a device-based process signal design of electric power plants

Journal of Computing and Information Technology - CIT 9, 2001, 1, 29–42 29

A Device-Based Process Signal Designof Electric Power Plants

Juraj Simunic1, Mirko Randic2, Marijana Zivic3

1Technical faculty, University of Rijeka, Rijeka, Croatia2Faculty of Electrical Engineering and Computing, University of Zagreb, Zagreb, Croatia3Technical faculty, University of Rijeka, Rijeka, Croatia

Automation and computerized control of processes inelectric power plants were intensively started at theend of seventies and at the beginning of eighties dur-ing the introduction of microprocessor–based computersystems. The first generation of the information pro-cessing equipment has in most cases already becomedisused. From that time, visibility of controlled pro-cess has been increased by installing new and moderndevices which enable better informing about all relevantevents. The increased quantity of information by whichprocesses can be described implies that new and moreefficient techniques for information modeling should bedeveloped.

In this paper a device-based approach to process infor-mation modeling is proposed. Such modeling approachis more efficient than function-based approach we usedbefore. The efficiency lies in the fact that device-basedapproach is in the very essence an object-oriented mod-eling approach. Therefore, device-based informationmodels can be easily mapped to object-oriented mod-els. Both function-based and device-based modelingapproaches are described in the paper and differencesbetween two modeling paradigms are emphasized. In thelast Chapter of the paper analogy between device-basedand object-oriented models is described. This analogyrepresents basis for the model mapping.

Keywords: electric power plant, information modeling,process signal base, device-based model, object-orientedmodel

1. Introduction

The starting point for electric power plant �EPP�modeling for the needs of building an attachedbuilding and maintenance of the automation andcontrol system is a process information model-ing. Structure of information and informationflows between the controlled power plant andcontrol system must be known. Determination

of the data and signals structure of the informa-tion flows is a very complicated task even forsmall EPPs.

There are problems arising out of:

� equipment diversity used in EPPs;

� complexity of technological process in con-trolled systems, which surpasses knowledgeof a single person and thus sets up an imper-ative to organize a group of people �experts�for a particular part of the process technol-ogy;

� a relatively great number of signals whichinterchange between controlled and controlsystems;

� a need for good expertness in concrete EPPand its specific qualities.

In Chapter 2 of the paper, the function-basedmodeling of process signals is presented. Suchmodeling approach is technology-dependent,and now we are treating it as an obsolete ap-proach. Nevertheless, a short description ofthe approach is included here because device-based approach is partly based on it. Thus, areader can consider the evolution of our model-ing paradigm more easily. The function-basedapproach has been used for information mod-eling of processes in EPPs during the years ofour projects �8�. In Chapter 3, methodology forprocess signal design based on devices as basicelement of each EPPs is presented. Device-based modeling approach is focused on iden-tification of devices by their location in EPPand assigning signals to each device type. Bythe paradigm, the process signal structure of

30 A Device-Based Process Signal Design of Electric Power Plants

Fig. 1. Function-based EPP process signal model.

the observed EPP is obtained in a modular andoptimal way. Besides, it is underlined in Chap-ter 4 that the described devices-based modelingfits into modern object-oriented modeling ap-proach. How the device-based model could bemapped into object-oriented model is also ex-plained in this chapter.

2. Function-Based Process Signal Model

The function-based process signal model rep-resents the first generation process signal de-sign, which originates from the beginning of

the eighties. It is based on the technologicalmodules of an EPP, along with signals by theirfunction in the EPP process �Figure 1�. Bysuch a model, EPP process signals are definedaccording to their location �particular techno-logical module in the EPP� and function i.e.signal function in the EPP operation descrip-tion. Technological modules are considered assources and sinks of signals, and signals arecategorized by their function. In the model,function-technological module �FTM� is usedas a base for signal structure definition. Thegenerator commands or transformer alarm sig-nals are examples of the FTMs �Table 1�.

Table 1. Function-technological modules.

A Device-Based Process Signal Design of Electric Power Plants 31

By introducing the third aspect of a signal —the signal value, the corresponding EPP signalstructure is defined as a three-dimensional vec-tor �Figure 2�.

The set of signals SFT on the level of an EPPfor all technological modules and for all typesof signals can be defined as:

�1�SFT � fαxyzg x � 1� 2� 3� � � � � m

y � 1� 2� 3� � � � � nz � 0� 1� 2� � � � � r�

where αxyz presents the signal defined by func-tion x, location y and value z. The signal subsetSx represents all signals of one FM from all tech-nological modules of an EPP. It can be definedby the equation �1� with x � cons. yz-planein Figure 2 relates to this subset. The signalsubset Sy represents all signals of all FM fromone technological module of an EPP. It can alsobe defined by the equation �1� with y � cons.�xz-plane from Figure 2�. Finally, the subsetSxy �FTM� depicts all signals from one techno-logical module and for one signal quality i. e.function. It can also be defined by the equation�1�, but with x � cons. and y � cons.

Fig. 2. EPP signal representation by vector.

Model of process signal structure organized inthe above-mentioned way and defined at the

level of an EPP, can be used for EPP opera-tion analysis and for estimation of various in-formation flows. However, it has some specificlimitations and drawbacks, as follows:

� Process signals are organized at the level oftechnological modules in EPP, the completeprocedure has to be repeated for eachEPP. The model is not independent of theEPP. Moreover, modular design is not possi-ble.

� Device, as a basic EPP component, is notseparated as an information bearing unit.

� Device states cannot be defined for the needsof a modern process signal design, and thelinks among devices cannot be determinedeither.

� Redundancy of the data entry is signifi-cantly greater.

As an example, one part of process signal basegenerated by function-basedmodeling approachis presented in Table 2. The records are ex-tended with additional data-encoded parameterand with the denoted places for signal usage�third column – REPORTS�. The first columndenotes the signal function; signals are groupedaccording to their function. The second columnrepresents signal value and the signal code. Inthe third column, locations for sending signalsor location within the EPP or in master sub-station �MS� are marked. Reports can be ob-tained from event list �E�, alarm list �A�, faultlist �F�, chronological event list �CEL�, singleline scheme �SLS�, cabinet �C� and synopticchart �SP�.

Three-dimensional signal encoding is based onthe following principle:

� the first group of digits �y dimension fromthe model� is divided into three subgroups:

� the first subgroup consists of two digitsand it marks the bay �01 – Feeder bay,02 – Link bay,� � � �;

� the second subgroup consists of one digitand denotes voltage level of the observedbay �1 – 110 kV, 2 – 220 kV, 3 – 35 kV�;

� the third subgroup is made up of two dig-its and marks the bay name �01 – Melina1, 02 – Melina 2,� � � �, it is used if thereare more bays of the same kind.


220kV LINK BAY

REPORTSFUN. SIGNAL VALUE �NAME� AND CODE MS EPP

E A F CEL SLS SP CEL C

Feeder connect 02200 3 � � �c Feeder disconnect 02200 3 � � �o Feeder connect 02200 3 � � �m. Feeder disconnect 02200 3 � � �

Circuit Breaker connect 02200 3 � � �Circuit Breaker disconnect 02200 3 � � �

s Feeder connected 02200 4 � � � � �i Feeder disconnected 02200 4 � � � � �g. Feeder intermediate 02200 4 � � � � � � �

Feeder failure 02200 4 � � � � � � �t Feeder connected 02200 4 � � � � �o Feeder disconnected 02200 4 � � � � �p Feeder intermediate 02200 4 � � � � � � �o Feeder failure 02200 4 � � � � � � �l Circuit Breaker connected 02200 4 � � � � �o Circuit Breaker diconnected 02200 4 � � � � �g Circuit Breaker intermediate 02200 4 � � � � � � �y Circuit Breaker failure 02200 4 � � � � � � �

p s >I Protection connected � 02200 1 � � �r i >I Protection connected � � � �o g <I Protection diconnected � 02200 1 � � �t n <I Protection connected � � � �e a Busbar Protection diconnected � 02200 1 � � �c. l Busbar Protection diconnected � � � �

Circuit Breaker Air <16B � 02200 2 � �a s Circuit Breaker Air<16B � � �l i Circuit Breaker Air <14B � 02200 2 � �a g Circuit Breaker Air<14B � � �r n Circuit Breaker Air <11B � 02200 2 � �m a Circuit Breaker Air<11B � � �

l 220V � UP�SIG failure � 02200 2 � �220V � UP�SIG failure � � �

Table 2. Process signals characterized by their function �extracted from the signal base�.

� the second group �one digit�determines qual-ities of the signal �x dimension from themodel�, i. e. divides the signals by their func-tion. They can be: 1 – protection signals, 2– alarm signals, 3 – commands, 4 – state sig-nals, 5 – measuring signals, 6 – regulationsignals, 7 – other signals, 8 – group signals.

� the third group �composed of three digits�defines the signal value �z dimension fromthe model�.

3. Device-Based Process Signal Model

Our new approach to designing the process sig-nal base is based on the device as the maininformation bearing and organizational unit �3�,�6�, �9�. There are three steps in the design:

1. Signal structure systematization bydevicetypes �determination of signals generated orreceived by devices of particular type�


2. EPP analysis by means of the technologi-cal module �decomposition of an EPP intodisjunct modules and making associationsbetween devices and the modules�.

3. Determination of the signal usage �loca-tions of particular signal usage�.

With the new design approach, some new con-cepts necessary for the model description havecome up. The concepts �variable, variablevalue, signal by device type and signal by EPP�are described in the following sections �from3.1. to 3.3�.

3.1. Signal Structure Systematization byDevice Type

Signal structure systematization represents thecore of the EPPs process information model.The term signal structure systematization com-prehends �Figure 3�:

� identification of various device types,

� information analysis of the device types�identification variables and their possiblevalues�,

� definition of signal structure.

The device type identification points up andconsiders all devices in the EPPs which in anyway represent the signal source or sink, andwhich give us an insight into the state of thecontrolled process. A device can be observedas an abstraction of the technical device withoutregard to function of that technical device in theparticular EPP, but with regard to informationcharacteristics by which the EPP operation isdescribed. Devices are modeled regardless ofthe question whether they are used in several

different places in the EPP. Also, the operationfields of these devices have not been taken intoaccount. Such a model represents a device type.In Table 3, a part of device type list is presented.

Code Device Type1. feeder disconnector2. feeder MV disconnector

� � �7. circuit breaker SF68. oil breaker

� � �14. differential relay15. relay I> protection

� � �

Table 3. Device type list.

After the device types identification, variableswhich describe device operation have to be de-fined. In Figure 4 the device type and thevariables pertaining to this type are presented.The variable is a quantity that may assume anygiven value by which we can describe the de-vice operation in EPP. At a particular point oftime, a value is assigned to the variable and theytogether make up a signal. The device type isdetermined by at least one variable, but depend-ing on the operational complexity of the deviceit can have more than one.

Each variable is defined by at least two values.The device, i. e. the variable cannot be definedby only one variable value, because it meansthat the device doesn’t change its state. Thedevices, which do not change or cannot changetheir state do not have to be controlled. Vari-able values are given for the specific variable

Fig. 3. Signal structure systematization.


Fig. 4. The device type, its variables and variable values.

in operation. By them, the device states are de-fined. The variable can be described by two ormore values.

The arranged couple ��variable��variable val-ues�� form a signal. Thus, the signal is definedas a quantity made up of the variable name withvalues pertaining to it. Schematic presentationof a device type with associated signals is pre-sented in Figure 5. The group of signals repre-sents a static set of all possible signals by whichoperation of the device type is described.

Fig. 5.A schematic presentation of the device type withassociated signals.

An example of device types with associated sig-nals is presented in Table 4. The content of the

table is formed as follows:

� the first column of the table contains ordinalcodes of each device type, which can be usedin data processing;

� the second column of the table, contains thedevice type identification;

� the third column contains signals formed byvariable name and variable values.

From the list presented in Table 4, it is possi-ble to derive the set of static signals by devicetypes. An example of such a set of static signalsis presented in Figure 6.

The set of static signals per device types is cre-ated independently of any particular kind ofEPPs. So, its subsets could be applied to hydro-electric power plants, thermo-electric powerplants, transmission and distribution electricpower systems. Furthermore, signal structurecan be presented in a 3D coordinate system as avector according to Figure 7. Device types aremarked on the x axis, variable names on y andvariable values on the z axis.


Set of Signals by Device Types

signalscod device type variable name variable values

1 feeder disconnector feeder disconnector – command connectdisconnect

feeder disconnector connecteddisconnectedintermediate positionfailure

� � �

15 I> protection starting part of I> protection OKoperating

supply condition of I> protection OKloss

timing part of I> protection OKoperating

high current part of I> protection OKoperating

� � �

Table 4. Device types with associated signals.

By observing Figure 7. we can take into consid-eration the following organized sets of signals:

� Set of all process signals by device types SDis defined by points of the xyz space i. e. byexpression:

�2�SD � fσxyzg x � 1� 2� � � � � m

y � 1� 2� � � � � nz � 0� 1� � � � � r�

where σxyz presents the signal defined bydevice type, variable and variable values,where m is the number of device types, n is

Fig. 6.Part of the static signal set.

the number of variables and r is the numberof variable values of every existing variable.

� The set of signals of one device type is de-fined on yz-plane, i. e. by equation �2�, withx � cons.

� The set of signals of one variable is de-fined on xz-plane, i. e. by equation �2�, withy � cons.

� The points on the axis parallel with z rep-resent the signals of one variable and one

Fig. 7.Vector presentation of the device-based signals.


device type. The subset can also be definedby equation �2�, but with x � cons. andy � cons.

� Finally, the subset of points on the xy-planerepresent the set of all variables per devices.This variable set, each for itself defines onesignal and is presented by equation �2� withz � cons.

According to circumstances and application ofsuch amodel, one can define other characteristicsets of process signals. Comparing equation �2�and related equations with equation �1� and itsrelated equations, which are used in describingthe device-based and the function-based mod-els, the following may be concluded:

� Formally, the structural frame of expressionsof particular process signal sets i. e. sets SFTand SD is entirely analogue.

� In essence, SFT and SD sets represent com-pletely different process signal sets and en-able different approaches to process signaldesign.

� The SFT sets are strictly tied with the tech-nology of a particular EPP and cannot bedirectly applied to other EPPs.

� Device-based process signal setsSD are gene-ric �technology-independent� and open de-signed and they can be universally appliedto a great array of EPPs.

� Process signals of device-based design rep-resent technology-independent data base ofsignals which can be easily expanded withnew signals.

3.2. Technological Decomposition of an EPP

The first requirement in scope of informationmodeling is defining a device type model. Themodel is described in 3.1. The second require-ment is defining an EPP model. That modelshould allow unambiguous device identificationon the base of its location in EPP. In the model,device systematization by location follows tech-nological structure of an EPP.

Because even a small EPP is too complex a sys-tem to embrace its overall operation at once,internal functioning of its subsystems should bedescribed. Therefore, the model constructionbegins at the level of subsystems. Subsystems

have to be built according to the following prin-ciples:

� the borders between subsystems and ways oftheir interaction at these borders have to bedetermined;

� a subsystem has to be rather simple for theinternal operation description;

� subsystems mustn’t overlap;

� the whole modeled system has to be con-structed by combining all its subsystems.

To satisfy the condition that the subsystemsmustn’t overlap, we introduce the followingconcepts: technological unit, technological field,technological modules and technological sub-modules.

� Technological unit is a group of devices inthe EPP that performs some complex func-tion �command room, engine room�.

� Technological field is a part of a technolog-ical unit where voltage levels �400 kV, 220kV, 110 kV, 35 kV, etc.� are separated.

� Technological modules are made by sepa-rating the technological field by lines �220kV feeder bay Melina,� � � �. If necessary,technological submodules can be obtainedby further separating the technological mod-ule.

Fig. 8.Tehnological decomposition of an EPP.

Figure 8. illustrates division of one part of anEPP �a technological unit� into technologicalfields, technological modules and devices. De-termination of the technological fields i.e. mod-ules is a problem of EPP modeling. If chosen


technologicalmodules are too narrow, there willbe a great number of them, they will overlapand will not function as qualitative EPP model-ing. On the other hand, if chosen technologicalmodules are too wide, then it is possible that thesignal will not be precisely defined and located,especially if there are a number of devices of thesame type in one technological module. Even-tually, in such a situation we have to create new,smaller submodules within the very technolog-ical module which could enable unambiguousdefinition of signals.

Now, it is possible to explain the procedure forgenerating a set of static process signals for aparticular EPP. The signal set generating pro-cedure is based on the presented informationmodel of EPP and is supported by a computer.First, we have to identify the technologicalunits, fields and modules in the observed EPP.Then, we associate devices with those pertain-ing technological modules. When we associatedevices with technological modules, we actu-ally say that technological modules are “filledwith devices”. Table 5. presents the principle

how to associate devices to single technologicalmodules.

Because every device has its own type, signalsthat a device can send �receive� correspond tothe signals of that particular type. The proce-dure for generating a set of static signals perEPP is presented in Figure 9, and the printout ofthe set of signals per EPP is presented in Table6.

3.3. Signal Usage Location

After the set of static signals per EPP is gen-erated, signal usage location has to be deter-mined. If we consider, for instance, a hydro-electric power plant as an EPP, the plant wouldbe basically divided into the following techno-logical units: control room, engine room andwater power supply. Signal usage locationswithin a control room would be: control board�CB�, relay board �RB� and auxiliary switch-board �AS�. Signal usage locations in the en-gine room are: engine board �EB�, engine aux-iliary switchboard �EA�, actuator board �AB�,

code technological modules associated device �coded�

9 220 kV Feeder Bay Melina 1, 3, 7, 32, 33, 34, 36, 37, 38, 64, 74, 94, 97, 111, 123, 125

Table 5. The principle of association of the devices to technological modules.

Fig. 9. Procedure for generating set of static signals per EPP.


EPP SENJ 35 kV FB Senj feeder disconnector – command connectEPP SENJ 35 kV FB Senj feeder disconnector – command disconnectEPP SENJ 35 kV FB Senj feeder disconnector connectEPP SENJ 35 kV FB Senj feeder disconnector disconnectEPP SENJ 35 kV FB Senj feeder disconnector intermediate positionEPP SENJ 35 kV FB Senj feeder disconnector failureEPP SENJ 35 kV FB Rab feeder disconnector – command connectEPP SENJ 35 kV FB Rab feeder disconnector – command disconnectEPP SENJ 35 kV FB Rab feeder disconnector connectEPP SENJ 35 kV FB Rab feeder disconnector disconnectEPP SENJ 35 kV FB Rab feeder disconnector intermediate positionEPP SENJ 35 kV FB Rab feeder disconnector failureEPP SENJ 35 kV FB Senj I> protection starting OKEPP SENJ 35 kV FB Senj I> protection starting operatingEPP SENJ 35 kV FB Senj I> protection supply condition OKEPP SENJ 35 kV FB Senj I> protection supply condition operatingEPP SENJ 35 kV FB Senj I> protection timing OKEPP SENJ 35 kV FB Senj I> protection timing operatingEPP SENJ 35 kV FB Senj I> protection highcurrent OKEPP SENJ 35 kV FB Senj I> protection highcurrent operating

Table 6. Printout of the set of static signals.

and turbine engine splitting �TE�. In addition tothese usage locations, we have to point out tworemote signal usage locations: Regional Con-trol Center �RC� and National Control Center�NCC�. Table 6 shows EPP signals and theirusage locations. By defining Table 7, we havecompleted the EPP process signal designing.

At the end, it can be concluded that proposeddevice-based EPP modeling has to be done inthree phases:

� the result of the first phase is a generic set ofprocess signals per devices;

� the result of the second phase is concrete setof process signals at the EPP level;

� in the third phase, usage locations of everysingle signal should be determined.

EPP Signals EB EA AB TE CB AS RB oth RC NCC

EPP FB Senj 35kV feeder disconnector – state intermediate position � � �

EPP FB Senj 35kV feeder disconnector – state connected � � �

EPP FB Senj 35kV feeder disconnector – state disconnected � � �

EPP FB Senj 35kV feeder disconnector – state failure � � �

� � �

EPP Turbine 1 elektrovalve position cooling water operating � � � �

EPP Turbine 1 elektrovalve position cooling water restraint � � � �

� � �

EPP Generator 1 DC voltage ok � � �

EPP Generator 1 DC voltage loss � � �

� � �

Table 7. Presentation of one pattern of EPP signals per usage locations.


4. The Object-Oriented Characteristics ofDevice-Based Modeling

In the previous chapter, device-based informa-tion model of the EPP is described. The coreof the model are the devices arranged withintechnological EPP modules. The devices sendand receive various signals. Such modeling isbased on device abstractions and it can be ap-plied in information modeling of any type ofEPP. Functional modeling elaborated in Chap-ter 2 does not offer such flexibility.

In this chapter we want to underline and ex-plain one important characteristic of device-based modeling: modeling based on the de-vices in the very essence represents an objectoriented view of the EPP, i. e. its parts. Thefollowing describes how to supplement device-based model described in the previous chap-ter so as to become object model. Object-oriented modeling, nowadays, is considered tobe a very qualitative and effective approach tosystem modeling. Moreover, it is supported bymanymodeling languages and tools. Therefore,our effort to define principles for mapping thedevice-based model to the object-oriented oneis quite comprehensible �3�, �9�, �11�.

4.1. Analogy Between Device-Based andObject-Oriented Model

The object model is based on the followingconcepts: object, object type, attribute, signal,state, operation, and behavior �1�, �2�, �5�, �10�.Object is a concrete phenomenon of some ab-straction. It is a basic entity in the object modelwith good determined borders and identity. Theobject encapsulates state and behavior. It isalso an instance of some type of objects. In anEPP, devices represent sources of information.Some of them are also controllable elements inthe EPP and are responsible for some behavior.Consequently, the most important objects inobject-oriented information model of an EPPrepresent abstractions of real devices. Theseobjects represent abstractions of technical de-vices actually placed in an EPP.

Object identity can be defined by its locationin the EPP and following the technological de-composition described in 3.2. �Figure 8.�. For

example, object identifier which represents ab-straction of feeder disconnector �FD� connectedwith 110 kV busbar number 1 in feeder bayMelina of the hydro-electric power plant Senj,has the structure: HESenj.110kV.FBMelina.FD1.Generally, a device-representing object in EPPhas the identifier of the structure:EPP.VoltageLevelID.TechnologicalModulesID.DeviceID.

In a definitemoment of time an object is in a cer-tain state. During all its existence the object sat-isfies some conditions �feeder disconnector isconnected� performs some activity �feeder dis-connector is being connected� or expects someevent �feeder disconnector has just received thesignal Disconnect�. The object state is definedby momentary value of its state variables i. e.attributes. The object state depends also onthe state of some other object if the connec-tion between them exists. In the EPP, there isvery often an association between disconnectorand circuit breaker. Accordingly, apart from itsbasic states: Connected, Disconnected and In-termediate position and depending on the stateof associated breaker, the disconnector can alsobe in the state Blocked. For example, a simpleabstraction of the device feeder disconnectorcan result in an object type Feeder Disconnec-tor with one attribute: Position. The attributecan assume discrete values: Connected, Dis-connected and Intermediate.

Apart form being in some state, an object isresponsible for certain behavior. Behavior ofthe object is everything that can be registeredand is a result of some event �signal, elapseof time, change of state or a demand for a cer-tain operation�. Operation represents a serviceincorporated into the object. This service canbe required form the object of some specifictype by which a specific behavior is provoked.For example, we can require connection of theobjects of the Feeder Disconnector type by re-questing the operation Connect��.

In object-orientedmodel representing someEPP,the most frequent events are the object statechange and signal appearance. The appearance�sending� of the signal is therefore a sort ofevent. The signal is interchanged between theobjects, of which one represents sender of thesignals e. g. a device object, and the other rep-resents receiver of the signals e. g. usage lo-cation object. For example, the object of the


Fig. 10. Part of the state diagram of the Feeder Disconnector type.

Feeder Disconnector type can receive the sig-nal Disconnect from the controlling object. Acontrolling object is an abstraction of one partof the system to control the EPP. This signalwill provoke state change of the feeder discon-nector if it is in the state Connected. Havingchanged from the state Connected into Discon-nected, the feeder disconnector will send thestate change information signal to the control-ling object. This behavior can be illustratedby state diagram �Figure 10.a�. In an object-oriented model, even the signal is treated as theobject, the instance from the definite signal type�see Figure 10.b� which is mutually exchangedbetween object couple sender – receiver.

The concept object type represents a set of thesame sort of objects which share the same at-tributes, operations and associations with otherobjects.

Finally, analogy between the concepts of thedevice-based and object-oriented models of anEPP is illustrated in Table 8.

4.2. Object-Oriented Modeling Strategy

Basic steps toward object-oriented EPP model-ing are presented in Figure 11. The first step"finding of types and objects" is undertaken toidentify objects as technical device abstractionswhich preserve their characteristics of technicaldevices as such, regardless of their function inthe EPP, but with regard to information and pro-cess characteristics by which the EPP operationis described.

The second step is undertaken to identify struc-tures of the types: generalization – specializa-tion �G – S� Figure 12.a� and the type: whole –part �W – P�, Figure 12.b�.

Defining relevant attributes means identifica-tion of and giving names to relevant character-istics of devices. Attribute values depend on itstype. Attribute type in the model is specified

Device-based modeling concepts Object-oriented modeling concepts

device objectdevice type type

variable attributevariable values attribute values

signal per device signalsignal per EPP signaldevice state object statecommand operation

signal usage location signal receiver �object�

Table 8. Device-based modeling concepts and analog object-oriented modeling concepts.


Fig. 11. Object-oriented EPP modeling strategy.

by some standard notation system. Relevantoperations are the services offered by an objectto its environment. The focus is here on exter-nal methods perceptible to surrounding objectin the system. External operations representsignal specifications which can be directed tothe respective objects. For example, an objectof the type Feeder Disconnector can receive thefollowing signals:

HESenj.110kV.FBMelina.FD1.Connect

HESenj.110kV.FBMelina.FD1.Disconnect

State change signals transmitted to controllingobjects after the change of state, can be speci-fied in the context of the state diagram elabo-rated for each object type separately. In Figure10.a� only a part of the state diagram of the classFeeder Disconnector is shown. Complete statediagram should specify the minimum of threestate change signals:

HESenj.110kV.FBMelina.FD1.Connected

HESenj.110kV.FBMelina.FD1.Disconnected

HESenj.110kV.FBMelina.FD1.IntermediatePo-sition

The examples elaborated in this chapter have il-lustrated the most important aspects relevant forrelating the object modeling to the device-basedEPP process signal modeling strategy.

5. Conclusion

Efficient and high-quality designing of the EPPautomation and control systems was a real chal-lenge during the nineties and has been eversince. The problem of process signal base spec-ification is a significant design problem whichcan be resolved by using adequate informationmodeling technique. An efficient approach tothe EPP information modeling can significantly

Fig. 12. Generalization-specialization and whole-part structure.


improve the process of automation and devel-opment of the control system design.

Proposed device-based process signal model-ing offers a modular solution which enables ef-ficient, rational and open possibility to orga-nize a process signal base. The previously usedfunctional design has some specific limitations,because a model can be defined only for oneEPP and it cannot modularly and openly de-scribe a larger system with more than one EPP.The device is not separated as an informationbearing unit and device states cannot be de-fined for the needs of modern process signalsdesign. Redundancy of the data entry is sig-nificant. The device-based design of a processsignal base is, on the contrary,modular and openfor describing a large number of EPPs, whichis based on unique process signal base and itcan be efficiently supplemented accordingly tothe changes of primary process equipment. Itis based on the device as the main informationbearing and organizational unit. Besides themodularity, it can also be very easily mappedinto the modern object- oriented model. Thestrength of object-models opens entirely newpossibilities for EPP information modeling aswell as for improving automation and controlsystem design process.

Therefore, focus of the study will be on thefurther improvement of the described object-oriented modeling and also on development ofa tool for both EPP modeling and automaticprocess signal sets generating.

References

�1� G. BOOCH, ET AL., The Unified Modeling LanguageUser Guide, Addison-Wesley publishing company,Santa Clara, California, USA, 1998.

�2� G. BOOCH, Object – oriented analysis and de-sign with applications, Addison-Wesley publishingcompany, Santa Clara, California, USA, 1997.

�3� M. RANDIC, ET AL., Information Modeling ofPower Substations by Using Modeling Language,10th Mediterranean Electrotechnical ConferenceMELEKON 2000, Lemesos, Cyprus, 2000.

�4� J. SIMUNIC, ET AL., Object-oriented Approach toAnalysis in Power Substation Control, PSAC Sym-posium, Bled, Slovenia, October 1997.

�5� J. RUMBAUGH, ET AL., Object-Oriented Modelingand Design, Prentice-Hall, Inc., New Jersey, 1991.

�6� J. SIMUNIC, Z. DUROVIC, Basic Design of ProcessInformation Flow in Electric Power Substation,Korema, 37–39, Opatija, 1996.

�7� J. SIMUNIC, MSSI – Modular Structure of stochas-tic Process Information for Power System Control,CIT, 4(3), �1978�, 279–290.

�8� J. SIMUNIC, Electric Power System Analysis Us-ing Modular Information Structure, Energija, 1–2,�1994�, 39–51

�9� J. SIMUNIC, ET AL., Object-oriented InformationModeling of Power Substations, Daaam, 22–24thOctober, Cluj – Napoca, Romania, 1998.

�10� B. F. WEBSTER, Pitfals of Object-Oriented Devel-opment, M&T Books, New York, 1995.

Received: May, 1999Revised: November, 2000Accepted: February, 2001

Contact address:

Marijana ZivicYoung assistant

Technical facultyUniversity of Rijeka

Vukovarska 5851000 Rijeka

CroatiaPhone: �385 51 651438

Fax: �385 51 675818e-mail: marijana�zivic�rijeka�riteh�hr

JURAJ SIMUNIC is Assistant Professor at the Technical Faculty, Univer-sity of Rijeka. For seventeen years he has been working for “Hrvatskaelektroprivreda” as an expert in planning, operation and control of powersystem. He concentrates on modeling of stochastic process informationflow in power systems. This was the subject of his doctoral thesis uponwhich he received his Ph. D. in 1991. from the Faculty of ElectricalEngineering and Computing, University of Zagreb.

MIRKO RANDIC was born in Croatia in 1962. He received the M. S.and Ph. D. degrees �both in Electrical Engineering� from the Faculty ofelectrical engineering and Computing, University of Zagreb. Currentlyhe is Assistant at the same faculty �Department of Electrical Fundamen-tals and Measurement�. His research interests include object-orientedmodeling, formal specification techniques and ORB-centric softwaremodeling.

MARIJANA ZIVIC was born in Slavonski Brod in 1972. She received herB. Sc. degree in electrical engineering from the Faculty of ElectricalEngineering and Computing, University of Zagreb in 1996. In the sameyear she became a staff member of the Technical Faculty, University ofRijeka as a younger assistant. Her present research interests focus onthe signal processing.

a device-based process signal design of electric power plants

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