An Optmal Reactve Power Flow procedure for the evaluaton of the reactve support n presence of a Herarchcal Voltage Control P. Marannno, F. Zanelln Dpartmento d Ingegnera Elettrca Unverstà degl Stud d Pava Pava, Italy
Reactve Power as an Ancllary Servce (1) In the new lberalzed maret structure the Independent System Operator (ISO) has to manage the networ n a secure and relable way usng the so-called Ancllary Servces: AGC regulaton Spnnng Reserve Non Spnnng Reserve Replacement Reserve Blac Start Voltage and Reactve Power Support The management of the reactve power resources of an electrcal system pursues three man goals: the mantenance of adequate voltage levels on the EHV networ the mnmzaton of the real power losses the lmtaton of the congeston due to the attanment of voltage and current lmts
Reactve Power as an Ancllary Servce (2) Costs of the Voltage and Reactve Power Support: Explct costs: producton costs of the reactve power (generally neglgble wth respect to the actve power producton costs) captal cost for the generators equpments needed for reactve power generaton and voltage regulaton Implct costs: opportunty costs In order to develop an effcent structure of the Voltage/Var Ancllary Servce ISO must correspond dfferent retrbutons based not only on the source type (Capactors, Reactors, SVC and Generators) but also on the level of partcpaton at the Herarchcal Voltage Control (f present) Retrbutons can be calculated usng: Penaltes factors Fxed tarffs based on reactve power furnture (n terms of capablty and/or producton) and consumpton Margnal nodal prces (OPF applcatons)
Herarchcal Voltage Control n Italan EHV networ
Voltage/Var Support n the Italan Framewor The Italan ISO (Gestore della Rete d Trasmssone Nazonale) gves the followng ndcatons for the generators partcpant to the Voltage/Var Support: Prmary Voltage Regulaton Mandatory reactve power reserve for the voltage regulaton of the generators MV bus bar for unts wth rated power greater than 10 MVA Mandatory reactve power reserve for the voltage regulaton of the HV sde of step-up transformers for unts wth rated power greater than 100 MVA Secondary Voltage Regulaton Mandatory reactve power reserve for secondary voltage regulaton for unts wth rated power greater than 10 MVA Unts characterstcs have to satsfy the requrements reported n the document Partecpazone alla regolazone d tensone publshed by GRTN Performances of regulaton devces have to satsfy the requrements detaled n the document Regole tecnche d connessone publshed by GRTN
Methods for Voltage/Var Var Support Evaluaton (OPF procedures) ) (1) Baughman-Sddqu (IEEE Trans. On Power Systems 1991): coupled actve and reactve OPF, mnmzng producton costs of actve power wth operatonal and networ constrants: More effcent compensaton wth respect to the penaltes factors Generators are compensated for reactve power producton only f they wor at the capablty lmts El Keb - Ma (IEEE Trans. On Power Systems 1997): determnaton of Short Run Margnal Costs of actve and reactve power wth a decoupled OPF: Actve power optmzaton mnmzes total actve power producton cost wth operatonal and transmsson constrants and gves the system ncremental cost? Reactve power optmzaton mnmzes networ losses wth physcal and operatonal lmts gves the margnal costs of reactve power at the bus : = m+ 1 mn max δv mn max [ ν + ν ] ν ν n δl( VG, t) δpgl ρ Q = = λ + VD VD QG + δq δq δq Senstvty of the networ losses to reactve njecton n the bus LMs of voltage lmts at the bus Senstvty of the voltage V to reactve njecton n the bus QG LMs of reactve power generaton lmts at the bus
Methods for Voltage/Var Support Evaluaton (OPF procedures) (2) Bhattacharya - Zhong (IEEE Trans. On Power Systems 2002): reactve power maret based frst on REACTIVE POWER OFFERS from provders to ISO: 0 Qmn QA Qbase EPF = a0, + m1 dq + m2 dq + 3 Expected Payment Functon QB QA ( m Q ) a 0 : avalablty prce offer [ ] m 1 : cost of loss prce offer n underexctaton (Q mn =Q =0) [ /Mvarh] m 2 : cost of loss prce offer n the regon Q base =Q = Q A [ /Mvarh] m 3 Q: opportunty prce offer n the regon Q A =Q = Q B [ Mvarh/Mvarh] dq
Methods for Voltage/Var Support Evaluaton (OPF procedures) (3) Bhattacharya - Zhong (IEEE Trans. On Power Systems 2002): ISO can now calculates the reactve power maret prces and the reactve power contracts:? 0 : unform avalablty prce? 1,? 2 : unform cost of loss prces? 3 : unform opportunty prce usng three objectve functons: J P = gen Mnmzaton of the total payment J P : ρ W ρ W + ρ W Q + ρ W Q 1 + ρ 0 0, 1 1, 2 2, 2, 2 3, A, 2 3 W 3, Q 2 3, Mnmzaton of transmsson losses J L Mnmzaton of devaton from contracted transactons J D or the compromse functon J C : J C = J J P P 2 J + J L L 2 J + J D D 2
Methods for Voltage/Var Support Evaluaton (Values Curve) Kundur Xu Warrac Da Slva (IEEE Trans. On Power Systems 2001): Value curves are calculated wth the Equvalent Reactve Compensaton method (ERC): Fcttous capactors are connected to the load busses (settled PV) The reactve producton of the examned bus s reduced eepng the reactve producton of the remanng busses at the ntal value and the reactve power produced by fcttous capactors to eep the ntal voltage profle s evaluated Slac Bus 4 P 5 +jq 5 Bus 5 j0.1 j0.2 j0.3 G1 Bus 1 G2 Bus 2 G3 Bus 3 Value Curves (Mvar) 120 100 G3 G2 80 G1 60 40 20 0 0 20 40 60 80 100 120 Reactve producton of test generator (Mvar) 120 100 80 60 Equvalent Reactve Compensaton (Mvar) 40 G1 20 0 G3 G2 0 20 40 60 80 100 120 Reactve producton of test generator (Mvar)
The ORPF procedure (1) The Optmal Reactve Power Flow (ORPF) proposed s based on the mnmzaton of the real losses P L (or of the real power producton P S n the slac bus): where: v g s the vector of the voltages of the PV generaton busses q A s the vector of the reactve level of the SVR controlled areas q g s the vector of the reactve power productons of the PQ generaton busses In each SVR control area A the reactve power productons of the N g controllng unts [q g1, q g2,,q gng ] must satsfy the constrants: f q A s postve (over exctaton case) ( v, q q ) Mn Ps, g A pu g q g Q A j q = = = qa j = 1,... g j qg Q j max A max N g f q A s negatve (under exctaton case) pu q g Q A j q = = = q A j = 1,... g j qg Q j mn A mn N g N N g = max = 1 = 1 g Q A = q g Q A q g max g Q = q A mn g N = 1 mn
The ORPF procedure (2) The optmzaton problem s subject to the followng constrants: V ( V mn V v g, q A, q g ) for PQ busses (as plot nodes n SVR and sentnel nodes) max Q Q v, q, q ) Q for PV busses (capablty lmts for the PV generaton busses) g mn g ( g A g g max Q Q v, q, q Q lmtatons on the reactve power nterchanges between rs mn rs ( g A g ) rs max pu neghborng areas q = qa j = 1,... N g g, = 1,... N Ar algnment constrants n SVR j v g mn v g v g max q q q lower and upper bound on control varables q Amn A Amax q q g mn g g max
The margnal losses varaton consequent to a nodal reactve njecton at bus s calculated as a lnear combnaton of the real losses, of the Lagrange Multplers (LMs) of the actve constrants and of the actve constrants senstvtes to the nodal reactve power njectons at the ORPF soluton pont: where: dp dq L The ORPF procedure (3) N N N Ar g Q NV = P Q L j Ql + Aj + Ql + Q λ Q λ j Q = 1 = 1 l= 1 p= 1? A s the matrx of the LMs of the algnment constrants (4)? Q are the LMs assocated to the N Q bndng constrants n the nequaltes (2)? V are the LMs assocated to the N V bndng constrants n the nequaltes (1) The margnal cost (beneft) at bus wll depend on the margnal prce of electrc energy C MWh : M varh dpl C = CMWh dq λ Vp V p Q
The proposed ORPF procedure has been appled to the study of the EHV Italan networ (about 1500 busses ncludng an equvalent of the UCTE networ) Smulatons have been performed n two operatonal condtons: Generators n Centralzed Prmary Voltage Control (CPVC) Generators n SVR (only contnental system shared n 12 SVR control areas wth 32 power plants nvolved) Tests and Results Tests and Results TURBIGO BAGGIO ENTRACQUE S. MASSENZA OSTIGLIA FUSINA BARGI POGGIO A CAIANO MONTALTO DI CASTRO VILLANOVA S. SOFIA ROSSANO CALABRO VADO LIGURE PIACENZA LEVANTE MONFALCONE LA CASELLA TAVAZZANO PIOMBINO TORVADALIGA NORD TORVADALIGA SUD PRESENZANO ROSSANO CALABRO OSTIGLIA PORTO TOLLE SERMIDE PILOT NODE CONTROLLING GENERATOR PROVVIDENZA TRINO VERCELLESE VENAUS BRINDISI NORD BRINDISI SUD BRINDISI NAPOLI LEVANTE S. LUCIA S. GIACOMO MONTORIO CASANOVA S.BARBARA S. FIORANO EDOLO S. FIORANO RONCOVALGRANDE REDIPUGLIA PORTO CORSINI ADRIA LA SPEZIA
Tests and Results Base Case CPVC SVR Voltage (V) 420 415 410 405 400 395 390 385 Casanova Baggo S.Forano Ostgla Redpugla Adra Poggo a C. S.Luca Vllanova S.Sofa Brnds Rossano Plot Nodes CPVC reduces the real losses of about 4.5% wth respect to the base case, whle the algnment constrants n SVR cause a reducton of about 3.1%
Nodal reactve prcng dstrbuton n SVR arrangement (the darer s the color the hgher s the margnal prce) Hgh nodal prces n Turn, Mlan and Vence areas (hgh actve and reactve loads) and n Adratc area of Vllanova (large dstance between loads and generators) Low nodal prces n the South Italy areas of Rome, Brnds and Rossano (EHV networ lghtly loaded) Tests and Results
Tests and Results The largest values of nodal costs (benefts) are n the Mlan (Baggo) area (about 0.6 /Mvarh) The algnment constrants of SVR have a strong mpact on prce volatlty: Roncovalgrande and Turbgo power plants presents nodal benefts near the nodal cost of Baggo plot node La Casella and Pacenza power plants show much lower values (near to S. Rocco nodal prce) Reactve nodal prces - Baggo Area Reactve nodal prce ( /Mvarh) 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0 BAGGIO TURBIGO RONCOVAL. TAVAZZANO LA CASELLA CPVC SVR PIACENZA cslago Busses cagno char cremona laccharella s.rocco
Tests and Results The nfluence of the area coordnaton constrants are evdent also n other areas le Turn regon (Casanova plot node): the margnal beneft of hydro power plant of Entracque s negatve n SVR whle the other 4 power plants (and also load busses) show values near to the plot node margnal prce (n CPVC margnal prce n Castelnuovo bus s negatve for the attanment of the upper bound on ts voltage constrant) Nodal reactve prces - Casanova Area Nodal reactve prce ( /Mvarh) 0,6 0,4 0,2 0-0,2-0,4 CASANOVA ENTRACQUE TRINO Busses VADO VENAUS CPVC castelnuovo rondssone SVR possasco
Tests and Results Tang nto account the reactve prce sgnals comng from the analyss of SVR areas of Casanova, Baggo and Poggo a Caano (Florence area) addtonal smulatons have been performed wth a dfferent composton of controllng unts set: Entracque (Casanova area), Pacenza (Baggo area) and Pombno (Poggo a Caano area) are operatng no more n SVR but n CPVC Wth ths new SVR control scheme the losses reducton ncreases from 3.1 % to 3.5 % and: Reactve prce at Casanova plot node decreases to 0.255 /Mvarh Reactve prce at Baggo plot node decreases to 0.408 /Mvarh Reactve prce at Poggo a Caano plot node decreases to 0.207 /Mvarh Wth ths new SVR control scheme reactve benefts of the controllng unts are nearer to the correspondng plot node margnal prce, wth a strong reducton of prce volatlty
Conclusons An ORPF procedure for the evaluaton of the nodal reactve power prce connected to the cost of real losses tang nto account system operatonal constrants has been proposed Smulatons have been performed on Italan EHV networ n two man operatonal condtons: CPVC and SVR In the SVR, a sutable choce of control areas n necessary, not only to attan the requred regulaton performances, but also to allows the defnton of adequately extended regons wth a unform prcng of the reactve power support The correct defnton of SVR control areas wll be crtcal for the forecasted tme horzon of the years 2005-2008 when the nstallaton of several new CCGT power plants and the planned networ renforcements wll deeply modfy the system structure