7/29/2019 00808719

1/6

WM2-1 2:OOProceedings of the 1999 IEEEInternational Sympo sium on Comp uter Aided Control System DesignKohala Coast-Island of Hawai'i, Hawai'i, USA August 22-27, 1999

SCADA in Hydropower PlantsM. Mavrin, V. Koroman, B. BoroviCBrodarski InstituteAV.V. Holjevca 20, 10020 Zagreb, Croatiatel. +385 1 6504 342, fax. +385 1 6504 400e-mail: mavrin@brod.hrbi.hr

AbstractFor the purpose'of improving the supervisory control in ahydropower plant, the SCADA application was built induring the general overhaul of the hydropower plant"Miljacka" on the river Krka in Croatia. The lowest levelof the execution of the controlling algorithms was on theSIEMENS PLCs S7-400. The SCADA application is thetop of the supervisory control structure. The controllingapplication was made in the form of enclosed logicalparts of the process displayed on individua l control panelsused for supervisory control. The communication of theSCADA application with the PLCs is realised by thecommunication server Applicom PC 2000 ETH, usingSINEC H1 (Industrial Ethernet) protocol via fibre optics.

The SCADA application was made using the NationalInstruments programming package LOOKOUT on theoperating system Windows NT 4.0.

1. IntroductionThe SCADA application for control of the hydropowerplant was made using about fifty control panels, each ofthem representing one part of the controlled process. Thepanels were made in the form of the enclosed logical partsof the process displayed on particular control panels, sothat the operator can see the whole part of the process.

SCADA4

, MAINPANEL

0 00 t

'I 'II Y Y 'I .v .

WATFRSUPPLY SWITCHYARD ABOUTSYSTEMlJNll I LNIT 2 I K I T 3 IJNlT 44 4 44444 4 4 4 * 4 4

Fig 1:Control structure of the SCADA application for unit 2

0-7803-5500-8/99$10.000 1999 IEEE 624

7/29/2019 00808719

2/6

The control structure of the SCADA application wasmade in the "top-down'' form. On the top, there is the socalled Main Panel, which conveys the basic informationto the operator in the normal operating conditions. Fromthis panel the operator can go fixther to the panels whichrepresent particular power units. The main structure of theSCADA is shown i n Fig 1 .

2. Main Pailel'l'lic Main l':iticl 01' the SCADA application The MainPancl represents the top of the SCADA application,which is the starting panel to r particular panelsrcprcscnling particular power units and their respectiveproccsscs. 'The Main Pancl is shown in Fig. 2. Pushbuttonob jec ts on thc left top side in the picture are used for thesclcction bctwceti the controlled parts of the process.I'icssing on thc ptishbutton of a particda r power unit, theopcr;itor can go litrthcr into tlie controlled process to seetlic details 01' tlic process. Selection between units can be;iIso tiiadc by prcssitig on the graphics of tlie particular

units. In the lower part of the panel the basic values whichare important for the running of particular units aredisplayed. Here, the operator can control the power to beproduced by a unit by increasing or decreasing its value,or can stop any of the power units. From the M ain Panelthe SCADA application branches out to six fundamentalbranches of the process, shown in Fig. 1.

3. Control panel of the 2" dpower unitThe whole control structure for the control of the 2'ldpower unit is shown in the lower part of Fig. 1. Eachcontrol panel of a particular unit represents an enclosedprocess of that particular unit, with all fiindamental partsas shown in Fig 3.Particular parts of the process are represented bygraphical objects in order to facilitate the operator tolearn how to use the SCADA application in controllingthe proccss. The objects with their animation (turbinerotation animates also acceleration) and the changes ofthe graphical states show the operating states of some

m m U W*)l - e- nu' aaHydropower Plant Miljacka

Fig. 2: The Main Panel of the SCADA application

625

7/29/2019 00808719

3/6

Fig. 3: Control panel of the Unit 2critical parts in that particular unit. The control panel forunit 2 is represented in Fig 3.The panel is used as a starting panel to other panels thatrepresent the lower parts of the process related to unit 2.Going lower into the process is possible by pressing thepushbutton objects which activate desired panels, and inthis way the operator can see the appropriate controlpanel. IJsing the pushbutton objects in the lower lefrcomer of Fig. 3, the operator can switch on or off someparts of the process. Any command to switch on or offsome parts of the process must be acknowledged, so inthis way the accidental setting of the command isavoided. Operators have their accounts with passwords,because when an operator wants to set the command hemust be logged to the SCADA application, or otherwisehe cannot set the coinmand. In addition to the accounteach operator has been given the priority for hisusername, so if his priority is lower than the priority ofthe command he wants to set, he will not be able to se tthis coinmand. In this way, it is possible to define whohas responsibility to switch on some parts of the process(operators with higher priority). With the setting of thecommand, the name of the operator is automaticallyrecorded on the disk, so it is always possible to find outwho the command has been set by.

4. Supervisory control structureAll control algorithms are executed on the SIEMENSPLCs S7-400 and the SCADA communicates with themusing the Industrial Ethernet and fibre optics. There aretwo main parts to control: turbine control and the watersupply system. In normal conditions the water supplysystem operates automatically controlled by thealgorithms programmed in the PLC5 (Fig. 4).The turbine control algorithms are programmed into aparticular BI-PLC (each unit has its own BI-PLC).PL C S7 is a supervisory unit which executes all otheralgorithms and controls other parts of the process of thepower unit, for each unit separately. Each S7 PLC has itsown communication processor (CP 443-1) with theIndustrial Ethernet protocol, and it is connected to a starcoupler and also to an Applicom communication server inan industrial computer. On the top of the control structurethere is the SCADA application as shown in Fig. 4.As it can be seen from Fig. 4, the most remote unit isPLC6 which controls opening of the water supply gatesand other processes on the storage reservoir. The supplytunnel passes through a hill and it is 2.5 kmlong. Thefibre optics cable which runs parallel with the supplytunnel is connected to the PLCS which executes thealgorithms for the water supply system and opening thesupply gates.

626

7/29/2019 00808719

4/6

Engine-roomFig. 4: Supervisory control structure (with the co nfiguration of thecommunication web in the power plant)

The operator can control each muni using the SCADA(remote control) or using the Operation Panel (OP) of aparticular unit in the turbine-room (local control). In thecase of local control, the commands for the PL C are setvia the OP . Thus, the SCkDA can only observe theprocess, but cznnot set the commands, except thecommand to close the turbine blades in the case ofemergency.For the control of the HPP two industrial computers withtwo SCADA applications connected by NetDDE links areused. So, it is possible to use both computers to controlthe power production process. The third computer is astandby computer which is connected to the star couplerand in the case of failover the standby computer takescontrol of the process (all Lookout network DDE linksform other computers to the primary computer areautomatically redirected to the standby comp uter).

5. SCADA-PLC communicationThe communication of the SCADA application withPLCs, which control the process, is done using fibreoptics working with SINEC H I protocol (IndustrialEthernet). The SCADA application is installed on theindustrial computer. An Applicom PC 2000 ETHcommunication server is also installed in this computer,and in this way the communication with thecommunication processor CP443-1 of individual PLCunits is accomplished. All PLCs are connected to the starcoupler using optical Ethernet (PLCS is connected to thestar coupler using electrical profibus). SCADAapplication is connected to the star coupler using anApplicom communication server. The configuration ofthe working web in the power plant is shown in Fig. 4.A cyclic mode used for communication is accomplishedby creating cyclic functions which test (every 100ms) theaddresses of the variables in the PLCs memory to checktheir values have been changed and to write them in10 theApplicom database. The objects of the SCADAapplication, which represent the states of the controlledprocess, appropriately change their graphical symbols, or

627

7/29/2019 00808719

5/6

the information note. The cyclic way of thecomm unication is illustrated in Fig. 5.A particular cyclic function must be defined as a read orwrite function. For the cyclic functions the Applicomcommunication server has 32 K bit and 32 K wordmemory space (DATA-BASE in Fig. 5). The SCADAapplication either reads values ffom these addresses andwith a change of these values the graphical states of theobjects connected to the values changes, or the SCADAwrites the control values into these addresses and theApplicom card propagates these values as commands tothe PLCs. Such comm unication mode is useful because ofthe possibility of direct access to the Applicom databasewhere are all control values are written. So , it is possibleto access to these values using another Windows NTapplication. Thus, these values can be also accessed fi-oma remote data logging centre using TCP/IP.All communication functions are read (or written) inblocks, so in one cyclic function more variables are readto decrease the net traffic. Some variables change theirvalues slowly (like temperature for instance), so the readhnctions are activated every second, and this is also apossible way to decrease the net traffic.

5.1. Communication failureFor the purpose of connecting the power plant with thecatchment area Supervisory Control Centre it is importantthat any failure in communication between SCADA andPLCs controlling the process is indicated, so that themode of operation can be changed in time, and thedemand for the production of required electric energy canbe redirected to other power plants in the catchment area.The failure of communication between SCAD A and PLCs

, I IIF(Uln1 U(n 1 D - O No

CammunicalionOK I I

Work withfIksed valuerOf deruwd p w e r

IJlarm,

____ - ~ _ _ ~Applicominterface

' - 1-1PLC ~I . II

iYPLC

Fig 5: Cyclic way o f communication

results with the impossibility to control the power plantffom the catchment area Supervisory Control Centre. Thetest of communication is done on SCADA and on thePLCs as well, using the controlling algorithm shown inFig. 6. In this way, it is possible to overcome the problemencountered with the Applicom communication serverwhich in the case of a communication failure stores theold control values at the DATA-BASE addresses withoutinforming SCADA about the communication failure.Using this algorithm the time interval within whichcommunication failure alarm is activated can be defined.

SCADA

II

J' Infarmallon or theremoteSUpNiJOry ;~ Canire ,

Fig 6: Testing algorithm for the communication failure

628

7/29/2019 00808719

6/6

Thus, it is possible to extend the dead ba nd for the case ofshort interruptions in communication.In the event of communication interruption, the PLCsswitch to the mode of operation in which they keep thepreviously required power values to be produced byparticular power units. Meanwhile, the SupervisoryControl Centre is informed about the failure, and that theremotely increase or decrease of power production is notpossible. After the communication has been restored, thecontrol of the power plant is transferred again to theSupervisory Control Centre,

6. ConclusionThe described SCADA application consists of more than2000 objects which in groups b uild particular parts of thecontrolled process. These groups of objects (combinatedwith the real state graphics of the process) are connectedto particular PLC addresses. About 500 signals areconnected from the PLCs to the SCADA application.Most of the signals (about 70 %) are bit information,while the other signals are double word signals fiom themeasu red analogue values in the process. The output fromthe SCADA are 100 control signals (mostly bit signals).The graphical presentation is only a part of the SCADAapplication which does not show the internal logic thatexecutes particular control sequences. Some signals (likefor instance alaiin signals) start the sequences whichautomatically activate a certain panel to the screen onwhich the changes in the control process are shown.All signals are written to the database with a defineddeviation, otherwise any change of an analogue value willresult in a new point being logged to the d isk, so it wouldbe easy to generate very much useless, disk spaceconsuming information.The data logged to the disk can be read using SQLqueries fiom any of the Windows applications, becauseLookouts database includes an ODBC driver.The SCADA application is open to any W h e r add ingswhich will be m ade in the future, and to the conn ection tothe Supervisory Control Centre.

7. References1. M. Mavrin :SCADA for HPP Miljacka - manual fo roperator (in Croatian), Brodarski Institute, technicaldocumentation, 19982. Applicom International : Applicom communicationserver V2.9,Reference Manual3. National Instruments : Lookout process controlsoftware system, Reference Manual4. SIEMENS SIMATIC : System Software fo r S7-300and S7-400 Program Design, Programming Manual5. SIEMENS SIMATIC : SZMTZC S7/M7/C7Programmable Controllers, Catalog ST70, 19966. SIEMENS SIMATIC : S7-400/M7-400

Programmable Controllers Module SpeciJcations,Reference Manual

629