Transactions on Power Systems,Vol.7,No.1,February 1992 320 THE IMPLEMENTATION AND EVOLUTION OF A SCADA SYSTEM FOR A LARGE DISTRIBUTION NETWORK Eng-Kiat Chan Horst Ebenhoh Public Utilities Board Siemens AG Singapore Germany Abstract Automation of power distribution systems has Supervisory control was first introduced into Singapore in 1966 increasingly been adopted by power utilities worldwide in recent where a telephony relay-based system was installed to provide years.As part of its effort to provide a more reliable supply to its remote monitoring and control facilities for the 66 kV network and customers and to enhance operational efficiency.The Pubiic all major 22 kV substations. Utilities Board of Singapore has recently completed an important Then in 1979,with the introduction of the 230 kV network.a step in this direction by procuring and putting into service a computer-based SCADA system equipped with Automatic SCADA system for its 22 kV distribution network. Generation Control function was commissioned to monitor, supervise and control the generation and transmission systems The SCADA system was commissioned and became operational as well as to cater for their increasing sophistication in system in mid 1988.However.due to the continuous network expansion operation and coordination.Meanwhile.the relay-based system and increasingly higher expectations of the customers for a continues to be utilized for the major 22 kV substations to provide reliable supply.the system has been constantly undergoing remote monitoring and control facilities. extensions and upgradings to incorporate more remote terminal units (RTUs)as well as improved functional enhancements With the rapid development and expansion of the power system in Singapore in recent years.these systems were found to be This paper presents the approach adopted in implementing the reaching the limits of their full capacity and were proving SCADA system and the benefits accrued through incorporating inadequate to meet the required operational requirements.This such a system.It also describes the subsequent development of situation then led to the replacement and upgrading of the integrating a real-time expert system to the SCADA system in complete SCADA system for the generation and transmission preparation for the next steps in the progressive automation of the network with a new Energy Management System and the 22 kV distribution network. procurement of a new computer-based SCADA system for the 22 kV distribution network. KEYWORDS NETWORK SIZE Large distribution network.SCADA system.on-line database management.distribution automation,expert system. The 22 kV distribution network in Singapore presently consists of more than 1.330 substations.They are geographically grouped INTRODUCTION into four areas:East.West,Central and City.Each area has a total of 250 to 450 substations and the number of stations are The Public Utilities Board(PUB)is responsible for the generation growing at an annual rate of about 8 per cent.Table 1 below gives and supply of electricity to almost 850.000 customer accounts in an overview and comparison of the system size at the time of Singapore with a peak demand of about 2.450 MW.Electricity implementation,the present time.and the ultimate system generated in power stations is fed into PUB's transmission capacity. network at 230 kV and 66 kV levels.From the 66 kV network.it is then stepped down for distribution at 22 kV level and further Table 1:System sizes:Initial:Present and Ultimate stepped down to 6.6 kV or directly to the low voltage levels before being supplied to its customers. Initial Present Ultimate 91 SM 430-9 PWRS A paper recommended and approved Substations/RTU's 1.000 1.330 3.000 by the IEEE Power System Engineering Committee of the IEEE Power Engineering Society for presentation Status/Alarm Pts 30.000 41.000 120.000 at the IEEE/PES 1991 Summer Meeting,San Diego, California July 28 Au8ust1,1991, Commands 6.300 8.500 23.000 Manuscript submitted January 24,1991;made available for printing June 5,1991. Measurements 7.000 9.200 28.000 D885-8950/9203.001992EEE
320 Transactions on Power Systems, Vol. 7, No. 1, February 1992 THE IMPLEMENTATION AND EVOLUTION OF A SCADA SYSTEM FOR A LARGE DISTRIBUTION NETWORK Eng-Kiat Chan Public Utilities Board Singapore Abstract - Automation of power distribution systems has increasingly been adopted by power utilities worldwide in recent years. As part of its effort to provide a more reliable supply to its customers and to enhance operational efficiency. The Public Utilities Board of Singapore has recently completed an important step in this direction by procuring and putting into service a SCADA system for its 22 kV distribution network. The SCADA system was commissioned and became operational in mid 1988. However. due to the continuous network expansion and increasingly higher expectations of the customers for a reliable supply, the system has been constantly undergoing extensions and upgradings to incorporate more remote terminal units (RTUs) as well as improved functional enhancements. This paper presents the approach adopted in implementing the SCADA system and the benefits accrued through incorporating such a system It also describes the subsequent development of integrating a real-t:me expert system to the SCADA system in preparation for the next steps in the progressive automation of the 22 kV distribution network. KEYWORDS Large distribution network, SCADA system, on-line database management, distribution automation, expert system. INTRODUCTION The Public Utilities Board (PUB) is responsible for the generation and supply of electricity to almost 850.000 customer accounts in Singapore with a peak demand of about 2.450 MW. Electricity generated in power stations is fed into PUB'S transmission network at 230 kV and 66 kV levels. From the 66 kV network, it is then stepped down for distribution at 22 kV level and further stepped down to 6.6 kV or directly to the low voltage levels before being supplied to its customers. 91 SM 430-9 PWRS A paper recommended and approved by the IEEE Power System Engineering Committee of the IEEE Power Engineering Society for presentation at the IEEE/PES 1991 Summer Meeting, San Diego, California July 28 - August 1, 1991. Manuscript submitted January 24, 1991; made available for printing June 5, 1991. Horst Ebenhoh Siemens AG Germany Supervisory control was first introduced into Singapore in 1966, where a telephony relay-based system was installed to provide remote monitoring and control facilities for the 66 kV network and all major 22 kV substations. Then in 1979, with the introduction of the 230 kV network. a computer-based SCADA system equipped with Automatic Generation Control function was commissioned to monitor. supervise and control the generation and transmission systems as well as to cater for their increasing sophistication in system operation and coordination. Meanwhile, the relay-based system continues to be utilized for the major 22 kV substations to provide remote monitoring and control facilities. With the rapid development and expansion of the power system in Singapore in recent years, these systems were found to be reaching the limits of their full capacity and were proving inadequate to meet the required operational requirements. This situation then led to the replacement and upgrading of the complete SCADA system for the generation and transmission network with a new Energy Management System and the procurement of a new computer-based SCADA system for the 22 kV distribution network. NETWORK SIZE The 22 kV distribution network in Singapore presently consists of more than 1.330 substations. They are geographically grouped into four areas: East, West, Central and City, Each area has a total of 250 to 450 substations and the number of stations are growing at an annual rate of about 8 per cent. Table 1 below gives an overview and comparison of the system size at the time of implementation, the present time, and the ultimate system capacity. Table 1: System sizes: Initial; Present and Ultimate SubstationsiRTU's Status/Alarm Pts Commands Measurements initial Present 1.000 1.330 30.000 41.000 t 6.300 8.500 7.000 9.200 3.000 120.000 23.000 28.000 0885-8950/92$03.0001992 IEEE
321 To effectively implement a full SCADA system for such a large In any case.such a system is always formidable to realize due to and ever-changing distribution network.the chosen system must the scale of the network and the fact that the implementation be modular and versatile in Software and Hardware design such etfort is constantly grappling with the problems of network growth that it is able to be freely adapted to all network changes and and topology changes. expansions,without causing disruption to its operation.or resulting in any impairment in its effectiveness. 22kV Substations Area 一的0 444 阿 AEConoIC CHC RTU IOUP Fig.1: Initial System Configuration SYSTEM CONFIGURATION for the central and west area networks.The other system.located at the City Operation and Maintenance Depot,performs the data The initial setup called for a system with 1.000 RTUs with a acquisition and control functions for the east and city area capacity to ultimately extend up to 2.400 RTUs.Subsequently. networks. this capacity has been further extended to 3.000 RTUs with the intention to provide remote monitoring and control facilities for all The SCADA system hardware mirrors the network level concept the major 6.6 kV substations and to extend the network to achieve a high degree of system availability and modularity management functions to the 6.6 kV network and cover some (see Figure 1 for the initial system configuration).These levels 4,000 substations can be classified as follows: In order to serve such a high number of RTUs by a control centre Master Station: and to avoid any communication bottleneck at the master station. Main computer systems a "distributed system"approach was adopted.Here.two sets of Front-end (Telecontrol Interface)systems dual-computer systems were installed at two geographically Man-Machine Interface (Operator Consoles separated locations.One system.located at the Distribution Workstations) Control Centre.serves the overall network control functions as well as performs the data acquisition and remote control functions
To effectively implement a full SCADA system for such a large and ever-changing distribution network the chosen system must be modular and versatile in Software and Hardware design such that it is able to be freely adapted to all network changes and expansions. without causing disruption to its operation. or resulting in any impairment in its effectiveness 22kV Substations Area 321 In any case, such a system is always formidable to realize due to the scale of the network and the fact that the implementation effort is constantly grappling with the problems of network growth and topology changes. SM RTU TCI Telecontrol mterface hA hnodem Submaster 1250 units ,nciualng process interface Remote lerminal units 1750 Unllsl operator c Puo BuiIdNng Fig. 1: Initial System SYSTEM CONFIGURATION ' The initial setup called for a system with 1,000 RTUs with a capacity to ultimatoly extend up to 2,400 RTUs. Subsequently, this capacity has been further extended to 3,000 RTUs with the intention to provide remote monitoring and control facilities for all the major 6.6 kV substations and to extend the network management functions to the 6.6 kV network and cover some 4,000 substations. In order to serve such a high number of RTUs by a control centre and to avoid any communication bottleneck at the master station, a "distributed system" approach was adopted. Here. two sets of dual-computer systems were installed at two geographically separated locations. One system, located at the Distribution Control Centre, serves the overall network control functions as well as performs the data acquisition and remote control functions Configuration for the central and west area networks. The other system, located at the City Operation and Maintenance Depot, performs the data acquisition and control functions for the east and city area networks. The SCADA system hardware mirrors the network level concept to achieve a high degree of system availability and modularity (see Figure 1 for the initial system configuration). These levels can be classified as follows: Master Station: - Main computer systems - Front-end (Telecontrol Interface) systems - Man-Machine Interface (Operator Consoles/ Workstations)
322 Remote Station: 2 engineering consoles,one equipped with 2 colour monitors Submaster stations and the other with 1 colour monitor and a video hardcopy unit. Remote'Terminal Units These support the data entry and modification work. Main Computer Systems 2 remote consoles each equipped with 2 colour monitors exist at both Central and West ACCs and provide operational The two remotely located computer systems sit at the same data and network information for the maintenance crews. hierarchical level and form the core of the entire SCADA system. They are coupled to each other by two X.25 data links over public 1 remote console equipped with 2 colour monitors is located telephone lines for data exchange. at the head office and provides operational data and network information for management and network planning This arrangement allows real-time network data received by one system from its respective area network to be transmitted to the Connected to computer system 2 located at City ACC: other system for processing and updating of its database.thus enabling the databases in both systems to be identical at any 2 local consoles at City ACC and 2 remote consoles at East point of time.Furthermore in the command direction.output ACC.each equipped with 2 colour monitors.These provide command to a station not belonging to its own area will operational data and network information for the maintenance automatically be sent to the other system for execution.Thus crews. remote control as well as monitoring of the entire distribution network can be carried out from any operator console connected All the consoles are driven by microprocessor based display to any control centre of the system. controllers.which support semigraphic display.These are connected to the computer systems via the watchdog Each computer system consists of two identical main computers switch-over unit which automatically connect them to the online operating in an online/hot-standby mode to provide redundancy system. within each system and minimize system downtime.Their opera-tion is coordinated by the watchdog/switch-over unit. The semigraphic MMI extensively uses multiple windows technique which also supports scrolling and panning of displays Telecontrol Interface (TCI) to give a continuous enlargement of display area.Users can.by using the Database Management System.define and subdivide On the level between the RTUs and the main computers are the the display screen of 256 characters by 160 characters into a Telecontrol Interface front-end preprocessors.The TCls are maximum of four windows of different sizes and configure the responsible for the acquisition of the network data via the RTUs message text.alarm lists.stations and network diagrams in each and the local preprocessing of these data.For modularity and window to be displayed. simplicity purposes.two sets of dual telecontrol intertace units are used for each computer system.each serving one Submaster Stations and Remote Terminal Units geographic area of the network.Similar to the main computers.a dual redundant arrangement is also adopted at the telecontrol At the remote stations level.a two-level hierarchical layout has interface level which operates in a online/hot-standby mode to been adopted to organize the huge number of substations into a ensure highest system availability. manageable size.Two types of RTUs:one.a large multiple-board type and the other.a small single-board type.are Man-Machine Interface (MMI) used for this purpose.The large RTUs.which are also called "Submasters",are installed in all major 66/22 kV substations and At the man-machine interface level.a total of 6 local and 7 large 22 kV substations remote display consoles are utilized to support the operations at the Distribution Control Centre (DCC)and the four Area Control They communicate directly with the telecontrol interface to Centres (ACCs).These consoles are allocated as follows: acquire network data and perform switching operations at these substations.At the same time.they also function as "Data Connected to computer system 1 located at DCC: concentrators"which communicate to their small RTUs that are installed in those smaller substations to perform the data 2 operator consoles each equipped with 3 colour monitors acquisition and control functions. support the functions at DCC and coordinate the operations for the entire distribution network
322 Remote Station: - Submaster stations - Remote. Terminal Units Main Computer Svstems The two remotely 'located computer systems sit at the same hierarchical level and form the core of the entire SCADA system. They are coupled to each other by two X.25 data links over public telephone lines for data exchange. This arrangement allows real-time network data received by one system from its respective area network to be transmitted to the other system for processing and updating of its database. thus enabling the databases in both systems to be identical at any point of time. Furthermore in the command direction. output command to a station not belonging to its own area will automatically be sent to the other system for execution. Thus remote control as well as monitoring of the entire distribution network can be carried out from any operator console connected to any control centre of the system. Each computer system consists of two identical main computers operating in an onlineihot-standby mode to provide redundancy within each system and minimize system downtime. Their opera-tion is coordinated by the watchdogiswitch-over unit. Telecontrol Interface (TCI) On the level between the RTUs and the main computers are the Telecontrol Interface front-end preprocessors. The TCls are responsible for the acquisition of the network data via the RTUs and the local preprocessing of these data. For modularity and simplicity purposes. two sets of dual telecontrol interface units are used for each computer system. each serving one geographic area of the network. Similar to the main computers. a dual redundant arrangement is also adopted at the telecontrol interface level which operates in a onlineihot-standby mode to ensure highest system availability. Man-Machine Interface (MMI) At the man-machine interface level, a total of 6 local and 7 remote display consoles are utilized to support the operations at the Distribution Control Centre (DCC) and the four Area Control Centres (ACCs). These consoles are allocated as follows: Connected to comouter svstem 1 located at DCC: - 2 operator consoles each equipped with 3 colour monitors support the functions at DCC and coordinate the operations for the entire distribution network. - 2 engineering consoles, one equipped with 2 colour monitors and the other with 1 colour monitor and a video hardcopy unit. These support the data entry and modification work. - 2 remote consoles each equipped with 2 colour monitors exist at both Central and West ACCs and provide operational data and network information for the maintenance crews. - 1 remote console equipped with 2 colour monitors is located at the head office and provides operational data and network information for management and network planning. Connected to cornouter svstem 2 located at Citv ACC: - 2 local consoles at City ACC and 2 remote consoles at East ACC. each equipped with 2 colour monitors. These provide operational data and network information for the maintenance crews. All the consoles are driven by microprocessor based display controllers, which support semigraphic display. These are connected to the computer systems via the watchdog1 switch-over unit which automatically connect them to the online system. The semigraphic MMI extensively uses multiple windows technique which also supports scrolling and panning of displays to give a continuous enlargement of display area. Users can. by using the Database Management System, define ahd subdivide the display screen of 256 characters by 160 characters into a maximum of four windows of different sizes and configure the message text, alarm lists, stations and network diagrams in each window to be displayed. Submaster Stations and Remote Terminal Units At the remote stations level, a two-level hierarchical layout has been adopted to organize the huge number of substations into a manageable size. Two types of RTUs: one, a large multiple-board type and the other, a small single-board type, are used for this purpose. The large RTUs, which are also called "Submasters". are installed in all major 66/22 kV substations and large 22 kV substations. They communicate directly with the telecontrol interface to acquire network data and perform switching operations at these substations. At the same time, they also function as "Data concentrators" which communicate to their small RTUs that are installed in those smaller substations to perform the data acquisition and control functions
323 There is.therefore.no direct communication taking place Remote network control and monitoring between the small RTUs and the telecontrol interface unit and all All network switching operations can be performed from the information is exchanged through the submasters. control centre.Circuit breaker statuses are always up-to-date and available at all control centres thus improving the operational All submasters are configured in party line mode.They are efficiency and overall network management.The introduction of connected to the telecontrol interface in a loop circuit of no more this capability also sees an important development in network than 16.The loop arrangement is to enhance the availability of planning.Wherever possible.circuits are now arranged in a the submasters against the failure of a communication line. closed ring such that no customer will suffer a blackout in the Hence.during such instances.communication is still possible via event of a cable fault in the respective ring. the other end of the loop.Similarly.the small RTUs are also configured in loops with no more than 16 RTUs in a loop to a Alarm alert of impending equipment malfunction submaster.The layout is illustrated in Figure 2. The system maintains updates of information pertaining to the network's loading.protection system alarms and the status of DC supply used by the protection system and switchgear's tripping circuit.Early detection of warning alarms thus ensure corrective HOST CPU gL HOST CPU actions to take place long before false tripping could occur. 3267 3267 Post fault analysis with earth fault indications 2 As the entire PUB's 22 kV network employs only underground 2 密 密 54630B cables.earth fault indications are therefore of major importance and are closely monitored for post fault analysis.Together with the protective system alarms and indications messages received at the control centre.the operator will be able to analyze the cause and location of a failure and identify faulty equipment or 回 NOTE circuits.Fault isolation and supply restoration can then be 1e9eao8rmasterops speedily carried out by remote switching thus enhancing the efficiency to restore disrupted supply. 2.Up to 16 subraster per submaster loop. Network overview via semigraphic MMI Status overview of the 22 kV network is provided via displaying TU400 the network diagrams on the colour monitors.The entire 22 kV network diagram is organized into multiple diagrams according to 网 the 66 kV sources.so that all substations fed by the same source are grouped into the same overview diagram. Each network overview diagram shows the network topology as SUBMASTER-LOOF well as all associated circuit breakers status.In addition.the lines/circuits in the overview diagram are also distinctively coloured according to their loading condition so that any overloads can be effectively highlighted to the operator.With the Fig.2: Submasters and RTU's Communication Loop help of the scrolling/panning function.the operator can then freely move throughout the diagram to view the overall network status. With this configuration.the time required to complete a polling cycle is greatly reduced when compared with a scenario where Archiving and trending of circuit loading all RTUs (both large and small)are communicating to the To facilitate better network operation planning.all circuits loading telecontrol interface unit directly.Furthermore.the need to are constantly monitored and their actual daily and monthly provide an elaborate communication network to link all the RTUs maximum/minimum loadings recorded.In addition.any circuit to the master stations has also been reduced.as all the small loading can also be archived over a duration of 7 days at 5 RTUs now take the topology of the distribution network in their minutes interval. connection to the submasters. Feeder tagging for maintenance work SCADA FUNCTIONS AND THEIR BENEFITS When works are to be carried out on any circuit or equipment,the respective circuit can be tagged in the system to mark its The basic functions of the system and the benefits they have unavailability for service.To facilitate network management provided include the following:
323 There is, therefore, no direct communication taking place between the small RTUs and the telecontrol interface unit and all information is exchanged through the submasters. All submasters are configured in party line mode. They are connected to the telecontrol interface in a loop circuit of no more than 16. The loop arrangement is to enhance the availability of the submasters against the failure of a communication line. Hence, during such instances, communication is still possible Via the other end of the loop. Similarly, the small RTUs are also configured in loops with no more than 16 RTUs in a loop to a submaster. The layout is illustrated in Figure 2. U I A -+ U T NOTE: 1 up to 16 submaster loops per TCI block 2 up to 16 submaster per submaster loop i 3 Up to 16 small RTU per I U -+ U I RTU loop 'U RTU-LCOP Fig. 2: Submasters and RTU's Communics ion Lo P With this configuration, the time required to complete a polling cycle is greatly reduced when compared with a scenario where all RTUs (both large and small) are communicating to the telecontrol interface unit directly. Furthermore. the need to provide an elaborate communication network to link all the RTUs to the master stations has also been reduced, as all the small RTUs now take the topology of the distribution network in their connection to the submasters. SCADA FUNCTIONS AND THEIR BENEFITS The basic functions of the system and the benefits they have provided include the following: - $q All network switching operations can be performed from the control centre. Circuit breaker statuses are always up-to-date and available at all control centres thus improving the operational efficiency and overall network management. The introduction of this capability also sees an important development in network planning. Wherever possible, circuits are now arranged in a closed ring such that no customer will suffer a blackout in the event of a cable fault in the respective ring. - The system maintains updates of information pertaining to the network's loading, protection system alarms and the status of DC supply used by the protection system and switchgear's tripping circuit. Early detection of warning alarms thus ensure corrective actions to take place long before false tripping could occur. Alarm alert of imoendina eauiDment malfunction - As the entire PUB'S 22 kV network employs only underground cables, earth fault indications are therefore of major importance and are closely monitored for post fault analysis. Together with the protective system alarms and indications messages received at the control centre, the operator will be able to analyze the cause and location of a failure and identify faulty equipment or circuits. Fault isolation and supply restoration can then be speedily carried out by remote switching thus enhancing the efficiency to regtore disrupted supply. Post fault analvsis with earth fault indications - Status overview of the 22 kV network is provided via displaying the network diagrams on the colour monitors. The entire 22 kV network diagram is organized into multiple diagrams according to the 66 kV sources. so that all substations fed by the same source are grouped into the same overview diagram. Network overview via semiaraohic MMI Each network overview diagram shows the network topology as well as all associated circuit breakers status. In addition, the linesicircuits in the overview diagram are also distinctivelv coloured according to their loading condition so that any overloads can be effectively highlighted to the operator. With the help of the scrollingipanning function, the operator can then freely move throughout the diagram to view the overall network Status. - To facilitate better network operation planning. all circuits loading are constantly monitored and their actual daily and monthly maximum!minimum loadings recorded. In addition, any circuit loading can also be archived over a duration of 7 days at 5 minutes interval. Archivina and trendina of circuit loading - When'works are to be carried out on any circuit or equipment, the respective circuit can be tagged in the system to mark its unavailability for service. To facilitate network management Feeder taaaina for maintenance work
324 function,all switching and tagging operations messages Thus only minor changes are needed in defining the new data associated with the work can further be selected from the events point or display.thereby saving much time and effort.At each summary log and appended with a report to record its nature and input field.data validity checks are performed and plausible purpose of the operation. values are suggested and presented to the operator.thus making the data entry work easier and at the same time minimizing the ONLINE DATABASE MANAGEMENT SYSTEM risk of possible entry mistakes. The entire network definition and real-time data are maintained in To ensure the integrity of the network data.the online database both computer systems and are kept consistent with each other management system allows all data entry and editing to be done at all times.To facilitate data entry work.especially for the vast on a replica copy of the database in the online computer system volume of network data.and to cope with the never-ending data designated as Master and kept in the form of jobs.The jobs will modification work arising out of network growth and topology also be transmitted to the standby computer as well as to the changes.the online database management subsystem has remote pair.When activated,the new data and all the changes adopted a simple.reliable.user-friendly and interactive interface. will then be updated into the online database of the system.At the This DMS interface is availabie over all the operator and same time.these jobs will also be activated in standby as well as engineering consoles connected to the online system.When the remote pair.Throughout the inputs and activation of jobs. entering a new data point.or creating a new display.a similar there is neither interference with normal operation nor loss of data structure or section of any display already existing in the real-time information:neither is a system shutdown or reboot database can always be copied as a model and easily adapted. required. 22kV Substation 22kV Substation SM3 Area SM3 Area RTU2 RTU2 RTUn RTUn 52 SM2 RTU1 SM1 SMr SM1 SMn M... Host Computer IAYER RAJAHI (KALLANG BASINI T oss -50 96e0 267-60 267-50 1s Mbyte 16 Mbyte 16 Mbyte 16 Mbvte 8 LAN IISO/OSI A LAN ITCP/IP PARC IEC- C-BL SU. M-M 会 SPARC M DCC AYER RAJA ACC City (KALLANG BASIN) M--M FGC ws1.4 Plotte ACC Central M M SPARC ACC East SPARC 四四 LEGEND ACC Area Control Centre Remote Terminal Unit Brioge ACC West M M DBMS dcopy。 FGC Dcc Distribution Control Centre Workstation 口▣ Dana Link LAN COOD 055 Operator Support System Fig.3:New System Configuration
324 function, all switching and tagging operations messages associated with the work can further be selected from the events summary log and appended with a report to record its nature and purpose of the operation. ONLINE DATABASE MANAGEMENT SYSTEM The entire network definition and real-time data are maintained in both computer systems and are kept consistent with each other at all times. To facilitate data entry work. especially for the vast volume of network data. and to cope with the never-ending data modification work arising out of network growth and topology changes, the online database management subsystem has adopted a simple, reliable, user-friendly qpd interactive interface. This DMS interface is available over all the operator and engineering consoles connected to the online system.When entering a new data point, or creating a new display, a similar data structure or section of any display already existing in the database can always be copied as a model and easily adapted. - 22kV Substation . Area Thus only minor changes are needed in defining the new data point or display, thereby saving much time and effort. At each input field, data validity checks are performed and plausible values are suggested and presented to the operator, thus making the data entry work easier and at the same time minimizing the risk of possible entry mistakes. To ensure the integrity of the network data, the online database management system allows all data entry and editing to be done on a replica copy of the database in the online computer system designated as Master and kept in the form of jobs. The jobs will also be transmitted to the standby computer as well as to the remote pair. When activated, the new data and all the changes will then be updated into the online database of the system. At the same time, these jobs will also be activated in standby as well as the remote pair. Throughout the inputs and activation of jobs. there is neither interference with normal operation nor loss of real-time information; neither is a system shutdown or reboot required. Substation Area Host Computer System 2 IAYER RAJAH) (KALLANG BASIN) LEGEND ACC Area Control Centre RTU Remote Terminal Unit B Bridge SM Submaster CHC Colour Hardcopy SU Switchover Unit DBMS Data Basis Management TCI Telecontrol Interface DCC Distribution Control Centre WS Workstation FGC Fullgraphic Console -.- X 25 Data Link M Modem /y LAN Coupling via Bridge LAN Local Area Network n RTU LOOP PUB Building FGC OSS Operator Support System Fig. 3: New System Configuration
325 This is an important feature which has greatly eased the phased form of jobs and are also transmitted to the partner and remote implementation of the entire system and the progressive add-on systems automatically for updating. of substations under its surveillance since commissioning. The new configuration is shown in Figure 3. SYSTEM IMPLEMENTATION AND SUBSEQUENT EXPANSION IHE EXPERT SYSTEM The system was implemented in two phases.Phase I was Since implementation.the SCADA system has provided the commissioned in mid'87 and involved the master station necessary basic infrastructure for quick response in the operation equipment at the City Operation Maintenance Depot and the and management of the 22 kV network.To further improve the respective telecontrol interfaces for city and east areas network. operation efficiency and network reliability.an expert system is ohase II was commissioned in mid'88 and encompassed the being implemented and integrated to the online SCADA system to master station equipment at the Distribution Control Centre.the provide artificial intelligence in analyzing disturbances and respective telecontrol interface for west and central areas proposing suitable switching sequences to effect supply network and the X.25 computer-computer coupling. restoration,performing switch check and proposing switching. sequences for load transfer. Commissioning of RTUs was a lengthy process due to the enormous amount of RTUs to be installed at the substations,and The expert system is implemented on a powerful workstation the huge volume of substation data and network diagrams to be utilizing an object-oriented Knowledge Engineering Environment entered and constructed inside the database plus having to (KEE)shell.It is connected to the oniine SCADA system via the prepare the communication links between the RTUs and the LAN.During the system initialization,the expert system will read master station.The RTUs were therefore progressively from the SCADA system's database all the substations and commissioned and hooked-on to the SCADA system network data to build up its own knowledge-base.Program one-by-one soon after the first master station equipment was functions written in LISP are then called upon to compute and commissioned.The phase-commissioning approach was evaluate the network topology.The results of the evaluation are therefore aimed to build -up the system more effectively and put then stored in the knowledge-base in the form of object-oriented the system into service as early as possible. representa-tion.and are to be used by the disturbance analysis package.No data entry is needed for the expert system. With the successful implementation of SCADA facilities on the 22 kV network.PUB has also decided to extend all the facilities to SCADA/EMS Expert System some 300 major 6.6 kV substations and bring the network Process management functions to the entire 6.6 kV network which,covers some 4.000 substations.However,unlike the 22 kV network the semigraphic MMI was too restrictive in providing clear network overview to the operators due to the complexity and the scale of PD the 6.6 kV network. Database 日age Hence.a fullgraphic MMI was introduced instead to take AAF TWF advantage of multiple windowing techniques and smooth EM DS panning/zooming and decluttering functions to display different 453079a levels of details and information for the network overview. LEGEND: Affected Area Focusing Two powerful workstations each equipped with two monitors are stem utilized to provide the fuligraphic MMI.These are connected to the EM Event Manager Main process computers through the LAN and co-exist with the ere-Diag Interface 20 present semigraphic consoles which probably will be retired after Trigger Time Window Function their usetul lifespan. Fig.4: Data Flow for IAP In addition.a third computer is also introduced to takeover the online database management function from the online process system thus enhancing the response of the process system.The The expert system adopts a combination of model-based and rule-based approaches for its disturbance analysis and fault third computer system is connected to the online and standby reasoning.All alarms and circuit breaker status changes system through the LAN by taking advantage of the distributed received by the SCADA system will then be passed on to the architecture capabilities of the system.Functionally.the expert system for analysis.in the expert system.an Event procedure for the online database management system remains unchanged.All data entries and modification tasks are kept in the Manager (a program module written in LISP)is used to coordinate
This IS an important feature which has greatly eased the phased implementation of the entire system and the progressive add-on of substations under its surveillance since commissioning. The system was implemented in two phases. Phase I was commissioned in mid'87 and involved the master station equipment at the City Operation & Maintenance Depot and the respective telecontrol interfaces for city and east areas network, phase II was commissioned in mid'88 and encompassed the master station equipment at the Distribution Control Centre, the respective telecontrol interface for west and central areas network and the X.25 computer-computer coupling. Commissioning of RTUs was a lengthy process due to the enormous amount of RTUs to be installed at the substations, and the huge volume of substation data and network diagrams to be entered and constructed inside the database plus having to prepare the communication links between the RTUs and the master station. The RTUs were therefore progressively commissioned and hooked-on to the SCADA system one-by-one soon after the first master station equipment was commissioned. The phase-commissioning approach was therefore aimed to build -up the system more effectively and put the system into service as early as possible. With the successful implementation of SCADA facilities on the 22 kV network, PUB has also decided to extend all the facilities to some 300 major 6.6 kV substations and bring the network management functions to the entire 6.6 kV network which, covers some 4,000 substations. However, unlike the 22 kV network the semigraphic MMI was too restrictive in providing clear network overview to the operators due to the complexity and the scale of the 6.6 kV network. Hence, a fullgraphic MMI was introduced instead to take advantage of multiple windowing techniques and smooth panninglzooming and decluttering functions to display different levels of details and information for the network overview. Two powerful workstations each equipped with two monitors are utilized to provide the fullgraphic MMI. These are connected to the process computers through the LAN and CO-exist with the present semigraphic consoles which probably will be retired after their useful lifespan. In addition. a third computer IS also introduced to takeover the online database management function from the online process system thus enhancing the response of the process system The third computer system is connected to the online and standby system through the LAN by taking advantage of the distributed architecture capabilities of the system Functionally. the procedure for the online database management system remains unchanged All data entries and modification tasks are kept in the 325 form of jobs and are also transmitted to the partner and remote systems automatically for updating. The new configuration is shown in Figure 3. THE EXPERT SYSTEM Since implementation, the SCADA system has provided the necessary basic infrastructure for quick response in the operation and management of the 22 kV network. To further improve the operation efficiency and network reliability, an expert system is being implemented and integrated to the online SCADA system to provide artificial intelligence in analyzing disturbances and proposing suitable switching sequences to effect supply restoration, performing switch check and proposing switching sequences for load transfer. The expert system is implemented on a powerful workstation utilizing an object-oriented Knowledge Engineering Environment (KEE) shell. It is connected to the online SCADA system via the LAN. During the system initialization, the expert system will read from the SCADA system's database all the substations and network data to build up its own knowledge-base. Program functions written in LISP are then called upon to compute and evaluate the network topology. The results of the evaluation are then stored in the knowledge-base in the form of object-oriented representa-tion, and are to be used by the disturbance analysis package. No data entry is needed for the expert system. SCADAlEMS I I Database 1 Pro;ess I Expert System AAF Affected Area Focusing DA Data Acquisition DS Diagnostic System EM Event Manager MD Main Diagnosis MMI Man Machine Interface PD Pre Diagnosis T Trigger TWF Time Window Function Fig. 4: Data Flow for IAP The expert system adopts a combination of model-based and rule-based approaches for its disturbance analysis and fault reasoning. All alarms and circuit breaker status changes received by the SCADA system will then be passed on to the expert system for analysis. In the expert system. an Event Manager (a program module written in LISP) is used to coordinate
326 all the activities.such as,to filter and split the different events CIGRE.Session of Study Committees 39,Paper No.39-15. according to the network topology:to decide whether the Paris.27.Sept.-4.Oct.1988 disturbance analysis and fault should be triggered and when should the reasoning process be started.The process data flow 7]John Chen.A.C.Liew,Seng-Foo Ho.Eng-Kiat Chan. is demonstrated in Figure 4.An algorithmn will also be "Automated Power Supply Restoration in Distribution Network" incorporated to support the load restoration and load transfer 2nd Symposium,Export Systems Application to Power functions Systems.Seattle,Washington,17-20 July 1989 CONCLUSIONS ACKNOWLEDGEMENT The PUB's SCADA system has.since implementation,evolved from a pure SCADA application to a Distribution Management The authors would like to thank the Chief Executive of the Public System for the 22 kV and 6.6 kV network.supporting the roles of Utilities Board for his permission to publish and present this paper. network operation and planning. It has helped to bring about a dramatic drop in the number of Eng-Kiat Chan received the B.Eng (Hons)in Electrical biackouts caused by 22 kV outages because of the network ring Engineering and M.Sc in Industrial Engineering from the University configuration.and to slash the average outage time of a 22 kV of Singapore in 1975 and 1980 respectively.In 1975.he joined the power failure to a fraction of what it used to be.its latest Public Utilities Board of Singapore as a System Commissioning& development phase will be the incorporation of probably the Protection Engineer and was mainly involved in the world's first real-time Expert System for its disturbance analysis. commissioning of 230 kV and 66 kV protection system.From network restoration.load transfer and switching check functions. 1980 to 1982.he worked in the Operation Maintenance Division The disturbance analysis module was implemented in Nov.'90. and was responsible for the eastern distribution network.Since When fully completed.this will pave way for full distribution 1983.he has held the rank of Senior engineer and has been automation.thereby enhancing the supply reliability and heading the Supervisory Control and Communication Section.He operation efficiency. is the Project Manager for the 22 kV SCADA System as well as a member of the Energy Management System(EMS)project team. Reterences Mr.Chan is a Professional Engineer registered in Singapore and is also a member of the Institution of Engineers.Singapore. 1 Dy Liacco.T.E. "Toward a Functional Control Centre Design" Horst Ebenhoh graduated in Electrical Machines and Apparatus IFAC-Symposium,Beijing,August 1986 and received his diploma in 1965. In 1972 he joined the Power System Control Department of the 12]Eng-Kiat Chan.Chee-Kiong Koh. Siemens AG and worked as System Designer.Group leader and Supervisory Control and Data Acquisition System for the 22 kV Project Manager for large Power System Control Projects.He Distribution Network in Singapore" holds the rank of Senior Engineer and is at present Manager for International Symposium on Electrical Distribution and Energy the marketing and implementation of major Power System Control Management.Singapore.26.-27.Oct.1988 Projects in China.South East Asia.Australia and Africa. 3]Wolfgang Flandorfer.Jochen Frick and David North. "Energy Data Management in Realtime" Energy Automation Vol.XI,No.4.July/August 1989 4 Horst Ebenhoh. "Evolutionary Architectures for SCADA and EMS Systems" Technical Papers of the 8th CEPSI Conference.Volume 4. Paper 4-11.Singapore.5-9 Nov.1990 5 Gunther Schellstede. "Design Aspects for an upgradable and stepwise renewable Control Centre System" CIGRE.Symposium of Study Committees 38 and 39 in Bangkok.20-22 Nov.1989 6 Franz Hein and Gunther Schellstede. "Use of Expert Systems in Energy Control Centres
326 all the activities. such as. to filter and split the different events according to the network topology: to decide whether the disturbance analysis and fault should be triggered and when should the reasoning process be started. The process data flow is demonstrated in Figure 4. An algorithmn will also be incorporated to support the load restoration and load transfer functions. CIGRE, Session of Study Committees 39, Paper No. 39-15. Paris, 27. Sept. - 4. Oct. 1988 171 John Chen. A.C. Liew, Seng-Foo Ho, Eng-Kiat Chan. "Automated Power Supply Restoration in Distribution Network" 2nd Symposium. Export Systems Application to Power Systems, Seattle. Washington, 17 - 20 July 7989 CONCLUSIONS ACKNOWLEDGEMENT The PUB'S SCADA system has. since implementation, evolved from a pure SCADA application to a Distribution Management System for the 22 kV and 6.6 kV network, supporting the roles of ' network operation and planning. It has helped to bring about a dramatic drop in the number of blackouts caused by 22 kV outages because of the network ring configuration, and to slash the average outage time of a 22 kV power failure to a fraction of what it used to be. Its latest development phase will be the incorporation of probably the world's first real-time Expert System for its disturbance analysis, network restoration, load transfer and switching check functions. The disturbance analysis module was implemented in Nov. '90. When fully completed, this will pave way for full distribution automation, thereby enhancing the supply reliability and operation efficiency. References 11) Dy Liacco. T.E.. "Toward a Functional Control Centre Design" IFAC-Symposium, Beijing, August 1986 121 Eng-Kiat Chan, Chee-Kiong Koh. "supervisory Control and Data Acquisition System for the 22 kV Distribution Network in Singapore" International Symposium on Electrical Distribution and Energy Management, Singapore, 26. - 27. Oct. 1988 131 Wolfgang Flandorfer, Jochen Frick and David North, "Energy Data Management in Realtime" Energy & Automation Vol. XI. No. 4, JulyiAugust 1989 141 Horst Ebenhoh, '*Evolutionary Architectures for SCADA and EMS Systems" Technical Papers of the 8th CEPSI Conference, Volume 4, Paper 4 - 7 1, Singapore. 5 - 9 Nov. 1990 151 Gunther Schellstede, "Design Aspects for an upgradable and stepwise renewable Control Centre System" CIGRE. Symposium of Study Committees 38 and 39 in Bangkok, 20 - 22 Nov. 1989 161 Franz Hein and Gunther Schellstede, "Use of Expert Systems in Energy Control Centres'' The authors would like to thank the Chief Executive of the Public Utilities Board for his permission to publish and present this paper. Ena-Kiat Chan received the B.Eng (Hons) in Electrical Engineering and M.Sc in Industrial Engineering from the University of Singapore in 1975 and 1980 respectively. In 1975, he joined the Public Utilities Board of Singapore as a System Commissioning & Protection Engineer and was mainly involved in the commissioning of 230 kV and 66 kV protection system. From 1980 to 1982, he worked in the Operation & Maintenance Division and was responsible for the eastern distribution network. Since 1983, he has held the rank of Senior engineer and has been heading the Supervisory Control and Communication Section. He is the Project Manager for the 22 kV SCADA System as well as a member of the Energy Management System (EMS) project team. Mr. Chan is a Professional Engineer registered in Singapore and is also a member of the Institution of Engineers, Singapore. Horst Ebenhoh graduated in Electrical Machines and Apparatus and received his diploma in 1965. In 1972 he joined the Power System Control Department of the Siemens AG and worked as System Designer, Group leader and Project Manager for large Power System Control Projects. He holds the rank of Senior Engineer and is at present Manager for the marketing and implementation of major Power System Control Projects in China, South East Asia, Australia and Africa