Life Science Journal 2013;10(4) Thyristor Controlled Series Capacitor (TCSC) for Power System Stabilization

Transcription

1 Thyristor Controlld Sris Capacitor () or or Systm Stabilization Mansour Babikr dris and Ali Juma Elzubia Dpt. o Elctrical Enginring, Faculty o Enginring, Misurata Univrsity Abstract: Th dynamic stability (DS) o th por systm is a big challng that acing th por systm nginrs. This DS can b improvd by providing suitably tund por systm stabilizrs on slctd gnrators to provid damping to critical oscillatory mods. Suitably tund por systm stabilizrs, ill introduc a componnt o lctrical torqu in phas ith gnrator rotor spd dviations rsulting in damping o lo rquncy por oscillations in hich th gnrators ar participating. Th clar improvmnt in por lctronic dvics maks such problms adjustmnt asir and mor controllabl. This papr discusss th us o or damping th rotor oscillations o th synchronous machin by controlling its citation. A systm ormd o a synchronous gnrator connctd to ininity bus through a transmission lin is discussd. Th rsults o simulation ar obtaind using MATLA SMULN hich ar discussd in som hat dtails in this papr. [Mansour Babikr dris and Ali Juma Elzubia. Thyristor Controlld Sris Capacitor () or or Systm Stabilization. Li Sci J 2013;10(4): ]. (SSN: ) yord: Dynamic stability, stabilizr,, rotor oscillation, ininity bus, synchronous gnrator 1- ntroduction:- Th us o or Systm Stabilizrs has bcom incrasingly important to provid improvd stabilization o th systm. Th disturbancs occurring in a por systm induc lctromchanical oscillations o th lctrical gnrators. Ths oscillations, also calld por sings, must b ctivly dampd to maintain th systm stability. n som cass th stabilizrs ar usd as an additional control atur so that citation systm ith a high rspons may b usd ithout compromising th small signal instability o th gnrators [1]. Th output signal o th stabilizrs is usd as an additional input to th Ecitation Systm block. or systm is a complicat nonlinar systm hich structur, paramtr and running mod usually chang. Th study o th linarzd systm is ncssary or som purposs, such as control loop dsign. Th most common disturbanc is load variations, but paramtr variations ar also common, and th closd loop control systm is usd to compnsat or such variations. Lo or ngativ damping in a por systm can lad to spontanous apparanc o larg por oscillations. Svral mthods or incrasing th damping in a por systm ar availabl such as static voltag condnsr (SVC), high voltag dirct currnt (HYDC) and por systm stabilizr (SS) [2]. Omr M. Ad-Badb discuss th us o SS or damping por systm oscillation [1]. or systm stabilization ith synchronizd masurmnt is prsntd in [3]. 2- Thiristor Controlld Sris Capacitor () Construction:- Th gnral construction is shon bllo in igur (1), hich contains capacitors in paralll ith controlld ractor, and it is connctd in sris ith th transmission lin [5]. Th quivalnt impdanc across th dvic is th capacitiv ractanc in paralll ith inductiv ractanc. Th practical circuit o consists o paralll capacitors connctd ith mtal oid varistor (MOV) to protct it against suddn high voltags, as ll as som valvs to limit th currnt during th connction and disconnction o th capacitors. Figur (1) Construction 3- Modl:- A connctd to a transmission lin is shon blo in igur (2). 3147

2 V V r i L i (3-2) a, b, c a, b, c a, b, c q a, b, c Thyristor ash out Circuit Figur (2) connctd to a transmission lin : s th ractanc hich is connctd in sris ith th transmission lin ith ractanc, so th quivalnt ractanc is givn by: q (3-1) Wash out Circuit: s a iltr or high rquncis, and it has th tim constant. controllr: t is usd or partial shit o th motion quation roots to th most stabl plac in th compl lvl, so th systm ill b mor stabl and liminat th ngativ ct o th citation systm. Tyristor: t is prssd by th tim constant s,hich implmnt th tim dlay o th thyristot opration. F : Rprsnts th transr unction. To study th ct o in damping por systm oscillation, it is connctd to a systm ith synchronous gnrator connctd ith ininity busbar through a transmission lin as shon in igur (3) blo: Lq L L Applying ark transormation to quation (3-2), th olloing quation can b obtaind [6]:- 0 0 V0. d, q V sin r 0. d, q q q (3-3) cos d V V r sin sin sin d d q q V V r d d q V V r d d q q (3-4) Equation (3-4) can b prssd in a linar orm as ollos: V V cos r d 0 0 d q (3-5) q q0 Similarly Vq can b prssd as ollos:- V V sin r q 0 0 q d (3-6) d d 0 4- Variabls Stat Equations o :- Variabls stat that dscrib can b obtaind by dividing igur (2) into to as in igur (4) and igur (5) as shon blo:- - + s 1 s Figur (4) Wash out Circuit o Figur (3) Th systm ith V t : s th synchronous gnrator trminal voltag. V :s th ininity bus voltag. Nglcting th ct o th damprs or th classical modl o th synchronous gnrator, th voltag quation or th phass (a,b,c) can b prssd as ollos:- Th transr unction o igur (4) can b obtaind as ollos:- s G1 s (4-1) 1 s S 1 1 s s Figur (5) Thyristor and controllr o 3148

3 Th transr unction G ( ) 2 s o th igur is as ollos:- S G2 S (4-2) 1 S S So th transr unction G(s) o th is : G s G s * G s 1 2 S S G s * (4-3) 1 S 1 S S th rnc currnt is constant, 0 s G1 s 1 s 1 (4-4) S G2 s 1 S Substituting rom (4-4) it is ound that: (4-5) Equations (4-4) and (4-5) ar th variabls stat quations and can b prssd in matri orm as ollos: 1, (4-6) 1 0, 1 5- Simulation Rsults:- Simulation is don using MATLAB SMULN or a systm ormd o a synchronous gnrator connctd to ininity bus through a transmission lin. Th systm data ar prsntd in Tabl (1) blo. Th study is don or th mntiond systm in th availablnss o citation systm irstly ithout, and th rsults ar prsntd. Thn th study is don atr addition o th dvic. Th rlations btn (,, ) and th tim hn th systm is subjctd to a suddn and continus disturbanc or th input mchanical por by 0.1 pu, ar plotd during th to dirnt cass. Tabl (1) Systm data Th synchronous and transmission lin data: 1.7 pu 1.67 pu d pu R pu d 0.4 pu R 0.02 pu 1pu 0.85 lag r.p.m d sc H 2.37 sc Th citation systm data: sc A sc 5-1 Systm Rspons ithout :- Figurs [(6) (7), (8)] hos that th oscillations or, and is incrasing ith th tim, in othr ords it can b said that th systm is not stabl. This is du to th ngativ ct o th citation systm in th stability. Figur (6) Rlation btn Figur (7) Rlation btn dvic q a A and th tim ithout and th tim ithout 3149

4 Figur (8) Rlation btn ithout and th tim 5-2 Systm Rspons atr Addition o Dvic:- Atr addition o th systm has bcom stabl, and this is clarly shon in igurs [(9), (10), (11)] hich sho th rlations btn, and ith tim Figur (11) Rlation btn and th tim ith 6- Conclusion:- or systm stability implmnts a big sid o por systm nginrs car, du to its clar ct in th li tim and saty o th synchronous gnrator. Th rsults sho that th citation systm causs a larg oscillation or th por systm, sinc it is adding a ngativ damping torqu du to its high rspons. This maks a shit or th roots o motion quation rom th ngativ part to th positiv on. According to th rsults addition o solvs this problm compltly and th systm bcam stabl. Morovr por lo control through th transmission lin is improvd by controlling th lin impdanc by th triggring angl according to th rquird loading conditions. Figur (9) Rlation btn Figur (10) Rlation btn and th tim ith and th tim ith Rrncs:- 1. Omr M. Ad-Badb, Damping o Elctromchanical Mods Using or Systms Stabilizrs (SS) Cas: Elctrical Ymni Ntork, Journal o ELECTRCAL ENGNEERNG, VOL. 57, NO. 5, 2006, Rupal V. atl, H. A. Mhta,. Aay Mhta, Novl Approach or Dsigning a or Systm Stabilizr, National Conrnc on Rcnt Trnds in Enginring & Tchnology, May 2011 B.V.M. Enginring Collg, V.V. Nagar, Gujarat, ndia. 3. tr orba, Valrijs nazkins, Mats Larsson, or Systm Stabilizr ith Synchronizd hasor Masurmnt, 17th or Systms Computation Conrnc Stockholm Sdn - August 22-26,

5 4. undr., or Systm Stability and Control, Elctric Rsarch nstitut 3412, Hillvi Avnu alo Alto, liornia. 5. Mohammd H. Rashid, or Elctronics Circuits Dvics and Applications, Andrson.M., A.A Fouad, or Systm Control and Stability, Loa Stat Univrsity rss, loa, Al-Alai S.M.,. A. Ellithy, Z. S. El- Razaz, Tuning o Damping Controllrs or SVC ovr a Wid Rang o Load Modls using Artiicial Nural Nt-orks. GGRE, Cairo, Egypt, Spt, 1997, pp Claudio A. Canizars, or Flo and Transint Stability Modls o FACTS Controllrs or Voltag and Angl Stability Studis, EEE/ES anl on Modling, Simulation and Application o FACTS Controllrs in Angl and Voltag Stability Studis, Singapor, Jan. 2000, pp /12/