined shaft positions corresponding to states of the second signals, and for comparing the rate of change for identifying variations in response to characteristics of the NR valve. A status report is provided by the computer to indicate the state of the operability of the NR valve.
Description
~3~
53.735 DIACNOSTIC SYSTEM FOR EVALUATING THE PERFQRMANCE
OF CRITICAL VALYES I~ A STEAM TURBINE SYSTEM
FIELD OF THE INV~NTION
This invention relates to steam turbines and, more particularly, to an automated dia~nostic system for periodically evaluatin~ the operatin~ condition of steam valves in a steam turbine system.
BACKGROUND OF THE INVENTION
Steam turbine systems such as the type used in commercial electric power plants contain many critical non-return (NRl valves havin~ stationary and non-stationary components which de~rade in service. Thesecomponents must be periodically examined in order to assess their condition. In the past, many of the necessary inspections required valve disassembly and could only be made when the turbine system was taken off-line. Because lost revenua associated with taking a turbine off-line for even a few hours is prohibitive, limited on-line tests are normally performed to assess the operating condition of many critical valves. However, this limited on-line testin~ has been a time consuming, labor intensive , , 53,735 process requirin~ concurrent involvement of control room operators to adjust turbine operating parameters and mechanics to observe valve action and perfo-rm tes~s at the valve sites and personnel to coordinate test activities between the control room and the valve site. and for immediate interpretation of the data.
On-line testing procedures have also required that personnel work in close proximity to hot. hi~h energy steam. As a result of these manual procedures which require the participation of numerous power plant personnel each time a valve is tested, the large number of steam valves requiring periodic inspection and other competing maintenance demands in a power plant, the testing of critical valves is often postponed, being performed less frequently than necessary in order to assure proper valve operation.
Furthermore. on-line testing does not always reveal defects. Consequently, valve failures may not be detected until they cause si~nificant turbine dama~e.
An e~ample of one critical valve that may develop defects which are not readily detectable is the non-return valve positioned to prevent reverse flow in an extraction pipe of a large steam turbine system.
Extraction pipes remove high ener~y steam from intermediate blading stages of the steam turbine in order to reheat turbine feedwater which flows between the condenser and the boiler. The hot extracted steam transfers heat to the relatively cooler water flowin~
from the condenser usually inside feedwater heater tubes. This extraction steam eventually condenses in the feedwater heater tanks. This process improves the efficiency of the steam cycle by reducin~ boiler thermal stresses and by reducing the temperature differential between the boiler and feedwater which is 53,7~5 circulated from the condenser to the boiler for reheating, and also reduces boiler thermal stresses.
When the power plant experiences a drop in electrical load, e.g., a major power loss due to a faulted line, or even a lesser power loss of the type incurred during a planned shutdown when turbines must be taken off-line, the condensed water on the shell side of the feedwater heater, de-aerating heaters or inside the extraction pipes of turbines is subject to reduced pressure resulting in vapori~ation and a reverse flow of wet steam may occur through the extraction pipes toward the turbine. Because an off-line turbine is not under load, this reverse flow can result in an overspeed condition in addition to a harmful infiltration of water or cool vapor into the turbine structure, leading to blade and seal damage, bolting damage, casin~ distortion, thrust imbalance, bearin~
dama~e, etc., and it may also dama~e other components in the steam lines. To prevent this reverse flow, fast acting non-return valves are placed in the extraction pipes, These valves de~ra~e in service and must be periodically examined in order to avoid malfunctions during shutdowns, especially emer~ency shutdowns. Defects in a non-return valve are 3 difficult to detect without disassembly, and only a limited number of on-line tests may be performed to confirm the inte~rity of valve components. Necessary testing and inspection to assure proper operation of non-return valves is often postponed due to the nature of the manual test procedures and because of competing maintenance demands. As a result, there have been numerous occurrences of turbine damaBe caused by reverse flow of steam and feedwater through extraction pipes. It is therefore desirable to provide an automated diagnostic system for periodically or .
53,735 3~
continuously monitoring the operating condition of the many critical valves in a steam turbine system.
SUMMARY OF THE INVENTION
Among the several objects of the present invention may be noted the provision of an automated dia~nostic system for testin~ the operating condition of critical valves in a steam turbine system which overcomes the above discussed limitations and disadvanta~es associated with prior on-line testin~
procedures.
It is an object of the present invention to provide a diagnostic system for monitorin8 the performance of critical valve components through sensors including dispiacement measurements within a high temperature, hi8h pressure vessel.
It is another object of the invention to provide a non-manual means for detecting concealed valve degradation before they result in dama~e to steam turbines or other apparatus.
It is a further object of the invention to provide a diagnostic system which evaluate the operational status of valves during normal on-line operation or shutdowns of steam turbine systems.
In one form. the present invention comprises a computerized diagnostic system for determinin~ the operational status of various steam valves in a steam turbine electric power gen0rating system. The system monitors operational parameters of individual valves, correlates parameters to evaluat0 operational status of valve components and compares parameter values with expected values in order to assess deterioration and the health in valve performance and predict failures in critical valve components.
53,735 ~3~
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present invention, reference may be had to the followin~
detailed description taken in conjunction with the accompanyin~ drawings in which:
FIG. l is a cross-sectional view of a non-return valve taken along the direction of steam flow through the valve;
FIG. 2 is a cross-sectional view of the valve of FIG. l taken transvçrsely to the direction of steam flow:
FIG. 3 is a functional dia8ram of a valve monitorin8 system with which the present invention may be employed;
FIG. 4 is a cross-sectional view of a non-return valve incorporating condition sensors;
FIG. 5 is a cross-sectional view of the valve of FIG. 4 taken transverse thereto:
FIG. 6 is a simplified representation of a non-return valve and isolation valve in a steam turbine extraction system;
FIGS. 7-8 are logic diagrams of the inventive monitorin8 and diagnostic system:
FIG. 9 is a logic chart of the functions and diagnostic logic of FIGS. 7-~: and FIG. lO is a logic chart of a selective testing procedure incorporating the system of FIGS. 7-8.
DETAILED DESCRIPTION OF THF-INVENTION
Althou~h the invention is generally applicable to a variety of valves and useful in piping systems containing a variety of fluids, it is described herein with particular application to monitoring the 53, 135 8~
operational parameters of a non-return valve in a steam turbine system. With reference to FIGS. 1 and 2. there is illustrated a power assisted non-return valve 10 of the type used to control reverse flow in steam turbine extraction pipes. FIC. 1 illustrates a cross-sectional view of a non-return valve tak~n along the direction of steam flow throu~h the valve. FIG. 2 illustrates a cross-sectional view of the valve of FIG. 1 taken transversely to the direction of steam flow. The valve 10 is comprised of a valve housing 12 which has an inlet 14 for receiving steam from a first segment 16A of an extraction pipe 16 and an outlet 1 for transmitting steam throu~h a second se~ment 16B of the extraction pipe 16. A valve seat 20 is disposed circumferentially about that portion of th~ valve housing adjacent the valve inlet 14. A cover plate 22, removable for valve inspection and repair, is bolted to an upper portion of the valve housing 12. A
valve disc 24 (sometimes refe-red to as a flapper or clapper) is connected for rotation about a valve shaft 26. This rotatable valve disc connection is effected by a valve arm 34 secured at a first end 36 to the valve disc 24 with a threaded fastener 38. A second end 40 of the valve arm 34 is fixedly coupled to the valve shaft 26 such that rotation of the valve shaft occurs concurrently with opening and closing of disc 24. The shaft 26 rotates within bearings 44 which also support the shaft with respect to the valve 10. The bearings 44 are retained within bearing supports 47 while seals 51 prevent steam leakage.
During normal operation. a servo -motor 46, operating under pneumatic or hydraulic fluid pressure, maintains an actuator piston 48 and rod 49 in extended positions so that the valve shaft 26 can be rotated by the pressure of moving fluid in extraction pipe 16 53.735 operatin~ a~ainst the valve disc 24 to force the valve disc into the open position 50 as illustrated by the phantom lines in ~IG. l. Upon receiving a trip signal associated with turbine shutdown from a turbine S control room. a solenoid actuated dump valve 52 releases r luid pressure in the servo-motor 46 (or remotely in the fluid supply line to servo-motor 46) and a spring 54 retracts the actuator piston 48, startin~ rotation of the valve shaft 26 and the coupled arm 34 at least partially movin~ the valve disc 24 toward a closed position so that the valve disc 24 becomes subject to fluid forces associated with reverse steam flow. The reverse flow rotates the valve disc 24 into a fully closed position 56 against the valve seat 20.
The above described non-return valve lO may be monitored on-line with the inventive dia~nostic system for several modes of valve de~radation which are known to result in valve failures. These modes include: l) improper seating of the valve disc 24 due tc warpage or other distortion of the valve disc 24; 2) loosening or breaka~e of fasteners connecting the valve disc 24 to the valve arm 34, possibly causin~ the valve disc 24 to fall out of alignment with the valve seat 20 or to completely disconnect from the valve arm 34; 3) breaka8e or permanent deformation of the valve arm 34 or the connection between the valve arm 34 and the valve shaft 26: 4) corrosion or ~allin~ of the interfaces between the shaft bearing surfaces, causing sufficient friction to prevent timely, consistent rotation of the valve disc 24 from an open position 50 to a fully closed position 56; 5) breaka8e or permanent distortion of the linkage 57 between the valve shaft 26 and the actuator piston 48, thereby preventin~ consistent, timely rotation of the valve 53,735 7~3~
disc 24 or resulting in no initial rotational assistance at all; and 6) mispositioning a counterweight 59 movably attached to the valve linkage 57 by set screw 59A resultin~ in a mispositionin~ of the valve disc during operation or improper closin~
action.
With reference to FIG. 3. there is illustrated schematically for one form of the inven-tion a diagnostic system 60 for testin~ and evaluatin~ the operation of a series of valves 62. Each valve 62 is instrumented with several sensors 64 each coupled to a valve component in order to measure an operational parameter associated with a valve function. Sensor si~nals can be transmitted directly to a valve monitor lS computer 66 on a data highway 67 wherein signals provided by each sensor carry a distinct address label. The computer 66 is also interactive with a turbine control system 68. which may be the power plant computer and controller for the valves 62. to monitor system variables, e.g., power output and turbine speed. in order to verify operation of control valve actuators during diagnostic testin~. The si~nals provided by individual s0nsors coupled to a valve 62 are not always adequate for fully diagnosin~
the operational status of a valve 62, but when the combination of these signals and other turbine operatin~ si~nals are correlated by means of computer logic. valve operational status can be monitored and diagnosed for all turbine operating modes.
The dia~nostic test sequence for a series of valves 62 may be initiated on a preprogrammed basis as a function of elapsed time or based on data provided by valve sensors 64 during a recent valve actuation associated with turbine operation, i.e., a non-test activity. The test sequence can also be 53,735 g operator initiated by closure of a switch.
Alternatively, an operator can direct specific tests on selected valves by providing input to the diagnostic system 60 through a control keyboard 69.
The system 60 evaluates valve perforrnance by monitoring sensor data while testing valve response for each of several turbine operatin~ modes. The ability to artificially e~ercise valves in a turbine system test performed at any given time may be limited by the operatin~ mode of the turbine. For example, the performance of a control valve in a multiple valve turbine might only be evaluated during low levels of turbine load operation by the simultaneous opening and closing of individual control valves. Otherwise, the evaluation could significantly alter the turbine output.
For the non-return valve lO of FIGS. l and 2, positioned in an extraction pipe l6 of a steam turbine system, the operating modes of interest for which valve performance may be evaluated by the diagnostic system 60 include: l) the turbine start-up mode wherein the line l6 containing the non-return valve is isolated by an isolation valve 94 (see FIG. 6) until the turbine reaches a low threshold level at which point the isolation valve is opened and steam flow commences; 2) the normal operating mode, wherein steam flow is passed through the non-return valve lO in order to reheat feedwater; 3) the normal shutdown mode wherein the turbine is tripped from a low load level during an anticipated shutdown, the valve lO closing in order to prevent a moderate level of reversed steam flow (in some cases, the isolation valve is closed prior to tripping the unit off-line); 4) the emergency mode wherein the turbine is tripped from a hi8h load level, the valve lO bein8 closed in order to prevent a 53.735 ~3~
substantial level of reverse steam flow since the isolation valve does not close in time to play a role in prevention of the initial reverse flow: and 5) the load control mode wherein the turbine load is reduced significantly, possibly causing reverse flow and requiring closure of the valve lO, especially when a hi~h level of water is found in a feedwater heater, for example, if a level control system in a feedwater heater malfunctions.
In further explanation of the dia~nostic system 60, FIGS. 4 and 5 illustrate a non-return valve lO
instrumented with a plurality of sensors (corresponding to sensors 64) for evaluating performance during the above described modes of operation. A position sensor 70, such as an incremental shaft encoder together with its associated signal conditionin~ electronics (which may be remotely located), can be positioned adjacent the valve shaft 26 to provide di~itally encoded information through the data hi~hway or other communication link 67 to the valve monitor computer 66 indicating the angular position of the rotatable valve shaft 26. In another form, the position sensor may constitute a proximity sensor 72 positioned adjacent to a cam 74 attached to shaft 26. Rotation of the shaft 26 alters the gap between the proximity sensor 72 and the cam surface 74. An abnormal gap indicates an improper valve position, while the time of operation may indicate a sticky valve. Information provided by the position sensor 70 or 72 can be coded with a unique address label for identification purposes. The valve housing l2 may include first and second pressure monitoring bores 78 and 76 located respectively on the upstream and downstream (with respect to normal flow direction) sides of the valve seat 20. 'The bores 76 and 78 are 53, 735 coupled to each other by a pressure tube 80 containin~
a differential pressure sensor 8~. which can provide data indicativ~ of pressure drops across the valve seat 20. The output of the differential pressure sensor is also digitally encoded and provided with a unique address label prior to bein~ transmitted alon3 the data highway 67 to the computer 65. A pressure sensor 86 is positioned along the tube 80 near the second bore 78 to provide data indicative of pressure in the first segment 16A of the extraction pipe 16. A
voltage sensor 90 monitors the trip si~nals sent to the dump valve 52 and on this basis provides data indicative of dump valve status. Information provided by the pressure sensor 86 and the voltage sensor 90 is also digitally converted and transmitted alon~ the communication link 67 with unique address labels.
Evaluation of the non-return valve is based on both si~nal correlation to confirm proper valve positioning and comparison of sensor signals with acceptance criteria to identify degradation of operating characteristics. This information is useful for predicting valve failures. For example, the early stages of de~radation of the shaft bearing interface (shaft 26 to bearin8 44) or deterioration of the linkage between the valve shaft 26 and the actuator piston 48 may be identified by monitorin~ increases in the time delay between provision of a trip si~nal to the dump valve 52 and seatin~ of the valve disc 24.
Based on monitored data, the control room display provides information on the measured valve performance. The system 60 also predicts future valve performance and anticipated failures based on the measured data trends and correlations of sensor output signals.
53,735 - l2 ~
Before turning to a more detailed description of the inventive diagnostic s,vstem, referenc0 is first made to FIG. 6 in which there is shown a simplified functional diagram of the position of a non-return valve in a steam turbine system 92. The valve lO is positioned between an isolation valve 9~ and a feedwater heater 96. The isolation valve 94 and non-return valve lO are located in an extraction line 98 coupling a steam turbine 99 to the feedwater heater 96. During normal turbine operation, the isolation v~lve 94 and non-return valve lO are fully open to allow extraction steam to flow to feedwater heater 96.
The isolation valve 94 is often an electrically driven, motorized valve and does not have a hi~h rate of closing. The non-return valve lO is a fast actin~
valve and provides protection for the turbine 99 in the event of a malfunction of the type described above.
FIG. 6 also shows the plant computer 68 and monitor computer 66 coupled for receivin~ and supplying various sensor and control signals. The sensor signals in addition to those previously described, typically include temperature and pressure information from selected areas or components of the turbine 99 alon~ with similar information from the steam extraction line 98 and the feedwater heater 96.
The blocks 9l, 93 and 95 are indicative of such sensors. Since these sensors are common to such turbine systems and are well known in the art, no further description is deemed necessary.
FIGS. 7 and 8 are fault tree charts describing the monitorin~ and evaluatin~ functions implemented by valve monitor computer 66 in conjunction with monitorin~ of a valve such as the non-return valve 10.
Considerin~ first FIG. 7, block 100 represents the 53,735 - 13 - ~ ~3~
ultimate conclusion. i.e.. that the valve 10 has failed to restrict reverse steam flow when it should, or restricting forward flow when it should not. The remaining functional blocks relate to determinin8 the cause of the potential failures. Blocks 102 and 104 distinguish between the two possible operational malfunction states of the valve, i.e., when the valve 10 should either be in an open or a closed condition.
The logical OR symbol in the line from block 100 indicates that either of the paths to that block could create the malfunction. A logical AND symbol in a line indicates concurrent tests, operations, or conditions. Whenever the turbine steam pressure is significantly greater than the feedwater heater pressure, and the isolation valve is open, the NRV
should be open to permit forward steam flow. Whenever the isolation valve is closed, or if the turbine pressure is equal to or less than the feedwater heater pressure. the NRV should be closed. In the latter case, it prevents reverse steam flow. Information relating to these two states can be evaluated from the state of the isolation valve ~4 or, more accurately, by the signals sent to the valve 94 coupled with steam flow sufficient to move a non-return valve to effectuate opening or closing of the valve. Limit switches (not shown) could be connected to the valve 94 so as to monitor valve position. Alternatively, a sensor 65 could be coupled to the system control computer 68 to monitor si~nals being generated for controlling the valve 94. In either event, the sensor signals will provide an indication of the desired state of valve 94. If the sensor associated with valve 94 indicates that the valve should be closed, then any malfunction of valve 10 will relate to a reverse flow condition as indicated by block 102. If 53,735 the valve 94 should be open, then a malfunction of valve 10 relates to a forward flow condition as indicated by block 104.
Considering a forward flow condition firsk, there are at least two possible malfunction states, i.e., either the valve 10 is not open (partially or fully closed), block 106, or the valve flapper or disc 24 vibrates, block 108. Either condition can be detected by the an~ular position sensor 70 usin~, for example, an incremental encoder or a cam proximity sensor 72.
810cks 110 and 112 indicate that an out-of-position counterwei6ht 59 can cause these malfunctions for a non-return valve. Upon such detection, it is necessary to send a technician to manually adjust the counterweight. (The counterweight 59, as shown in FIG. l. is normally connected to shaft Z6 to balance the wei~ht of the flapper or disc 24 and is readily moved by steam flow through the valve 10.) The valve monitor computer 66 can quickly evaluate the valve 10 condition by monitoring the si~nal indicative of the desired state of isolation valve 94, the angular position of valve arm 26, and the power load level on tur~ine 99.
A reverse flow malfunction may relate to more types of problems. The role of the NRV is to prevent reverse flow in the transient period, typically lasting less than several minutes while the isolation valve is closing and/or the water is drained from the heaters. Blocks 114, 116, 118 and 120 represent possible malfunctions. Erratic closing, block 114, may be caused by erratic operation of the power assist servo-motor 52, block 122. Erratic closin~ refers to a condition in which the valve 10 is intermittent, i.e., sometimes it does not operate in a repeatable fashion. The monitor 66 can detect when the valve 10 53,735 - 15 ~ 2~3~
malfunctions, block 102 when it should close and its actual state, block 114, (from position sensor 70) and whether the servo-motor is operatin~ properly, block 122, from sensor 90. If sensor 90 does not indicate a 5malfunction, the possible causes may be a misadjusted counterwei~ht 59 on the shaft 26, block 12~, or shaft friction too hi6h. block 126. A sin~le letter symbol, such as "8", in a circle is a logical indicator showing that the conditions depending from the letter lO"B" in another location also apply to the tests in this location. Hence, the blocks 124, 126 indicate conditions applicable to erratic closing. The symbol "A", under block 120, can be similarly traced to the conditions shown in FIG. 8. Note that blocks 124 and 15126 also indicate possible failure modes in the event that the valve 10 i5 slow closin~, block 116. Slow closing is readily detected by timin~ in the monitor computer 66 the shaft 26 closing time from data obtained from sensor 70.
20A leaking valve 10, block 118, can be detected by differential pressure sensor 82. This mode assumes valve closure. The four potential causes of a leak are disc 24 warped, failure of fastener 38, valve seat 20 damaged, and flapper or disc arm 34 distorted, all 25indicated respectively by blocks 128, 129, i30, and 132. Any of these failures may r0quire valve répair or replacement.
A total failure to restrict flow, block 120, can be detected by shaft position sensor 70 and/or by differential pressure sensor 82. FIG. 8 indicates the possible failure modes for this condition. If shaft 26 is frozen, block 134. the snaft position sensor 70 will indicate no movement. If the flapper or disc 24 is separated from shaft 26, block 136, the sensor 70 will show shaft movement but differential pressure 53.135 - 16 ~
sensor 82 will lndicate no change in pressure.
Similarly, if the shaft 26 to clapper arm 34 key is sheared. block 138. the position sensor 70 will show shaft rotation but the pressure sensor 82 will hold constant. A broken shaft 26, block 140, will be indicated by no movement of shaft 26 accompanied by constant differential pressure, i.e.. the same response as for a frozen shaft. A broken flapper arm 34 will be indicated by shaft 25 motion accompanied by constant differential pressure. Two external failure conditions are indicated by blocks 144 and 146 in which the counterweight on shaft 26 is out of position or the power assist servo-motor 52 is not operative.
Both of these latter conditions are described above with reference to valve opening failures and are the same for valve closing.
The diagnostic system of the present invention may be used in either a monitoring mode during turbine operation or in a test mode when a turbine is on or off-line. Referring to FIG. 9. block 150 represents a valve monitorins mode. The system may be passively monitored, block 152, or actively tested, block 154.
The central test mode of the diagnostic system, as indicated by block 154. first requires that the steam turbine or power utility station parameters be verified to assure that testing may be performed.
block 15~. Assuming that it is satisfactory to conduct testing, testin~ may be performed in either an automatic test mode, block 158, or a selective test mode, block 160. The only difference between the selective test mode and the automatic test mode is that in the selective test mode, the system operator selects particular valves to be tested while in the automatic test mode. the system is programmed to sequentially step through a preselected ~roup of 53,735 - 17 ~
valves and perform the test in sequence on each valve, block 159. Since the automatic test mode is readily implemented and is merely repetition of the selective test mode, the description following will only address the test to be conducted in the selective test mode.
Both automatic and selectin~ testing utilize the tests indicated by symbol "K" in FIG. 10.
Referrin8 now to FIG. 10, testin~ of the NRV may occur as a full test with the turbine on-line with active steam extraotion, block 1~2, or as a partial test for other conditions, block 164. In an active on-line test, the system must first verify that the isolation valve 94 is open, block 166, the feedwater heater 96 is active, block 168, and the non-return dump valve is energized enabling the NRV to be fully open, block 170. To test the non-return valve, the isolation valve 94 is held open and the non-return valve servo-motor dump valve is opened briefly by providing a signal to its servo-motor, and then re-closed, as is indicated by block 172. Since the isolation valve 94 is still open passin~ substantial flow, the non-return valve 10 transitions from an opened to a partially closed condition and then reopens, all of the potential malfunctions described above with regard to FIGS. 7 and 8 can be detected by the test sequence described. Preferably, the data collected from monitoring the operation of the non-return valve 10 can be stored for statistical analysis. For example, the NRV trip with an open isolation valve tests may be designed to operate the NRV valve 10 a predetermined number of times, such as, for example, five times, and then to statistically evaluate the operation of the non-return valve 10 for those five sample~ to verify consistent oper~tion.
Note that the system describei thus far can provide 5~,735 ~3~
not only an indication of a failure of the non-return valve but also the response time of the valve by means of the sensor 70 so as to anticipate potential failure modes. All of the data with re8ard to testing of the S valve can be stored and compared to data obtained by subsequent testing so that deterioration of the valve can be detected by variations in the data. It will be appreciated that the response time of the non-return valve lO may be affected ~y temperature and pressure of the steam in the extraction line and that any readings of the non-return valve response time may have to be normalized as a function of such temperature and pressure. Sensors providing information relatin~ to temperature and pressure are well known in the art and are common elements of the steam turbine system with which the present invention may be used.
With regard to partial testing as indicated by block 164, the only difference between the partial testing and the full on-line testin6 is that the extraction is not active. In this event, the same technique can be used to operate the non-return valve and the status of the non-return valve ch0cked using the same sensors. However, when there is no extraction steam flowing in the extraction line 98, the normal status of the non-return valve lO will be to remain in the closed position in response to actuation of the power assisted servo-motor 52, since there is no steam flow to lift the valve. Preferably, the NRV servo-motor can be actuated to trip the associated dump valve brief!y, block 173, while performing the tests indicated by symbol "L".
Returning now to FI~. 9, the monitorin~ and diagnostic mode can be utilized when the unit is off-line, block 174, when the turbine unit is on-line, ~3,735 block 176, when the turbine ~oes throu~h a turbine trip, block 178. and when there is a local reverse flow in the extraction line, block 180. In the diagnostic mode, the status of the valves, i.e., both the isolation valve 94 and the non-return valve 10, are periodically sampled and time and date of samples are associated with each sample. Each sample value is compared to preselected acceptance criteria to provide an assessment of the health of the non-return valve 10. As discussed above with re8ard to the selective test mode, the data collected from the periodic sampling can be used to compute trends, averages, and variations over time of the non-return val~e. The temperature and pressure of steam in the extraction pipe 98 may also be monitored in order to correct or normalize the data associated with the non-return valve. Malfunctions may be detected as was described with regard to FIGS. 7 and 8 during the monitorine and dia~nostic mode.
In the unit on-line mode, there may be active extraction in extraction line 98 as indicated by block 182 or there may be isolated extraction as indicated by block 184. In both cases, the isolation valve status and the non-return valve status are periodically sampled and associated with the correspondin~ times and dates, block 186. The sample values may be compared to acceptance criteria such as computed derived variables to determine whether or not the non~return valve is properly operatin~, blocks 188 and 190. Trends may be dete.^mined, block 190, to forecast probable failures and allow repair or replacement before failure. As with other samples, temperature and pressure of the steam throu~h the valve may also be sampled and used to normalize any 53,735 - ~o - ~3~
readings on the valve. If the line is isolated, the same logic described for block 164 applies.
Unit off-line tests and processes, indicated by biock 174, are essentially the same as are performed for isolated extraction tests indicated by block 184.
Unit trip, indicated in block 178, provides an opportunity to compute the valve closing time under operating conditions. Otherwise, the monitoring of the sensors provides the same basic type of information as is provided under other test conditions.
The tests under the local reverse flow block 180 are essentially the same as under the unit trip bock 178. However, the comparison may be to other non-return valve actions. The dia~nosis under block 180 can follow the same process as was described with re~ard to FIGS. 7 and 8.
While the principles of the invention have now been made clear in an illustrative embodiment, it will become apparent to those skilled in the art that many modifications of the structures, arrangements, and components presented in the above illustrations may be made in the practice of the invention in order to develop alternate embodiments suitable to specific operating requirements without departing from the spirit and scope of the invention as set forth in the claims which follow. For example, the selected malfunctions at the isolated valve, such as steam leakage past the seat, can be detected by notin~
abnormal behavior of the non-return valve.
53.735 DIACNOSTIC SYSTEM FOR EVALUATING THE PERFQRMANCE
OF CRITICAL VALYES I~ A STEAM TURBINE SYSTEM
FIELD OF THE INV~NTION
This invention relates to steam turbines and, more particularly, to an automated dia~nostic system for periodically evaluatin~ the operatin~ condition of steam valves in a steam turbine system.
BACKGROUND OF THE INVENTION
Steam turbine systems such as the type used in commercial electric power plants contain many critical non-return (NRl valves havin~ stationary and non-stationary components which de~rade in service. Thesecomponents must be periodically examined in order to assess their condition. In the past, many of the necessary inspections required valve disassembly and could only be made when the turbine system was taken off-line. Because lost revenua associated with taking a turbine off-line for even a few hours is prohibitive, limited on-line tests are normally performed to assess the operating condition of many critical valves. However, this limited on-line testin~ has been a time consuming, labor intensive , , 53,735 process requirin~ concurrent involvement of control room operators to adjust turbine operating parameters and mechanics to observe valve action and perfo-rm tes~s at the valve sites and personnel to coordinate test activities between the control room and the valve site. and for immediate interpretation of the data.
On-line testing procedures have also required that personnel work in close proximity to hot. hi~h energy steam. As a result of these manual procedures which require the participation of numerous power plant personnel each time a valve is tested, the large number of steam valves requiring periodic inspection and other competing maintenance demands in a power plant, the testing of critical valves is often postponed, being performed less frequently than necessary in order to assure proper valve operation.
Furthermore. on-line testing does not always reveal defects. Consequently, valve failures may not be detected until they cause si~nificant turbine dama~e.
An e~ample of one critical valve that may develop defects which are not readily detectable is the non-return valve positioned to prevent reverse flow in an extraction pipe of a large steam turbine system.
Extraction pipes remove high ener~y steam from intermediate blading stages of the steam turbine in order to reheat turbine feedwater which flows between the condenser and the boiler. The hot extracted steam transfers heat to the relatively cooler water flowin~
from the condenser usually inside feedwater heater tubes. This extraction steam eventually condenses in the feedwater heater tanks. This process improves the efficiency of the steam cycle by reducin~ boiler thermal stresses and by reducing the temperature differential between the boiler and feedwater which is 53,7~5 circulated from the condenser to the boiler for reheating, and also reduces boiler thermal stresses.
When the power plant experiences a drop in electrical load, e.g., a major power loss due to a faulted line, or even a lesser power loss of the type incurred during a planned shutdown when turbines must be taken off-line, the condensed water on the shell side of the feedwater heater, de-aerating heaters or inside the extraction pipes of turbines is subject to reduced pressure resulting in vapori~ation and a reverse flow of wet steam may occur through the extraction pipes toward the turbine. Because an off-line turbine is not under load, this reverse flow can result in an overspeed condition in addition to a harmful infiltration of water or cool vapor into the turbine structure, leading to blade and seal damage, bolting damage, casin~ distortion, thrust imbalance, bearin~
dama~e, etc., and it may also dama~e other components in the steam lines. To prevent this reverse flow, fast acting non-return valves are placed in the extraction pipes, These valves de~ra~e in service and must be periodically examined in order to avoid malfunctions during shutdowns, especially emer~ency shutdowns. Defects in a non-return valve are 3 difficult to detect without disassembly, and only a limited number of on-line tests may be performed to confirm the inte~rity of valve components. Necessary testing and inspection to assure proper operation of non-return valves is often postponed due to the nature of the manual test procedures and because of competing maintenance demands. As a result, there have been numerous occurrences of turbine damaBe caused by reverse flow of steam and feedwater through extraction pipes. It is therefore desirable to provide an automated diagnostic system for periodically or .
53,735 3~
continuously monitoring the operating condition of the many critical valves in a steam turbine system.
SUMMARY OF THE INVENTION
Among the several objects of the present invention may be noted the provision of an automated dia~nostic system for testin~ the operating condition of critical valves in a steam turbine system which overcomes the above discussed limitations and disadvanta~es associated with prior on-line testin~
procedures.
It is an object of the present invention to provide a diagnostic system for monitorin8 the performance of critical valve components through sensors including dispiacement measurements within a high temperature, hi8h pressure vessel.
It is another object of the invention to provide a non-manual means for detecting concealed valve degradation before they result in dama~e to steam turbines or other apparatus.
It is a further object of the invention to provide a diagnostic system which evaluate the operational status of valves during normal on-line operation or shutdowns of steam turbine systems.
In one form. the present invention comprises a computerized diagnostic system for determinin~ the operational status of various steam valves in a steam turbine electric power gen0rating system. The system monitors operational parameters of individual valves, correlates parameters to evaluat0 operational status of valve components and compares parameter values with expected values in order to assess deterioration and the health in valve performance and predict failures in critical valve components.
53,735 ~3~
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present invention, reference may be had to the followin~
detailed description taken in conjunction with the accompanyin~ drawings in which:
FIG. l is a cross-sectional view of a non-return valve taken along the direction of steam flow through the valve;
FIG. 2 is a cross-sectional view of the valve of FIG. l taken transvçrsely to the direction of steam flow:
FIG. 3 is a functional dia8ram of a valve monitorin8 system with which the present invention may be employed;
FIG. 4 is a cross-sectional view of a non-return valve incorporating condition sensors;
FIG. 5 is a cross-sectional view of the valve of FIG. 4 taken transverse thereto:
FIG. 6 is a simplified representation of a non-return valve and isolation valve in a steam turbine extraction system;
FIGS. 7-8 are logic diagrams of the inventive monitorin8 and diagnostic system:
FIG. 9 is a logic chart of the functions and diagnostic logic of FIGS. 7-~: and FIG. lO is a logic chart of a selective testing procedure incorporating the system of FIGS. 7-8.
DETAILED DESCRIPTION OF THF-INVENTION
Althou~h the invention is generally applicable to a variety of valves and useful in piping systems containing a variety of fluids, it is described herein with particular application to monitoring the 53, 135 8~
operational parameters of a non-return valve in a steam turbine system. With reference to FIGS. 1 and 2. there is illustrated a power assisted non-return valve 10 of the type used to control reverse flow in steam turbine extraction pipes. FIC. 1 illustrates a cross-sectional view of a non-return valve tak~n along the direction of steam flow throu~h the valve. FIG. 2 illustrates a cross-sectional view of the valve of FIG. 1 taken transversely to the direction of steam flow. The valve 10 is comprised of a valve housing 12 which has an inlet 14 for receiving steam from a first segment 16A of an extraction pipe 16 and an outlet 1 for transmitting steam throu~h a second se~ment 16B of the extraction pipe 16. A valve seat 20 is disposed circumferentially about that portion of th~ valve housing adjacent the valve inlet 14. A cover plate 22, removable for valve inspection and repair, is bolted to an upper portion of the valve housing 12. A
valve disc 24 (sometimes refe-red to as a flapper or clapper) is connected for rotation about a valve shaft 26. This rotatable valve disc connection is effected by a valve arm 34 secured at a first end 36 to the valve disc 24 with a threaded fastener 38. A second end 40 of the valve arm 34 is fixedly coupled to the valve shaft 26 such that rotation of the valve shaft occurs concurrently with opening and closing of disc 24. The shaft 26 rotates within bearings 44 which also support the shaft with respect to the valve 10. The bearings 44 are retained within bearing supports 47 while seals 51 prevent steam leakage.
During normal operation. a servo -motor 46, operating under pneumatic or hydraulic fluid pressure, maintains an actuator piston 48 and rod 49 in extended positions so that the valve shaft 26 can be rotated by the pressure of moving fluid in extraction pipe 16 53.735 operatin~ a~ainst the valve disc 24 to force the valve disc into the open position 50 as illustrated by the phantom lines in ~IG. l. Upon receiving a trip signal associated with turbine shutdown from a turbine S control room. a solenoid actuated dump valve 52 releases r luid pressure in the servo-motor 46 (or remotely in the fluid supply line to servo-motor 46) and a spring 54 retracts the actuator piston 48, startin~ rotation of the valve shaft 26 and the coupled arm 34 at least partially movin~ the valve disc 24 toward a closed position so that the valve disc 24 becomes subject to fluid forces associated with reverse steam flow. The reverse flow rotates the valve disc 24 into a fully closed position 56 against the valve seat 20.
The above described non-return valve lO may be monitored on-line with the inventive dia~nostic system for several modes of valve de~radation which are known to result in valve failures. These modes include: l) improper seating of the valve disc 24 due tc warpage or other distortion of the valve disc 24; 2) loosening or breaka~e of fasteners connecting the valve disc 24 to the valve arm 34, possibly causin~ the valve disc 24 to fall out of alignment with the valve seat 20 or to completely disconnect from the valve arm 34; 3) breaka8e or permanent deformation of the valve arm 34 or the connection between the valve arm 34 and the valve shaft 26: 4) corrosion or ~allin~ of the interfaces between the shaft bearing surfaces, causing sufficient friction to prevent timely, consistent rotation of the valve disc 24 from an open position 50 to a fully closed position 56; 5) breaka8e or permanent distortion of the linkage 57 between the valve shaft 26 and the actuator piston 48, thereby preventin~ consistent, timely rotation of the valve 53,735 7~3~
disc 24 or resulting in no initial rotational assistance at all; and 6) mispositioning a counterweight 59 movably attached to the valve linkage 57 by set screw 59A resultin~ in a mispositionin~ of the valve disc during operation or improper closin~
action.
With reference to FIG. 3. there is illustrated schematically for one form of the inven-tion a diagnostic system 60 for testin~ and evaluatin~ the operation of a series of valves 62. Each valve 62 is instrumented with several sensors 64 each coupled to a valve component in order to measure an operational parameter associated with a valve function. Sensor si~nals can be transmitted directly to a valve monitor lS computer 66 on a data highway 67 wherein signals provided by each sensor carry a distinct address label. The computer 66 is also interactive with a turbine control system 68. which may be the power plant computer and controller for the valves 62. to monitor system variables, e.g., power output and turbine speed. in order to verify operation of control valve actuators during diagnostic testin~. The si~nals provided by individual s0nsors coupled to a valve 62 are not always adequate for fully diagnosin~
the operational status of a valve 62, but when the combination of these signals and other turbine operatin~ si~nals are correlated by means of computer logic. valve operational status can be monitored and diagnosed for all turbine operating modes.
The dia~nostic test sequence for a series of valves 62 may be initiated on a preprogrammed basis as a function of elapsed time or based on data provided by valve sensors 64 during a recent valve actuation associated with turbine operation, i.e., a non-test activity. The test sequence can also be 53,735 g operator initiated by closure of a switch.
Alternatively, an operator can direct specific tests on selected valves by providing input to the diagnostic system 60 through a control keyboard 69.
The system 60 evaluates valve perforrnance by monitoring sensor data while testing valve response for each of several turbine operatin~ modes. The ability to artificially e~ercise valves in a turbine system test performed at any given time may be limited by the operatin~ mode of the turbine. For example, the performance of a control valve in a multiple valve turbine might only be evaluated during low levels of turbine load operation by the simultaneous opening and closing of individual control valves. Otherwise, the evaluation could significantly alter the turbine output.
For the non-return valve lO of FIGS. l and 2, positioned in an extraction pipe l6 of a steam turbine system, the operating modes of interest for which valve performance may be evaluated by the diagnostic system 60 include: l) the turbine start-up mode wherein the line l6 containing the non-return valve is isolated by an isolation valve 94 (see FIG. 6) until the turbine reaches a low threshold level at which point the isolation valve is opened and steam flow commences; 2) the normal operating mode, wherein steam flow is passed through the non-return valve lO in order to reheat feedwater; 3) the normal shutdown mode wherein the turbine is tripped from a low load level during an anticipated shutdown, the valve lO closing in order to prevent a moderate level of reversed steam flow (in some cases, the isolation valve is closed prior to tripping the unit off-line); 4) the emergency mode wherein the turbine is tripped from a hi8h load level, the valve lO bein8 closed in order to prevent a 53.735 ~3~
substantial level of reverse steam flow since the isolation valve does not close in time to play a role in prevention of the initial reverse flow: and 5) the load control mode wherein the turbine load is reduced significantly, possibly causing reverse flow and requiring closure of the valve lO, especially when a hi~h level of water is found in a feedwater heater, for example, if a level control system in a feedwater heater malfunctions.
In further explanation of the dia~nostic system 60, FIGS. 4 and 5 illustrate a non-return valve lO
instrumented with a plurality of sensors (corresponding to sensors 64) for evaluating performance during the above described modes of operation. A position sensor 70, such as an incremental shaft encoder together with its associated signal conditionin~ electronics (which may be remotely located), can be positioned adjacent the valve shaft 26 to provide di~itally encoded information through the data hi~hway or other communication link 67 to the valve monitor computer 66 indicating the angular position of the rotatable valve shaft 26. In another form, the position sensor may constitute a proximity sensor 72 positioned adjacent to a cam 74 attached to shaft 26. Rotation of the shaft 26 alters the gap between the proximity sensor 72 and the cam surface 74. An abnormal gap indicates an improper valve position, while the time of operation may indicate a sticky valve. Information provided by the position sensor 70 or 72 can be coded with a unique address label for identification purposes. The valve housing l2 may include first and second pressure monitoring bores 78 and 76 located respectively on the upstream and downstream (with respect to normal flow direction) sides of the valve seat 20. 'The bores 76 and 78 are 53, 735 coupled to each other by a pressure tube 80 containin~
a differential pressure sensor 8~. which can provide data indicativ~ of pressure drops across the valve seat 20. The output of the differential pressure sensor is also digitally encoded and provided with a unique address label prior to bein~ transmitted alon3 the data highway 67 to the computer 65. A pressure sensor 86 is positioned along the tube 80 near the second bore 78 to provide data indicative of pressure in the first segment 16A of the extraction pipe 16. A
voltage sensor 90 monitors the trip si~nals sent to the dump valve 52 and on this basis provides data indicative of dump valve status. Information provided by the pressure sensor 86 and the voltage sensor 90 is also digitally converted and transmitted alon~ the communication link 67 with unique address labels.
Evaluation of the non-return valve is based on both si~nal correlation to confirm proper valve positioning and comparison of sensor signals with acceptance criteria to identify degradation of operating characteristics. This information is useful for predicting valve failures. For example, the early stages of de~radation of the shaft bearing interface (shaft 26 to bearin8 44) or deterioration of the linkage between the valve shaft 26 and the actuator piston 48 may be identified by monitorin~ increases in the time delay between provision of a trip si~nal to the dump valve 52 and seatin~ of the valve disc 24.
Based on monitored data, the control room display provides information on the measured valve performance. The system 60 also predicts future valve performance and anticipated failures based on the measured data trends and correlations of sensor output signals.
53,735 - l2 ~
Before turning to a more detailed description of the inventive diagnostic s,vstem, referenc0 is first made to FIG. 6 in which there is shown a simplified functional diagram of the position of a non-return valve in a steam turbine system 92. The valve lO is positioned between an isolation valve 9~ and a feedwater heater 96. The isolation valve 94 and non-return valve lO are located in an extraction line 98 coupling a steam turbine 99 to the feedwater heater 96. During normal turbine operation, the isolation v~lve 94 and non-return valve lO are fully open to allow extraction steam to flow to feedwater heater 96.
The isolation valve 94 is often an electrically driven, motorized valve and does not have a hi~h rate of closing. The non-return valve lO is a fast actin~
valve and provides protection for the turbine 99 in the event of a malfunction of the type described above.
FIG. 6 also shows the plant computer 68 and monitor computer 66 coupled for receivin~ and supplying various sensor and control signals. The sensor signals in addition to those previously described, typically include temperature and pressure information from selected areas or components of the turbine 99 alon~ with similar information from the steam extraction line 98 and the feedwater heater 96.
The blocks 9l, 93 and 95 are indicative of such sensors. Since these sensors are common to such turbine systems and are well known in the art, no further description is deemed necessary.
FIGS. 7 and 8 are fault tree charts describing the monitorin~ and evaluatin~ functions implemented by valve monitor computer 66 in conjunction with monitorin~ of a valve such as the non-return valve 10.
Considerin~ first FIG. 7, block 100 represents the 53,735 - 13 - ~ ~3~
ultimate conclusion. i.e.. that the valve 10 has failed to restrict reverse steam flow when it should, or restricting forward flow when it should not. The remaining functional blocks relate to determinin8 the cause of the potential failures. Blocks 102 and 104 distinguish between the two possible operational malfunction states of the valve, i.e., when the valve 10 should either be in an open or a closed condition.
The logical OR symbol in the line from block 100 indicates that either of the paths to that block could create the malfunction. A logical AND symbol in a line indicates concurrent tests, operations, or conditions. Whenever the turbine steam pressure is significantly greater than the feedwater heater pressure, and the isolation valve is open, the NRV
should be open to permit forward steam flow. Whenever the isolation valve is closed, or if the turbine pressure is equal to or less than the feedwater heater pressure. the NRV should be closed. In the latter case, it prevents reverse steam flow. Information relating to these two states can be evaluated from the state of the isolation valve ~4 or, more accurately, by the signals sent to the valve 94 coupled with steam flow sufficient to move a non-return valve to effectuate opening or closing of the valve. Limit switches (not shown) could be connected to the valve 94 so as to monitor valve position. Alternatively, a sensor 65 could be coupled to the system control computer 68 to monitor si~nals being generated for controlling the valve 94. In either event, the sensor signals will provide an indication of the desired state of valve 94. If the sensor associated with valve 94 indicates that the valve should be closed, then any malfunction of valve 10 will relate to a reverse flow condition as indicated by block 102. If 53,735 the valve 94 should be open, then a malfunction of valve 10 relates to a forward flow condition as indicated by block 104.
Considering a forward flow condition firsk, there are at least two possible malfunction states, i.e., either the valve 10 is not open (partially or fully closed), block 106, or the valve flapper or disc 24 vibrates, block 108. Either condition can be detected by the an~ular position sensor 70 usin~, for example, an incremental encoder or a cam proximity sensor 72.
810cks 110 and 112 indicate that an out-of-position counterwei6ht 59 can cause these malfunctions for a non-return valve. Upon such detection, it is necessary to send a technician to manually adjust the counterweight. (The counterweight 59, as shown in FIG. l. is normally connected to shaft Z6 to balance the wei~ht of the flapper or disc 24 and is readily moved by steam flow through the valve 10.) The valve monitor computer 66 can quickly evaluate the valve 10 condition by monitoring the si~nal indicative of the desired state of isolation valve 94, the angular position of valve arm 26, and the power load level on tur~ine 99.
A reverse flow malfunction may relate to more types of problems. The role of the NRV is to prevent reverse flow in the transient period, typically lasting less than several minutes while the isolation valve is closing and/or the water is drained from the heaters. Blocks 114, 116, 118 and 120 represent possible malfunctions. Erratic closing, block 114, may be caused by erratic operation of the power assist servo-motor 52, block 122. Erratic closin~ refers to a condition in which the valve 10 is intermittent, i.e., sometimes it does not operate in a repeatable fashion. The monitor 66 can detect when the valve 10 53,735 - 15 ~ 2~3~
malfunctions, block 102 when it should close and its actual state, block 114, (from position sensor 70) and whether the servo-motor is operatin~ properly, block 122, from sensor 90. If sensor 90 does not indicate a 5malfunction, the possible causes may be a misadjusted counterwei~ht 59 on the shaft 26, block 12~, or shaft friction too hi6h. block 126. A sin~le letter symbol, such as "8", in a circle is a logical indicator showing that the conditions depending from the letter lO"B" in another location also apply to the tests in this location. Hence, the blocks 124, 126 indicate conditions applicable to erratic closing. The symbol "A", under block 120, can be similarly traced to the conditions shown in FIG. 8. Note that blocks 124 and 15126 also indicate possible failure modes in the event that the valve 10 i5 slow closin~, block 116. Slow closing is readily detected by timin~ in the monitor computer 66 the shaft 26 closing time from data obtained from sensor 70.
20A leaking valve 10, block 118, can be detected by differential pressure sensor 82. This mode assumes valve closure. The four potential causes of a leak are disc 24 warped, failure of fastener 38, valve seat 20 damaged, and flapper or disc arm 34 distorted, all 25indicated respectively by blocks 128, 129, i30, and 132. Any of these failures may r0quire valve répair or replacement.
A total failure to restrict flow, block 120, can be detected by shaft position sensor 70 and/or by differential pressure sensor 82. FIG. 8 indicates the possible failure modes for this condition. If shaft 26 is frozen, block 134. the snaft position sensor 70 will indicate no movement. If the flapper or disc 24 is separated from shaft 26, block 136, the sensor 70 will show shaft movement but differential pressure 53.135 - 16 ~
sensor 82 will lndicate no change in pressure.
Similarly, if the shaft 26 to clapper arm 34 key is sheared. block 138. the position sensor 70 will show shaft rotation but the pressure sensor 82 will hold constant. A broken shaft 26, block 140, will be indicated by no movement of shaft 26 accompanied by constant differential pressure, i.e.. the same response as for a frozen shaft. A broken flapper arm 34 will be indicated by shaft 25 motion accompanied by constant differential pressure. Two external failure conditions are indicated by blocks 144 and 146 in which the counterweight on shaft 26 is out of position or the power assist servo-motor 52 is not operative.
Both of these latter conditions are described above with reference to valve opening failures and are the same for valve closing.
The diagnostic system of the present invention may be used in either a monitoring mode during turbine operation or in a test mode when a turbine is on or off-line. Referring to FIG. 9. block 150 represents a valve monitorins mode. The system may be passively monitored, block 152, or actively tested, block 154.
The central test mode of the diagnostic system, as indicated by block 154. first requires that the steam turbine or power utility station parameters be verified to assure that testing may be performed.
block 15~. Assuming that it is satisfactory to conduct testing, testin~ may be performed in either an automatic test mode, block 158, or a selective test mode, block 160. The only difference between the selective test mode and the automatic test mode is that in the selective test mode, the system operator selects particular valves to be tested while in the automatic test mode. the system is programmed to sequentially step through a preselected ~roup of 53,735 - 17 ~
valves and perform the test in sequence on each valve, block 159. Since the automatic test mode is readily implemented and is merely repetition of the selective test mode, the description following will only address the test to be conducted in the selective test mode.
Both automatic and selectin~ testing utilize the tests indicated by symbol "K" in FIG. 10.
Referrin8 now to FIG. 10, testin~ of the NRV may occur as a full test with the turbine on-line with active steam extraotion, block 1~2, or as a partial test for other conditions, block 164. In an active on-line test, the system must first verify that the isolation valve 94 is open, block 166, the feedwater heater 96 is active, block 168, and the non-return dump valve is energized enabling the NRV to be fully open, block 170. To test the non-return valve, the isolation valve 94 is held open and the non-return valve servo-motor dump valve is opened briefly by providing a signal to its servo-motor, and then re-closed, as is indicated by block 172. Since the isolation valve 94 is still open passin~ substantial flow, the non-return valve 10 transitions from an opened to a partially closed condition and then reopens, all of the potential malfunctions described above with regard to FIGS. 7 and 8 can be detected by the test sequence described. Preferably, the data collected from monitoring the operation of the non-return valve 10 can be stored for statistical analysis. For example, the NRV trip with an open isolation valve tests may be designed to operate the NRV valve 10 a predetermined number of times, such as, for example, five times, and then to statistically evaluate the operation of the non-return valve 10 for those five sample~ to verify consistent oper~tion.
Note that the system describei thus far can provide 5~,735 ~3~
not only an indication of a failure of the non-return valve but also the response time of the valve by means of the sensor 70 so as to anticipate potential failure modes. All of the data with re8ard to testing of the S valve can be stored and compared to data obtained by subsequent testing so that deterioration of the valve can be detected by variations in the data. It will be appreciated that the response time of the non-return valve lO may be affected ~y temperature and pressure of the steam in the extraction line and that any readings of the non-return valve response time may have to be normalized as a function of such temperature and pressure. Sensors providing information relatin~ to temperature and pressure are well known in the art and are common elements of the steam turbine system with which the present invention may be used.
With regard to partial testing as indicated by block 164, the only difference between the partial testing and the full on-line testin6 is that the extraction is not active. In this event, the same technique can be used to operate the non-return valve and the status of the non-return valve ch0cked using the same sensors. However, when there is no extraction steam flowing in the extraction line 98, the normal status of the non-return valve lO will be to remain in the closed position in response to actuation of the power assisted servo-motor 52, since there is no steam flow to lift the valve. Preferably, the NRV servo-motor can be actuated to trip the associated dump valve brief!y, block 173, while performing the tests indicated by symbol "L".
Returning now to FI~. 9, the monitorin~ and diagnostic mode can be utilized when the unit is off-line, block 174, when the turbine unit is on-line, ~3,735 block 176, when the turbine ~oes throu~h a turbine trip, block 178. and when there is a local reverse flow in the extraction line, block 180. In the diagnostic mode, the status of the valves, i.e., both the isolation valve 94 and the non-return valve 10, are periodically sampled and time and date of samples are associated with each sample. Each sample value is compared to preselected acceptance criteria to provide an assessment of the health of the non-return valve 10. As discussed above with re8ard to the selective test mode, the data collected from the periodic sampling can be used to compute trends, averages, and variations over time of the non-return val~e. The temperature and pressure of steam in the extraction pipe 98 may also be monitored in order to correct or normalize the data associated with the non-return valve. Malfunctions may be detected as was described with regard to FIGS. 7 and 8 during the monitorine and dia~nostic mode.
In the unit on-line mode, there may be active extraction in extraction line 98 as indicated by block 182 or there may be isolated extraction as indicated by block 184. In both cases, the isolation valve status and the non-return valve status are periodically sampled and associated with the correspondin~ times and dates, block 186. The sample values may be compared to acceptance criteria such as computed derived variables to determine whether or not the non~return valve is properly operatin~, blocks 188 and 190. Trends may be dete.^mined, block 190, to forecast probable failures and allow repair or replacement before failure. As with other samples, temperature and pressure of the steam throu~h the valve may also be sampled and used to normalize any 53,735 - ~o - ~3~
readings on the valve. If the line is isolated, the same logic described for block 164 applies.
Unit off-line tests and processes, indicated by biock 174, are essentially the same as are performed for isolated extraction tests indicated by block 184.
Unit trip, indicated in block 178, provides an opportunity to compute the valve closing time under operating conditions. Otherwise, the monitoring of the sensors provides the same basic type of information as is provided under other test conditions.
The tests under the local reverse flow block 180 are essentially the same as under the unit trip bock 178. However, the comparison may be to other non-return valve actions. The dia~nosis under block 180 can follow the same process as was described with re~ard to FIGS. 7 and 8.
While the principles of the invention have now been made clear in an illustrative embodiment, it will become apparent to those skilled in the art that many modifications of the structures, arrangements, and components presented in the above illustrations may be made in the practice of the invention in order to develop alternate embodiments suitable to specific operating requirements without departing from the spirit and scope of the invention as set forth in the claims which follow. For example, the selected malfunctions at the isolated valve, such as steam leakage past the seat, can be detected by notin~
abnormal behavior of the non-return valve.
Claims (15)
1. A diagnostic system for evaluating the operation of a non-return (NR) valve in a steam extraction line of a steam turbine, the NR valve being connected in a steam flow path in series with an isolation valve between the turbine and a feetwater heater, the NR valve including a flapper pivotable on a shaft for selectively blocking reverse flow through the valve, a counterweight attached to the shaft external of the valve for balancing the weight of the flapper, and a power assist servo-motor coupled to the shaft for providing an initial assist to rotation of the shaft to start the flapper in a closing direction, the system comprising:
first sensor means coupled to the shaft supporting the flapper for providing first signals representative of shaft angular position;
second sensor means coupled for sensing a desired state of the isolation valve for providing second signals representative of the desired state of the isolation valve; and 53,735 computer means coupled for receiving said first and second signals, said computer means including timing means for determining the rate of change of said shaft angular position upon receipt of said second signals and further including means for comparing said shaft position to predetermined shaft positions corresponding to states of said second signals, and for comparing said rate of change for identifying variations in response to characteristics of said NR valve, said computer means providing a status report indicative of the state of operability of said NR valve.
first sensor means coupled to the shaft supporting the flapper for providing first signals representative of shaft angular position;
second sensor means coupled for sensing a desired state of the isolation valve for providing second signals representative of the desired state of the isolation valve; and 53,735 computer means coupled for receiving said first and second signals, said computer means including timing means for determining the rate of change of said shaft angular position upon receipt of said second signals and further including means for comparing said shaft position to predetermined shaft positions corresponding to states of said second signals, and for comparing said rate of change for identifying variations in response to characteristics of said NR valve, said computer means providing a status report indicative of the state of operability of said NR valve.
2. The system of claim 1 and further comprising:
a third sensor coupled to said NR valve for providing third signals representative of differential pressure between an inlet and an outlet of said NR
valve, said third signals being coupled to said computer means for providing an indication of the position of the flapper; and said computer means comparing said third signals to predetermined pressure signals for determining the state of the flapper in comparison to the desired state of the isolation valve as established by said second signals, and said computer means providing a malfunction indication of said NR valve when said desired state of said isolation valve is different from said state of said NR valve,
a third sensor coupled to said NR valve for providing third signals representative of differential pressure between an inlet and an outlet of said NR
valve, said third signals being coupled to said computer means for providing an indication of the position of the flapper; and said computer means comparing said third signals to predetermined pressure signals for determining the state of the flapper in comparison to the desired state of the isolation valve as established by said second signals, and said computer means providing a malfunction indication of said NR valve when said desired state of said isolation valve is different from said state of said NR valve,
3. The system of claim 2 and further comprising:
fourth sensor means coupled to the power assist servo-motor for providing fourth signals representative of pdwer being applied to the servo-motor for initiated operation of said NR valve; and 53.735 said computer means being adapted for receiving said fourth signals and for comparing said fourth signals to at least said first signals for determining rotation of the valve shaft in response to actuation of the servo-motor, said computer means providing a malfunction indication when said first signals do not indicate shaft annular rotation in response to said fourth signals.
fourth sensor means coupled to the power assist servo-motor for providing fourth signals representative of pdwer being applied to the servo-motor for initiated operation of said NR valve; and 53.735 said computer means being adapted for receiving said fourth signals and for comparing said fourth signals to at least said first signals for determining rotation of the valve shaft in response to actuation of the servo-motor, said computer means providing a malfunction indication when said first signals do not indicate shaft annular rotation in response to said fourth signals.
4. The system of claim 2 and further comprising:
means for periodically energizing the isolation valve to effect a cycling thereof from an open to a closed state and back to an open state; and said computer means being operative to monitor each of said first, second, and third sensors for determining the response of the NR valve when the isolation valve is cycled, said computer means compiling a record of the operation of the NR valve sufficient to establish failure trends evidenced by variation in responses of the NR valve.
means for periodically energizing the isolation valve to effect a cycling thereof from an open to a closed state and back to an open state; and said computer means being operative to monitor each of said first, second, and third sensors for determining the response of the NR valve when the isolation valve is cycled, said computer means compiling a record of the operation of the NR valve sufficient to establish failure trends evidenced by variation in responses of the NR valve.
5. The system of claim 4 and further comprising:
means for providing signals representative of steam temperature and pressure in the turbine extraction line; and computer means for normalizing the shaft rotational velocities as a function of steam temperature and pressure.
means for providing signals representative of steam temperature and pressure in the turbine extraction line; and computer means for normalizing the shaft rotational velocities as a function of steam temperature and pressure.
6. A method for evaluating the operability of steam valves in a steam flow path in a steam turbine system comprising the steps of:
53,735 sensing a desired operating state of at least one of the valves;
determining steam flow conditions in the steam flow path in which at least one valve is located;
sensing the actual state of the at least one valve;
determining whether the state of the at least one valve is dependent on steam flow;
comparing the desired state of the at least one valve to the actual state of the at least one valve;
for each difference in desired state compared to actual state, evaluating whether the difference is steam flow dependent from the steps of determining such dependence; and providing a malfunction signal for each difference between desired and actual valve states not attributable to steam flow conditions.
53,735 sensing a desired operating state of at least one of the valves;
determining steam flow conditions in the steam flow path in which at least one valve is located;
sensing the actual state of the at least one valve;
determining whether the state of the at least one valve is dependent on steam flow;
comparing the desired state of the at least one valve to the actual state of the at least one valve;
for each difference in desired state compared to actual state, evaluating whether the difference is steam flow dependent from the steps of determining such dependence; and providing a malfunction signal for each difference between desired and actual valve states not attributable to steam flow conditions.
7. The method of claim 6 wherein the at least one of the valves includes a flapper connected to a rotatably mounted shaft, the method including the further steps of:
providing signals to effect cycling of the at least one valve;
sensing the angular orientation of the flapper shaft;
timing the rate of change of shaft position while the flapper is moving to its final position;
comparing the rate of change of shaft position to a preselected rate of change; and generating a malfunction signal when the rate of change indicates a deviation from the preselected rate of change greater than a predetermined magnitude.
53,735
providing signals to effect cycling of the at least one valve;
sensing the angular orientation of the flapper shaft;
timing the rate of change of shaft position while the flapper is moving to its final position;
comparing the rate of change of shaft position to a preselected rate of change; and generating a malfunction signal when the rate of change indicates a deviation from the preselected rate of change greater than a predetermined magnitude.
53,735
8. The method of claim 6 and further comprising the steps of:
sensing the differential pressure between an inlet and an outlet of the at least one valve and determining therefrom the state of the at least one valve;
comparing the determined state of the at least one valve from the step of sensing the differential pressure to the desired state of the at least one valve: and generating a malfunction signal when the determined state of the at least one valve differs from the desired state.
sensing the differential pressure between an inlet and an outlet of the at least one valve and determining therefrom the state of the at least one valve;
comparing the determined state of the at least one valve from the step of sensing the differential pressure to the desired state of the at least one valve: and generating a malfunction signal when the determined state of the at least one valve differs from the desired state.
9. The method of claim 8 wherein the at least one valve is coupled in a steam flow path in series with a power driven valve and wherein the step of sensing a desired operating state of the at least one valve comprises the step of sensing the operating state of the power driven valve and comparing its state to that of the at least one valve.
10. The method of claim 9 and further comprising the steps of:
periodically energizing the power driven valve to cycle from a present state to an alternate state and to return to the present state;
sensing the shaft angular position of the at least one valve during the energizing and cycling step:
comparing the sensed angular positions to predetermined angular positions corresponding to states of the power driven valve: and 53,735 generating a malfunction signal when the sensed angular positions deviate from the predetermined angular positions.
periodically energizing the power driven valve to cycle from a present state to an alternate state and to return to the present state;
sensing the shaft angular position of the at least one valve during the energizing and cycling step:
comparing the sensed angular positions to predetermined angular positions corresponding to states of the power driven valve: and 53,735 generating a malfunction signal when the sensed angular positions deviate from the predetermined angular positions.
11. The method of claim 10 and further comprising the steps of:
storing in an addressable memory each of the results of the step of comparing the sensed angular positions to predetermined angular positions: and correlating the stored results to produce a trend analysis of the operation of the at least one valve.
storing in an addressable memory each of the results of the step of comparing the sensed angular positions to predetermined angular positions: and correlating the stored results to produce a trend analysis of the operation of the at least one valve.
12. The method of claim 11 and further comprising the steps of sampling temperature and pressure of steam in the steam flow path and normalizing the stored results of each of the periodic cycles of the at least one valve to correct for changes in temperature and pressure.
13. The method of claim 12 and including the steps of:
determining when the at least one valve is in a closed state from the sensed angular position of the shaft: and comparing the sensed differential pressure of the least one valve to a predetermined differential pressure for determining the effectiveness of the at least one valve in the closed state.
53,735
determining when the at least one valve is in a closed state from the sensed angular position of the shaft: and comparing the sensed differential pressure of the least one valve to a predetermined differential pressure for determining the effectiveness of the at least one valve in the closed state.
53,735
14. The method of claim 13 and including the additional step of automatically evaluating the condition of the at least one valve and thereafter sequentially cycling each of the others of the cyclicable valves in the turbine system to establish the condition of all valves.
15. The method of claim 9 and further including the steps of comparing the status of the NR valve to the status of the power driven valve and evaluating the operability of the power driven valve from the response of the NR valve to preselected stimuli.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US46997490A | 1990-01-25 | 1990-01-25 | |
| US469,974 | 1990-01-25 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2034844A1 true CA2034844A1 (en) | 1991-07-26 |
Family
ID=23865776
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002034844A Abandoned CA2034844A1 (en) | 1990-01-25 | 1991-01-24 | Diagnostic system for evaluating the performance of critical valves in a steam turbine system |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPH0771206A (en) |
| KR (1) | KR0152445B1 (en) |
| CN (1) | CN1053660A (en) |
| CA (1) | CA2034844A1 (en) |
| ES (1) | ES2026076A6 (en) |
| IT (1) | IT1245113B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP3067665A1 (en) * | 2011-06-02 | 2016-09-14 | Linde Aktiengesellschaft | A flow apparatus and monitoring system relating thereto |
| US10337356B2 (en) | 2014-03-13 | 2019-07-02 | Siemens Aktiengesellschaft | Steam power installation comprising valve-stem leakage steam line |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100336210B1 (en) * | 1999-12-29 | 2002-05-10 | 김형국 | Diagnostic circuit for power plant valves in operating |
| WO2006079294A1 (en) * | 2005-01-25 | 2006-08-03 | Daniel Aguilar Arrieta | Inclined valve with forced rotation (valforzo) |
| FI120375B (en) * | 2008-05-29 | 2009-09-30 | Abb Oy | Method and apparatus for verifying a leak in connection with a flow prevention device |
| JP5595306B2 (en) * | 2011-02-25 | 2014-09-24 | 三菱重工コンプレッサ株式会社 | Steam turbine operation control device and operation control method |
| CN102721541B (en) * | 2012-07-02 | 2015-10-28 | 山东电力集团公司电力科学研究院 | Steam extraction check valve of steam turbine shut-in time method of testing |
| US10626749B2 (en) * | 2016-08-31 | 2020-04-21 | General Electric Technology Gmbh | Spindle vibration evaluation module for a valve and actuator monitoring system |
| US10969029B2 (en) | 2016-12-02 | 2021-04-06 | Applied Materials, Inc. | Low particle protected flapper valve |
| CN110005484B (en) * | 2019-03-07 | 2021-10-15 | 大唐东营发电有限公司 | Horizontal steam turbine low pressure heater |
| CN110307389B (en) * | 2019-06-28 | 2020-12-18 | 国网浙江省电力有限公司电力科学研究院 | Steam turbine hydraulic valve fault diagnosis method based on state feedback |
| CN110645057B (en) * | 2019-09-29 | 2022-06-10 | 大唐东营发电有限公司 | Monitoring equipment for adjusting door based on steam turbine of power plant |
| CN113465825A (en) * | 2021-06-29 | 2021-10-01 | 西安热工研究院有限公司 | Logic control method for valve tightness test of coaxial steam turbine of circulating unit |
| CN114354177B (en) * | 2021-12-10 | 2024-03-12 | 国电长源汉川第一发电有限公司 | Automatic test system and method for steam extraction check valve of steam turbine |
-
1991
- 1991-01-24 IT ITMI910168A patent/IT1245113B/en active IP Right Grant
- 1991-01-24 ES ES9100184A patent/ES2026076A6/en not_active Expired - Lifetime
- 1991-01-24 CA CA002034844A patent/CA2034844A1/en not_active Abandoned
- 1991-01-24 KR KR1019910001213A patent/KR0152445B1/en not_active IP Right Cessation
- 1991-01-25 JP JP3025486A patent/JPH0771206A/en active Pending
- 1991-01-25 CN CN91100453A patent/CN1053660A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP3067665A1 (en) * | 2011-06-02 | 2016-09-14 | Linde Aktiengesellschaft | A flow apparatus and monitoring system relating thereto |
| US9683705B2 (en) | 2011-06-02 | 2017-06-20 | Linde Aktiengesellschaft | Flow apparatus and monitoring system relating thereto |
| US10508772B2 (en) | 2011-06-02 | 2019-12-17 | Linde Aktiengesellschaft | Flow apparatus and monitoring system relating thereto |
| US10337356B2 (en) | 2014-03-13 | 2019-07-02 | Siemens Aktiengesellschaft | Steam power installation comprising valve-stem leakage steam line |
Also Published As
| Publication number | Publication date |
|---|---|
| KR0152445B1 (en) | 1998-10-01 |
| ITMI910168A0 (en) | 1991-01-24 |
| ES2026076A6 (en) | 1992-04-01 |
| ITMI910168A1 (en) | 1992-07-24 |
| IT1245113B (en) | 1994-09-13 |
| KR910014588A (en) | 1991-08-31 |
| CN1053660A (en) | 1991-08-07 |
| JPH0771206A (en) | 1995-03-14 |
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| FZDE | Discontinued |