Models of Objects of Control in SCADA System for Monitoring and Operational Dispatching in Sofia Metropolitan

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1 Models of Objects of Control n SCADA System for Montorng and Operatonal Dspatchng n Sofa Metropoltan Key Words: SCADA (Supervsory Control and Data Acquston systems); metropoltan; modelng. Abstract. Supervsory Control and Data Acquston systems (SCADA) are often used n some mportant ndustry sectors, such as producton and dstrbuton of electrcty, transport management, etc. The purpose of ths paper s to establsh models of SCADA system, DISIM that s ncorporated nto the Central Dspatchng Staton of Sofa Metropoltan. Its functons are related to remote vsualzaton and management of the structures and devces n both drectons Trans operaton (DISIM-V) and Power transmsson system (DISIM-Å). The suggested structural models and mathematcal descrpton are used as a bass for realzaton of a smulator of both SCADA systems. 1. Introducton The purpose of SCADA systems s centralzed data acquston of remote geographcal stes, nformaton processng and vsualzaton and generaton of manageral mpacts. The correct and relable functonng of a SCADA system s crucal for the functonng of the whole system [1,11]. The pont of the management s that these complcated techncal systems mplement an objectve functon when the external condtons are changed wthn fxed lmts: ther behavor s set up, dependng on the assessment of the external stuaton under a defnte crteron n complance wth the fxed purpose. Therefore, the management s a process of formng the most effcent behavour of the system, amng at mplementaton of the apponted functons. The means for realzaton of the management are the control unts (where decson makng s accomplshed) and the actuators (whch convert the nformaton about the adopted decsons nto actons, drected towards achevement of the management purposes). The followng processes could be added to the more mportant and basc technologcal ones, subject to management n the metropoltan: Operaton of underground trans. Unnterruptable power supply of the rollng stock and many other consumers of electrc power (for ther own needs). Dfferent engneerng santary and techncal structures (escalators, pumps, fans, heatng and lghtnng). Ensurng a possblty for local management of the trans n the regon of each staton. Gvng nformaton to the passengers for the remanng tme untl the arrval of the followng tran, etc. The great complexty of these processes s determned Prnt ISSN: ; Onlne ISSN: DOI: /tc E. Dmtrova by the fact that each one s dstrbuted n all statons on the terrtory of the metro and the management has to cover all these parts. In ths sense the metropoltan represents a typcal non-concentrated object. It s known that many specal requrements for automatc control of such objects ndependently of the manufacturng ndustry are presented [3]. The complexty of the processes n a metropoltan s growng because of the management needs to ensure safe transport, accordng to strct European standards. The SCADA system DISIM s mplemented n Sofa Metropoltan. It s a complex structure of techncal, software and organzatonal resources related to certan rules, provdng control and operatng on the tran traffc processes and power supply of the electrcal equpment. Its purpose s to montor and drectly automatcally control the processes and foremost, to ensure the passengers safety. In general, the control s performed automatcally, whle operatng s done ether automatcally or through operator commands submtted by the dspatchers of the Central Dspatcher Post (CDP). Ths SCADA system conssts of several ndependent systems, the most mportant of whch are DISIM-V for dspatchng of the tran traffc and DISIM-E for montorng of the tracton substatons and electrcal equpment [8,9]. The am of ths paper s the establshment of structural models and mathematcal descrpton of processes at the object levels of SCADA systems, DISIM-V and DISIM- E. The suggested models could be used as a bass for elaboraton of a smulator of both SCADA systems. 2. Structural Model of a System for Montorng and Control of Sofa Metropoltan Each SCADA system conssts of three formal levels [1,6]: Upper (Dspatchng) level, Communcaton level, Lower (Objec level. The overall structural model of the object level of DISIM-V system for dspatchng of the tran traffc s shown n fgure 1. The trans operaton n the metropoltan s marked as an object of control. The object adopted n ths manner ncludes: all the trans stuated along the route at a fxed moment, the elements of the ralway track, the sgnalng devces. The rght nteracton between the trans and the elements of the ralway track has to ensure runnng of the techncal process under the gven algorthm, n ths case the actual tmetable of the trans nformaton technologes Unauthentcated

2 dsturbances q Tran traffc u 1 u 2 u m o 1 o 2.. Object.. o n v 1 v 2 v r Observance of the schedule communcaton channel a1 a 2 a m s r s 2 s 1 vsualzaton schedule y m y 2 y 1 Control Unt (regulators) w r w 2 w 1 F Fgure 1. A structural model of the object level of a system for dspatchng of the tran traffc operaton for a fxed perod. Normally, dfferent dsturbng mpacts (damages of the rollng stock or the ralway track, ncorrect actons of the operatonal staff, etc.) could nfluence the process passng. In most of the cases the dsturbng actons represent a reason for dsco-ordnaton of the system ext. Each dsco-ordnaton,.e. dvergence from the tmetable, has to be consdered a warnng for generaton of a sutable management decson. All the trans operatng along the secton represent the system entrance. The system ext s the real mplementaton of the traffc tmetable and the data reflectng the status of the dfferent ralway track elements. The nformaton about the moment locaton of the trans s receved from sensors s (=1,, p, where p s the number of the track crcuts, mounted along the secton). The rest part of sensors s j (j=p+1,, r) are stuated n the sgnalng devces, ponts and other elements of the ralway track. The actuators a 1,..., a m are used for realzaton of swtchng of traffc lghts, ponts, etc. The overall structural model of the object level of DISIM-E system for montorng of the tracton substatons and electrcal equpment, s shown n fgure 2. In ths case the object for management ncludes all man physcal objects subjected to control and management by the system: a complex swtchgear (a dsconnector and a three-postonal swtchgear) 10 kv; a tracton transformer 10 kv/825 V; tracton rectfers; a transformer 10 kv/0.4 kv; a swtchgear 825 V; a dsconnector 825 V; a dsconnector 0.4 kv; charger devces and accumulator batteres. Most of the sensors and actuators are embedded n multfuncton protecton relays mounted on swtchgears, transformers and other devces. These physcal objects are stuated around the whole layout of the metropoltan n many tracton substatons. The data for the normal state of these objects s embedded n the control unt memory. In contrast to DISIM-V system, a fxed number of programmes, correspondng to the system reacton n case of certan events, needs to be ncluded n the managng devce. These programmes defne an algorthm of swtchng over the object after assessment of the partcular stuaton. The vsualzaton of the object status s envsaged n both models. It ensures montorng by the dspatchers n the Central Dspatchng Post (CDP) and by the traffc manager on duty n the respectve metro staton (only for DISIM-V). In both models the object of control conssts of n subsystems (o 1,..., o n ). It has m nputs of enterng nput effects [ u () t,..., um() t ] U 1 and r outputs, whch are obtaned respectvely by the output sgnals of the system [ v1 () t,..., vr () t ] V. These sgnals are fed to the control unt by r number of sensors (s 1,..., s r ) [3]. The control unt has a correspondng number of r nformaton technologes Unauthentcated

3 power supply 10 kvac u 1 u 2 u m dsturbances o 1 o 2 a1 a 2 a m s r s 2 s1 q Object.... communcaton channel o n v 1 v 2 v r unnterruptble power supply 825 VDC and 400 VAC vsualzaton Programs (algorthms) y m y 2 y 1 Control Unt (regulators) F w r w 2 w 1 Data for normal state of the objects Fgure 2. A structural model of the object level of a system for montorng of the tracton substatons and electrcal equpment nputs (w 1,..., w r ) and m outputs (y 1,, y m ). The control system affects on the object by m actuators (a 1,..., a m ). The techncal state X of the object of control s defned on the bass of the nformaton receved from the sensors and after computng operatons. It can be nterpreted as a techncal grade of state G, whch corresponds to a response of the control system. Each state x of -th subsystem, [ 1,n ] ts current state. Thus [ x () t,..., xn () t ] X, expresses 1 expresses the current state of the object of control. The transton of a subsystem from one state x ( t 1 ) to another ( ) t 2 x at t 2 > t1 determnes ts dynamcs. It may be a result of the acton of external control sgnals or due to nternal dsturbances. If at ntal tme t 0 the subsystem s n a state x ( t 0 ) X 0 and there are no dsturbances, then the change of ts state s descrbed by the equaton: (1) x () t F[ t, t x ( t )] = 0, 0, where F s an objectve functon. If the change n the state of the system s due to the acton of an external sgnal, the changes n the state are descrbed by the equaton (2) x () t = F[ t, t0, x ( t0 ), u() t ], where n the output sgnal s formed by (3) v( = F[t, x (, u(]. The dynamc model G p of the object of control of the structures shown n fgures 1 and 2 may be expressed n the form x ( = Ap. x( + B p. u( (4) v( = C p. x( where x(, u(, v( and matrces wth constant coeffcents A p, B p and C p are the relevant dmenson. The control unt s a specalzed computng system and t operates n dscrete tme wth a samplng perod T. The Programmable Logc Controllers (PLC) are wdely used as control unts n the contemporary systems for montorng of complex techncal objects [2]. They offer hgh level of performance n the executon of the control program set n a mcroprocessor. They are also equpped wth a large number of dgtal and analog nputs and outputs, whch can be ncreased by ncludng addtonal expanson modules. PLC can be connected to a network and work as master or slave devces, and offer the ablty to transmt data at hgh speed (12 Mbps) nformaton technologes Unauthentcated

4 The techncal state Z(ê) of the control unt at the sample tme kt can be expressed as a functon of the techncal state Z(ê-1) n the prevew sample tme and nformaton receved about ts nputs. Thus the dynamc model G c of the control unt n the sample tme kt can be expressed by the followng equaton: Z( = D. Z( k 1) + E. w( (5) y( = G. Z( + H. w( where z( = z(kt), w( = w(kt), y( = y(kt) and matrces D, E, G and H are the relevant dmenson. Each of these matrces conssts of not only constant coeffcents, but of regulators, assocated to the approprate nput sgnal as well. A programmed PID (Proportonal-Integral-Dervatve) regulator allows the process control to accurately mantan the setpont by adjustng the control outputs. PID can be used to obtan a fast response to a dsturbance appearance. In steady state operaton, t regulates the value of the output so as to drve the error e to zero. A measure of the error s gven by the dfference between the setpont (the desred operatng pont of the approprate sub-object of control) and the process varable (the actual operatng pont calculated on the bass of the receved nformaton). The prncple of PID control s based upon the followng equaton that expresses the output, y, as a functon of a proportonal term, an ntegral term, and a dfferental term: t (6) де y ( = K. e + K. e. dt + y0 + K. дt 0 where: y ( s the -th output as a functon of tme ( = 1,, m); K s the loop gan of the approprate regulator; e s the loop error (the dfference between the setpont and the process varable); y 0 s the ntal value of -th output. In order to mplement ths control functon n a dgtal descrpton, the contnuous functon must be quantzed nto perodc samples of the error value wth subsequent calculaton of the output [2]. The correspondng equaton, whch s the bass for the soluton of the dgtal algorthm s: (7) y ( = K * e ( + KI * e ( j) + y0 + KD *[ e ( e ( k 1)] j= 1 where: y ( s the calculated value of -th output at sample tme k; e ( s the value of the loop error of the approprate regulator at sample tme k; e (k-1) s the prevous value of the loop error (at sample tme k-1) e (j) s the value of the loop error at sample tme j; K I s the proportonal constant of the ntegral term of -th output sgnal T (8) K I = K *. TI T s the sample tme (ths s the cycle tme, at whch the processor recalculates the output values); k T I s the ntegraton perod of -th output (also called the ntegral tme or rese; K D s the proportonal constant of the dfferental term of the -th output sgnal. TD (9) K D = K * ; T T D s the dfferentaton perod of -th output (also called the dervatve tme or rate). The dfferental term s proportonal to the change n the error. As a result of the repettve nature of the dgtal algorthm soluton, a smplfcaton n Equaton (7), whch must be solved at any sample tme, can be made. The smplfed equaton s: (10) y ( = K * e ( + K * e ( + Y ( k 1) + K *[ e ( e ( k 1)] where: Y (k-1) s the value of the ntegral term at sample tme k-1 (also called the ntegral sum or the bas): (11) Y ( k 1) = K * e + y. I I k 1 j= 1 The bas s the runnng sum of all prevous values of the ntegral term. Several constants are also a part of the ntegral term, the gan (K ), the sample tme (T) and the ntegral tme or reset (T I ), whch s the tme used to control the nfluence of the ntegral term n the output calculaton. In many control systems, t mght be necessary to employ only one or two methods of loop control. Settng the value of the constant parameters makes the selecton of the loop control type desred. If the dervatve acton s not requred and PI regulator may be used, then a value of 0.0 should be specfed for the dervatve tme T D. If the ntegral acton s also not requred, then a value of nfnty INF should be specfed for the ntegral tme T I. Even wth no ntegral acton, the value of the ntegral term mght not be zero, due to the ntal value of the ntegral sum y 0. Then the proportonng control contnuously adjusts the output dependng on the relatve values of the process varable and the setpont. Many control desgns ncorporate the offset as a dgtal programmable value that allows redefnng of the output requrement at the setpont. A proportonng control wthout an offset wll settle out somewhere wthn the proportonng band, but lkely not on the setpont. The offset may be used n conjuncton wth the Integral tme (rese that allows the qucker settlng at the setpont. Reset redefnes the output requrements at the setpont untl the process varable and the setpont are equal. Most of the objects of control n SCADA systems - DISIM-V and DISIM-E are slowly actng ther reactons have low repeatable frequency. In ths case there s no need to use more complcated regulators than P regulators. PID functons allow the precse control of dffcult processes (for example, control of the voltage, current, temperature, postonng of the actuators, etc.). The rate (Dervatve tme) s actvated at a slope change of the error. Its effect apples the brakes n an attempt to prevent the j 0 D nformaton technologes Unauthentcated

5 overshoot (or undershoo on process upsets or startup. The process varable can be controlled wthout oscllatons around the setpont. The communcatonal level for both systems s constructed n complance wth the prncple of the Optcal Open Transport Network (OTN). Ths s a dgtal communcaton network for real-tme and msson-crtcal applcatons [4,7,10]. Bascally, OTN s a communcaton backbone bult up by nodes whch are nterconnected by a double optcal fber rng. Because of the double rng structure, OTN guarantees an unparalleled degree of relablty. In case one fber rng or node fals because of any reason (fre, rupture, etc.), then the other rngs and nodes take over mmedately, thus keepng the whole network operatonal around the clock. The system wll always fnd a way around any problem wthout affectng ts users. The OTN nodes offer also redundancy of the man components, such as power supples, common logc cards and optcal modules. OTN allocates a dedcated amount of bandwdth to each applcaton. Each applcaton has ts own lane or layer n the fber tunnel, wth guaranteed bandwdth. Ths allows all applcatons the to run smoothly on OTN, not nterferng wth each other. An OTN network s often applcable for extended transport envronments, such as tunnels, ralways, subways, etc. All exstng applcatons are lnked by a fully transparent manner. Ths network s Open because t transfers all avalable communcaton applcatons, provdes Accdent Preventon and lmtng applcatons, ncludes Interface cards for voce, data, dgtal vdeo and Ethernet. Transport means secure transmsson wth complete transparency, mnmal delays and retenton of the orgnal protocols. Ths Work network s based on fber optc technology over almost unlmted dstances. The dspatcher level realzes the logc functons n accordance wth the requrements of the technology for tran traffc, passengers safety, and montorng of the electrcal equpment. Ths process ncludes also functons of dsplayng the nformaton and human-system dalogue (dsplayng the track development, sgnals status, locaton and movement of the trans at any tme, status of all electrcal equpments n the substaton, etc.), as well as workng-out and startng-up commands. Ths level conssts of functonal modules representng these functons and an approprate one or more wndows, by whch the Dspatcher communcates wth the system. The functons of ths level are fully descrbed n [1,5,12 and 13]. 3. Conclusons The structural and functonal models developed n ths paper are the bass for elaboraton of an mtaton model of the system for montorng and management of the processes n a metropoltan. Such a model has been syntheszed and a smulator of SCADA systems, DISIM-V and DISIM-E has been structured at Todor Kableshkov Unversty of Transport. The mtaton models of the object levels of both systems have been nstalled on a server usng specal software. The dspatcher level has been nstalled on fve computers that use the server for communcatons wth the objects. Opportuntes for smulaton of dfferent real workng modes of both systems have been created. The traners would be capable to approach n depth the essence of the contemporary SCADA technologes adopted to be the man and ncreasngly perspectve method for automatc management of complcated dynamc processes n crucal and crtcal felds n terms of safety and relablty. A comprehensve survey of the contemporary, modern and effectve SCADA system DISIM s not possble, due to the specal workng mode and admsson n the metropoltan. Thus, the avalablty of such a system model s extremely useful for personnel tranng and t s ncreasng the qualfcaton of the operatonal specalsts n the metropoltan, electrcty dstrbuton companes and ralway nfrastructure. Many examnatons on ths smulator have been carred out and ts proper work has been verfed [5,12 and 13]. Thus an expermental verfcaton of the models developed s done. References 1. Goranov, E., E. Dmtrova. Remote Control Systems and Management n Transport. Manual, Todor Kableshkov Unversty of Transport, Sofa, n bulgaran. 2. Dmtrov, V. D. Indrect Identfcaton of the Dsturbances by Programmable Logc Controller Smatc S Proceedngs of XLVI Internatonal Scentfc Conference on Informaton, Communcaton and Energy Systems and Technologes, ICEST 2011, Ns, Serba, 29 June 1 July 2011, ISBN , III, Baranov, L. Models of Automatc Control Systems. Moscow, MIIT, ISBN , Stouffer, K., J. Falco, K. Kent. Gude to Supervsory Control and Data Acquston (SCADA), and Industral Control Systems Securty. Natonal Insttute of Standards and Technology, Gathersburg, Dmtrova, E. Laboratory SCADA System for Control on Ralway Traffc. XLVIII Internatonal Scentfc Conference on Informaton, Communcaton and Energy Systems and Technologes ICEST 2013, Proceedng of Papers, 2, Sokolov, B. V. Optmal Structure Reconfguraton n a Complex Techncal Systems (CTS): Prncples, Models, Methods and Algorthms for the CTS Structure Dynamcs Control, VI ISTC, Moscow, Clarke, G., D. Reynders, E. Wrght. Practcal Modern SCADA Protocols. Newness, ISBN: , Techncal Documentaton of SCADA-system DISIM-V Techncal Documentaton of SCADA-system DISIM-E OTN Systems Dedcated Networks for Crtcal Envronments. Avalable on Remote Power Management Systems, Tahoe. Avalable at Dmtrova, E. Smulator of SCADA System for Remote Control of Electrcal Equpment. Annual Book of the Techncal Unversty Sofa, 63, 2013, No. 5/6, , ISSN Dmtrova, E., V. Dmtrov. SCADA System for Control of Ralway Traffc Laboratory Smulator. Scentfc Works of the nformaton technologes Unauthentcated

6 Unversty of Ruse, 52, 2013, seres 3.2, 91-95, ISSN McCrady, S. G. Desgnng SCADA Applcaton Software a Practcal Approach. Elsever Inc., ISBN , Baley, D, E. Wrght. Practcal SCADA for Industry. Newness, ISBN: , Strauss, C. Practcal Electrcal Network Automaton and Communcaton Systems. Newness, ISBN: , Manuscrpt receved on Emlya Dmtrova was born n Sofa. She receved the M.Sc. degree n Telecommuncatons and Sgnallng from the Hgher School of Transport Todor Kableshkov Sofa. Snce 2003 she s a Lecturer n the Department of Telecommuncatons and Sgnallng at Todor Kableshkov Unversty of Transport Sofa. Currently, she s an Assstant Professor and Ph.D. student. Her research nterests are n feld of contemporary SCADA systems for automatc montorng and management of complex techncal objects n dfferent sectors of the economy. Her man researches are amed at modelng, smulaton and optmal control of processes n power supply and transport. Contacts: Todor Kableshkov Unversty of Transport Sofa Faculty of Telecommuncatons and Electrcal Equpment n Transport 158, Geo Mlev St., 1574 Sofa e-mal: edmtrova@btex.bg nformaton technologes Unauthentcated