Voltage Current based Time Inverse Relay Coordination for PV feed distribution Systems

Transcription

1 Voltage Current based Tme Inverse Relay Coordnaton for PV feed dstrbuton Systems Anubha Agrawal & Manohar Sngh* Power Systems Dvson Central Power Research Insttute Bangalore, Inda Abstract Integraton of dstrbuted energy resources n dstrbuton systems results n change n network topology and fault currents levels. Partcularly n case of solar based dstrbuted energy resources, the fault feedng capablty s extremely poor and a very thn margn exsts between ther loadng and fault feedng capabltes. The conventonal tme nverse over current relays may not accurately and quckly dscrmnate between the normal loadng and fault condtons. Ths dentfed protecton coordnaton problem s addressed n ths research artcle, by developng a voltage current based tme nverse relay. The operatng prncple of ths proposed relay s based on reducton n nodal voltage and margnal rse n fault feedng capablty of PV based dstrbuted energy resource connected wth dstrbuton system. The protecton coordnaton problem for voltage current based tme nverse relay s formulated as a non-lnear optmzaton problem. In ths optmzaton problem, the ftness functon s defned as summaton of operatng tme of all prmary relays and non-lnear constrants are consttuted wth fve decson varables lke tme dal settng, over current pckup, voltage pckup and relay parameters. The proposed protecton coordnaton s smulated for 8 bus test system and solved wth the help of evolutonary based optmzaton algorthm. The performance of the proposed voltage current based tme nverse relay s compared wth conventonal relay and observed that ther performances are superor to the conventonal tme nverse over current relays n term of ther operatng tme. Keywords Dstrbuton system; Protecton coordnaton; Voltage current tme nverse relay characterstc; Dfferental evoluton algorthm. I. INTRODUCTION Protecton system plays a vtal role n the operaton & control of power systems. Relablty of power supply suppled to customers can be enhanced by desgn of proper protecton schemes. Man electrc power components n a power dstrbuton system must be protected wth protecton scheme whch should operate adequately durng abnormal network operatng condtons [1]. To provde the contnuous electrc power supply and to meet the requred customer electrc, demand,, the populaton of dstrbuted renewable energy resources (RES) are growng n utltes networks. RES are preferably and potental future source of power snce they are renewable n nature and have zero emsson []. Tradtonally, most of the dstrbuton networks are radal n network wth man supply at one end and loads wll be at the other end. In a radal network, fault current contrbuton s only from one end.the desgn of protecton scheme s qute smple and Tejeswn M.V Electrcal Engneerng Department Unversty Vsvesvaraya College of Engneerng Bangalore, Inda straght forward and ncludes fuses, crcut breaker, reclosers and over current relays normally [3]. In the lterature attempts have been made to control the mpact of fault level from dstrbuted energy resources (DER) [4]. These nclude ether the applcaton of fault current lmter to block the fault current from DER or dsconnectng the DER durng the faults [5]. Some papers dscussed about the localzng the DER mpact n the local area rather than spreadng t towards the upstream transmsson sde. These technques are qute helpful for small percentage of penetraton level [6]. However, as the penetraton level of dstrbuted RES s ncreasng, a more robust protecton scheme s requred whch can mantan the protecton coordnaton durng large scale penetraton of DERs [7]. Presently penetraton of photovoltac based DER s rapdly ncreasng n Inda as well as n abroad. These power generatng resources have lmted fault feedng capabltes due to ther nvertor ratng lmtaton as compare to the synchronous machnes [8]. When these power generatng resources are connected at remote end of utltes, these results n weak fault to the nstalled over current, whch are set to operate for upstream large fault currents. Under these scenaro, the over current relay based protecton coordnaton scheme fals to dscrmnate between weak fault current and over load current feeded from the photovoltac based system [9-10]. In ths research artcle, the performance to over current relays s enhanced by addng an exponental term to the standard tme nverse over current relay model. A new relay model s proposed whch utlzes the voltage and current sgnal to enhance the operatng tme of the relay. The proposed relay model have fve varables as compare to standard tme nverse over current relay whch has only Tme dal settng(tds) and plug settng(ps) parameters [11]. Ths relay model requres the nodal voltage and fault current as nput sgnals and gves faster operatng tme as compared to tme nverse over current relay. The proposed relay model s hghly non-lnear and makes the ftness functon hghly nonlnear n the relay coordnaton problem formulaton. Dfferental evoluton algorthm (DEA) s used to obtan the optmal relay settngs for the proposed relay model [1]. Ths artcle s organzed as ntroducton, problem formulaton and results and dscusson.

2 II. PROTECTION COORDINATION PROBLEM FORMULATION Sequental trppng of mnmum nuer of protectve relays for dsconnecton of faulty secton n best mnmum possble tme s known as protecton coordnaton. Coordnaton studes are requred to select or verfy the fault clearng characterstcs of devces such as fuses, crcut breakers, and relays used n the protecton scheme. The best mnmum possble operatng tme s obtaned by solvng the relay coordnaton problem as optmzaton problem. The relay coordnaton problem s hghly non-lnear n terms of ftness functon and constrants sets. The ftness functon s defned as summaton of operatng tme of the prmary over current relays. The mathematcal expresson for the ftness functon s defned as per Eq. (1). N r M k P J = mn. ( ) ( ) mod Penalty = T α + 1 * Penalty (1) pr = 1 p= 1 EV, Δt < 0.3, () 0, Δt 0.3 EV = α * 0.3 Δt *( Δt < 0.3) + β * Δt 1.0 *( Δt 1.0) + Z (3) 1 > T T Z = ( 0.06) * ( < 0.06) β (4) pr pr Where, th denote prmary relay notaton for a fault at locaton k. N r s nuer of relays. ( T ) k s operatng tme pr of prmary relay for fault at locaton k. Mostly dstrbuton systems are protected by conventonal over current relays ( havng standard tme-nverse over current relay characterstcs) and ther operatng tme s adequate due hgh fault current feed from the upstream synchronous machnes. But fault feedng capabltes of PV based power staton s hghly weak lmted by ther nverter ratng. Therefore, operaton of over current relay becomes hghly sluggsh partcularly when they are only feed from the PV based power sources. In ths research artcle, the operatng tme of relay nstalled n a PV feed dstrbuton system s enhanced by proposng a new mathematcal relay model, whch operates faster for a small rse n the load current and notceable fall n nodal voltage. The proposed relay model s compared wth the exstng tme nverse relay model as per Table I below. In the proposed relay model the nput sgnal are taken from current transformer (CT) and potental transformer (PT). The CT sgnal s small rse n load current durng fault and ths results n sluggsh operatng tme of nstalled over current relays. Ths s enhanced by feedng the voltage sgnal to the relay n the proposed relay method. Operatng tme performance s tuned by proper selecton of varable A and Z as mentoned n relay model equaton for the proposed relay model n Table.1 S. No Descrpton Relay Modeloperatng tme equaton No. of decson varables Tme dal settng(tds) Current Pckup( ) Voltage Pckup( ) TABLE.I: COMPARISON BETWEEN CONVENTIONAL METHOD AND PROPOSED METHOD Conventonal Method ( Standard Tme nverse relay) T α = pr TDS * β I fault 1 I pckup T = pr TDS * I I Proposed Method (Voltage current tme nverse relay) fault α pckup β log Two(TDS and pckup ) Fve(TDS, pckup, v pckup, A and Z) Vares from 0.1 to 1.0 Vares from 0.1 to 1.0 Vares from 1.5% of loadng to /3rd of lne to lne current Vares from 1.1% to 150% of loadng Should be less than 0.9 P.U 6 A 1 to 3 7 Z 1 to 5 8 Relay characterstcs Standard tme nverse relay The operatng tme of PV feed relay s enhanced by defnng a new mathematcal operatng tme expresson for the proposed User defned. * A V pckup relay. Ths s acheved by addng an addtonal voltage tme nverse logarthmc functon to the exstng tme nverse over current relay equaton. The proposed mathematcal expresson Z

3 for the proposed method s lsted n Table.1. As mentoned, n the proposed mathematcal expresson of proposed relay model, the operatng tme s nversely proportonal to the rse n current and falls n nodal voltage and hence termed as voltage current tme nverse over current relay n ths artcle. The operatng tme s further enhanced by computng the operatng tme wth power of A on the v pckup and Z on the voltage nverse term of the operatng tme expresson n operatng tme expresson n Table 1. Z s optmzed between 1 to 5 and A s between 1 to 3 n ths artcle. In the PV based connected dstrbuton system whenever there s rse n the loadng more than 110% of the nomnal loadng t s classfed as fault condton. Snce these power sources are weak n nature and ther nodal voltage falls below 0.9 P.U. The ntersecton of rse n current and fall n nodal voltage below 0.9 P.U s classfed as operatng regon of the proposed relay. The operatng tme regon of the proposed voltage current tme nverse relay s marked n Fg.1 below. compared wth other exact method. The sequence of soluton of the proposed non-lnear relay coordnaton problem s explaned n Fg.. Steps nvolved n DEA 1. Intalze all the parameters used n dfferental evoluton (DE) codng whch ncludes upper and lower bounds, populaton sze, no. of relays used.. Generate the vector randomly between the gven lmts called target vector. 3. Calculate the mutant vector by usng below gven generated target vector. Mutant Vectors = Best Target Vector+ F1*(Target Vector - Target Vector 1 ). 4. In crossover t wll compare wth mutant vector and target vector and generate new tral vector. 5. If the penaltes generated are zero, then t termnates otherwse step-3 repeats. Fg.1: Operatng regon of proposed relay Selectvty Constrant Fault s sensed by both prmary as well as backup over current relays smultaneously. To avod mal-operaton n the over current relay coordnaton studes, the backup over current relay should trp only f prmary over current relay fals to trp. If R s the prmary relay for fault at k and R s backup relay j of R for the same fault, then the coordnaton selectvty constrant s stated as; t t j, Δt k, k (5) where, t j, s the operatng tme of the k R for fault at k; j t, s k the operatng tme for the R for the same fault at k. Where Δ t s known a coordnaton tme margn and s commonly known as coordnaton tme nterval (CTI). In the proposed relay over current coordnaton problem t s taken as 0.3 sec. The proposed relay coordnaton problem s solved wth the help of an evolutonary algorthm [13] and results are Fg.: Flow chart of DEA

4 III. RESULTS & DISCUSSION The proposed new voltage current tme nverse relay model s mplemented n modfed 8 bus test dstrbuton system wth DER penetraton. The sngle lne dagram of IEEE 8 bus system s as shown n the Fgure 3. The lne data and generators data are taken from [14]. The local crcut DG s connected at bus 4 of 8 bus dstrbuton shown n Fg.3 (a). The local mcrogrd network whch s connected n sub fg. (a) s shown n sub fg(b). The ratng of each PV based power staton s 1.5MVA. The ratng of each generator s 150MVA n sub fg (a) of Fg.3. The penetraton level of DG power n 8 bus dstrbuton system s 5/300=8.34%. There are relays nstalled at each lne end. The operatng drecton of each drectonal relays are marked n Fg.3.The performance of the proposed relay model s compared wth the conventonal tme nverse relay model as under. nverse and proposed relay model s computed for lne fault and lsted n Table III. TABLE II: OPTIMSED RELAY SETTINGS. Standard tme Relay Proposed relay model nverse relay no. TDS PSM TDS PSM VP A Z R R R R R R R R (a) (b) Fg. 3: IEEE 8bus dstrbuton system (a) 8 bus test dstrbuton system (b) local mcrogrd The relay coordnaton problem s solved as optmzaton problem and optmsed relay settngs are obtaned wth standard tme nverse over current relays and proposed voltage-current tme nverse models. The optmsed TDS and PSM and other parameters are lsted n Table II and operatng tme of each relay model correspondng to standard tme Fault at mddle L-1 L- L-3 L-4 L-5 L-6 L-7 TABLE III: OPERATING TIME OF RELAYS Standard tme nverse relay Proposed relay model R,k Rj1,k Rj,k R,k Rj1,k Rj,k (T,k) (Tj1) (Tj) (T,k) (Tj1) (Tj) R1 R6 R1 R6 (0.586) (0.897) (0.06) (0.513) (0.678) R (0.7) (0.676) (0.808) (0.558) (0.644) (0.697) (0.66) R1 (0.74) (0.63) R6 (0.618) (0.79) (1.317) R1 (1.037) (1.011) R (1.31) (0.899) (0.946) R1 (1.338) (1.03) (1.066) (0.96) (1.36) (1.47) (0.980) (1.07) (0.946) (0.951) (1.054) (0.97) (0.067) R (0.064) (0.383) (0.74) (0.381) (0.558) (0.938) (0.47) R1 (0.060) (0.511) R6 (0.380) (0.9) (0.54) R1 (0.365) (0.69) R (0.317) (1.07) (0.87) R1 (0.07) (0.776) (0.866) (0.577) (0.684) 0.884) (0.555) (0.46) (0.881) (0.881) (5.998)

5 L-8 L-9 L-10 L-11 (0.758) (1.309) (0.439) (0.741) (0.446) (0.91) R17 (0.136) (1.38) (0.434) R0 (0.898) R1 (0.14) R (1.649) (0.778) (1.38) (0.446) R0 (0.891) (0.778) R (1.649) (0.434) (0.91) (0.365) (0.798) R17 (0.06) (1.10) (0.361) R0 (0.691) R1 (0.060) R (1.1) R0 (0.691) (1.10) (0.365) (0.947) (0.798) R (1.109) (0.361) (0.947) The over current relays whch are nstalled n local dstrbuton network of mcrogrd shown n Fg.3 (b) have sluggsh operatng tme, when they are sensng the fault current from PV based system only. Ther operatng tme s enhanced wth the help of new proposed relay model. The operatng tme of all relays for fault n mddle of ther correspondng lne s mentoned n Table IV below for both the relay models. It s observed that relay whch are facng fault current from PV based power staton are R,R0, and durng ther prmary and backup operatons. Ther operatng tme s enhanced sgnfcantly wth the help of proposed relay model. The % change n operatng tme for relay durng ther prmary and backup operaton s lsted n Table IV below for varous fault locatons. However, n few relays, where there s deteroraton n operatng tme due to re- dstrbuton of fault current due to b-drectonal flow of the fault current from the remote end PV system R R R In Table III, the new operatng tme of relays s for ther coordnated operaton s also lsted as per fault locaton wth the proposed relay model. In general, t s observed that there s remarkable mprovement n ther operatng tme of prmary and backup relays for weak fault currents suppled from the PV based power statons. The performance of the proposed relay model s also analyzed n terms of total reducton n value of the ftness functon as per table V. TABLE V: FITNESS FUNCTION Method Ftness functon(s) Standard tme nverse relay Proposed relay model %Reducton The mprovement n operatng tme and CTI for prmary relay R0 and backup relay R for fault at mddle of Lne-10 s plotted n Fg. 4 below correspondng to standard tme nverse and proposed relay model. TABLE IV IMPROVEMENT IN OPERATING TIME OF RELAY WITH PROPOSED RELAY MODEL Relay no. Standard tme nverse relay Operatng tme (s) Proposed relay model % change n operatng tme Prmary Backup Prmary Backup Prmary Backup R R R R R Fg. 4: Operatng tme characterstcs of R0 and R. The convergence of the proposed ftness functon s carred out wth DEA and ts performance s compared wth genetc algorthm (GA) as per Fg.5 below. The proposed relay model gves the better mnmzed value of ftness functon lsted n Table 5.

6 Fg. 5: Convergence characterstcs. IV CONCLUSION: Operatng tme of a standard tme nverse over current nstalled n a PV fault feed dstrbuton feeders s sluggsh due to poor fault feedng capabltes of PV based power statons. Although, the poor fault level s not a predomnant threat to the overloadng/short crcut break down of the power equpment n servce. But these faults need to be cleared for safety hazards and restoraton of power supply at the earlest. The exstng over current relays are not sutable for quck fault clearance for such system. The operatng tme of conventonal over current relays s enhanced by addton of an addtonal term to the standard tme nverse over current relay operatng equaton. The proposed relay model requres two nput sgnals vz voltage and current and gves fast operatng tme as compared to the standard tme nverse over current relays. ACKNOWLEDGEMENT Authors would lke to thank the Research and development department of Central Power Research Insttute, Government of Inda, for the fnancal assstance. The Work presented n ths paper s a part of the n house research and development (IHRD) project on Development and desgn of an adaptve protecton scheme for dstrbuton systems under hgh penetraton of dstrbuted energy resources IHRD/015/DG/5/ funded by Mnstry of Power Government of Inda. [] Frede Blaabjerg & Dan M. Ionel, Renewable Energy Devces and Systems State-of-the-Art Technology, Research and Development, Challenges and Future Trends, Electrc Power Components and Systems, vol. 43, Iss. 1, pp , 015. [3] Xangnng Ln, Ru Zhang, Nng Tong, Xanshan L, Mng L, Dexan Yang, Regonal protecton scheme desgned for low-voltage mcro-grds, Internatonal Journal of Electrcal Power & Energy Systems, vol. 64, pp , Jan [4] J. Keller and B. Kroposk, Understandng Fault Characterstcs of Inverter-Based Dstrbuted Energy Resources, Chapter 4, Natonal Renewable Energy Laboratory, Techncal Report REL/TP , Jan [5] W. El-khattam and T. Sdhu, Restoraton of drectonal over current relay coordnaton n dstrbuted generaton systems utlzng fault current lmter, IEEE Transactons on Power Delvery., vol. 3, no., pp , Apr [6] H. H. Zeneldn, H. M. Sharaf, D. K. Ibrahm and E. E. D. A. El-Zahab, "Optmal Protecton Coordnaton for Meshed Dstrbuton Systems Wth DG Usng Dual Settng Drectonal Over-Current Relays," IEEE Transactons on Smart Grd, vol. 6, no. 1, pp , Jan [7] H. Zhan et al., "Relay Protecton Coordnaton Integrated Optmal Placement and Szng of Dstrbuted Generaton Sources n Dstrbuton Networks," n IEEE Transactons on Smart Grd, vol. 7, no. 1, pp , Jan [8] N. Nmptwan, G. T. Heydt, R. Ayyanar and S. Suryanarayanan, "Fault Current Contrbuton From Synchronous Machne and Inverter Based Dstrbuted Generators," n IEEE Transactons on Power Delvery, vol., no. 1, pp , Jan [9] Esmael Ebrahm, Mohammad Javad Sanjar, Gevork B. Gharehpetan, Control of three-phase nverter-based DG system durng fault condton wthout changng protecton coordnaton, Internatonal Journal of Electrcal Power & Energy Systems, vol 63, pp , Dec [10] K. A. Saleh, H. H. Zeneldn, A. Al-Hna and E. F. El-Saadany, "Optmal Coordnaton of Drectonal Overcurrent Relays Usng a New Tme Current Voltage Characterstc," n IEEE Transactons on Power Delvery, vol. 30, no., pp , Apr [11] A. J. Urdaneta, R. Nadra and L. G. Perez Jmenez, "Optmal coordnaton of drectonal overcurrent relays n nterconnected power systems," n IEEE Transactons on Power Delvery, vol. 3, no. 3, pp , Jul [1] Manohar Sngh, B.K. Pangrah, A.R. Abhyankar, Swagatam Das, Optmal coordnaton of drectonal over-current relays usng nformatve dfferental evoluton algorthm, Journal of Computatonal Scence, vol. 5, Iss., pp.69-76, Mar [13] C. W. So and K. K. L, "Tme coordnaton method for power system protecton by evolutonary algorthm," n IEEE Transactons on Industry Applcatons, vol. 36, no. 5, pp , Sep/Oct [14] R. Benabd, M. Zellagu, A. Chagh and M. Boudour, "Optmal coordnaton of IDMT drectonal overcurrent relays n the presence of seres compensaton usng Dfferental Evoluton algorthm," 3rd Internatonal Conference on Systems and Control, Algers, pp , 013. REFERENCES [1] Y.G. Pathankar and S.R. Bhde, Fundamentals of power system protecton. Chapter 1, New Delh, 003.