ROLE OF FACTS DEVICES ON ZONAL CONGESTION MANAGEMENT ENSURING VOLTAGE STABILITY UNDER CONTINGENCY

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1 Internatonal Journal of Advances n Engneerng & Technology, May 01. ROE OF FACTS DEVICES ON ZONA CONGESTION MANAGEMENT ENSURING VOTAGE STABIITY UNDER CONTINGENCY J.Srdev 1, J.Amarnath and G. Govnda Rao 3 1 Department of Electrcal and Electroncs Engneerng, Gokarau Rangarau Insttute of Engneerng and Technology, Bachupally, Hyderabad, A.P., Inda Department of Electrcal and Electroncs Engneerng, Jawaharlal Technologcal Unversty, Kukatpally, Hyderabad, A.P., Inda 3 Department of Electrcal and Electroncs Engneerng, Gayatr Vdya Parshad College of Engneerng, Madhurawada, Vsakhapatnam, A.P., Inda ABSTRACT Congeston management s one of the most mportant ssues for secure and relable system operatons n deregulated electrcty market. In the compettve electrcty market, t s not always possble to dscharge all of the contracted power transactons due to congeston n the transmsson lnes. In most cases, Independent System Operator tres to remove congeston by reschedulng output power of the generators. Ths paper presents an optmal allocaton method for flexble ac transmsson system (FACTS) devces for market-based power systems consderng congeston relef and voltage stablty. In ths paper, transmsson congeston dstrbuton factors based on senstvty of lne real power has been proposed to dentfy the congeston clusters. The system operator can dentfy the generators from the most senstve congeston clusters to reschedule ther generaton optmally to manage transmsson congeston based on generator senstvty effcently. The role of Thyrstor controlled seres Capactor and Statc Var Compensator have been nvestgated for reducng the transmsson congeston cost ensurng voltage stablty after locatng t optmally n the system based on mproved performance ndex. The effectveness of the proposed method has been carred out on a 14 bus Indan Utlty System. KEYWORDS: Congeston Management, Voltage Stablty, Senstvty, Thyrstor Controlled Seres Capactor, Statc Var Compensator. I. INTRODUCTION Transmsson lnes are often drven close to or even beyond ther thermal lmts n order to satsfy the ncreased electrc power consumpton and trades due to ncrease of the unplanned power exchanges. If the exchanges were not controlled, some lnes located on partcular paths may become overloaded, ths phenomenon s called congeston. In a compettve electrcty market, congeston occurs when the transmsson network s unable to accommodate all of the desred transactons due to volaton of system operatng lmts [1]. Congeston management means the actvtes of the transmsson system operator to releve transmsson constrants n compettve electrcty market. For consstent servce, power system must reman ntact and be able to endure a wde varety of dsturbances []. It should operate n normal and secured condton. Therefore, t s mportant that the system to be desgned and operated so that the more possble contngences can be sustaned wth no loss of load. Operatng condtons of power system can be determned f the network model and complex phasor voltages at every system bus s known. If all the loads n the system can be suppled power wthout volaton of any operatonal constrans, then the system s n normal state. 635 Vol. 3, Issue, pp

2 Internatonal Journal of Advances n Engneerng & Technology, May 01. II. MATHEMATICA FORMUATION.1. ne Model wth Thyrstor Controlled Seres Capactor (TCSC) Transmsson lnes are represented by lumped π equvalent parameters. The seres compensator TCSC s smply a statc capactor wth mpedance. The controllable reactance s drectly used as the control varable n the power flow equatons et complex voltage at bus- and bus- are δ V and V δ respectvely. The real and reactve power flow from bus- to bus- can be wrtten as P = V G V V G cos δ + B sn( δ ) (1) sh [ ( ) ] VV [ G sn( δ ) B cos( δ )] Q = V ( B + B ) () The actve and reactve power losses n the lne are P = P + P = G ( V + V ) VV G cosδ (3) sh Q = Q + Q = ( V + V )( B + B ) + VV G cosδ (4) The model of transmsson lne wth a TCSC connected between bus- and bus- s shown n Fgure.1 Fgure.1 Model of Transmsson lne wth TCSC Durng the steady state the TCSC can be consdered as a statc reactance xc. The actve and reactve power losses n the lne wth TCSC are ' ' ' ' ' P = P + P = G ( V + V ) VV G cosδ (5) Q δ ' ' ' ' ' = Q + Q = ( V + V )( B + Bsh ) + VV G cos (6). Statc VAR Compensator(SVC) Statc VAR Compensator (SVC) s a shunt connected FACTS controller [3] whose man functonalty s to regulate the voltage at a gven bus by controllng ts equvalent reactance. The Shunt Compensator SVC s smply consdered as a statc capactor/reactor wth susceptance B svc. Fgure. shows the equvalent crcut of the SVC can be modeled as a shunt connected varable susceptance B svc at bus-. Fgure. Varable shunt susceptance The reactve power nected nto the bus due to SVC can be expressed as Q = B V (7) SVC SVC.3 Transmsson Congeston Dstrbuton Factors 636 Vol. 3, Issue, pp

3 Internatonal Journal of Advances n Engneerng & Technology, May 01. Transmsson [4,5] congeston dstrbuton factors are defned as the change n real power flow n a transmsson lne-k connected between bus- and bus- due to unt change n the power necton (P ) at bus-. Mathematcally, TCDF for lne-k can be wrtten as: k P TCDF = (8) P Where P s the change n real power flow of lne-k. k TCDF n denotes that how much actve power flow over a transmsson lne connectng bus- and bus would change due to actve power necton at bus-n. III. OPTIMA OCATION OF FACTS DEVICES 3.1 Thyrstor Controlled Seres Capactor(TCSC) The statc condtons consderng here for the placement of TCSC devce n the power system [6] s based on the senstvty of the total system reactve power loss (Q ) wth respect to the control varables whch s the net lne seres reactance (X ) for a TCSC placed between buses and. The reactve power loss senstvty factor wth respect to these control parameter X of TCSC placed between buses and, s gven by Q a = (9) X Ths factor can be computed for a base case power flow soluton. Consder a lne connected between buses and and havng a net seres mpedance of X, that ncludes the reactance of a TCSC, f present. The loss senstvtes wth respect to X can be computed as: Q R X a = = [ V + V VV cos( δ δ ) ] (10) X ( R + X ) Usng the loss senstvtes, the TCSC must be placed n the lne havng the most postve loss senstvty ndex a. 3. Statc VAr Compensator(SVC) For computng the loss senstvty ndex wth respect to SVC [7] an exact loss formula has been used, whch expresses Q as, NB NB Q = c ( P P + Q Q ) + d ( Q P P Q ) (11) [ ] = 1 = 1 where c and d are the loss coeffcents defned as, X c = cos( δ δ ) V V d = V X V sn( δ δ ) P +Q s the complex nected power at bus and X s the magnary part of the th element of [Zbus]. At bus, the senstvty ndex (C ) wth respect to the SVC parameter usng the above loss formula can be expressed as, C NB Q = = ( Q c + P d ) =1 NB (1) Q = 1 The SVC should be placed at a bus havng most negatve senstvty ndex C. The placement of SVC has been consdered at load buses only. IV. CONGESTION ZONE BASED TRANSMISSION MANAGEMENT The TCDFs obtaned based on the methodology dscussed have been utlzed for dentfyng dfferent congeston clusters (zones) for a gven system [8,9]. The congeston zone of type 1 s the one havng large and non-unform TCDFs and the congeston zones of type and hgher order have small or 637 Vol. 3, Issue, pp

4 Internatonal Journal of Advances n Engneerng & Technology, May 01. smlar TCDFs. Therefore, the transactons n the congeston zone 1 have crtcal and unequal mpact on the lne flow [10]. The congeston zones of types, 3 and hgher are farther from the congested lne of nterest. Therefore, any transacton outsde the most senstve zone 1 wll contrbute very lttle to the lne flow. Thus, the dentfcaton of congeston zones wll reduce the effort of SO n selectng the partcpants for congeston management and that wll also reduce the computaton burden. In ths paper, based on the TCDFs, the SO dentfes the most senstve zones and optmally selects the generators for reschedulng based on real power generator Senstvty factors n the senstve zones for congeston management. V. RESUTS AND DISCUSSIONS The Proposed concept of congeston zone based congeston management system utlzng the TCDFs s llustrated on a 14 bus Indan Utlty system. For ths system the congeston clusters/zones based on the proposed method for a lne of nterest 46-0 are shown n Fgure. 3. Fgure.3 Congeston Zones for 14 Bus System The congeston zones are decded on the bass of TCDFs and accordngly the SO selects most senstve congeston zones for managng congeston. The most senstve zone 3 s based on TCDFs, whch are hghly non-unform and large n magntude. The congeston zones of order and hgher comprse TCDFs of smaller magntude wth almost unform varaton. The TCDFs for the congested lne 46-0 correspondng to each bus are gven n Table 1 for the four dfferent zones. The zone 3 s the most senstve zone wth larger magntude and strongest nonunform dstrbuton of TCDFs. The magntudes of TCDFs n zone are hgher than zone but due to unform dstrbuton of TCDFs, the zone s least senstve zone. It s assumed that the two generators at bus 30 from most senstve zones partcpate for congeston management based on the generator senstvtes. TCSC s located optmally at two locatons on lne 19(60-61) and lne 139(68-10) wth 80% and 0% of lne reactance respectvely from the senstvty based approach. The performance ndex for ths lne s found to be maxmum. The Senstvty ndces for SVC are calculated, by observng the senstvty ndces, bus 66 has most negatve senstvty ndex. Therefore, bus 66 s chosen as the optmal locaton for placng SVC whch s havng the most negatve senstvty ndex. SVC s placed at bus 66. Table and Fgure.4 shows the congeston costs wthout FACTS, wth TCSC and wth combnaton of TCSC &SVC under normal condtons. Table 3 and Fgure.5 shows the congeston costs wthout FACTS, wth TCSC and wth combnaton of TCSC &SVC under crtcal contngency condton at lne By observng Fgure.4&5, t shows that the combnaton of TCSC and SVC located 638 Vol. 3, Issue, pp

5 Internatonal Journal of Advances n Engneerng & Technology, May 01. optmally n the system s hghly effectve n reducng the congeston cost both n normal and contngency condtons. Table 1. TCDFs and Zones for 14 bus system for congested lne 46-0 Zone 1 Zone Zone 3 Zone 4 Bus, Bus, Bus, Bus, Bus, Bus, Bus, TCDF TCDF TCDF TCDF TCDF TCDF TCDF 1, , ,0.1 71, , ,-0. 89,-0.004, , , 0.1 7, , , , , , , , , ,0.06 9,0.09 4, , , , , , , 5, , , 0.1 8, , , ,-0.0 6, , , , , , , , , , , , , , , , , , , ,0.4 10, , , , 0.1 1, , ,0.4 11, , , , , , ,0.4 1, , , , ,0.1 13, , , , ,0.1 14, , , , ,0.1 15, , , ,0.1 16, , , ,0.1 17, , , ,0.1 18, , , ,0.1 19, , , ,0.09 1, , , ,0.09, , , ,0.0 3, , , , , , , , , , , ,-0.04 Table. Congeston Cost for 14 bus system wth and wthout FACTS under normal condton Wthout FACTS Wth TCSC Wth TCSC & SVC Congeston Cost ($/hr) Fgure.4 Congeston Cost for 14 Bus System wthout and wth FACTS under normal condton Table 3. Congeston Cost for 14 bus system wth and wthout FACTS under contngency at Wthout FACTS Wth TCSC Wth TCSC & SVC Congeston Cost ($/hr) Vol. 3, Issue, pp

6 Internatonal Journal of Advances n Engneerng & Technology, May 01. Fgure.5 Congeston Cost for 14 Bus System wthout and wth FACTS under contngency at Fgure.6 shows the PV curve at bus 80 for a base case and by placng TCSC and combnaton of TCSC and SVC. It s observed from Fg.6, that the voltage stablty margn at bus 80 s greatly mproved by the applcaton of combnaton of TCSC and SVC than by placng only TCSC. VI. CONCUSIONS Fgure. 6 PV Curve at bus 80 for 14 bus system Ths paper proposes a smple and effcent congeston management method based on congeston zones/clusters obtaned wth new set of transmsson congeston dstrbuton factors. In ths paper, we have presented TCSC & SVC allocaton for congeston relef and voltage stablty n deregulated electrcty market envronment. Control coordnaton among FACTS devces, generaton reschedulng, and load sheddng under contngency are also consdered. By usng the proposed approach, detaled cost and beneft evaluaton can be provded. The optmal locaton of TCSC and SVC has been determned based on mproved performance ndex and ts mpact on congeston cost reducton under normal and contngency condtons has also been studed. Combnaton of TCSC & SVC reduces consderably the congeston cost ensurng voltage stablty compared to ndvdual TCSC both n normal and contngency condtons. REFERENCES [1] Seyed Abbas Taher,Had Besharat., Transmsson Congeston Management by determnng Optmal ocaton of FACTS Devces n Deregulated Power Systems, Amercan Journal of Appled Scences.Scence Publcatons, Vol. 3, Issue, pp

7 Internatonal Journal of Advances n Engneerng & Technology, May 01. [] Ashwan Kumara, S.C. Srvastava b, S.N. Sngh., A zonal congeston management approach usng ac transmsson congeston dstrbuton factors, Electrc Power Systems Research,85 93, 004. [3] S. Sakthvel, D. Mary, M. Devaraaman, Reactve Power Plannng for Voltage Stablty mt Improvement wth FACTS Devces n Most Crtcal Contngency Condton, European Journal of Scentfc Research, Vol.66 No.3, pp , 011. [4] Roberto Méndez and Hugh Rudnck, Congeston Management and Transmsson Rghts n Centralzed Electrc Markets, IEEE TRANSACTIONS ON POWER SYSTEMS, VO. 19, NO.,004. [5] A.Kumar, S. C. Srvastava, and S. N. Sngh, Impact of TCPAR on Cluster-Based Congeston Management Usng Improved Performance Index, IRANIAN JOURNA OF EECTRICA AND COMPUTER ENGINEERING, VO. 7, NO.,008. [6] Rony Seto Wbowo, Naoto Yorno, Mehd Eghbal, Yoshfum Zoka, and Yutaka Sasak, FACTS Devces Allocaton Wth Control Coordnaton Consderng Congeston Relef and Voltage Stablty, IEEE Transactons On Power Systems,011. [7] J. G. Sngh, S. N. Sngh, and S. C. Srvastava, Placement of FACTS Controllers for Enhancng Power System oadablty, IEEE Transactons On Power Systems, Vol. 3, No. 1, February 006. [8] A. Fattah Meyabad, H. Barat, and M. Ehsan., SIMUTANEOUS CONGESTION MANAGEMENT AND COST AOCATION IN A SHORT-RUN MARKET MODE, Iranan Journal of Scence & Technology, Transacton B, Engneerng, Vol. 31, No. B6, 007. [9] Chen-Nng Yu Mara D. Hd., Congeston Clusters-Based Markets for Transmsson Management, IEEE Transactons on Power Systems, [10] Elango.K, Paranoth.S.R., Congeston management n restructured power systems by FACTS devces and load sheddng usng extended Quadratc nteror pont method, INTERNATIONA JOURNA OF APPIED ENGINEERING RESEARCH, DINDIGU,Volume 1, No 4,011. Authors Srdev Jam receved her B.E n electrcal engneerng from GITAM n 00 and her M.E n Electrcal Engneerng (Power systems and Automaton) from Andhra Unversty n 006. She s currently pursung Ph.D n the department of electrcal engneerng, JNTU, Hyderabad. Her research nterests nclude power systems economcs, power system operaton and management and the applcaton of FACTS n power systems J. Amarnath obtaned the B.E degree n electrcal engneerng from Osmana Unversty, Hyderabad, A.P. Inda n 198 and the M.E. degree n power systems from Andhra Unversty, Vsakhapatnam n1984. He worked n Tata Electrc Company, Bombay durng In 1987 he was a ecturer n Andhra Unversty for a perod of years and then he oned n Nagaruna Unversty for a perod of 4 years as ecturer. In 199 he oned JNTU College of Engneerng, Kukatpally, Hyderabad. Presently he s professor and head of the department of Electrcal and Electroncs engneerng department, JNTU, Hyderabad, A.P. He presented more than 50 research papers n natonal and nternatonal conferences. Hs research nterests ncludes hgh voltage engneerng, gas nsulated substatons, ndustral drves, power electroncs, power systems, mcroprocessors and mcrocontroller applcatons to power systems and ndustral drves. G. Govnda Rao obtaned B.E.(EE) and M.E.(Power Systems) from Andhra Unversty, Vsakhapatnam, Inda and Ph.D. n the area of ong Term Dynamcs n Power Systems from IISc, Bangalore, Inda. Workng after a short whle as an Electrcal Engneer, he oned on the Teachng Faculty of Andhra Unversty College of Engg., Vsakhapatnam, Inda and served for more than 40 years n dfferent postons. After relnqushng hs servce there, he s presently workng as a Senor Professor n the GVP College of Engg., Vsakhapatnam, Inda, puttng forth a total servce of over 53 years. To hs credt he presented and publshed more than 55 Papers n Conferences and Journals of Natonal and Internatonal Repute. He was awarded the Best Teacher Award by the A.P. State Government. Hs research nterests are n fundamentals of Crcut Analyss, Power System dynamcs, Voltage Stablty and Reactve power Management. 641 Vol. 3, Issue, pp