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Complex and Multi-Level Hierarchical Control System for City Gas Production and Supply - Total Gas Control System (TGCS)
COMPLEX AND MULTI-LEVEL HIERARCHICAL CONTROL SYSTEM FOR CITY GAS PRODUCTION AND SUPPLY - TOTAL GAS CONTROL SYSTEM (TGCS)
Tatuo Yamazaki Plant Construction Devision Tokyo Gas Corp., Yaesu 1-2-16, Chuo, Tokyo, Japan
Sachie Moriya Distribution Control Center Tokyo Gas Corp., Yaesu 1-2-16, Chuo, Tokyo, Japan
Abstract TGCS is a centralized controlling system to totally systemize various transactions ·for the control and operation of gas production and supply using the latest computers. It enables operation of plants and holder stations at an optimum and safe condition at all times. This paper introduces a computer hierarchy consisting of large computers (IBM 370/155), medium computers (IBM 1800), mini computers (IBM S/7), telemeter/telecontrol equipment, groups of plant computers including the DDC computer, and functions for planning, coordination and control of production and supply through man-machine communication with the aid of graphic displays, character displays, and announcement devices. 1.
Introduction
In the Tokyo Gas Company, city gas is manufactured from various raw materials at 5 seaside plants, transferred to one point and then distributed through the pipeline network to about 5 million customers located in the metropolitan region. In the production and supply system for city gas, gas demand varies considerably by season and time. Therefore to operate the system effectively and safely, it is most essential to control output, receiving and delivery quantities of holders and the pressures at principal points in the supply network, in response to the projected demand based upon data such as consuming status in the whole supply area, gas pressures, storage in holders, production quantities of plants and the working condition of plants. As a matter of course, application of a company wide hierarchic centralized controlling system is an indispensable measure to satisfy the above requirements. 2.
Outline of the Prod.-Supply Control System (TGCS)
Configuration of TGCS software and hardware are shown in Fig. 1 and Fig. 2. The production and supply control system, which has a multi-level structure, has the following features:
76
(1)
Possesses a computing capacity to process complex calculations such as large-scale LP and analysis of network problems in a very short time.
(2)
Performs man-machine communication at high speed for information retrieval, trial and error method of computing, diagrammatic understanding of the network condition (especially DOCS which corresponds to the coordinating level), and possesses a functional ability to perform discrimination of high density by communication with the computer. The gas production control system (GPCS) and automatic supply network control system (TACS) are also man-machine system which are easy to operate, providing announcement devices, CRT and others.
(3)
Control commands computed by the DOCS are transmitted to the GPCS and TACS of a lower level system through circuits as they are, the DDC in plants controls the starting, stopping and operating rate of plants automatically. Fourteen holder stations and about twenty pressure stations in the supply network control gas storage and pressure automatically. In short, the system commands from the upper level system are communicated to the lower level system directly by data transmission.
(4)
In the processing procedures, the function of the "Plan - Do - See" cycle is maintained.
(5)
Reliability of the whole system has been improved by appropriate dividing up of the hardware hierarchy which facilitates back-up since each divided hierarchy provides an effective and pertinent back-up function when required.
(6)
Necessary data for information retrieval, computing and tabulating are collected from the production and supply network and are stored in large capacity file in a form able to be retrieved even after ten years.
2.1.
TGCS developmental history
As stated above, to properly process the data received from the centralized production-supply networks, the online realtime system using TOSBAC3400 as the main computer was established at the end of 1965. It was called GCS (Gas Computing Supervisor) and was facilitated production-supply monitoring, demand forecast, optimal control commands for individual plants, operation commands of the supply networks, automatic listup, various offline computations, etc. Later, the production-supply networks were expanded and became more complicated due to the introduction of LNG (Liquefied Natural Gas) and the construction of the Sodegaura Plant and the Chiba High Pressure Gas Trunk Line, etc. Because of out limited amount of raw materials, it is a very difficult matter to maintain the hourly optimum production and supply operation while securing the yearly long range optimum program under the gradually increasing severeness of the seasonal movements and the rapidly shifting daily demand. Thence it became necessary to level up our control system from raw materials to supply operation. TGCS was developed to satisfy the real time operation of the above dynamic adaptation requirements, and at present it satisfies most of our expectations. This system makes possible the following functions on the bases of the systematically compiled production-supply network real time data and of the updating and efficient information retrieval system.
*
Long and short range programs for optimal receiving and utilization of raw materials.
*
Online and real time optimal control of the production-supply networks.
*
Supply network station telecontrol.
*
Online realtime commands to the production networks.
*
High grade monitoring of the operation of the production-supply network. In particular, the properly constructed hierarchies and the man-machine communication system facilitates the easy and reliable operation of the large scale system.
2.2.
formed into networks. There are holder stations in the networks that have the function of storage and pressure adjustment of city gas. There are also pressure control stations where the city gas is branched and distributed from the high pressure and medium pressure A pipes to the lower pressure pipes. The demand for city gas, of course, has seasonal fluctuations, as well as those during the daytime hours. 2.3.
TGCS software configuration
Table 1 shows the configuration of the TGCS software. It is roughly divided into four sections: planning, coordination, control and service. In the planning-use software, MOPS, WOPS and PILOT are- used for operation as well as for planning at the time of the yearly program planning. In Table 1 we shall show that there are functional and partial hierarchy structures existent in the TGCS, which is eventually related to the processing frequency. 2.4.
TGCS hardware configuration
Fig. 4 shows the TGCS hardware configuration. The hardware configuration of the TGCS has a multi level hierarchy structure corresponding to that of the software to carry out the large scale control operation of directly connecting the lower level distribution network stations. 2.5. (1)
TGCS operating procedures Planning procedures
The import, transportation and storage of LNG is very important to both the raw material utilization planning and the cost saving features, so we calculate the yearly production policy for the LNG with YOPS, PILOT, and TOCS. The detailed optimal plant utilization program is computed using MOPS. (2)
Performance program procedures
The performance program can be made in reference to the yearly planned quantity; however, in practice, this involves adjustment to the production-supply network status, to on-the-spot estimates and the modification to the difference between the yearly program and the performance program. A computational algorithm is designed to satisfy the realistic response requirement.
Outline of the production and supply networks
As shown in Fig.3, there are at present five plants around the periphery of Tokyo: Sodegaura, Toyosu, Omori, Tsurumi (including Suehiro), Negishi. The gas produced at these plants is fed into the supply networks and sent to the consumers. There are four kinds of supply networks classified according to the gas pressure: high pressure, medium A pressure, medium B pressure, and low pressure. General household consumers are supplied from the low pressure networks. The different pressure tubes are connected through a pressure control facility and these pressure tubes are
77
(3)
Daily operation procedures
The operators in the command center issue hourly moving production-supply commands. The DOCS can be a main force for the operation, and the operator issues the optimal production-supply commands. DOCS can be driven by the operators using graphic displays and talking with the computer interactively on a scheduled basis five times daily, and other times if necessary. In DOCS, we can not only select and analyze the necessary information retrieved from the data bank which compiles information on the production and
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supply over the last ten years and, with reference to the weather data, determine the daily supply prediction, but also we can retrieve past similar data such as what day of the week and the hourly weather data to determine the hourly supply of city gas. While securing the production required in case of an emergency, after computing the necessary production for all plants efficiently utilizing the holder, optimal utilization of the individual plants can be computed under the proper constraints of supply network administration, thus determining the plant production. In this way, after confirming the attainable production-supply status, we send production commands to the plants and simultaneously send the designated control values at the supply points to TACS. Upon receiving these values, TACS automatically controls the supply networks. The following information exchange programs can be utilized interactively by the operators with the TGCS through graphic displays: multiple regression analysis, demand pattern forecasting, similar date information retrieval, emergency simulation, data sets for linear programming, production level simulation, linear programming analysis, plant production pattern decisions, holder storage pattern decisions, holder storage patterns, pressure patterns, medium pressure (A, B) distribution network and the Chiba-Negishi line networks computations, etc. Approximately 100 graphic display images may be necessary for anyone of the above operations. Fig. 5 shows .the TGCS graphic display operation and Fig. 6 shows the various images displayed. 2.6.
2.8. 2.8.1
Outline
Th~ Sodegaura Plant is used as the example. This is the main plant in the Tokyo Gas Company mostly receiving LNG as raw material. It also supplies all of the fuel required by the neighbouring Sodegaura Power Plant of the Tokyo Electric Power Company. During the system design of this plant, we planned a total control system, considering on-line real time connection with the TACS. It became apparent that a control system of this level affects management organization, plant operational methods and form, and there appeared further problems to be studied for future development of super advanced systemization. Change of plant operational condition is given audibly through a computer edited automatic announcing system, and the visual displays, as shown in Fig. 9, are used only when detailed information is needed by the operator or an emergency condition exists. (In normal conditions, the plants are automatically started and stopped.) In case of an emergency, most sections will be de.alt with automatically, and the operator has only to issue repair and spare equipment commands. To perform these functions, we have a hierarchical system at the plant level consisting of a SCC (Supervisory Control Computer) system which performs planning and control functions, a DDC which directly controls plants and a monitoring computer. This system has been designed assuming the following items to be included in the scope of future control:
Telemeter system
The first step in the centralization must be the centralization of data. In our company, a telemeter system was introduced at the Head Office in Nihonbashi Tokyo in 1956, making possible the hourly observation of the gas supply trends at strategic points of the production-supply networks. The variables are gas pressure, volume flow, holder storage, operating valve opening, and several digital signals such as valve pOSitions, seismograph, etc. In this system, all of these variables are data processed by computer and some of them are displayed and recorded for use in supervison by the operating personnel. 2.7.
Operation Control of Plants
LNG tanks Primary pumps •...•.••••••• Secondary pumps ••.•.••.•. LPG pumps .•.•.......•...• Boil off gas compressors .• Vapourizers ••.........•.. Calorific value regulating systems •......•......• Boiler, water and utility facilities
Telecontrol system
2.8.2
In 1959, we started installing telecontrol apparatus following the installation of the telemeter apparatus. With the telecontrol apparatus we made possible direct operation of the remote pressure control stations and the holder stat.ions by the data communication network as shown in Fig. 7, thus eliminating the need for the mannual operations at these stations. This made possible the complete control of the remote operations at the key points of the supply networks which made our comprehensive control possible. Considerable care was taken, as in the case of the telemeter system, in sequential matching of the logic of the command entry to avoid noises and the
30 60 10 15 15 25
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The SCC is directly connected on a computer-tocomputer basis with the TACS and with the Tokyo Electric Power Company Sodegaura Power Plant Control Computer. Upon receiving information from these computers, it carries out an optimal operation automatic scheduling with consideration of load variation forecasts, safety margin of operating capacity, various LNG stocks, machine operating time, distribution route, equipment running costs, etc., and delivers the operation commands to the DDC. In addition, the SCC carries out the following operations: superv~s~on of DDC operations, supervision of detecting and diagnosing various
79
times higher than possible by human control and a stability much greater and far beyond comparison.
instrument irregularities, information communication to the operators, to the Tokyo Electric Power Company and to the TACS, computation of LNG transactions based on the output gas, utility, electricity, storage quantity and received amounts, and data processing such as miscellaneous statisticals, daily loggings, and journal computations. Upon receiving the above commands from the SCC, the DDC automatically performs all the necessary operations for computing required units of equipment, optimal load distribution, for each unit, starting and stopping the machine, and PID control. In addition, a monitor system is established to facilitate the monitoring of the plant and the electric apparatuses. 2.8.3
(3)
Since the DDC was applied, the rate of trouble occurence decreased to a fractional value of around one tenth of the former rate. This result confirms a remarkable improvement in over all reliability of the total control ~ vstem. (4)
Hardware Configuration
Effectiveness of the DDC
3.
The role of peripheral control equipment is particularly essential when considering the total system. The TGCS adopted the DDC at control level, and demonstrates the following merits. (1) a)
b)
(2)
Composite evaluation
As can be seen from the above facts, the DDC system reveals level functions different from the current analogue system and mo s t of there achieved success in our company's application. The DDC is not a subject to be discussed by compari s on with the analogue system. It should be evaluated by its performance in complete automated business trans actions at the control level, receiving commands from a planning level and coordinating level in the complex hierarchical control system. The DDC introduced here as an example is displaying these functions satisfactorily and present daily operation is carried out by only three persons per shift.
Fig. 8 shows the hardware configuration. In the DDC system, the system reliability must have the highest priority, in this way the use of auxiliary storage can be avoided all the programs required were written using an assembler language for efficient utilization of the main memory units. Further, a dual system was introduced for greater reliability . 2.8.4
Maintenance factors
Conclusions
Development of the TGCS was schieved by coordination of more than 30 staff members, inaugurated in September 1973, and has since been performing satisfactory for one year. It i s considered that the TGCS of the multi-level hierarchy structure suggests a way for similar systems to be established in the future. Details about various control algorithm, optimizing method and planning processes were not possible to be approached in this paper due to a limited space, to our regret.
Control Control function of a higher order The current analogue control system is composed of integrated feed-back routes of the tree type, but to control the somewhat complicated processes with good responses dynamically , control of the parallel feed-forward type is required and for this purpose the control computing algorithm is introduced which is of a different level than the PID. To enable compensating computation for security, minute control and extremely accurate operation, a method called "advanced control" i s incorporated to perform control operations which are beyond the capacity of the current analogue system.
-\
Total control function Toward such a complicated process, current analogue instrumentation could not perform effective control of the whole system in answer to miscellaneous change demands with one touch despite the implementation of unique methods, yet owing to the flexibility of digital computer techniques cooperative operation between plants became feasible.
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Special operations such as shut down processing, re-starting, etc., are very difficult operation subjects for operators. But by realization of the DDC, process operations are being performed at a re-starting speed several
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Tatuo Yamazaki Plant Construction Devision Tokyo Gas Corp., Yaesu 1-2-16, Chuo, Tokyo, Japan
Sachie Moriya Distribution Control Center Tokyo Gas Corp., Yaesu 1-2-16, Chuo, Tokyo, Japan
Abstract TGCS is a centralized controlling system to totally systemize various transactions ·for the control and operation of gas production and supply using the latest computers. It enables operation of plants and holder stations at an optimum and safe condition at all times. This paper introduces a computer hierarchy consisting of large computers (IBM 370/155), medium computers (IBM 1800), mini computers (IBM S/7), telemeter/telecontrol equipment, groups of plant computers including the DDC computer, and functions for planning, coordination and control of production and supply through man-machine communication with the aid of graphic displays, character displays, and announcement devices. 1.
Introduction
In the Tokyo Gas Company, city gas is manufactured from various raw materials at 5 seaside plants, transferred to one point and then distributed through the pipeline network to about 5 million customers located in the metropolitan region. In the production and supply system for city gas, gas demand varies considerably by season and time. Therefore to operate the system effectively and safely, it is most essential to control output, receiving and delivery quantities of holders and the pressures at principal points in the supply network, in response to the projected demand based upon data such as consuming status in the whole supply area, gas pressures, storage in holders, production quantities of plants and the working condition of plants. As a matter of course, application of a company wide hierarchic centralized controlling system is an indispensable measure to satisfy the above requirements. 2.
Outline of the Prod.-Supply Control System (TGCS)
Configuration of TGCS software and hardware are shown in Fig. 1 and Fig. 2. The production and supply control system, which has a multi-level structure, has the following features:
76
(1)
Possesses a computing capacity to process complex calculations such as large-scale LP and analysis of network problems in a very short time.
(2)
Performs man-machine communication at high speed for information retrieval, trial and error method of computing, diagrammatic understanding of the network condition (especially DOCS which corresponds to the coordinating level), and possesses a functional ability to perform discrimination of high density by communication with the computer. The gas production control system (GPCS) and automatic supply network control system (TACS) are also man-machine system which are easy to operate, providing announcement devices, CRT and others.
(3)
Control commands computed by the DOCS are transmitted to the GPCS and TACS of a lower level system through circuits as they are, the DDC in plants controls the starting, stopping and operating rate of plants automatically. Fourteen holder stations and about twenty pressure stations in the supply network control gas storage and pressure automatically. In short, the system commands from the upper level system are communicated to the lower level system directly by data transmission.
(4)
In the processing procedures, the function of the "Plan - Do - See" cycle is maintained.
(5)
Reliability of the whole system has been improved by appropriate dividing up of the hardware hierarchy which facilitates back-up since each divided hierarchy provides an effective and pertinent back-up function when required.
(6)
Necessary data for information retrieval, computing and tabulating are collected from the production and supply network and are stored in large capacity file in a form able to be retrieved even after ten years.
2.1.
TGCS developmental history
As stated above, to properly process the data received from the centralized production-supply networks, the online realtime system using TOSBAC3400 as the main computer was established at the end of 1965. It was called GCS (Gas Computing Supervisor) and was facilitated production-supply monitoring, demand forecast, optimal control commands for individual plants, operation commands of the supply networks, automatic listup, various offline computations, etc. Later, the production-supply networks were expanded and became more complicated due to the introduction of LNG (Liquefied Natural Gas) and the construction of the Sodegaura Plant and the Chiba High Pressure Gas Trunk Line, etc. Because of out limited amount of raw materials, it is a very difficult matter to maintain the hourly optimum production and supply operation while securing the yearly long range optimum program under the gradually increasing severeness of the seasonal movements and the rapidly shifting daily demand. Thence it became necessary to level up our control system from raw materials to supply operation. TGCS was developed to satisfy the real time operation of the above dynamic adaptation requirements, and at present it satisfies most of our expectations. This system makes possible the following functions on the bases of the systematically compiled production-supply network real time data and of the updating and efficient information retrieval system.
*
Long and short range programs for optimal receiving and utilization of raw materials.
*
Online and real time optimal control of the production-supply networks.
*
Supply network station telecontrol.
*
Online realtime commands to the production networks.
*
High grade monitoring of the operation of the production-supply network. In particular, the properly constructed hierarchies and the man-machine communication system facilitates the easy and reliable operation of the large scale system.
2.2.
formed into networks. There are holder stations in the networks that have the function of storage and pressure adjustment of city gas. There are also pressure control stations where the city gas is branched and distributed from the high pressure and medium pressure A pipes to the lower pressure pipes. The demand for city gas, of course, has seasonal fluctuations, as well as those during the daytime hours. 2.3.
TGCS software configuration
Table 1 shows the configuration of the TGCS software. It is roughly divided into four sections: planning, coordination, control and service. In the planning-use software, MOPS, WOPS and PILOT are- used for operation as well as for planning at the time of the yearly program planning. In Table 1 we shall show that there are functional and partial hierarchy structures existent in the TGCS, which is eventually related to the processing frequency. 2.4.
TGCS hardware configuration
Fig. 4 shows the TGCS hardware configuration. The hardware configuration of the TGCS has a multi level hierarchy structure corresponding to that of the software to carry out the large scale control operation of directly connecting the lower level distribution network stations. 2.5. (1)
TGCS operating procedures Planning procedures
The import, transportation and storage of LNG is very important to both the raw material utilization planning and the cost saving features, so we calculate the yearly production policy for the LNG with YOPS, PILOT, and TOCS. The detailed optimal plant utilization program is computed using MOPS. (2)
Performance program procedures
The performance program can be made in reference to the yearly planned quantity; however, in practice, this involves adjustment to the production-supply network status, to on-the-spot estimates and the modification to the difference between the yearly program and the performance program. A computational algorithm is designed to satisfy the realistic response requirement.
Outline of the production and supply networks
As shown in Fig.3, there are at present five plants around the periphery of Tokyo: Sodegaura, Toyosu, Omori, Tsurumi (including Suehiro), Negishi. The gas produced at these plants is fed into the supply networks and sent to the consumers. There are four kinds of supply networks classified according to the gas pressure: high pressure, medium A pressure, medium B pressure, and low pressure. General household consumers are supplied from the low pressure networks. The different pressure tubes are connected through a pressure control facility and these pressure tubes are
77
(3)
Daily operation procedures
The operators in the command center issue hourly moving production-supply commands. The DOCS can be a main force for the operation, and the operator issues the optimal production-supply commands. DOCS can be driven by the operators using graphic displays and talking with the computer interactively on a scheduled basis five times daily, and other times if necessary. In DOCS, we can not only select and analyze the necessary information retrieved from the data bank which compiles information on the production and
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supply over the last ten years and, with reference to the weather data, determine the daily supply prediction, but also we can retrieve past similar data such as what day of the week and the hourly weather data to determine the hourly supply of city gas. While securing the production required in case of an emergency, after computing the necessary production for all plants efficiently utilizing the holder, optimal utilization of the individual plants can be computed under the proper constraints of supply network administration, thus determining the plant production. In this way, after confirming the attainable production-supply status, we send production commands to the plants and simultaneously send the designated control values at the supply points to TACS. Upon receiving these values, TACS automatically controls the supply networks. The following information exchange programs can be utilized interactively by the operators with the TGCS through graphic displays: multiple regression analysis, demand pattern forecasting, similar date information retrieval, emergency simulation, data sets for linear programming, production level simulation, linear programming analysis, plant production pattern decisions, holder storage pattern decisions, holder storage patterns, pressure patterns, medium pressure (A, B) distribution network and the Chiba-Negishi line networks computations, etc. Approximately 100 graphic display images may be necessary for anyone of the above operations. Fig. 5 shows .the TGCS graphic display operation and Fig. 6 shows the various images displayed. 2.6.
2.8. 2.8.1
Outline
Th~ Sodegaura Plant is used as the example. This is the main plant in the Tokyo Gas Company mostly receiving LNG as raw material. It also supplies all of the fuel required by the neighbouring Sodegaura Power Plant of the Tokyo Electric Power Company. During the system design of this plant, we planned a total control system, considering on-line real time connection with the TACS. It became apparent that a control system of this level affects management organization, plant operational methods and form, and there appeared further problems to be studied for future development of super advanced systemization. Change of plant operational condition is given audibly through a computer edited automatic announcing system, and the visual displays, as shown in Fig. 9, are used only when detailed information is needed by the operator or an emergency condition exists. (In normal conditions, the plants are automatically started and stopped.) In case of an emergency, most sections will be de.alt with automatically, and the operator has only to issue repair and spare equipment commands. To perform these functions, we have a hierarchical system at the plant level consisting of a SCC (Supervisory Control Computer) system which performs planning and control functions, a DDC which directly controls plants and a monitoring computer. This system has been designed assuming the following items to be included in the scope of future control:
Telemeter system
The first step in the centralization must be the centralization of data. In our company, a telemeter system was introduced at the Head Office in Nihonbashi Tokyo in 1956, making possible the hourly observation of the gas supply trends at strategic points of the production-supply networks. The variables are gas pressure, volume flow, holder storage, operating valve opening, and several digital signals such as valve pOSitions, seismograph, etc. In this system, all of these variables are data processed by computer and some of them are displayed and recorded for use in supervison by the operating personnel. 2.7.
Operation Control of Plants
LNG tanks Primary pumps •...•.••••••• Secondary pumps ••.•.••.•. LPG pumps .•.•.......•...• Boil off gas compressors .• Vapourizers ••.........•.. Calorific value regulating systems •......•......• Boiler, water and utility facilities
Telecontrol system
2.8.2
In 1959, we started installing telecontrol apparatus following the installation of the telemeter apparatus. With the telecontrol apparatus we made possible direct operation of the remote pressure control stations and the holder stat.ions by the data communication network as shown in Fig. 7, thus eliminating the need for the mannual operations at these stations. This made possible the complete control of the remote operations at the key points of the supply networks which made our comprehensive control possible. Considerable care was taken, as in the case of the telemeter system, in sequential matching of the logic of the command entry to avoid noises and the
30 60 10 15 15 25
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Software Design
The SCC is directly connected on a computer-tocomputer basis with the TACS and with the Tokyo Electric Power Company Sodegaura Power Plant Control Computer. Upon receiving information from these computers, it carries out an optimal operation automatic scheduling with consideration of load variation forecasts, safety margin of operating capacity, various LNG stocks, machine operating time, distribution route, equipment running costs, etc., and delivers the operation commands to the DDC. In addition, the SCC carries out the following operations: superv~s~on of DDC operations, supervision of detecting and diagnosing various
79
times higher than possible by human control and a stability much greater and far beyond comparison.
instrument irregularities, information communication to the operators, to the Tokyo Electric Power Company and to the TACS, computation of LNG transactions based on the output gas, utility, electricity, storage quantity and received amounts, and data processing such as miscellaneous statisticals, daily loggings, and journal computations. Upon receiving the above commands from the SCC, the DDC automatically performs all the necessary operations for computing required units of equipment, optimal load distribution, for each unit, starting and stopping the machine, and PID control. In addition, a monitor system is established to facilitate the monitoring of the plant and the electric apparatuses. 2.8.3
(3)
Since the DDC was applied, the rate of trouble occurence decreased to a fractional value of around one tenth of the former rate. This result confirms a remarkable improvement in over all reliability of the total control ~ vstem. (4)
Hardware Configuration
Effectiveness of the DDC
3.
The role of peripheral control equipment is particularly essential when considering the total system. The TGCS adopted the DDC at control level, and demonstrates the following merits. (1) a)
b)
(2)
Composite evaluation
As can be seen from the above facts, the DDC system reveals level functions different from the current analogue system and mo s t of there achieved success in our company's application. The DDC is not a subject to be discussed by compari s on with the analogue system. It should be evaluated by its performance in complete automated business trans actions at the control level, receiving commands from a planning level and coordinating level in the complex hierarchical control system. The DDC introduced here as an example is displaying these functions satisfactorily and present daily operation is carried out by only three persons per shift.
Fig. 8 shows the hardware configuration. In the DDC system, the system reliability must have the highest priority, in this way the use of auxiliary storage can be avoided all the programs required were written using an assembler language for efficient utilization of the main memory units. Further, a dual system was introduced for greater reliability . 2.8.4
Maintenance factors
Conclusions
Development of the TGCS was schieved by coordination of more than 30 staff members, inaugurated in September 1973, and has since been performing satisfactory for one year. It i s considered that the TGCS of the multi-level hierarchy structure suggests a way for similar systems to be established in the future. Details about various control algorithm, optimizing method and planning processes were not possible to be approached in this paper due to a limited space, to our regret.
Control Control function of a higher order The current analogue control system is composed of integrated feed-back routes of the tree type, but to control the somewhat complicated processes with good responses dynamically , control of the parallel feed-forward type is required and for this purpose the control computing algorithm is introduced which is of a different level than the PID. To enable compensating computation for security, minute control and extremely accurate operation, a method called "advanced control" i s incorporated to perform control operations which are beyond the capacity of the current analogue system.
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Total control function Toward such a complicated process, current analogue instrumentation could not perform effective control of the whole system in answer to miscellaneous change demands with one touch despite the implementation of unique methods, yet owing to the flexibility of digital computer techniques cooperative operation between plants became feasible.
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Special operations such as shut down processing, re-starting, etc., are very difficult operation subjects for operators. But by realization of the DDC, process operations are being performed at a re-starting speed several
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