Description: SUMMARY OF THE INVENTION

It is a primary objective of this invention to provide for a steam turbine and system for controlling same, which control system overcomes the shortcomings of the prior art turbine control systems by providing automatic means for startup of the turbine combined with both speed and load control during all phases of turbine operation, and including overriding steam flow control so as to maintain turbine differential expansion and turbine rotor stress within predetermined limits.

It is another objective of this invention to provide a steam turbine and system for controlling same, which control system provides automatic digital means for automatic startup of the turbine combined with both speed and load control during all phases of turbine operation, and which provides improved capacity for turbine startup under cold start or hot start conditions.

In accordance with the above stated objectives, the present invention provides a steam turbine system having a control subsystem for controlling steam flow as an intermediate variable and the turbine speed during startup and turbine load during load operation as end operating variables, which control subsystem comprises a programmable digital computer system in combination with input means for receiving signals representative of turbine operating conditions and parameters and output means for using signals generated by said digital computer, for controlling the steam flow. The digital computer is operated by an overall program system for carrying out a plurality of respective functions in accordance with a predetermined priority, which functions include calculating speed control and load control signals, and limiting such control signals as a function of monitored differential expansion or rotor stress. The computer control system also provides for automatically sequencing the turbine through startup, and providing means for alternately sequencing through either a hot start or a cold start.

BACKGROUND OF THE INVENTION

The present invention relates to the elastic fluid turbines and more particularly to systems and methods for operating steam turbines and electric power plants in which generators are operated by steam turbines.

With respect to steam turbine control, prime mover turbine control usually operates to determine turbine rotor shaft speed, tubine load, and/or turbine throttle pressure as end control system variables. In the case of large electric power plants in which throttle pressure is steam-generating system controlled, turbine control is typically directed to the megawatt amount of electric load and the frequency participation of the turbine after the turbine rotor speed has been controllably brought to the synchronous value and the generator has been connected to the electric power system.

In addition to the conventional steam turbine generated system, another type of power generating system in which steam turbine control is needed is a combined cycle generating system. The combined cycle generating system involves a combination of heat sources and energy conversion apparatus organized to produce an electric power output. For example, gas turbines can drive generators and use their exhaust gases to supply heat for steam to be used in driving a steam turbine. A separate boiler can also be included in the system to provide steam generating heat. Electric power is supplied by separate generators driven by the turbines.

The end controlled plant or plant system variables and the turbine operation are normally determined by controlled variation of the steam flow to one or more of the various stages of the particular type and particular design of the turbine in use. In prime mover turbine applications such as drum type boiler electric power plants where turbine throttle pressure is extremely controlled by the boiler operation, the turbine inlet steam flow is an end controlled steam characteristic or an intermediately controlled system variable which controllably determines in turn the end control system variables, i.e., turbine speed, electric load or the turbine speed and the electric load. It is noteworthy, however, that some supplemental or protective control may be placed on the end control variable by additional downstream steam flow control such as by control of reheat valving and to that extent inlet turbine steam flow control is not strictly wholly controllably determinative of the end controlled system variables under all operating conditions.

In determining turbine operation and the end controlled system variables, turbine steam flow control has generally been achieved by controlled operation of valves disposed in the steam flow path or paths. To illustrate the nature of the turbine valve control in general and to establish simultaneously some background for subsequent description, consideration will now be directed to the system structure and the operation of a typical large electric power tandem steam turbine design for use with a fossil fuel drum-type boiler steam generating system.

Steam generated at controlled pressure may be admitted to the turbine steam chest through one or more throttle or stop valves operated by the turbine control system. Governor or control valves are arranged to supply steam inlets disposed around the periphery of a high pressure turbine section casing. The governor valves are also operated by the turbine control system to determine the flow of steam from the steam chest through the stationary nozzles or vanes and the rotor blading of the high pressure turbine section.

Torque resulting from the work performed by steam expansion causes rotor shaft rotation and reduced steam pressure. The steam is usually then directed to a reheat stage where its enthalpy is raised to a more efficient operating level. In the reheat stage, the high pressure section outlet steam is ordinarily directed to one or more reheaters associated with the primary steam generating system where heat energy is applied to the steam. In large electric power nuclear turbine plants, turbine reheater stages are usually not used and instead combined moisture separator reheaters are employed between the tandem nuclear turbine sections.

Reheated steam croses over the next or intermediate pressure section of a large fossil fuel turbine where additional rotor torque is developed as intermediate pressure steam expands and drives the intermediate pessure turbine blading. One or more interceptor and/or reheater stop valves are usually installed in the reheat steam flow path or paths in order to cut off or reduce the flow of turbine contained steam as required to protect against turbine overspeed. Reheat and/or interceptor valve operation at best produces late corrective turbine response and accordingly is normally not used controllably as a primary determinant of turbine operation.

Additional reheat may be applied to the steam after it exits from the intermediate pressure section. In any event, steam would typically be at a pressure of about 1200 psi as it enters the next or low pressure turbine section usually provided in the large fossil fuel turbines. Additional rotor torque is accordingly developed and the vitiated steam then exhausts to a condenser.

In both the intermediate pressure and the low pressure sections, no direct steam flow control is normally applied as already suggested. Instead, steam conditions at these turbine locations are normally determined by mechanical system design subject to time delayed effects following control placed on the high pressure section steam admission conditions.

In a typical large fossil fuel turbine just described, 30% of the total steady state torque might be generated by the high pressure section and 70% might be generated by the intermediate pressure and low pressure sections. In practice, the mechanical design of the turbine system defines the number of turbine sections and their respective torque ratings as well as other structural characteristics such as the disposition of the sections of one or more shafts, the number of reheat stages, the blading and vane design, the number and form of turbine stages and steam flow paths in the sections, etc.

A variety of valve arrangements may be used for steam control in the various turbine types and designs, and hydraulically operated valve devices have generally been used for steam control in the various valving arrangements. The use of hydraulically operated valves has been predicated largely on their relatively low cost coupled with their ability to meet stroke operating power and positioning speed and accuracy requirements.

Turbine valve control and automatic turbine operation have undergone successive stages of development. With increasing plant sizes, mechanical-hydraulic controls have been largely subplanted by analog electrohydraulic controllers sometimes designated as AEH controllers. The aforementioned Giras and Birnbaum Patent application, Ser. No. 319,115, provides a further description of the turbine control technology development and the earlier prior patent and publication art. The latter application discloses a programmed digital computer controller which generally provides improved turbine and electric power plant operation over the earlier prior art. U.S. Pat. No. 3,588,265 issued to W. Berry, entitled "System And Method For Providing Steam Turbine Operation With Improved Dynamics", and assigned to the present assignee, is also directed to a digital computer controller which provides improved automatic turbine startup and loading operations. U.S. Pat. No. 3,552,872 issued to T. Giras and T. C. Barns, Jr. entitled "Computer Positioning Control System With Manual Backup Control Especially Adapted For Operating Steam Turbine Valves", and assigned to the present assignee, discloses a digital computer controller interfaced with a manual backup controller. A general publication pertaining to turbine digital controllers has appeared in Electrical World Magazine.

At this point in the background writeup, it is noted that prior art citations are made herein in an attempt to characterize the context within which the presently disclosed subject matter has been developed. No representations are made that the cited art is the best art nor that the cited art is immune to alternative interpretations.

Generally, the earlier Berry and the earlier Giras and Birnbaum DEH turbine operating system comprise basic hardware and software elements and control loops which bear some similarity to a number of basic elements and loops described herein. However, the present disclosure involves improvements largely stemming from the combined application of principles associated with turbine technology and principles associated with the computer and control technologies in the determination of a particular detailed system arrangement and operation. Thus, the earlier DEH is largely directed to central control concepts which, although implementable with conventional know-how, open up opportunities for improvement-type developments related to the more central aspects of turbine control and operation as well as the more supportive aspects of turbine control and operation including areas such as turbine protection, remote system interfacing, accuracy and reliability, computer utilization efficiency, operator interface, maintenance and operator training.

In particular, earlier turbine control systems did not comprise a fully integrated programmable digital computer system for providing all phases of sequential and monitoring control of the turbine during speed startup, load control during load operation, and monitoring capability during load operation. More specifically, there has been a need for such a fully integrated turbine control system capable of monitoring differential expansion and rotor stress, and for providing means for efficiently controlling the turbine during startup as a function of these temperature-related conditions. In relation to such temperature conditions, there has been an existing need for more flexibility in turbine control at startup to start under different rotor temperature conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram on an electric power plant including a large steam turbine and a fossile fuel fired drum type boiler and control devices which are all operable in accordance with the principles of the invention;

FIG. 2 shows a schematic diagram on a programmed digital computer control system operable with a steam turbine and its associated devices shown in FIG. 1 in accordance with the principles of the invention;

FIG. 3 shows a hydraulic system for supplying hydraulic fluid to valve actuators of the steam turbine;

FIG. 4 shows a schematic diagram of a servo system connected to the valve actuators;

FIG. 5 shows a schematic diagram of a hybird interface between a manual backup system and the digital computer connected with the servo system controlling the valve actuators;

FIG. 6 shows a simplified block diagram of the digital Electro Hydraulic Control System in accordance with the principle of the invention;

FIG. 7 shows a block diagram of a control program used in accordance with the principles of the invention;

FIG. 8 shows a block diagram of the programs and subroutines of the digital Electro Hydraulic and the automatic turbine startup and monitoring program in accordance with the principles of the invention;

FIG. 9 shows a table of program or task priority assignments in accordance with the principles of the invention;

FIG. 10 shows the location of subroutines in accordance with the principles of the invention;

FIG. 11 shows a block diagram of a subroutine for scanning contact close inputs of the Digital Electro Hydraulic System which is operable in accordance with the principles of the invention; and

FIG. 12 shows a block diagram of an auxiliary synchronizer computer program which is operable in accordance with the principles of the invention.

FIG. 13 is a block diagram of a contact input scan program with a sequence of events interrupt program therein which is operable in accordance with the principles of the invention;

FIG. 14 is a flow chart of the sequence of events interrupt program which is operable in accordance with the principles of the invention;

FIG. 15 is a block diagram of error action with a task error program which is operable in accordance with the principles of the invention;

FIG. 16 is a block diagram of a turbine trip interrupt program which is operable in accordance with the principles of the invention;

FIG. 17 is a block diagram of a panel interrupt program which is operable in accordance with the principles of the invention;

FIG. 18 is a block diagram of an analog scan system which is operable in accordance with the principles of the invention;

FIG. 19 is a timing chart of the various programs and functions within the Digital Electro Hydraulic System which is operable in accordance with the principles of the invention;

FIG. 20 is a flow chart of a logic contact closure output subroutine which is operable in accordance with the principles of the invention;

FIG. 21 is a block diagram of conditions which cause initiation of a logic program which is operable in accordance with the principles of the invention;

FIG. 22 is a simplified block diagram of a portion of the logic function which is operable in accordance with the principles of the invention;

FIG. 23 is a block diagram of the logic program which is operable in accordance with the principles of the invention;

FIG. 24 is a block diagram of a megawatt feedback loop subroutine which is operable in accordance with the principles of the invention;

FIG. 25 is a block diagram of an impulse pressure loop with megawatt loop in service which is operable in accordance with the principles of the invention;

FIG. 26 is a flow chart of an automatic turbine startup program which is operable in accordance with the principles of the invention;

FIG. 27 shows a block diagram of an operating mode selection function which is operable in accordance with the principles of the invention;

FIG. 28 shows a symbolic diagram of the use of a speed/load reference function which is operable in accordance with the principles of the invention;

FIG. 29 shows a speed/load reference graph which is operable in accordance with the principles of the invention;

FIG. 30 shows a block diagram of the sense parameters in the automatic turbine startup and monitoring program which is operable in accordance with the principles of the invention;

FIG. 31 shows a flow chart of a program for determining the rotor stresses in the turbine rotor which is operable in accordance with the principles of the invention;

FIG. 32 shows a flow chart of the ATS roll-off subroutine which is operable in accordance with the principles of the invention;

FIG. 33 shows a flow chart of the ATS turbine latching and load references which are operable in accordance with the principles of the invention;

FIGS. 34A and 34B show a portion of the flow chart of the ATS program which is operable in accordance with the principles of the invention;

FIGS. 35A and 35B show a flow chart of the ATS program with library charts which is operable in accordance with the principles of the invention;

FIGS. 36A and 36B show the flow chart of the ATS acceleration program which is operable in accordance with the principles of the invention;

FIG. 37 shows a chart of generator conditions which is operable in accordance with the principles of the invention;

FIGS. 38A and 38B show a flow chart of the ATS program for drain valve control supervision of differential expansion which are operable in accordance with the principles of the invention;

FIGS. 39A and 39B show a flow chart of the ATS program sensor failure detection subroutine which is operable in accordance with the principles of the invention;

FIGS. 40A and 40B show a flow chart of the ATS vibration scan, reaheat temperature monitoring and heat soak time calculation which are operable in accordance with the principles of the invention;

FIGS. 41A and 41B show a flow chart of the ATS program resetting and clear functions which are operable in accordance with the principles of the invention;

FIGS. 42A and 42B show a flow chart of the ATS generator monitor which is operable in accordance with the principles of the invention;

FIGS. 43A and 43B show a flow chart of the ATS transfer logic front speed to load control which is operable in accordance with the principles of the invention;

FIGS. 44A and 44B show a flow chart of the ATS program turbine latch which is operable in accordance with the principles of the invention;

FIG. 45 shows a graph of no load and light load guides which are operable in accordance with the principles of the invention;

FIG. 46 shows a schematic representation of turbine generator differential expansion which is operable in accordance with the principles of the invention;

FIG. 47 shows a schematic representation of turbine generator differential expansion which is operable in accordance with the principles of the invention;

FIG. 48 shows a section with an indication of buildup of rotor stresses in the rotor of the turbine generator which is operable in accordance with the principles of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A. POWER PLANT

More specifically, there is shown in FIG. 1 a large single reheat steam turbine constructed in a well known manner and operated and controlled in an electric power plant 12 in accordance with the principles of the invention. As will become more evident through this description, other types of steam turbines can also be controlled in accordance with the principles of the invention and particularly in accordance with the broader aspects of the invention. The generalized electric power plant shown in FIG. 1 and the more general aspects of the computer control system to be described in connection with FIG. 2 are like those disclosed in the aforementioned Giras and Birnbaum patent application Ser. No. 319,115. As already indicated, the present application is directed to general improvements in turbine operation and control as well as more specific improvements related to digital computer operation and control of turbines.

The turbine 10 is provided with a single output shaft 14 which drives a conventional large alternating current generator 16 to produce three-phase electric power (or any other phase electric power) as measured by a conventional power detector 18 which measures the rate of flow of electric energy. Typically, the generator 16 is connected through one or more breakers 17 per phase to a large electric power network and when so connected causes the turbo-generator arrangement to operate at synchronous speed under steady conditions. Under transient electric load change conditions, system frequency may be affected and conforming turbo-generator speed changes would result. At synchronism, power contribution of the generator 16 to the network is normaly determined by the turbine steam flow which in this instance is supplied to the turbine 10 at substantially constant throttle pressure.

In this case, the turbine 10 is of the multistage axial flow type and includes a high pressure section 20, an intermediate pressure section 22, and a low pressure section 24. Each of these turbine sections may include a plurality of expansion stages provided by stationary vanes and an interacting bladed rotor connected to the shaft 14. In other applications, turbines operating in accordance with the present invention may have other forms with more or fewer sections tandemly connected to one shaft or compoundly coupled to more than one shaft.

The constant throttle pressure steam for driving the turbine 10 is developed by a steam generating system 26 which is provided in the form of a conventional drum type boiler operated by fossil fuel such as pulverized coal or natural gas. From a generalized standpoint, the present invention can also be applied to steam turbines associated with other types of steam generating systems such as nuclear reactor or once through boiler systems.

The turbine 10 in this instance is of the plural inlet front end type, and steam flow is accordingly directed to the turbine steam chest (not specifically indicated) through four throttle inlet valves TV1-TV4. Generally, the plural inlet type and other front end turbine types such as the single ended type or the end bar lift type may involve different numbers and/or arrangements of valves.

Steam is directed from the admission steam chest to the first high pressure section expansion stage through eight governor inlet valves GV1-GV8 which are arranged to supply steam to inlets arcuately spaced about the turbine high pressure casing to constitute a somewhat typical governor valving arrangement for large fossil fuel turbines. Nuclear turbines might on the other hand typically utilize only four governor valves.

During start-up, the governor valves GV1-GV8 are typically all fully opened and steam flow control is provided by a full arc throttle valve operation. At some point in the start-up process, transfer is made from full arc throttle valve control to full arc governor valve control because of throttling energy losses and/or throttling control capability. Upon transfer the throttle valves TV1-TV4 are fully opened, and the governor valves GV1-GV8 are normally operated in the single valve mode. Subsequently, the governor valves may be individually operated in a predetermined sequence usually directed to achieving thermal balance on the rotor and reduced rotor blade stressing while producing the desired turbine speed and/or load operating level. For example, in a typical governor valve control mode, governor valves GV5-GV8 may be initially closed as the governor valves GV1-GV4 are jointly operated from time to time to define positions producing the desired corresponding total steam flows. After the governor valves GV1-GV4 have reached the end of their control region i.e., upon being fully opened, or at some overlap point prior to reaching their fully opened position, the remaining governor valves GV5-GV8 are sequentially placed in operation in numerical order to produce continued steam flow control at higher steam flow levels. This governor valve sequence of operation is based on the assumption that the governor valve controlled inlets are arcuately spaced about the 360.degree. periphery of the turbine high pressure casing and that they are numbered consecutively around the periphery so that the inlets corresponding to the governor valves GV1 and GV8 are arcuately adjacent to each other.

The preferred turbine start-up method is to raise the turbine speed from the turning gear speed of about 2 rpm to about 80% of the synchronous speed under throttle valve control and then transfer to governor valve control and raise the turbine speed to the synchronous speed, then close the power system breakers and meet the load demand. On shutdown, similar but reverse practices or simple coastdown may be employed. Other transfer practice may be employed, but it is unlikely that transfer would be made at a loading point above 40% rated load because of throttling efficiency considerations.

After the steam has crossed past the first stage impulse blading to the first stage reaction blading of the high pressure section, it is directed to a reheater system 28 which is associated with a boiler or steam generating system 26. In practice, the reheater system 28 may typically include a pair of parallel connected reheaters coupled to the boiler 26 in heat transfer relation as indicated by the reference character 29 and associated with opposite sides of the turbine casing.

With a raised enthalpy level, the reheated steam flows from the reheater system 28 through the intermediate pressure turbine section 22 and the low pressure turbine section 24. From the latter, the vitiated steam is exhausted to a condenser 32 from which water flow is directed (not indicated) back to the boiler 26.

To control the flow of reheat steam, a stop valve SV including one or more check valves is normally open and closed only when the turbine is tripped. Interceptor valves IV (only one indicated), are also provided in the reheat steam flow path, and they are normally open and if desired they may be operated over a range of position control to provide reheat steam flow cutback modulation under turbine overspeed conditions. Further description of an appropriate overspeed protection system is presented in U.S. Pat. 3,643,437 issued to M. Birnbaum, A. Braytenbah and A. Richardson and assigned to the present assignee.

In the typical fossil fuel drum type boiler steam generating system, the boiler control system controls boiler operations so that steam throttle pressure is held substantially constant. In the present description, it is therefore assumed as previously indicated that throttle pressure is an externally controlled variable upon which the turbine operation can be based. A throttle pressure detector 38 of suitable conventional design measures the throttle pressure to provide assurance of substantially constant throttle pressure supply, and, if desired as a programmed computer protective system override control function, turbine control action can be directed to throttle pressure control as well as or in place of speed and/or load control if the throttle pressure falls outside predetermined constraining safety and turbine condensation protection limits.

In general, the steady state power or load developed by a steam turbine supplied with substantially constant throttle pressure steam is determined as follows:

Equation (1) ##EQU1## where P.sub.i = first stage impulse pressure P.sub.O = throttle pressure

K.sub.P = constant of proportionality

S.sub.F = steam flow

K.sub.F = constant of proportionality

Where the throttle pressure is held substantially constant by external control as in the present case, the turbine load is thus proportional to the first stage impulse pressure P.sub.i. The ratio P.sub.i /P.sub.O may be used for control purposes, for example to obtain better anticipatory control of P.sub.i (i.e. turbine load) as the boiler control throttle pressure P.sub.O undergoes some variation within protective constraint limit values. However, it is preferred in the present case that the impulse pressure P.sub.i be used for feedback signalling in load control operation as subsequently more fully described, and a conventional pressure detector 40 is employed to determine the pressure P.sub.i for the assigned control usage.

Within its broad field of applicability, the invention can also be applied in nuclear reactor and other applications involving steam generating systems which produce steam without placement of relatively close steam generator control on the constancy of the turbine throttle pressure. In such cases, throttle control and operating philosophies are embodied in a form preferred for and tailored to the type of plant and turbine involved. In cases of unregulated throttle pressure supply, turbine operation may be directed with top priority to throttle pressure control or constraint and with lower priority to turbine load and/or speed control.

Respective hydraulically operated throttle valve actuators indicated by the reference character 42 are provided for the four throttle valves TV1-TV4. Similarly, respective hydraulically operated governor valve actuators indicated by the reference character 44 are provided for the eight governor valves GV1-GV8. Hydraulically operated actuators indicated by the reference characters 46 and 48 are provided for the reheat stop and interceptor valves SV and IV. A computer monitored high pressure fluid supply 50 provides the controlling fluid for actuator operation of the valves TV1-TV4, GV1-GV8, SV and IV. A computer supervised lubricating oil system (not shown) is separately provided for turbine plant lubricating requirements.

The respective actuators 42, 44, 46 and 48 are of conventional construction, and the inlet valve actuators 42 and 44 are operated by respective stabilizing position controls indicated by the reference characters 50 and 52. If desired, the interceptor valve actuators 48 can also be operated by a position control 56 although such control is not employed in the present detailed embodiment of the invention. Each position control includes a conventional analog controller (not shown in FIG. 1) which drives a suitably known actuator servo valve (not indicated) in the well known manner. The reheat stop valve actuators 46 are fully open unless the conventional trip system or other operating means causes them to close and stops the reheat steam flow.

Since the turbine power is proportional to steam flow under the assumed control condition of substantially constant throttle pressure, steam valve positions are controlled to produce control over steam flow as an intermediate variable and over turbine speed and/or load as an end control variable or variables. Actuator operation provides the steam valve positioning, and respective valve position detectors PDT1-PDT4, PDG1-PDG8 and PDI are provided to generate respective valve position feedback signals for developing position error signals to be applied to the respective position controls 50, 52 and 56. One or more contact sensors CSS provides status data for the stop valving SV. The position detectors are provided in suitable conventional form, for example, they may make conventional use of linear variable differential transformer operation in generating negative position feedback signals for algebraic summing with respect to position setpoint signals sp in developing the respective input error signals. Position controlled operation of the interceptor valving IV would typically be provided only under a reheat steam flow cutback requirement.

The combined position control, hydraulic actuator, valve position detector element and other miscellaneous devices (not shown) form a local hydraulic electric analog valve position control for each throttle or governor inlet steam valve. The position setpoints SP are computer determined and supplied to the respective local loops and updated on a periodic basis. Setpoints SP may also be computed for the interceptor valve controls when the latter are employed. A more complete general background description of electrohydraulic steam valve positioning and hydraulic fluid supply systems for valve actuation is presented in the aforementioned Birnbaum and Noyes paper.

In the present case, the described hybrid arrangement including local loop analog electrohydraulic position control is preferred primarily because of the combined effects of control computer operating speed capabilities and computer hardware economics, i.e., the cost of manual backup analog controls is less than that for backup computer capacity at present control computer operating speeds for particular applications so far developed. Further consideration of the hybrid aspects of the turbine control system is presented subsequently herein. However, economic and fast operating backup control computer capability is expected and direct digital computer control of the hydraulic valve actuators will then likely be preferred over the digital control of local analog controls described herein.

A speed detector 58 is provided for determining the turbine shaft speed for speed control and for frequency participation control purposes. The speed detector 58 can for example be in the form of a reluctance pickup (not shown) magnetically coupled to a notched wheel (not shown) on the turbo-generator shaft 14. In the detailed embodiment subsequently described herein, a plurality of sensors are employed for speed detection. Analog and/or pulse signals produced by the speed detector 58, the electric power detector 18, the pressure detectors 38 and 40, the valve position detectors PDT1-PDT4, PDG1-PDG8 and PDI, and status contact or contacts CSS, and other sensors (not shown) and status contacts (not shown) are employed in programmed computer operation of the turbine 10 for various purposes including controlling turbine performance on an on-line real time basis and further including monitoring, sequencing, supervising, alarming, displaying and logging.

B. DEH - COMPUTER CONTROL SYSTEM

As generally illustrated in FIG. 2, a Digital Electro-Hydraulic control system (DEH) 1100 includes a programmed digital computer 210 to operate the turbine 10 and the plant 12 with improved performance and operating characteristics. The computer 210 can include conventional hardware including a central processor 212 and a memory 214. The digital computer 210 and its associated input/output interfacing equipment is a suitable digital computer system such as that sold by Westinghouse Electric Corporation under the trade name of P2000. In cases when the steam generating system 26 as well as the turbine 10 are placed under computer control, use can be made of one or more P2000 computers or alternatively a larger computer system such as that sold by Xerox Data Systems and known as the Sigma 5. Separate computers, such as P2000 computers, can be employed for the respective steam generation and turbine control functions in the controlled plant unit and interaction is achieved by interconnecting the separate computers together through data links or other means.

The digital computer used in the DEH control system 1100 is a P2000 computer which is designed for real time process control applications. The P2000 typically uses a 16 bit word length with 2's complement, a single address and fixed word length operated in a parallel mode. All the basic DEH system functions are performed with a 16,000 word (16K), 3 microsecond magnetic core memory. The integral magnetic core memory can be expanded to 65,000 words (65K).

The equipment interfacing with the computer 210 includes a contact interrupt system 124 which scans contacts representing the status of various plant and equipment conditions in plant wiring 1126. The status contacts might typically be contacts of mercury wetted relays (not shown) which operate by energization circuits (not shown) capable of sensing the predetermined conditions associated with the various system devices. Data from status contacts is used in interlock logic functioning and control for other programs, protection analog system functioning, programmed monitoring and logging and demand logging, etc.

Operator's panel buttons 1130 transmit digital information to the computer 2010. The operator's panel buttons 1130 can set a load reference, a pulse pressure, megawatt output, speed, etc.

In addition, interfacing with plant instrumentation 1118 is provided by an analog input system 1116. The analog input system 1116 samples analog signals at a predetermined rate from predetermined input channels and converts the signals sampled to digital values for entry into the computer 210. The analog signals sensed in the plant instrumentation 1118 represent parameters including the impulse chamber pressure, the megawatt power, the value positions of the throttle values TV1 through TV4 and the governor values GV1 through GV8 and the interceptor valve IV, throttle pressure, steam flow, various steam temperatures, miscellaneous equipment operating temperature, generator hydrogen cooling pressure and temperatue, etc. A detailed list of all parameters is provided in Appendix 1. As used here and subsequently in this specification, the Appendix referred to is that of Ser. No. 408,962 filed as a Continuation of Ser. No. 247,877, and which is incorporated by reference supra. Such parameters include process parameters which are sensed or controlled in the process (turbine or plant) and other variables which are defined for use in the programmed computer operation. Interfacing from external systems such as an automatic dispatch system is controlled through the operator's panel buttons 1130.

A conventional programmer's console and tape reader 218 is provided for various purposes including program entry into the central processor 212 and the memory 214 thereof. A logging typewriter 1146 is provided for logging printouts of various monitored parameters, as well as alarms generated by an automatic turbine startup system. (ATS) which includes program system blocks 1140, 1142, 1144 (FIG. 8) in the DEH control system 1100. A trend recorder 1147 continuously records predetermined parameters of the system. An interrupt system 124 is provided for controlling the input and output transfer of information between the digital computer 210 and the input/output equipment. The digital computer 210 acts on interrupt from the interrupt system 124 in accordance with an executive program. Interrupt signals from the interrupt system 124 stop the digital computer 210 by interrupting a program in operation. The interrupt signals are serviced immediately.

Output interfacing is provided by contacts 1128 for the computer 210. The contacts 1128 operate status display lamps, and they operate in conjunction with a conventional analog/output system and a valve position control output system comprising a throttle valve control system 220 and a governor valve control system 222. A manual control system is coupled to the valve position control output system 220 and is operable therewith to provide manual turbine control during computer shut-down. The throttle and governor valve control systems 220 and 222 correspond to the valve position controls 50 and 52 and the actuators 42 and 44 in FIG. 1. Generally, the manual control system is similar to those disclosed in prior U.S. Pat. 3,552,872 by T. Giras et al and U.S. Pat. 3,741,246 by A. Braytenbah, both assigned to the present assignee.

Digital output data from the computer 210 is first converted to analog signals in the analog output system 224 and then transmitted to the valve control system 220 and 222. Analog signals are also applied to auxiliary devices and systems, not shown, and interceptor valve systems, not shown.

C. SUBSYSTEMS EXTERNAL TO THE DEH COMPUTER

At this point in the description, further consideration of certain subsystems external to the DEH computer will aid in reaching an understanding of the invention. Making reference now to FIG. 3, a high pressure HP fluid supply system 310 for use in controlled actuation of the governor valves GV1 through GV8, the throttle valves TV1 through TV4 and associated valves is shown. The high pressure fluid supply system 310 corresponds to the supply system 49 in FIG. 1 and it uses a synthetic, fire retardant phosphate ester-based fluid and operates in the range of 1500 and 1800 psi. Nitrogen charged piston type accumulators 312 maintain a flow of fluid to the actuators for the governor valves GV1-GV8, the throttle valves TV1-TV4, etc. when pumps 314 and 316 are discharging to a reservoir 318 through unloader valves 320 and 321. In addition, the accumulators 312 provide additional transient flow capacity for rapid valve movements.

Referring now to FIG. 4, a typical electrohydraulic valve actuation system 322 is shown in greater detail for positioning a modulating type valve actuator 410 against the closing force of a large coil spring. A servo-valve 412 which is driven by a servo-amplifier 414 controls the flow of fluid therethrough. The servo-valve 412 controls the flow of fluid entering or leaving the valve actuator cylinder 416 relative to the HP fluid supply system 310. A linear voltage differential transformer LVTD generates a valve position indicating transducer voltage which is summed with a valve position demand voltage at connection 418. The summation of the two previously mentioned voltages produces a valve position error input signal to the servo-amplifier 414. The linear voltage differential transformer LVTD has a linear voltage characteristic with respect to displacement thereof in the preferred embodiment. Therefore, the position of the valve actuator 410 is made proportional to the valve position demand voltage at connection 418.

Making reference now to FIG. 5, a hardwired digital/analog system forms a part of the DEH control system 1100 (FIG. 2). Structurally, it embraces elements which are included in the blocks 50, 52, 42 and 44 of FIG. 1 as well as additional elements. A hybrid interface 510 is included as a part of the hardwired system. The hybrid interface 510 is connected to actuator system servoamplifiers 414 for the various steam valves which in turn are connected to a manual controller 516, an overspeed protection controller, not shown, and redundant DC power supplies, not shown.

A controller shown in FIG. 5 is employed for throttle valve TV1-TV4 control in the TV control system 50 of FIG. 1. The governor valves GV1-GV8 are controlled in an analogous fashion by the GV control system 52.

While the steam turbine is controlled by the digital computer 210, the hardwired system 511 tracks single valve analog outputs 520 from the digital computer 210. A comparator 518 compares a signal from the digital-to-analog converter 522 of the manual system with the signal 520 from the digital computer 210. A signal from the comparator 518 controls a logic system 524 such that the logic system 524 runs an up-down counter 526 to the point where the output of the converter 522 is equal to the output signal 520 from the digital computer 210. Should the hardwired system 511 fail to track the signal 520 from the digital computer 210 a monitor light will flash on the operator's panel.

When the DEH control system reverts to the control of the backup manual controller 516 as a result of an operator selection or due to a contingency condition, such as loss of power on the automatic digital computer 210, or a stoppage of a function in the digital computer 210, or a loss of a speed channel in the wide range speed control all as described in greater detail infra, the input of the valve actuation system 322 (FIG. 4) is switched by switches 528 from the automatic controllers in the blocks 50, 52 (FIG. 1) or 220, 222 (FIG. 2) to the control of the manual controller 516. Bumpless transfer is thereby accomplished between the digital computer 210 and the manual controller 516.

Similarly, tracking is provided in the computer 210 for switching bumplessly from manual to automatic turbine control. As previously indicated, the presently disclosed hybrid structural arrangement of software and hardware elements is the preferred arrangement for the provision of improved turbine and plant operation and control with backup capability. However, other hybrid arrangements can be implemented within the field of application of the invention.

D. DEH PROGRAM SYSTEM

DEH Program System Organization, DEH Control Loops And Control Task Program

With reference now to FIG. 6, an overall generalized control system of this invention is shown in block diagram form. The digital electrohydraulic (DEH) control system 1100 operates valve actuates 1012 for the turbine 10. The digital electrohydraulic control system 1100 comprises a digital computer 1014, corresponding to the digital computer 210 in FIG. 2, and it is interconnected with a hardwired analog backup control system 1016. The digital computer 1014 and the backup control system 1016 are connected to an electronic servo system 1018 corresponding to blocks 220 and 222, in FIG. 2. The digital computer control system 1014 and the analog backup system 1016 track each other during turbine operations in the event it becomes necessary or desirable to make a bumpless transfer of control from a digital computer controlled automatic mode of operation to a manual analog backup mode or from the manual mode to the digital automatic mode.

In order to provide plant and turbine monitor and control functions and to provide operator interface functions, the DEH computer 1014 is programmed with a system of task and task support programs. The program system is organized efficiently and economically to achieve the end operating functions. Control functions are achieved by control loops which structurally include both hardware and software elements, with the software elements being included in the computer program system. Elements of the program system are considered herein to a level of detail sufficient to reacch an understanding of the invention. More functional detail on various programs is presented in Appendix 2. Further, a detailed listing of a DEH system program substantially conforming to the description presented herein is presented in Appendix 3 in symbolic and machine language. Most of the listing is compiled by a P2000 compiler from instructions written in Fortran IV. A detailed dictionary of system parameters is presented in Appendix 1, and a detailed computer input/output signal list is presented in Appendix 4. Appendix 5 mainly provides additional hardware information related to the hardwired system previously considered as part of the DEH control system.

As previously discussed, a primary function of the digital electrohydraulic (DEH) system 1100 is to automatically position the turbine throttle valves TV1 through TV4 and the governor valves GV1 through GV8 at all times to maintain turbine speed and/or load. A special periodically executed program designated the CONTROL task is utilized by the P2000 computer along with other programs to be described in greater detail subsequently herein.

With reference now to FIG. 7, a functional control loop diagram in its preferred form includes the CONTROL task or program 1020 which is executed in the computer 1010. Inputs representing demand and rate provide the desired turbine operating setpoints. The demand is typically either the target speed in specified revolutions per minute of the turbine systems during startup or shutdown operations or the target load in megawatts of electrical output to be produced by the generating system 16 during load operations. The demand enters the block diagram configuration of FIG. 7 at the input 1050 of a compare block 1052.

The rate input either in specified RPM per minute or specified megawatts per minute, depending upon which input is to be used in the demand function, is applied to an integrator block 1054. The rate inputs in RPM and megawatts of loading per minute are established to limit the buildup of stresses in the rotor of the turbine-generator 10. An error output of the compare block 1052 is applied to the integrator block 1054. In generating the error output the demand value is compared with a reference corresponding to the present turbine operating setpoint in the compare block 1052. The reference value is representative of the setpoint RPM applied to the turbine system or the setpoint generator megawatts output, depending upon whether the turbine generating system is in the speed mode of operation or the load mode of operation. The error output is applied to the integrator 1054 so that a negative error drives the integrator 1054 in one sense and a positive error drives it in the opposite sense. The polarity error normally drives the integrator 1054 until the reference and the demand are equal or if desired until they bear some other predetermined relationship with each other. The rate input to the integrator 1054 varies the rate of integration, i.e. the rate at which the reference or the turbine operating setpoint moves toward the entered demand.

Demand and rate input signals can be entered by a human operator from a keyboard. Inputs for rate and demand can also be generated or selected by automatic synchronizing equipment, by automatic dispatching system equipment external to the computer, by another computer automatic turbine startup program or by a boiler control system. The inputs for demand and rate in automatic synchronizing and boiler control modes are preferably discrete pulses. However, time control pulse widths or continuous analog input signals may also be utilized. In the automatic startup mode, the turbine acceleration is controlled as a function of detected turbine operating conditions including rotor thermal stress. Similarly, loading rate can be controlled as a function of detected turbine operating conditions.

The output from the integrator 1054 is applied to a breaker decision block 1060. The breaker decision block 1060 checks the state of the main generator circuit breaker 17 and whether speed control or load control is to be used. The breaker block 1060 them makes a decision as to the use of the reference value. The decision made by the breaker block 1060 is placed at the earliest possible point in the control task 1020 thereby reducing computational time and subsequently the duty cycle required by the control task 1020. If the main generator circuit breaker 17 is open whereby the turbine system is in wide range speed control the reference is applied to the compare block 1062 and compared with the actual turbine generator speed in a feedback type control loop. A speed error value from the compare block 1062 is fed to a proportional plus reset controller block 1068, to be described in greater detail later herein. The proportional plus reset controller 1068 provides an integrating function in the control task 1060 which reduces the speed error signal to zero. In the prior art, speed control systems limited to proportional controllers are unable to reduce a speed error signal to zero. During manual operation an offset in the required setpoint is no longer required in order to maintain the turbine speed at a predetermined value. Great accuracy and precision of turbine speed whereby the turbine speed is held within one RPM over tens of minutes is also accomplished. The accuracy of speed is so high that the turbine 10 can be manually synchronized to the power line without an external synchronizer typically required. An output from the proportional plus reset controller block 1068 is then processed for external actuation and positioning of the appropriate throttle and/or governor valves.

If the main generator circuit breaker 17 is closed, the CONTROL task 1020 advances from the breaker block 1060 to a summer 1072 where the REFERENCE acts as a feedforward setpoint in a combined feedforward-feedback load control system. If the main generator circuit breaker 17 is closed, the turbine generator system 10 is being loaded by the electrical network connected thereto.

In the control task 1020 of the DEH system 1100 utilizes the summer 1072 to compare the reference value with the output of speed loop 1310 in order to keep the speed correction independent of load. A multiplier function has a sensitivity to varying load which is objectionable in the speed loop 1310.

During the load mode of operation the DEMAND represents the specified loading in MW of the generator 16 which is to be held at a predetermined value by the DEH system 1100. However, the actual load will be modified by any deviations in system frequency in accordance with a predetermined regulation value. To provide for frequency participation, a rated speed value in box 1074 is compared in box 1078 with a "two signal" speed value represented by box 1076. The two signal speed system provides high turbine operating reliability to be described infra herein. An output from the compare function 1078 is fed through a function 1080 which is similar to a proportional controller which converts the speed error value in accordance with the regulation value. The speed error from the proportional controller 1080 is combined with the feedforward megawatt reference, i.e., the speed error and the megawatt reference are summed in summation function or box 1072 to generate a combined speed compensated reference signal.

The speed compensated load reference is compared with actual megawatts in a compare box or function 1082. The resultant error is then run through a proportional plus reset controller represented by program box 1084 to generate a feedback megawatt trim.

The feedforward speed compensated reference is trimmed by the megawatt feedback error multiplicatively to correct load mismatch, i.e. they are multiplied together in the feedforward turbine reference path by multiplication function 1086. Multiplication is utilized as a safety feature such that if one signal e.g. MW should fail a large value would not result which could cause an overspeed condition but instead the DEH system 1100 would switch to a manual mode. The resulting speed compensated and megawatt trimmed reference serves as an impulse pressure setpoint in an impulse pressure controller and it is compared with a feedback impulse chamber pressure representation from input 1088. The difference between the feedforward reference and the impulse pressure is developed by a comparator function 1090, and the error output therefrom functions in a feedback impulse pressure control loop. Thus, the impulse pressure error is applied to a proportional plus reset controller function 1092.

During load control the megawatt loop comprising in part blocks 1082 and 1084 may be switched out of service leaving the speed loop 1310 and an impulse pressure loop operative in the DEH system 1100.

Impulse pressure responds very quickly to changes of load and steam flow and therefore provides a signal with minimum lag which smooths the output response of the turbine generator 10 because the lag dynamics and subsequent transient response is minimized. The impulse pressure input may be switched in and out from the compare function 1090. An alternative embodiment embracing feedforward control with impulse pressure feedback trim is applicable.

Between block 1092 and the governor valves GV1-GV8 a valve characterization function for the purpose of linearizing the response of the values is interposed. The valve characterization function described in detail in Appendix III infra herein is utilized in both automatic modes and manual modes of operation of the DEH system 1100. The output of the proportional plus reset controller function 1092 is then ultimately coupled to the governor valves GV1-GV8 through electrohydraulic position control loops implemented by equipment considered elsewhere herein. The proportional plus reset controller output 1092 causes positioning of the governor valves GV1-GV8 in load control to achieve the desired megawatt demand while compensation is made for speed, megawatt and impulse pressure deviations from desired setpoints.

Making reference to FIG. 8, the control program 1020 is shown with interconnections to other programs in the program system employed in the Digital Electro Hydraulic (DEH) system 1100. The periodically executed program 1020 receives data from a logic task 1110 where mode and other decisions which affect the control program are made, a panel task 1112 where operator inputs may be determined to affect the control program, an auxiliary synchronizer program 1114 and an analog scan program 1116 which processes input process data. The analog scan task 1116 receives data from plant instrumentation 1118 external to the computer as considered elsewhere herein, in the form of pressures, temperatures, speeds, etc. and converts such data to proper form for use by other programs. Generally, the auxiliary synchronizer program 1114 measures time for certain important events and it periodically bids or runs the control and other programs. An extremely accurate clock function 1120 operates through a monitor program 1122 to run the auxiliary synchronizer program 1114.

The monitor program or executive package 1122 also provides for controlling certain input/output operations of the computer and, more generally, it schedules the use of the computer to the various programs in accordance with assigned priorities. For more detail on the P2000 computer system and its executive package, reference is made to Appendix 4. In the appendix description, the executive package is described as including analog scan and contact closure input routines, whereas these routines are considered as programs external to the executive package in this part of the disclosure.

The logic task 1110 is fed from outputs of a contact interrupt or sequence of events program 1124 which monitors contact variables in the power plant 1126. The contact parameters include those which represent breaker state, turbine auto stop, tripped/latched state interrogation data states, etc. Bids from the interrupt program 1124 are registered with and queued for execution by the executive program 1111. The control program 1110 also receives data from the panel task 1112 and transmits data to status lamps and output contacts 1128. The panel task 1112 receives data instruction based on supervision signals from the operator panel buttons 1130 and transmits data to panel lamps 1132 and to the control program 1020. The auxiliary synchronizer program 1114 synchronizes through the executive program 1111 the bidding of the control program 1020, the analog scan program 1116, a visual display task 1134 and a flash task 1136. The visual display task transmits data to display windows 1138.

The control program 1020 receives numerical quantities representing process variables from the analog scan program 1116. As already generally considered, the control program 1020 utilizes the values of the various feedback variables including turbine speed, impulse pressure and megawatt output to calculate the position of the throttle valves TV1-TV4 and governor valves GV1-GV8 in the turbine system 10, thereby controlling the megawatt load and the speed of the turbine 10.

To interface the control and logic programs efficiently, the sequence of events program 1124 normally provides for the logic task 1110 contact status updating on demand rather than periodically. The logic task 1110 computes all logical states, according to predetermined conditions and transmits this data to the control program 1020 where this information is utilized in determining the positioning control action for the throttle valves TV1-TV4, and the governor valves GV1-GV8. The logic task 1110 also controls the state of various lamps and relay type contact outputs in a predetermined manner.

E. TASK PRIORITY ASSIGNMENTS

With reference now to FIG. 9, a table of program priority assignments is shown as employed in the executive monitor. A program with the highest priority is run first under executive control if two or more programs are ready to run. The stop/initializer program function has top priority and is run on startup of the computer or after the computer has been shut down momentarily and is being restarted. The control program 1020 is next in order of priority. The operator's panel program 1130, which generates control data, follows the control task 1020 in priority. The analog scan program 1116 also provides information to the control task 1020 and operates at a level of priority below that of the operator's panel 1130. The automatic turbine starting (ATS) periodic program 1140 is next in the priority list. ATS stands for automatic turbine startup and monitoring program, and is shown as a major task program 1140 of FIG. 8 for the operation of the DEH system 1100. The ATS-periodic program 1140 monitors the various temperatures, pressures, breaker states, rotational velocity, etc. during start-up and during load operation of the turbine system.

The logic task 1110, which generates control and operating mode data, follows in order of operating priority. The visual display task program 1134 follows the logic task program 1110 and makes use of outputs from the latter. A data link program for transmitting data from the DEH system to an external computer follows. An ATS-analog conversion task program 1142 for converting the parameters provided by the ATS-periodic program 1142 to usable computer data follows in order of priority. The flash task program 1136 is next, and it is followed by a programmer's console program which is used for maintenance testing and initial loading of data tapes. The next program is an ATS-message writer 1144 which provides for printout of information from the ATS analog conversion program 1142 on a suitable typewriter 1146. The next program in the priority list is an analog/digital trend which monitors parameters in the turbine system 10 and prints or plots them out for operator perusal. The remaining two programs are for debugging and special applications.

In the preferred embodiment, the stop/initialize program is given the highest priority in the table of FIG. 9 because certain initializing functions must be completed before the DEH system 1100 can run. The auxiliary synchronizer program 1114 provides timing for all programs other than the stop/initialize program while the DEH system 1100 is running. Therefore, the auxiliary snychronizer task program 1400 has the second order of priority of the programs listed. The control program 1020 follows at the third descending order of priority since the governor valves GV1 through GV8 and the throttle valves TV1 through TV4 must be controlled at all times while the DEH system 1100 is in operation.

The operator's panel progam 1130 is given the next order of priority in order to enable an operator to exercise direct and instantaneous control of the DEH system 1100. The analog scan program 1116 provides input data for the control program 1020 and, therefore, is subordinate only to the initialize, synchronizer control and operator functions.

In the preferred embodiment the ATS-periodic program 1140 is next in order of priority. During automatic turbine startup, the scanning of inputs by the ATS-periodic program 1140 is almost on the same order of priority as the inputs to the DEH system 1100. However, the ATS program 1140 in alternative embodiments, could be reduced in its priority, without any considerable adverse effect, because of the relatively limited duty cycle problems in the ATS system.

The logic task 1110 which control the operations of some of the functions of the control task program 1020 is next in order of priority. The visual display task 1134 follows in order of priority in order to provide an operator with a visual indication of the operation of the DEH program 1100. The visual display program 1134 is placed in the r