Opimizaion of Overcurren Relay Operaion wih Geneic Algorihm Arulnahan Gynasegaran College of Engineering, Universiy Tenaga Nasional, Malaysia, Email: ArulnahanGyna@gmail.com Aidil Azwin bin Zainul Abidin College of Engineering, Universiy Tenaga Nasional, Malaysia, Email: AidilAzwin@unien.edu.my Absrac: This paper discusses opimizaion of he overcurren relay s operaion via Geneic Algorihm (GA). By using values of currens and volages obained during normal operaion and faul condiions from a MATLAB simulaion of a IEEE 4-bus newor, a GA is applied o idenify suiable relay seings for all IDMT direcional overcurren relays in he simulaion. The objecive of he GA opimizaion is o minimise he relay operaing ime while ensuring he coordinaion beween he main and bac-up relays are achieved. The moivaion of his sudy is o prove ha suiably fas and coordinaed overcurren relay seings for large newors can be produced by GA if he bacup and main relaionships are already esablished. This developmen could reduce he complexiy of performing relay seings manually for overcurren relays in large newors. Keywords Direcional Overcurren; Opimizaion; Geneic Algorihm; Arificial Inelligence; Relay Seing Coordinaion; Newor Topology I. INTRODUCTION Inverse Definie Minimum Time (IDMT) direcional overcurren relay is sill an economical choice for proecing elecrical equipmen in he elecrical power newor [1, 2]. The relay is simple o configure for radial newors where he faul level drops as he disance from he source increases [1]. Proper coordinaion of overcurren relays requires he selecion of picup curren (I p ) and ime muliplier seings (TMS) such ha hey saisfy all he consrains and operae wihin he shores ime [1-3]. Among he ey consrains are for he overcurren relay o operae immediaely for fauls deeced wihin is viciniy and o operae wih a delay for fauls deeced remoely in he newor which is wihin he zone of proecion of anoher relay. This coordinaion is vial o ensure ha he proecion sysem s seleciviy is maximised while he porion of he elecrical newor ha is isolaed is minimized o ensure maximized supply reliabiliy in he newor [1, 2]. The relay seing coordinaion for direcional overcurren relays in radial newors is sraighforward as he faul level furher down he supply line is lower han he faul level a he supply line [4, 5]. However, for large power ransmission newors, he sources are usually presen a muliple poins in he newor which means ha he faul levels vary grealy along he many differen power lines. Therefore his varying faul level poses a problem for coordinaing overcurren relays [6]. The usage of non-direcional overcurren relays may allow he relay o isolae fauls currens ha are flowing in eiher direcion hrough is elecric newor, bu he relay seings would hen require picup currens (I p ) and ime muliplier seings (TMS) ha could isolae a faul on eiher side [1, 2, 7]. These dual zones may have differing faul levels due o newor opology changes and finding one seing o sui boh faul levels may no be feasible if he faul levels are sufficienly differen. Direcional overcurren relays on he oher hand can be implemened bu require newor opology analysis o ensure a minimum amoun of ime delay beween he relay s operaion for fauls occurring in is baced up zone and for fauls ha occur wihin is main proecion zone. Several mehods o opimise relay seings for varying opologies have been proposed [3-5,8-11]. RSVIES is a mehod of idenifying errors in relay seings for changes in newor opologies using exper sysems [12]. There are wo inds of opimisaion echniques used, one is where an objecive funcion is minimised while saisfying he consrains, while he oher mehod is where he consrains are solved wihou minimising any objecive funcion [5]. There is also wo mehods for adaping relay seings for newor opology changes, one which is o predeermine all possible newor configuraions and choose relay seings ha cover hem all, he oher mehod is o have relay seings ha adap o each newor configuraion [5,8,13]. Differenial evoluion algorihms can be used for opimal coordinaion of overcurren relays [14]. In his sudy, he relay seings shall be based on all possible newor opologies of he IEEE 4-bus newor and have an objecive funcion o minimise he relay operaion ime whils saisfying he consrain of coordinaion beween he main and bacup relays. II. METHODOLOGY The IEEE 4-bus newor is used as he basis for his sudy. The newor opology may be sudied using mehods described in [6,15]. For simpliciy, he newor is modelled wih SIMULINK MATLAB wih he desired elecrical parameers. Once he newor was modelled, a Graphical User Inerface (GUI) from MATLAB is used o provide he user wih ools o analyze he expeced load curren (I L ), minimum faul curren (I FMIN ), and maximum faul curren (I FMAX ) of all elemens in he newor which shall be used as inpus during relay seing wih GA. The GUI hen performs relay seing o sui he curve profile seleced by he user. The GUI shall creae one se of 1 61
seings based on GA and anoher based on convenional algorihm. The GUI hen provides a ploer for comparing relay operaing ime vs. faul curren for boh algorihms. The wo ses of relay seings may also be esed by simulaing fauls in he newor hrough he GUI and he relay operaion imes are displayed. Figure 1 below describes he flowchar of he opimizaion algorihm. Line Lengh 100 m Line Resisance, Zero Sequence 0.3864 Ω/m Line Inducance, Zero Sequence 4.1264 μω/m Line Capaciance, Zero Sequence 7.751 pf/m Line Resisance, Posiive Sequence 12.73 μω/m Line Inducance, Posiive Sequence 93.97 nω/m Line Capaciance, Posiive Sequence 12.74 pf/m Load Acive Power 85 MW Load Power Facor 0.85 Figure 1. Flowchar of Relay Seing Coordinaion Opimizaion Algorihm A. Iniialise SIMULINK Newor The SIMULINK newor is invoed by he GUI and allows he user o deermine he volage level of he newor, impedances of he sources, lines and loads, frequency of supply and he lengh of lines. By defaul he componens of he IEEE 4-bus newor in Fig. 2 are iniialised wih he parameers in Table 1 below. The generaion sources were labelled G1 and G2 while he hree-phase loads were labelled L1 and L2. The circui breaers are labelled based on he bus where i is placed and also he remoe end bus. For example, he circui breaer a bus near G1 bu conneced o he line conneced o bus near L1 is labelled BG1L1. The remoe end circui breaer is labelled BL1G1. The parameers may be alered by he user before proceeding wih newor curren flow analysis. Table 1. Defaul Elecrical Parameers for SIMULINK IEEE 4- bus Newor Newor Bus Volage 132V Newor Frequency 50Hz Generaion Capaciy 200 MVA Generaor X/R Raio 20 Generaor 3 phase Shor Circui Level 200 MVA Circui Breaer Resisance 1 mω Circui Breaer Snubber Resisance 1 μω Circui Breaer Snubber Capaciance Inf Circui Breaer Iniial Saus Closed Figure 2. MATLAB GUI for Iniialising IEEE 4-bus Newor B. Deermine Load Curren, I L The load currens, volage levels of he SIMULINK newor can be obained using he power_analyze funcion ha is available in MATLAB. The funcion is performed under normal operaing opology and under condiions where 1 o 3 lines are disconneced from newor. The larges curren observed by each line shall be he I L for he specified line. This sep ensures ha he increase in load curren due o changes in newor opology is no considered as a faul by he relay. This i o ensure ha here shall be no ripping of he overcurren relay due o changes in newor opology. C. Deermine Faul Currens, I FMIN & I FMAX Three phase symmerical earh fauls are inroduced one a a ime a each circui breaer excluding he generaor circui breaers BG1 and BG2. A oal of 12 faul locaions are simulaed in he newor a each oher 12 circui breaers. The value of I FMIN for each relay shall be he lowes faul curren observed by he relay for fauls ha have occurred wihin is main and bacup zones under he varied newor opologies. The I FMIN mus be larger han he I L o avoid maloperaion of he overcurren relays. This is o ensure ha he overcurren relays do no mal-operae when here is no acual faul. For L1 and L2 which are he loads a he very end of he newor, he I FMIN is an overload of 25% above he load curren. The I FMAX shall be he larges faul curren observed 2 62
by he relay which is ypically for a faul occurring wihin is main zone of proecion. D. Relay Seing, TMS & I P Overcurren relay ripping ime can be calculaed based upon he fundamenal equaion (1). Where is he ime aen for relay operaion, m is he TMS muliplier consan, I F is he faul curren observed, I P is he picup curren of he relay, and is he plug seing muliplier index. mtms I F 1 I P The relay seings shall be based on he sandard characerisics ha have been idenified in IEC 60255 as shown below in Table 2 [1]. Table 2. Relay Characerisics from IEC 60255 Relay Characerisic TMS Muliplier Consan, m Plug Seing Muliplier Index, Sandard Inverse (SI) 0.14 0.02 Very Inverse (VI) 13.5 1 Exremely Inverse (EI) 80 2 The objecive funcion of he relay opimisaion problem ha needs o be minimised is as in (2). Where, m is he ime aen for he relay o operae for a faul occurring inside is main zone of proecion. Minimising his funcion would ensure ha he relay operaes insananeously for fauls occurring wihin is main zone of proecion. m m TMS I FMAX 1 I P The operaing ime of he relay for fauls occurring wihin is bacup zone of proecion is as given in (3). b m b m TMS I FMIN 1 I P I I I I FMIN P FMAX P 1 1 The oal operaing ime for a relay o operae and for he circui breaer o compleely disrup he curren flow is usually 0.1s. For he purpose of his sudy, 300ms was considered he minimum Coordinaion Time Inerval (CTI) (2) (3) (4) (1) beween a relay s operaion as main proecion and is bacup s operaion. The bacup is anoher relay whose b mus a leas be 0.3s more han he m of he relays i is bacing up. This relaionship applies o all relays in he newor which creaes a complex bacup relaionship in he newor. Therefore he coordinaion consrain equaion is as given in (4). Using he max(x) funcion, shall reurn he larges of any se of values passed o i. The bmin and m of each relay shall be calculaed as shown in Table 3 below using (2) and (3). b bmin b 0. 45s Table 3. Minimum Bacup Time Relay m (s) bmin (s) G1 m_1 bmin_1 = max( m_5, m_6, m_7 )+0.3 G2 m_2 bmin_2 = max( m_8, m_9 )+0.3 L1 m_3 bmin_3 = 0.3 L2 m_4 bmin_4 = 0.3 G1L1 m_5 bmin_5 = max( m_3, m_11 )+0.3 G1L2 m_6 bmin_6 = max( m_4, m_12, m_14 )+0.3 G1G2 m_7 bmin_7 = m_9 +0.3 G2G1 m_8 bmin_8 = max( m_5, m_6 )+0.3 G2L2 m_9 bmin_9 = max( m_12, m_4, m_13 )+0.3 L1G1 m_10 bmin_10 = 0.3 L1L2 m_11 bmin_11 = max( m_4, m_13, m_14 )+0.3 L2L1 m_12 bmin_12 = max( m_3, m_10 )+0.3 L2G1 m_13 bmin_13 = 0.3 L2G2 m_14 bmin_14 = 0.3 The opimisaion oolbox in MATLAB is configured o use geneic algorihm (gaopimse funcion) o minimise he objecive funcion (7) which is he average m of he 14 relays [16]. The selecion of TMS and I P by he GA ensures ha m in (3) is minimised while b in (4) saisfies he consrain equaions in (5) and (6) o ensure proper coordinaion beween he main and bacup relays. The b of each relay is ep smaller han 0.45s via (6) o ensure minimum faul clearance ime of 0.45s is me. 14 m _ n (7) 1 f ( x) n 14 A oal of 5 parameers wih fixed values and 2 parameers wih a range of values are used in he relay seing algorihm as shown in Table 4 below. The values for m and would be aen from Table 2 depending on he characerisic seleced, i.e. SI, VI or EI. A saring poin is seleced for he GA where all relays have b values equal o CTI. The opimisaion oolbox reurns he TMS and I P for each relay ha minimises (5) and saisfies (4). (5) (6) 3 63
Table 4. Parameers for Opimisaion Toolbox Parameer Type Value Time Muliplier Seing, TMS Range 0.0001-0.1 Picup Curren, I P Range I L - I FMIN Min. Faul Curren, I FMIN Fixed I FMIN Max. Faul Curren, I FMAX Fixed I FMAX TMS Muliplier Consan, m Plug Seing Muliplier Index, Fixed Fixed Table 2 Coordinaion Time Inerval, CTI Fixed 0.3s average m were on par wih he GA seings based on Table 5. Figure 3 shows he operaion of relays when a hree-phase faul is simulaed a L1. The relay a L1 operaes a 36ms o clear he faul. The oher relays a he bus do no operae as indicaed by NOP. The relays a BL2L1 and BG1L1 operae a 300ms and 299ms respecively as bacup. The operaion proves he coordinaion of relays have been achieved while ensuring speedy operaion of he overcurren relays. The convenional mehod of relay seing requires he calculaion of he suiable TMS value based on a given I P, I FMIN, m, and b. Since he relay mus operae a CTI for a remoe end faul, b is equal o 0.3s, and I P is se a an arbirary value beween I L and I FMIN. Subsiuing hese values ino (3), we can solve for TMS. These resuls are used as he saring poin for he GA o improve convergence ime. The convenional mehod will use his saring guess o calculae he b for all relays based on Table 4. III. RESULTS & DISCUSSION The resuls of he relay seings for boh convenional and opimised mehods are abulaed in Table 5. The value of he load currens are based on all possible newor opologies o ensure ha he relays may no operae due o newor opology change. The use of direcional overcurren also is necessary wih he IEEE 4-bus newor as he direcion of curren flow can change wih respec o he newor opology. The analysis of he faul level was based on he newor being fully conneced o ensure ha he faul currens simulaed are he smalles possible. When he simulaion is repeaed wih a faul placed a each line, each line experiences a large faul curren when he faul is placed neared o is curren ransformer and experiences he smalles faul curren for fauls furher away. The GA aes a long ime o converge when given a large range of values o wor wih. In his scenario he GA has 28 variables wih infinie possible values for each variable. A good saring poin value helps he GA o converge more quicly wih more persisence. When he values of I L and I FMIN are close, i becomes no feasible o saisfy he consrain equaion while operaing wihin he range of variables provided. The larger he difference beween I L and I FMIN, he lesser he deviaion from he CTI requiremen shall be. The CTI compliance of he relay seings were compued and abulaed in Table 6. The b_min was calculaed based on Table 3. The b_min is he minimum b he relay mus operae wih o ensure he minimum CTI is achieved. Table 6 shows ha wih he GA seings, all relays had successfully achieved coordinaion wih is bacup wihou compromising on speed of operaion. The convenional seings had negaive average deviaions in Table 6. This shows ha using convenional mehod produces relay seings which are caused some relays o no saisfy he CTI requiremen alhough he average b and Figure 3. MATLAB GUI for Iniialising IEEE 4-bus Newor IV. CONCLUSION Using he resuls from Table 5, he deviaion from he consrain equaion (5) is calculaed o show in Table 6 ha he GA is capable of producing relay seings which: a) Saisfy he CTI consrain equaions in (5) and (6) b) Good operaion ime for fauls wihin is main zone of proecion. c) Operaion for fauls ouside is main zone of proecion wihin pracical requiremens. d) Performance a par or beer han convenional mehods. The simulaneous relay seing for all overcurren relays wihin he newor wih GA may be adaped o larger newors lie he IEEE 14-bus and 30-bus newor which will reduce he effor aen by he proecion engineer o se all he relays while providing beer CTI for he relays. The scalabiliy of his mehod depends on nowing he faul levels wihin he enire newor and in predeermining he main and bacup relay relaionships beween all relays before aemping o produce relay seings. ACKNOWLEDGEMENT A.G. hans he Malaysian Minisry of Higher Educaion for is sponsorship of his posgraduae uiion fees. The suppor of he universiy and is academic saff has also been crucial via faciliies and guidance provided. 4 64
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