An Active Islanding Detection Method for Small-Scale Distributed Generators

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1 Wen-Yea Can An Active Islandin Detection Metod for Small-Scale Distribted s WN-YAU CHANG Department of lectrical nineerin St. Jon s University No. 499, Sec. 4, Tam Kin Road, Tamsi, Taipei 251, Taiwan TAIWAN Abstract: - Tis paper proposes a new islandin detection metod for se in a small-scale, rid-interconnected distribted enerator system. Te proposed islandin detection metod is based on voltae flctation injection, wic can be obtained tro i-impedance load switcin on te rid periodically. Te correlation factor between te periodic switcin sinal and te pertrbed voltae is ten sed as an islandin detection index in te proposed islandin detection metod. xperimental reslts demonstrate te principles of te proposed tecniqe and sow te new proposed metod is reliable, economical, and easy to implement. Key-Words: - Islandin detection, Distribted enerator, oltae flctation injection, Correlation factor 1 Introdction Distribted enerator (DG) is defined as te enerator of power inside te distribtion system. DG is driven by prime movers sc as a wind trbine, water trbine, micro-trbine, etc. to enerate electricity. De to te tecnoloical innovations related to te enery conversion in te last decade, it is now possible to ave competitive electricity eneration wit DG nits. Many papers ave been presented in literatre reardin te sizin, placement, reliability, and expansion plannin of DG [1-3]. Te main merits of DG can be listed as follows: redction of power loss, voltae profile improvement, power qality improvement (in some cases), possibility to exploit CHP (Combined Heat and Power) eneration, less polltin emissions (wit respect to traditional plants) [4]. Since DG is inside te distribtion system, it canes te caracteristics of te distribtion system, casin an impact in te voltae relation and protection sceme [5-8]. An essential reqirement of te ridinterconnected DG system is te capability of islandin detection [9]. Islandin occrs wen a part of te distribtion system is electrically isolated from te main sorce of spply, yet contines to be enerized by DG. Te islandin operation of DG may case potential azards to line-maintenance personnel, and risk te DG in bein damaed by otof pase reconnection to te rid. Te majority of tilities reqire tat DG sold be disconnected from te rid as soon as te islandin occrs. I standard 1547 stiplates a maximm delay of 2 seconds for detection of an islandin [10]. Te islandin detection metods can be enerally cateorized into two rops, passive metods and active metods. Passive metods detect te islandin operation of DG by monitorin selected power system parameters, sc as voltae manitde, te cane rate of freqency, pase displacement, and power otpt. Te passive metods inclde te cane of voltae manitde relay [11], te rate of cane of freqency relay [12], te vector sre relay [13], te voltae nbalance and total armonic distortion of crrent relay [14], te cane of otpt power relay [15], te ratio of te freqency cane to te otpt power cane relay [16], te rate of cane of voltae and power factors relay [17], and te loical rle-based detection tecniqe [18]. Te principles of tese metods were developed based on te fact tat an islandin will case variations in system parameters. However, wen te amont of power mismatc between te DG and local load is not sinificant eno drin islandin, te metods mentioned above may fail to sinal te abnormality. Besides, anoter drawback to te passive metods is tat tey cannot effectively differentiate between te islandin and oter non-islandin transients, like voltae flicker or sa. Active metods detect te islandin by directly interactin wit te system nder consideration. Te tree main metods are te reactive error export detection (RD) [19], te positive feedback for power loop metod [20], and te voltae flctation ISSN: Isse 6, olme 7, Jne 2008

2 Wen-Yea Can correlated metod [21]. Te RD controls te excitation crrent of DG so tat it enerates a known vale of reactive crrent, wic cannot be spported nless te enerator is connected to te rid [19]. Te positive feedback for power loop metod will reslt in an nstable freqency or voltae, once te DG is islanded. ventally, te nstable freqency or voltae will trip te freqency or voltae relay to protect islandin [20]. Te small-scale DG as simple excitation, peraps sin permanent manets. Hence, islandin of small-scale DG cannot be detected effectively by controllin te reactive power export, as in RD or te positive feedback for power loop metod. Anoter metod is called te voltae flctation correlated metod [21]. Usin power transistor switcin i-impedance load periodically near te voltae zero crossin point, it measres te voltae flctation tro te tility-interconnected point, enablin evalation of system sorce impedance and detection of islandin. It provides a very effective means of detection, wit te disadvantae of introdcin a small voltae pertrbation at te zero crossin point. Active metods are more effective and robst tan te passive ones, bt most existin active scemes ave te disadvantaes of i cost and deradation of power qality to a certain extent. To overcome te disadvantaes of te existin islandin detection metods, te aim of tis paper is to propose a new correlation factor islandin detection metod for small-scale, typically less tan 1 kw, rid-interconnected DG. Te proposed metod is more effective and economical tan conventional active metods, and as very little impact on te power qality. 2 Basic Principle of te Proposed Metod Te proposed islandin detection metod is based on te featre tat te variation at te terminal voltae of DG as a stron correlation wit its voltae pertrbation sorce wen DG is operatin in islandin state. On te contrary, te variation at te terminal voltae of DG as a weak correlation wit its voltae pertrbation sorce wen DG is operatin in parallel wit te rid. Terefore, measrin te correlation between variation at terminal voltae and its voltae pertrbation sorce wold sow weter te DG is operatin in parallel wit te rid or fnctionin independently of te rid. In te proposed islandin detection applications, a periodically switcin i-impedance load is sed, so tat variation of load voltae is restricted to te level, wic wold not inflence te spply. Te eqivalent circit of a DG parallel wit te rid in normal operation is sown in Fi. 1, were and are te open circit voltaes of te tility and te DG; is te sorce impedance of te tility rid; is te internal impedance of DG; is te impedance of te local load; is te impedance of te i-impedance load; S is te periodical switc of. Te terminal voltae of rid-interconnected point wen S is trn-off can be expressed as: 1 ( ) (1) Since is sinificantly reater tan for distribtion system, even for te lon radial system or te weak rid system [21], term is sinificantly reater tan expressed as: term in (1). If te term is inored, 1 can be approximately 1 (2) Te terminal voltae of rid-interconnected point wen S is trn-on can be expressed as: ' 1 Utility Grid ( ) S1 1 ocal oad S Periodical Switc Hi Impedance oad Distribted Fi. 1 qivalent circits of a DG parallel wit te rid (3) ISSN: Isse 6, olme 7, Jne 2008

3 Wen-Yea Can If te approximately expressed as: ' 1 term is inored, 1 can be (4) Te variation at terminal voltae de to te S switcin can be approximately expressed as: ' (5) Te eqivalent circit of a DG sbject to islandin operation is sown in Fi. 2. Te terminal voltae of rid-interconnected point wen S is trnoff can be expressed as: 2 (6) Te terminal voltae of rid-interconnected point wen S is trn-on can be expressed as: ' 2 (7) Te variation at terminal voltae de to te S switcin can be approximately expressed as: ' (8) Since te internal impedance of DG ( ) is sinificantly reater tan te sorce impedance of tility ( ), comparin (8) wit (5), we ave 2 is larer tan 1. ariation at te terminal voltae de to te switcin of te i-impedance load drin islandin operation is ts larer tan tat in normal operation. Te experimental system was performed, and te reslts are sown in Fis. 3 to 4. Te DG employed in te tests consisted of a ridinterconnected, tree-pase, 220, 300W syncronos enerator and a 2000 i-impedance indctive load. As an example of te typical test for te DG in normal operation, Fi. 3 exibits tat te variation at te terminal voltae de to te switcin of te i-impedance load is very small. Te freqency in te terminal voltae is 60Hz, and te freqency of te switcin sinal is 10Hz. As an example of te typical test for te DG in islandin operation, Fi. 4 exibits tat te variation at te terminal voltae de to te switcin of te i-impedance load in islandin operation is larer tan tat in normal operation. In Fis. 3 to 4, Cannel 1 denotes te waveform of te terminal voltae (100/div), Cannel 2 indicates te waveform of te switcin sinal of te i- S1 Utility Grid S Periodical Switc Distribted 2 ocal oad Hi Impedance oad Fi. 2 qivalent circits of a DG drin islandin operation (1)CH1:100/div (2)CH2:10/div Time:50 ms/div Fi. 3 Waveform of terminal voltae and switcin sinal drin normal operation ISSN: Isse 6, olme 7, Jne 2008

4 Wen-Yea Can (1)CH1:100/div (2)CH2:10/div Time:50 ms/div Fi. 4 Waveform of terminal voltae and switcin sinal drin islandin operation impedance load (10/div). Measrin te periodical pertrbation of terminal voltae at te rid-interconnected point, de to switcin a known i-impedance load, allows one to estimate indirectly te DG operatin state. Wen te variation at te terminal voltae caned, te islandin operation can be easily detected accordinly. However, variations in te terminal voltae may reslt from some load switcin, oter tan te switcin of te i-impedance load. Conseqently, to avoid false alarms, te measred variation of terminal voltae sold be closely related wit te iven i-impedance load switcin sinal as in te islandin operation. Neverteless, in te case of some load canes occrrin coincidentally wit te intentional i-impedance load switcin, te measred voltae flctation may not represent te spply impedance cane. Distinction between intentional and coincidental load canes sold be made by observin a nmber of more switcin instances and terminal voltae canes [21]. To effectively distinis variations of te terminal voltae de to switcin of te iven iimpedance load from te oters sold ts be based on correlation of te measred terminal voltae canes wit te iven load switcin. 3 Te Proposed Detection System Te arcitectre of te proposed correlation factor detection system is illstrated in Fi. 5. Te inslated ate bipolar transistor based periodical electronic switcin circit performs te i-impedance load switcin. A voltae detectin interface measres te manitde of terminal voltae at te ridinterconnected point. Te diital sinal processor calclates te correlation factor between te periodical switcin sinal and te pertrbed voltae at te rid-interconnected point and decides weter te trip conditions are met. At te zero crossin point of te terminal voltae, te periodical electronic switcin circit trns on/off every tree cycles. Te voltae flctation de to te periodical switcin in an islandin operation wold be sinificantly reater tan tat in te normal operation. Since te periodical electronic switc trns on/off every tree cycles, te switcin sinal S(j) as a period of six cycles. S(j) as two vales, -1 for trn-on stats and 1 for trn-off stats. Te differential sinal ΔS(j) of S(j) wit 3-cycle time la is described as follows: S ( j) S ( j) S ( j 3) (9) Te correspondin time series of differential terminal voltae wit time la of 3 cycles is expressed as: ( j) ( j) ( j 3) (10) were te (j) is te averae terminal voltae vale at te jt cycle. Since te averae terminal voltae proressively increases drin te switc trn-off period and decreases proressively drin te switc trn-on period, a proportional fnction P(j) is sed to express tis featre. P(j) is experimentally set to be 1 for te first cycle after switcin, 2 for te second cycle, and 3 for te tird cycle for enancement of te voltae proressive varyin trends after Ternimal oltae Distribted oltae Detectin Circit ero Crossin Detectin Circit DG Connectin Switc S2 Hi Impedance oad Periodical Switcin Sinal Periodical Switc Correlation Factor Calclation Proram ocal oad Grid Tie Switc S1 Switcin Command Proram Islandin Decision Proram DSP Cip (TI TMS320F2407A) Utility Grid Trip Command Periodic Switcin Command Fi.5 System confiration of te correlation factor islandin detector ISSN: Isse 6, olme 7, Jne 2008

5 Wen-Yea Can switcin on and off. Te correlation factor between ΔS(j) and Δ (j) is expressed as follows: F k j 1 ( k) S( k) P ( k ) N k j N (11) were F k is te proposed correlation factor, as an islandin detection index, N is te nmber of cycles of te observin window, and N is set as 6 in tis paper. As described previosly, in normal operation te correlation between Δ (j) and ΔS(j) is weak and F k is mc lower tan a tresold vale. In contrast, as islandin occrs, Δ (j) and ΔS(j) ave a stron correlation and F k becomes sinificantly larer tan tat in normal operation [22]. Tro te proposed sceme, te correlation factor can be sed as an islandin detection index and serves as a sefl reference to activate te protective relays. Fi. 6 depicts te procedre of te correlation Start ero Crossin Detectin Periodical Switcin Command Otpt factor metod. It consists of zero crossin detection, periodical switcin command eneration, terminal voltae detection, correlation factor calclation, and decision process. Te DSP measres te vale of terminal voltae over 6 cycles, so tat it avoids te impacts of varios load variations and real power or reactive power distrbances. As sown in Fi. 6, a tresold for te islandin detection correlation factor is defined; te tresold is set to be 36 in tis paper. Compter simlations were performed, and te simlation reslts of te variation of te correlation factor F k before and after te islandin operation are sown in Fi. 7. As sown in Fi.7, if te islandin falt is occrrin at te 6 t cycle, ten te correlation factor F k increases drin te next 6 cycles. At te 12 t cycle te correlation factor F k larer tan te tresold Top F k, and te islandin as been detected. 4 xperimental Reslts To verify te proposed metod, experiments were condcted to demonstrate its effectiveness of te islandin detection approac. Te experimental tests were carried ot on two kinds of enerators: syncronos enerator and indction enerator. Te procedres of te tests are to verify tat te DG systems cease to enerize te tility rid as specified in I Standard 1547 wen an nintentional island condition is present. Terminal oltae Detectin (a),rms (j) (1) (4) (10) (16) (22) (7) (13) (19) Correlation Factor Calclatin (b) Δ,rms (j) Δ(1) Δ(4) Δ(7) Δ(10) Δ(13) Δ(16) Δ(19) Δ(22) t t S(4) S(10) S(16) S(22) No Fk>Tresold? (c) S(j) S(1) S(7) S(13) S(19) t Yes Trip Command Otpt (d) ΔS(j) ΔS(1) ΔS(4) ΔS(7) ΔS(10) ΔS(16) ΔS(22) ΔS(13) ΔS(19) FK(12) FK(13) FK(16) FK(19) FK(22) t (e) Top Fk FK(10) nd F k FK(1) FK(4) FK(7) F k(12) >Top Fk t Fi. 6 Procedre of te correlation factor metod Fi.7 Te simlation of te variation of F k before and after te islandin operation ISSN: Isse 6, olme 7, Jne 2008

6 Wen-Yea Can 4.1 Islandin test for syncronos enerators Te eneration system employed in te islandin tests for syncronos enerator consisted of a ridinterconnected, tree-pase, 220, 300W syncronos enerator driven by a DC motor wit 4 types of loads, incldin (a) maximm real load at nity power factor, (b) maximm real load at rated power factor lain, (c) maximm real load at rated power factor leadin, and (d) minimm load at nity power factor. Te test circit, specified in I Standard 1547, is confired as sown in Fi. 8. Te DG was started, syncronized to te tility rid, and ten te tie-switc S 2 was closed to interconnect te DG to te rid. Open switc S 1 and record te time between te openin of switc S 1 and wen te DG ceases to enerize te load. Repeat test to 4 types of loads for a total of 5 times. Te test is sccessfl wen te DG ceases to enerize te test load witin te timin reqirements of I Standard 1547 after switc S 1 is opened. Te effectiveness of te correlation factor metod for syncronos enerator as been validated in te experiments. Te test reslts for 4 types of loads are sown in Table 1. Te testin reslts sow tat te correlation factor, sed as an index of islandin detection, can detect te islandin operation easily and accrately. Te verification reslts also reveal tat te proposed correlation factor metod detected te islandin event wit a maximm delay time of 0.19 seconds in te 20 tests for 4 types of loads. Te averae detection time of te 20 tests is seconds. Te detection time needed is mc less tan te maximal 2 seconds as specified by I standard In te typical test for te type (a) load, as sown in Fi. 9 of te typical test for te resistive load as an instance, te detection sinal for islandin was issed in seconds (totally 9.5 cycles for estimatin te differential voltae manitdes were needed) after te islandin operation started. In te typical test for te type (b) load, as sown in Fi. 10, te detection sinal for islandin was iven in 0.15 seconds (totally 9 cycles needed) after te islandin operation started. Utility Grid S1 oad S2 Distribted Syncronos Fi.8 Te islandin test confiration for syncronos enerators Fi.9 Te reslts of te experiment for syncronos enerator sin type (a) load Table 1 Islandin test reslts of syncronos enerator oad combinations Averae Maximm Minimm Sccess times (a) (b) (c) (d) Fi.10 Te reslts of te experiment for syncronos enerator sin type (b) load ISSN: Isse 6, olme 7, Jne 2008

7 Wen-Yea Can In te typical test for te type (c) load, as sown in Fi. 11, te detection sinal for islandin was likewise annonced sccessflly in seconds (totally 11 cycles needed) after te islandin operation started. In te typical test for te type (d) load, as sown in Fi. 12, te detection sinal for islandin was likewise annonced sccessflly in seconds (totally 9.5 cycles needed) after te islandin operation started. In Fis. 9 to 12, Cannel 1 denotes te waveform of rid voltae (400/div), Cannel 2 indicates te waveform of local load terminal voltae (400/div), Cannel 3 depicts te switcin sinal of periodical electronic switc (5/div) and Cannel 4 sows te trippin sinal (5/div). Te capability of te proposed system to avoid false alarms was verified tro te experiments of randomly switcin te loads. Te random load switcin tests were taken 200 times for eac type of load; reslts depict tat no false alarm occrred ot of te 800 switcin tests. As an example of te typical test for te load at nity power factor, Fi. 13 exibits tat te detection system does not ave false alarms de to te load switcin. In Fi. 13, Cannel 1 denotes te waveform of rid voltae (400/div), Cannel 2 indicates te waveform of load crrent (1A/div), Cannel 3 depicts te switcin sinal of periodical electronic switc (5/div) and Cannel 4 sows te trippin sinal (5/div). To frter evalate te impact on te power qality de to te periodical voltae flctation injection by sin te correlation factor metod, tree power qality indices were measred tro a power qality analyzer. Te tree power qality indices evalated were total armonic distortion (THD), voltae flctation (P ST ) and tree pase nbalance. Comparison reslts between wit and witot te voltae flctation injection are iven in Table 2. Te table sows tat in normal operation of Table 2 Impact on te power qality by voltae flctation injection (syncronos enerator) Condition Wit voltae flctation injection Witot voltae flctation injection Power qality Pase index A B C THD 0.8% 0.6% 0.6% PST nbalance 0.4% THD 0.7% 0.6% 0.6% PST nbalance 0.5% Fi.11 Te reslts of te experiment for syncronos enerator sin type (c) load Fi.12 Te reslts of te experiment for syncronos enerator sin type (d) load Ti m e :2 0 ms/div Fi.13 Te reslts of te experiment for random switcin of te load ISSN: Isse 6, olme 7, Jne 2008

8 Wen-Yea Can syncronos enerator interconnected wit te tility rids, to te i-impedance load switcin occrred at te rid-interconnected point, te terminal voltae almost was not inflenced. Te differences between wit and witot te voltae flctation injection as sown in Table 2 are spposed to reslt from errors or noise from te measrement instrment. 4.2 Islandin test for indction enerators Te eneration system employed in te islandin tests for indction enerator consisted of a ridinterconnected, tree-pase, 220, 300W indction enerator driven by a DC motor wit 3 types of loads, incldin (a) 33% rated load at nity power factor, (b) 100% rated load at nity power factor, (c) 120% rated load at nity power factor. Te test circit, specified in I Standard 1547, is confired as sown in Fi. 14. Te DG was started, syncronized to te tility rid, and ten te tie-switc S 2 was closed to interconnect te DG to te tility rid. Adjst te islandin RC load circit in Fi. 14 to provide a qality factor of 1.0 ± Te reactive load is balanced so tat te resonant freqency of te island circit is witin te nder-freqency (59.5Hz) and over-freqency (60.5Hz) trip settins of te DG and as close to nominal freqency (60Hz) as possible. Open switc S 1 and record te time between te openin of switc S 1 and wen te DG ceases to enerize te load. Repeat test for 3 types of loads for a total of 5 times. Te test is sccessfl wen te DG ceases to enerize te test load witin te timin reqirements of I Standard 1547 after switc S 1 is opened. Te effectiveness of te correlation factor metod for indction enerator as been validated in te experiments. Te test reslts for 3 types of loads are sown in Table 3. Te testin reslts sow tat te correlation factor, sed as an index of islandin detection, can detect te islandin operation easily and accrately. Te verification reslts also reveal tat te proposed correlation factor metod detected te islandin event wit a maximm delay time of seconds in te 15 tests for 3 types of load combinations. Te averae detection time of te 15 tests is 0.11 seconds. Te detection time needed is mc less tan te maximal 2 seconds as specified by I standard In te typical test for te type (a) load, as sown in Fi. 15, te detection sinal for islandin was issed in seconds (totally 7 cycles for estimatin te differential voltae manitdes were needed) after te islandin operation started. In te typical test for te type (b) load, as sown in Fi. 16, te detection sinal for islandin was likewise annonced sccessflly in seconds (totally 8.5 cycles needed) after te islandin operation started. In te typical test for te type (c) load, as sown in Fi. 17, te detection sinal for islandin was likewise annonced sccessflly in 0.15 seconds (totally 9 cycles needed) after te islandin operation started. In Fis. 15 to 17, Cannel 1 denotes te waveform of rid voltae (400/div), Cannel 2 indicates te waveform of local load terminal voltae (400/div), Cannel 3 depicts te switcin sinal of periodical electronic switc (5/div) and Cannel 4 sows te trippin sinal (5/div). To frter evalate te impact on te power Utility Grid S1 S3 S2 RC oad Distribted Indction Fi.14 Te islandin test confiration for indction enerators CH1 :4 0 0 /div, CH2 :4 0 0 /div, CH3 :5 /div, CH4 :5 /div, Fi.15 Te reslts of te experiment for indction enerator sin type (a) load Table 3 Islandin test reslts of indction enerator oad Type Averae Maximm Minimm Sccess times (a) (b) (c) ISSN: Isse 6, olme 7, Jne 2008

9 Wen-Yea Can qality de to te periodical voltae flctation injection by sin te correlation factor metod, tree power qality indices were measred tro a power qality analyzer. Comparison reslts between wit and witot te voltae flctation injection are iven in Table 4. Te table sows tat in normal operation of indction enerator interconnected wit te tility rids, to te i-impedance load switcin occrred at te rid-interconnected point, te terminal voltae almost was not inflenced. Te differences between wit and witot te voltae flctation injection as sown in Table 4 are spposed to reslt from errors or noises of te measrement instrment. parameters will be investiated in te passive islandin detection metod. 5 Conclsions Based on a correlated voltae flctation sceme, tis paper as proposed a new metod to qickly and reliably detect islandin operation of a DG system. Te voltae flctation is injected on to te ridinterconnected point by switcin a i-impedance load periodically. Observin te correlation factor of te proposed sceme tro a diital sinal processor, discrimination between islandin and oter non-islandin distrbances can ts be made accrately. To verify te effectiveness of te proposed tecniqe, reslts obtained from experiments were sed in tis paper. Te experimental reslts sow tat te proposed index of te islandin detection correlation factor can detect te islandin operation satisfactorily for different types of loads witin seconds. Te detection performance is sown to be less dependent on load qality factor and power level. Besides, te test reslts also reveal tat te new proposed metod is easier and more economical for implementation as compared to te existin active detection approaces. Te directions for ftre researc of te islandin detection metod can be described as follow: To frter improve te detection performance of te proposed active islandin detection metod, te passive islandin detection metods tat detect te islandin operation of DG by monitorin te selected power system parameters will be investiated and interated in te proposed active metod. Besides, for te passive islandin detection metods, tere are many power system parameters to be monitored, sc as voltae manitde, te cane rate of freqency, pase displacement, and power otpt. Te sin of optimization searc metods, sc as enetic aloritm or neral networks, for te best combination selection of te selected power system Fi.16 Te reslts of te experiment for indction enerator sin type (b) load Fi.17 Te reslts of te experiment for indction enerator sin type (c) load Table 4 Impact on te power qality by voltae flctation injection (indction enerator) Condition Wit voltae flctation injection Witot voltae flctation injection Power qality index Pase A B C THD 0.5% 0.5% 0.5% P ST nbalance 0.4% THD 0.6% 0.7% 0.8% P ST nbalance 0.5% ISSN: Isse 6, olme 7, Jne 2008

10 Wen-Yea Can Acknowledements Te ator wold like to express is acknowledements to te National Science Concil of ROC for te financial spport nder Grant No. NSC References: [1].. Santos, A.G. Martins, and C.H. Antnes, A Mlti-Objective Model for Sizin and Placement of Distribted Generation, WSAS Transactions on Power Systems, olme 1, Isse 7, 2006, pp [2] Y.G. Heazy and M.A. Mostafa, Reliability Indices of lectrical Distribted Generation Systems, WSAS Transactions on Systems, olme 4, Isse 10, 2005, pp [3] A.H. Mantawy and M. Al-Maini, A New Particle-Swarm-Based Aloritm for Distribtion System xpansion Plannin Incldin Distribted Generation, Proceedins of te 2nd IASM/WSAS International Conference on nery & nvironment, ('07), Portoroz, Slovenia, 2007, pp [4] M.H. Aliabadi, M. Mardane, and B. Bebaani, Sitin and Sizin of Distribted Generation Unit Usin GA and OPF, Proceedins of te 2nd WSAS International Conference on Circits, Systems, Sinal and Telecommnications, (CISST'08), Acaplco, Mexico, 2008, pp [5] T.H. Cen, M.S. Wan, and N.C. Yan, Impact of Distribted Generation on oltae Relation by UTC Transformer sin arios xistin Metods, Proceedins of te 7t WSAS International Conference on Power Systems, Beijin, Cina, 2007, pp [6] A.S. Bretas and R.H. Salim, A New Falt ocation Tecniqe for Distribtion Feeders wit Distribted Generation, WSAS Transactions on Power Systems, olme 1, Isse 5, 2006, pp [7] K. Maki, S. Repo, and P. Jarventasta, Protection Coordination to Meet te Reqirements of Blindin Problems Cased by Distribted Generation, WSAS Transactions on Circits and Systems, olme 4, Isse 7, 2005, pp [8] D. Ardito, S. Conti, N. Messina, and S. Nicotra, Operatin Conflicts in Distribtion Networks Protection wit Distribted Generation, WSAS Transactions on Circits and Systems, olme 4, Isse 9, 2005, pp [9] G. Dalke, et al., Application of Islandin Protection for Indstrial and Commercial s an I Indstrial Application Society Workin Grop Report, Proceedins of te 59t Annal Conf. Protective Relay nineers, Texas, USA, 2006, pp [10] I Std. 1547, Standard for Interconnectin Distribted Resorces wit lectric Power Systems, [11] J.C.M. ieira, D.S. Correa, W. Freitas, and W. X, Performance Crves of oltae Relays for Islandin Detection of Distribted s, I Transactions on Power Systems, ol. 20, No. 3, 2005, pp [12] C.M. Affonso, W. Freitas, W. X,.C.P. da Silva, Performance of ROCOF Relays for mbedded Generation Applications, I Proceedins Generation Transmission Distribtion, ol. 152, No. 1, 2005, pp [13] W. Freitas,. Han, W. X, A Practical Metod for Assessin te ffectiveness of ector Sre Relays for Distribted Generation Applications, I Transactions on Power Delivery, ol. 20, No. 1, 2005, pp [14] S.I. Jan, K.H. Kim, An Islandin Detection Metod for Distribted Generations Usin oltae Unbalance and Total Harmonic Distortion of Crrent, I Transactions on Power Delivery, ol. 19, No. 2, 2004, pp [15] M.A. Redfern, O. Usta, G. Fieldin, Protection Aainst oss of Utility Grid Spply for a Dispersed Storae and Generation Unit, I Transactions on Power Delivery, ol.8, No.3, 1993, pp [16] F.S Pai, S.J. Han, A Detection Aloritm for Islandin-Prevention of Dispersed Consmer- Owned Storae and Generatin Units, I Transactions on nery Conversion, ol. 16, No. 4, 2001, pp [17] S.K. Salman, D.J. Kin, G. Weller, New oss of Mains Detection Aloritm for mbedded Generation Usin Rate of Cane of oltae and Canes in Power Factors, Proceedins of te 7t I International Conference on Developments in Power System Protection, Amsterdam, Neterlands, 2001, pp [18] S.I. Jan, K.H. Kim, Development of a oical Rle-Based Islandin Detection Metod for Distribted Resorces, Proceedins of te 2002 I Power nineerin Society Winter Meetin, New York, USA, 2002, pp [19] J.W. Warin, oss of Mains Protection, Proceedins of te RA Conference on Circit Protection for Indstrial and Commercial ISSN: Isse 6, olme 7, Jne 2008

11 Wen-Yea Can Installations, andon, UK, 1990, pp. 4/3/1 12. [20] P. D, J.K. Nelson,. Ye, Active Anti- Islandin Scemes for Syncronos-Macine- Based Distribted s, I Proceedins Generation Transmission Distribtion, ol.152, No.5, 2005, pp [21] P.D. Hopewell, N. Jenkins, A.D. Cross, ossof-mains Detection for Small s, I Proceedins lectrical Power Application, ol. 143, No. 3, 1996, pp [22] W.Y. Can, H.T. Yan, An Active Islandin Protection Metod for Distribted Syncronos s, Proceedins of te 7t IT International Conference on Advances Power System Control, Operation and Manaement, Hon Kon, Cina, 2006, Paper No. APSCOM ISSN: Isse 6, olme 7, Jne 2008