‘Tranemission ‘substation Transmission Distribution Distribution ‘substation Residential ‘Commercial Industrial Figure 1.1 Basic struccure of a power system, ial and residential loads are distributed equal, *0 form a balanced system. The structure of the Power system is choy. berween the three phases so as in Fig. 1.1 The transmission ‘stem ineerconnects all major generating stations, Normally,1.2) Operating States ofa Power System RESTORATIVE STATE E, | ALeATSTATE 1 |__ INSECURE! Preventive control NORMAL STATE E! ‘SECURE Economie dispatch and load tracking Resynchronization EMERGENCY STATE €,T IN EXTREMIS STATE E,T Protect equipment reduce losees Emergency contol ‘System disintegrated E = Equality constraints ‘System siilintact 1 = Inequality constraints ‘T= Inequality constraints Not satisfied Equality constraints not satisfied Figure 1.2 Operating states of a power system. different operating parameters, such as voltage, generation limits, currents, etc. The system states are classi- fied as follows: 1. Normal operating state: In this state, the equality constraints (B) and inequality constraints (I) are both satisfied. The generation is adequate to meet the demand, without any equipment being overloaded. Further, the reserve margins are sufficient to provide security for normal stresses 2, Alert state: In this state also, the equality and inequality constraints are satisfied. However, the reserve margins are reduced. Therefore, there is a possibility that some inequality constraints (limits on equipment) may be violated in the event of disturbances. Preventive control will lead the system from. the alert state to the normal state. 3. Emergency state: Due to severe disturbances, the system may enter an emergency state. This could be because of imbalance between generation and loads, either at the system level or at the local level. This could also be because of instability due to energy built-up in the system after a fault. Some strong control measures, such as direct or indirect load shedding, generation shedding, shunt capacitor or reactor switching, nework. splicing, called emergency control measures are to be taken. If these measures are not taken on time, the system stability may be under threat and the system may eventually break down and go to the In Extremis state. In extremis state: In this state, both the equality and the inequality constraints are violated. The viola- tion of the equality constraints implies that the generation and the load demand do not match. This means that some part of the system load is lost. Emergency measures must be taken to prevent a total gtid collapse. Restorative state: This is a transitional state, where the inequality constraints are satisfied by the emer- gency control actions taken, but the system has still not come to normalcy in terms of the equality con- traints. We can have a transition either to the alert state or to the normal state.Supervisory Control and Data Acquisition Ake; ect a careful Study of the - Dee ‘chapter, you would be able to understand: eee oF SCADA. * User interface. * Diffrencanchoe SCADA. * Guidelines for installation, . SCADA, ‘ectutes to implement * Constraints in application, Configuration of SCADA, + Sccurity and risk. Intro, az ‘ient informati fem ina safe and secu aa ve manner. This chapter deals with SCADA ¢ el Let us see what cach term in SCADA maa ‘ioe eae 12.1.1 Supervisory Control System i specific device to make idperform in accordance with a directed action. Some typical supervisory systems used in power systems are: TY SCADA: A SCADA system performs traditional operations of data acquisition and control functions, including a limited amount of record keeping and data reporting, 2 SCADA/AGC: It is similar to SCADA, except that AGC capabilities are included to calculate the afea control error, monitor system frequency and tie-line interchanges, dispatch. and. perform economic(Chaprer 12 sory Control and Data ent systems incorporate all features of SCADA and also includes other + ine rch kad oe oe elecoan mancgpmcy aula ieee teed Taeecn ieee y jeant to monitor and control distrib . DMS: Distribution management systems are mea " PDMS Gag ues topelogy analy a load Aa proginid AAT coed roration of services. IMs ro manage the peak load and is useful for de 5. LMS: Load management system is meant to managi agement. It can be a stand-alone program or integrated into EMS or DMS, 6 AMR; Automatic meter reading is incorporated into LM systems. computa. abilities of ution feeder loads ion of problems ang -mand-side man. 12.1.2 Telemetry Telemetry refers to the technique used in transmitting and receiving ‘Typical dara in a power system are the measurements information is transmitted over a medium, such as cal come from multiple locations. information or data over a medium, of voltage, power flows, circuit breaker status, ete. The ble, telephone, internet or radio. The information erg 12.1.3 Data Acquisition lephone, radio, ed 0 tell the system what to monitor, Bes, when to initiate alarms, controls, et. Further the system may consist of IEDs) that are smart sensors, what are the operating ran, intelligent electronic devices (I at times combinin,Sof SCADA System, = l = Figure 12.1 1 General §CAD, SCADA configuration control settings if necessary, should an emergency arise. T information, etc. ‘The major components of a SCADA system are thus clasifi are thus clasified as: and permits the find permits the opettor wove any atom HMI is also responsible for displays, epor, hao aloes , historical information, aus 1. Field instrumentation, 2. Remote stations, 3. Communication network, BS Central monitoring station and 5, Sofeware. 12.2.1 Field Instrumentation This refers to all the sensors and actuators that are anverfaced directly to the equipment. They generate the - igs are conditioned “analog and digital signals that are monitored ee compatible with che RTU/PLC ax che Fndustry values like 0-5 Vs 0-10 V, 0-20 mA, ete. Digit the equipment like On-OFF Full-Empry, Open-Closed, etc, 42.2.2 Remote Station entation connect. she Pa ‘i jnstrumé ae to the remote station to al Joubsetion/equipment whichis being, monitored and! 8, lo manipulaion a a remate site, The remote ston ma incerfaced ae ALC, The RTU isa compute vith good interfacing for communication ‘and flexible pro- bean Rey. The PLC used mostly in industries, Iehas very good programmability geamamabili and radio units for use with SCADA systems have extensi ‘communication features{Chaper12 Supervisory Consol and Data Acsitog Antenna Radio transmit | reciever [Power ] ["Genrat ] |[Voutte]/ Non )] fAnaioa] [Anata] [Dictal] [Digta: $e | [pcceesa] |fromony|voatie|| | nut | [ouret| | nee | [ouput se | | ‘nit smory|| module] |module| module| \module! | | l JL J L ‘Serial comms ports | (RS-292 / RS-422 / RS-485) Optional tone il Programmable logic controller CI J Spare RS-232 port Figure 12.2 RTU unit. 12.2.3 Communication Network {his refers othe communication equipment needed to transfer data to and from diferent ses, Commonly uted communication media are RS-232/RS-442/RS-485, dial-up telephone lines or dedicated landline, icrowave, sarelte,X.25 packet protocols and radio vi trunked/VHE/UHR, Cables are normally used in factories and are not practical for systems spread over wide geographical areas due to the high cost of cables. ‘The use of radio lines is common, Dial-up telephone lines are used for connecting remote ations cononny, cally. This is shown in Fig. 12.3 RTU = GS _« Figure 12.3 Use of telephone lines for communication,wpents of SCADA System __. ae + 467 Ethernet ison the rise since iis very cheap, spam eH mamniaion ifr esc or server-server communication. In general thi sis and uses the standard TCP/IP protaua. A server OWNS nu vie st wublish-sul Si hi thed by a client, and when this paramet Parameter changes, the information is communicated to the Fer subsoil ipserber client devices is d _ nccess #0 FemOne lone through a polling sys 2 ng em the data servers poll the controllers at a dened iret an interrupt system. In the Bh. Fecccclee at a defined polling rate which could be diffe & ae ke, eee: ae f AER by sending parameters to the ee aa s will have a unique aramé - ay pus, Worldip, ersision Conve voltage and SVC current are used as estat Gain reduction is donc in the case ‘ofthe function jrator produces the rin, er ofa aaa ink Pues forthe individual hyitor valves ofthe TCR. Ai ssion line can double the maximum power transferred through $205 capacitors are used to increase the contro Sere er ote atthe SVC vor une flags eleceae ree ee seat drawn oF supplcd wo the sytem, We can ony hak ans wee nl icato maintain the bus voltage nearly a constane ry that it acts as a variable reactive load, which is 9.4. STATCOM (COM is an acronym for a static synch cor is onous compensator, It is an advanced SVC where a volta wverter (VSC) is used instead of the passive elements used in a conventional SVC. Thc TAT source c0M) ‘fiers over conventional SVC are: 4, Faster response. +2, Occupies less space as bulky passive elements are not used. 43, Modiulat. 4, Can be interfaced with real power sources. §, Better performance under low voltage condition. “The basic scheme for the STATCOM is shown in Fig. 8.27. The DC voltage of the capacitor is converted to a set of controllable three-phases voltages at system fequency. Each output voltage is connected to the corresponding AC system voltage via a coupling trans- former, By varying the amplitude of the output voltages, the reactive power exchange between the converte and the ac power system can be controlled, a in a synchronous condenser. If V> V, the converter draws 1s like an inductor. If V< V,, the converter generates reactive tractive power from the bus. In essence, it at Veve ile |e a ve power (i increas is jynamical or che SV Figure 8.26 Switched capacitors.“x Transformer reactance Figure 8.27 STATCOM. V reactive power exchange is ero. The pe STATCOM are Bere cours, Wan compared toa synchronous condensct, ies rponss is Reser and ddan ae dant aychroni. The basic VSC ccui used in SATCOM is shown in Fg, 8.28, bi peep mt) TOBL or IGCTs are used, The steady-state control characteristic is shown in Fig, 8.29, The limits on the capacitive and inductive currents are symmetric. ‘The reference voltage cory cera catrent output. The STATCOM is operated close to zero output under normal operating, ~— nic thae full dynamic range is available during contingencies. power: itis capacitive. If V= ons ee pee HY Bh be ae a Figure 8.28 A six-pulse VSC circuit, VermrcomSunable-y pas atixea capacitor and a ine co be compensated h pac! at roller can be designed to control I ceased aeeraese Tein ination he fal inst In pre us the required compensation. wer How through " Static Synchronous Series Compensator 6 ion. The TCS he line, damp oscillations source converter based ser compensator (SSSC) is voltage-source co sed setcs cy a eee area of ic nial ar sees cepacnge PM, poorer and hence tansmived power by ca Ma the corresponding line current. : meee ane fe ine In an SSS lage ores concede “ns * theline cSt age "Pha, the series eapacitors to provide the required omen Tei HX Me degree of, is OMB San | 8.9.1 Seatie Synchronous posed by Gru Sa de physi ime er ee : Bee din he rcecofvantog line eure THe See saan current by 90°, In an SSSC, the Output te isshown in Fig, 832. ccan be reversed to make it lag or lead the line current by 90° ‘The transmitted power is given by i Sox The implication of Eq. (8.35) is that the SSSC can decrease as well as increase the power low mp ‘ Mpensated line jected voltage is made larger than the line drop of the uno, can be reversed. Further, the SSSC operates ar « selected 6 v sind + EV, cos degree. Further, ifthe inj line current and power flow directio and hence does not cause SSR. 8.9.7 Unified Power Flow Controller time control of AC transmission system Wi This concept was also proposed by Gyugyi in 1991 for real- multi-functions, By concept, the UPEC can simultaneously control all the Parameters that affect the Powe, Figure 8.32 Static synchrono * Series compensator: (a) Voltage injection and (b) injected voltage, @) Voltage inj. and (b) injController Fig 7 igure 8.33 Implementation of UPEC. jaa transmission line, namely voltage, i nalblock diagram ofthe UPFC isshows ng yh ame Hen, The UPFC consists of two back-to-back VSCs, optite “lage V, with concrollable magnitude and phase angio sare cae ik Comer? injec 2 injected voltage can be viewed as asynchronous acveluge oure trae eae ies calrmet Bae srelicicive power cachange, Convener Feapphat ce wee te ne cae, -convetter ae [ZMak a6 ippoke tie eal power nae s a the a power demand by . Ficic a I lang -sulting from the series v« injec- fon Inaddion, fecan also generate or absorb race power, an provide ndepenteneshune noes tion ike a STATCOM. To understand the function of the UPFC, the phasor V,. can be spilt into three components such that the name, “Unified,” The an aVivtYe 636) sabi? 1. AVis the component injected in phase with the terminal voltage. Hence, itchanges the magnitude ofthe terminal voltage and performs voltage regulation. 2, Viste component injected in quadraure tothe line curent Land hencss similar toa seties capacitive or inductive compensation. D _ Vis the component injected at an angle oto the terminal voltage and achieves the desired phase shift ichout a significant change in the magnitude. The phasors are shown in Fig, 8.34. UPEC provides complete control over the active and reactive power flow in the line. ps V Terminal vottage j ‘AV; Inphase with V V,: Quadrature to current + Angular to V injected voltage Figure 8.34 Components of UPEC injected voltage.