Grid Interaction of MV-connected CHP-plants during Disturbances

Transcription

1 Gid Intaction of MV-connctd CHP-plants duing Distubancs E.J. Cost, Studnt Mmb, IEEE, J.M.A. Myzik, and W.L. Kling, Mmb, IEEE Abstact Nowadays th amount of distibutd gnation (DG) units is incasing apidly. Most dominant a combind hat and pow (CHP) plants and wind tubins. At this momnt, in most systms, th a no quimnts dfind fo shotcicuit bhavio of such gnatos connctd to th mdium voltag gid. Howv in th futu this situation will not b accptabl anymo, sinc with th psnt potction sttings of DG a fault in th tansmission gid may lad to disconnction of a lag amount of DG ov a lag gogaphical aa. This pap focuss on CHP-plants connctd to th MV-gid. Nw sttings fo th und-voltag potction will b poposd. Ths sttings will b basd on voltag dip pofils and th fault id though capability of th CHP-plants. With th aid of dynamic simulations it is shown that th nw sttings of th und-voltag potction can lad to a significant impovmnt of th availability pfomanc without loosing th stability of th gnatos. Indx Tms Distibutd gnation, Voltag covy, Fault Rid though, Stability, Mdium voltag gids, T I. INTRODUCTION HE sha of distibutd and nwabl ngy soucs in th total ngy poduction is gowing. This is du to dvlopmnt of small on-sho and lag off-sho wind fams as wll as an incasing sha of Combind Hat and Pow plants (CHP-plants). Small wind fams and small CHP-plants a usually connctd to th distibution systm whil lag off-sho wind fams and lag pow plants with additional hat gnation a connctd to th tansmission systm. In od not to distub th fault-claing pocss wind tubins and small CHP-units a mostly disconnctd immdiatly aft a distubanc in th gid. Fo faults in th tansmission gid this can lad to a disconnction of a lag amount of gnatos which can caus a lag pow imbalanc. To pvnt this situation gid opatos hav st fault id though quimnts fo wind fams connctd to th tansmission systm. This sach has bn pfomd in coopation with STEDIN and Univsity of Tchnology Eindhovn. Th pojct is pat of th sach pogam Intllignt Pow Systms which is financially suppotd by Snt Novm. SntNovm is an agncy of th Dutch Ministy of Economic Affais. Edwad Cost is with STEDIN and Univsity of Tchnology Eindhovn, Rottdam, th Nthlands (mail: dwad.cost@stdin.nt) Johanna Myzik is with Univsity of Tchnology Eindhovn, Eindhovn, th Nthlands (mail: j.m.a.myzik@tu.nl) Wil Kling is with Univsity of Tchnology Eindhovn, Eindhovn, th Nthlands (mail: w.l.kling@tu.nl) In th Nthlands local authoitis has dsignatd ual aas wh hoticultual activitis can b dvlopd. In ths aas gnhouss a built and ach gnhous might contain a CHP-plant. Th CHP-plant poducs hat and CO 2 which is usd in th gnhous and th lcticity is sold to th makt. Bcaus of th clusting of hoticultual activitis th CHPplants a clustd as wll which lad to a high pntation lvl of CHP-plants in th local Mdium Voltag gid (MVgid). In th Dutch gid cod no fault-id though quimnts a st up fo gnation units small than 5 MW so th small CHP-units will disconnct at a voltag lvl of.8 p.u. if it holds fo a ctain tim piod. Fault id though quimnts bcom standad fo wind fams connctd to th tansmission gid. Small wind paks connctd to th distibution gid a still xmptd bcaus thy a spad out ov th aa. An impotant qustion is how lag th amount of gnation will b, that will b disconnctd in cas of a fault. Whth o not a plant will disconnct, will dpnd on th dpth of th voltag dip in combination with th sttings of th und-voltag potction. Th aim of this pap is to study on what voltag dip th CHPplants will disconnct. This will b xamind fo an xisting MV-gid stuctu including a lag pntation of CHPplants. In th pap tchniqus a dscibd to obtain voltag dip pofils which will b usd to assss which distubancs lad to a disconnction of th CHP-plant. Th pap nds with a commndation fo nw potction sttings fo th undvoltag potction including coodination with th gid potction. II. VOLTAGE DIPS Voltag dips a causd by shot cicuits, ovloads and stating of lag motos. Ths dips popagat though th pow systm and can lad to malfunctioning of quipmnt. Moov in MV-gids including DG-units voltag dips can caus dsiabl o undsiabl disconnction of ths DGunits. In som standads disconnction of DG-units is vn obligd in od not to distub th fault-claing pocss 2. Th CHP-plants connctd to th MV-gid a quippd with an und-voltag potction. This potction disconncts th CHP-plant whn a dip of a ctain dpth and duation occus in th lin-voltag. In this way, fo gids opatd with an isolatd nutal disconnction on local singl phas-togound faults a pvntd. Common sttings of th undvoltag potction a.8 p.u. with a claing tim of -2 ms /9/$ IEEE Authoizd licnsd us limitd to: Eindhovn Univsity of Tchnology. Downloadd on Apil 3,2 at 2:23:7 UTC fom IEEE Xplo. Rstictions apply.

2 2 A. Voltag dip chaactistics Voltag dips a chaactizd by th dpth, duation and fquncy of occunc. Th dpth of th dip is dtmind by th fault location, fd impdanc and fault lvl. Th dip duation is mainly dtmind by th fault-claing tim of th potction schm. An xact dfinition of a dip and its chaactistics can b found in 3. In this pap only dips causd by gid distubancs a considd. To stimat th dip fquncy a pobabilistic appoach is ndd using ntwok liability data. B. Popagation of unbalancd voltag dips Sv voltag dips occu causd by balancd th phas faults howv, most faults a unbalancd. Ths unbalancd faults lad to unbalancd voltag dips. Th popagation of voltag dips though diffnt typs of tansfom connctions sults in a diffnt appaanc of voltag dips at th sconday sid of th tansfoms 4. Also nutal gounding can hav a significant ffct on voltag dip popagation 5. Th ffct of th tansfom connction on voltag dip popagation is dmonstatd with a simulation of a fault at th HV-sid of th tansfom which is shown in a simpl tst gid in Fig.. systm has to b takn into account. In this pap an xisting tansmission gid of th wstn pat of th Nthlands is usd. A. Tansmission gid In Fig. 2 th tansmission systm of th povinc of Zuid Holland in th Nthlands is dpictd. Th tansmission systm consists of a 5 kv gid and is connctd to th national 38 kv tansmission gid at th locations. Lag pow plants a connctd to th tansmission gid. Fom th 5 kv nods th sub-tansmission gids a connctd via th winding tansfoms. In ach substation th nutal point of at last on tansfom is solidly goundd at th HVsid. Fault Fault Fig.. Tst gid to dtmin voltag dip popagation Fo vaious typs of faults th popagation of th voltag dips to th sconday sid of th tansfom is assssd. Bcaus th tip of CHP-plants is initiatd by a dip in th lin-voltag, dip popagation in th lin-voltag is studid. In tabl I fo vaious fault typs and tansfom connctions th voltag dip popagation is shown. A dtaild dsciption of th sults can b found in 4. TABLE I PROPAGATION OF UNBALANCED VOLTAGE DIPS Fault typ / tansfom typ Yy Yny Yd Ynd Singl phas-to-gound No No No Ys Phas-to-phas Ys Ys Ys Ys Doubl phas-to-gound Ys Ys Ys Ys Th phas fault Ys Ys Ys Ys Tabl I shows that th voltag dip causd by a multi phas fault always popagats to th sconday lin-voltag indpndnt of th tansfom connction. Fo a singl phasto-gound fault this only holds fo an Ynd connction. Du to th solid nutal gounding and th sconday dlta winding this tansfom connction has a low zo squnc impdanc. Most MV-gids a connctd via an Ynd tansfom to th tansmission gid hnc singl phas-togound faults can lad to disconnction of CHP-plants. Fig. 2. Tansmission systm of th povinc of Zuid Holland, th Nthlands B. Distibution gid Voltag dips which caus disconnction of CHP-plants oiginat fom gid distubancs at diffnt voltag lvls. Thfo th sub-tansmission gid and th MV-gid of th aa of intst a modld as wll. In this pap an xisting distibution gid stuctu is considd built in a hoticultual aa wh CHP-plants a connctd to. An ovviw of th distibution gid is dpictd in Fig. 3. Th considd distibution gid consists of a kv MV-gid which is connctd to a 25 kv sub-tansmission gid. Th subtansmission gid is via 5/25 kv tansfoms connctd to substation sub 23 of th 5 kv tansmission gid shown in Fig. 2. At th 25 kv sid all tansfoms a goundd via a sisto of Ω. Th kv distibution gid is opatd with an isolatd nutal point and adial fds wh th CHPplants a connctd to. Th data of th load and gnation connctd to th kv distibution gid is givn in tabl II. III. TEST NETWORK Tansmission systms nomally hav a ing o mshd gid stuctu. Faults in ths systms can caus voltag dips which cov a lag aa. Thfo in a dip analysis th tansmission Fig. 3. Ovviw of th distibution gid in a hoticultual aa Authoizd licnsd us limitd to: Eindhovn Univsity of Tchnology. Downloadd on Apil 3,2 at 2:23:7 UTC fom IEEE Xplo. Rstictions apply.

3 3 TABLE II DATA OF THE DISTRIBUTION GRID OF FIGURE 3 Numb of units S MVA Load Load Load Load Load CHP CHP CHP IV. VOLTAGE DIP PROFILES In this pap a voltag dip analysis is applid to dtmin what voltag dip can b xpctd at th tminals of th CHPplants. Basd on th dip pofil and th dip duation th ffct of th voltag dips on th CHP-plants can b assssd and nw sttings of th und-voltag potction can b poposd. To obtain th voltag dip pofil of th tst systm, this systm is modld in softwa packag Pow Factoy. As mntiond ali th voltag dip fquncy is latd to th failu at of th componnts in th systm. Basd on statistics of th Nthlands fo th failu at of HV-lins and MV-cabls spctivly a valu of.54 tims p annum/ km and.2 tims p annum/ km is usd and incopoatd in th modl. A. Voltag dip analysis In th simulation softwa th voltag dip analysis bgins with a simulation of vaious faults at all lvant busbas. It stats with th slctd busba and pocds to nighboing busbas until th voltag at th slctd busba dos not dop blow th xposd aa limit. Th voltag dip assssmnt continus with fault calculation at th middl of all lvant lins and cabls. Duing th simulation all valus of th maining voltags a stod and th fquncy of th voltag dips a dtmind with th aid of th failu ats of th vaious componnts. In th simulation softwa a tool is availabl to calculat voltag dip pofils. With th aid of this tool, th failu at and fault distibution vaious voltag dip pofils a constuctd fo a busba in th MV-gid of Fig. 3. In th voltag dip pofil th dpth of dip, fquncy of occunc and its oigin is shown. Fo th fault typ distibution th figus shown in tabl III a usd. TABLE III OVERVIEW OF THE FAULT DISTRIBUTION Componnt 3 ph ph 2 ph 2 ph-gound HV OH-lin 5% 7% 5% % MV cabl 2% 8% B. Effct of CHP-plants on voltag dip pofils In it is mntiond that th dip magnitud is mitigatd by local connctd gnatos. This holds fo faults in th local MV-gids as wll as fo dips du to faults in th st of th systm. Duing such faults th CHP-plants kp up th voltag at its local bus by fding into th fault. This is illustatd with th calculation of th voltag dip pofil of busba 28 in th distibution gid (Fig. 3). Th voltag dip pofil is obtaind fo th cas with and without all CHP-plants connctd. In Fig. 4 th voltag dip pofil xcluding th CHP-plants is shown..4.2 / a a.8 y p.6 s im T.4 kv 25 kv 5 kv 38 kv U p.u. Fig. 4. Voltag dip pofil of busba 28 xcluding CHP-plants Th voltag dip pofil fo th cas including th CHP-plants is dpictd in Fig. 5. It can b concludd that du to th contibution of th CHP-plants th numb of dp dips is dcasing and tansfomd to mo shallow dips..4.2 a / a.8 y p.6 s im T.4 kv 25 kv 5 kv 38 kv U p.u. Fig. 5. Voltag dip pofil of busba 28 including CHP-plants In Fig. 4 and 5 it can b sn that most voltag dips a causd by distubancs in th tansmission systm. This is bcaus of th mshd gid stuctu of th tansmission systm as wll as th long lngth of th HV-lins and cabls. Th MV-gid is opatd adial and th fd lngth is lativly shot in compaison with th lngth of th HV-lins and cabls. Howv, th most sv voltag dops a causd by distubancs in th local MV-gid. C. Fault typs Bsids th oigin of th voltag dip th typ of fault causing th voltag dip is also of impotanc. Th voltag dip pofil of Fig. 5 is convtd to a dip pofil with th distibution of fault typs. This pofil is shown in Fig a / a.8 y p.6 s im T.4 3 phas 2 phas 2 phas-to-gound Singl phas-to-gound U p.u. Fig. 6. Voltag dip pofil including fault typ distibution Whn compaing Fig. 5 and 6 it can b sn that th dips with magnitud <.8 a mainly causd by th phas and singl phas-to-gound faults. Compaing th sha of dips Authoizd licnsd us limitd to: Eindhovn Univsity of Tchnology. Downloadd on Apil 3,2 at 2:23:7 UTC fom IEEE Xplo. Rstictions apply.

4 4 oiginating fom th tansmission systm and th numb of singl phas-to-gound faults, it can b concludd that singl phas-to-gound faults in th tansmission systm also causs dips in th lin-voltag at mdium voltag lvl. This is du to th tansfom connctions of th HV/MV tansfoms as mntiond in sction II. D. Dip duation In gnal th duation of th voltag dip is dtmind by th fault-claing tim of th potction schm. Th faultclaing tim is stongly latd with th typ of applid potction. Th tansmission systm considd in this pap is potctd by distanc and diffntial potction. Th diffntial potction schm has a claing tim of 9-2 ms. That also stands fo th distanc potction whn th fault is clad in zon. In this pap only faults clad in zon a considd. Th sub-tansmission and distibution gid of Fig. 3 a potctd by ov-cunt lays. Th potction sttings a givn in tabl IV. TABLE IV OVERVIEW OF PROTECTION SETTINGS OF SUB-TRANSMISSION AND DISTRIBUTION GRID Substation I pick-up I ka t cla ms Sub 26 I nom 5 3 Sub 28 2 I nom.2 9 Sub 3 2 I nom.2 9 Sub 3 2 I nom.2 9 Slctiv fault claing in th sub-tansmission and distibution gid is obtaind by th diffntiation in pick-up cunt. Th stting of th pick-up cunt in th subtansmission gid is such that th potction only picks up th fault cunt in th sub-tansmission gid. Th gid contibution of th sub-tansmission gid to faults in th distibution gid stays blow th pick-up cunt of th potction. In this way in th sub-tansmission gid low faultclaing tims can b achd without lost of slctivity. Th fault-claing tims of tabl IV can b combind with th dip pofil of Fig. 5. In fig. 7 a scatt plot of th voltag dip vs. fault-claing tim is givn. In this plot it is assumd that voltag dips oiginating fom th 38 and 5 kv gid hav an avag duation of 9 ms u..6 p.5 g a lt o.4 V.3. claing tim 38/5 kv dips claing tim 25 kv dips Tim s Fig. 7. Ovviw of dip duation basd on dip pofil and fault-claing tim To chck th assumptions of th fault-claing tim of voltag dips oiginating fom th 38 and 5 kv gids, in Fig. 8 a scatt plot of masud voltag dips is shown. This plot is basd on tn ya histoical data of a fault coding databas wh all voltag dips at substation 3 a gistd. Th voltag dips a masud at a voltag lvl of 25 kv. In th plot it can b sn that tansmission gid faults a clad in a tim piod of 9-2 ms. Voltag dips of th subtansmission gid a also shown, howv th duation of th dips stongly dpnd on th fault-claing tim of th local potction schm. Bcaus of th mshd stuctu of th tansmission gid th sam kind of voltag dip masumnts can b xpctd at substation u. p.6 g a.5 l t o V.4.3 faults unknown location faults 2 and 25 kv faults 5 kv faults 38 kv Tim ms Fig. 8. Ovviw of voltag dip masumnts at substation 3 E. Effct of voltag dips on CHP-plants Cunt sttings of th und-voltag potction a put at.8 p.u. with a claing tim of -2 ms. Fom Fig. 7 it is obvious that all CHP-plants disconnct duing a distubanc in th sub-tansmission gid. Howv, du to th sisto gounding, this only occus duing a th phas fault and a two phas-to-gound fault (s Fig. 6). Fo th fault-claing tim of th tansmission gid faults a claing tim of 9 ms is assumd. Fig. 8 shows a scatt in th dip duation of tansmission gid faults and spcially fault-claing tim in th 5 kv gid can xcd 9 ms. This mans that th stting of th und-voltag potction at a claing tim of ms can lad to switching-off of a lag amount of CHP-plants. In th nxt sction nw sttings of th und-voltag potction will b poposd in such a way that unncssay disconnction of CHP-plants is pvntd as much as possibl. V. FAULT RIDE THROUGH OF CHP-PLANTS Duing gid distubancs synchonous machins tnds to acclat. In th stabl cas aft fault claing th oto swings via an oscillatoy motion to th quilibium point 6. Small CHP-plants, consisting of a gas ngin as pim mov and a synchonous machin as gnato, show ths dynamics as wll. Immdiat disconnction of CHP-plants duing a voltag dip pvnts instability of th gnatos. Howv this can jopadiz th scuity of supply. Hnc nw sttings of th und-voltag potction hav to b chosn in such a way that instability of th CHP-plants is pvntd. A. Citical Claing Tim Kping th CHP-plants connctd to th gid mans that th units hav to withstand a ctain voltag dip without losing synchonism. A masu fo stability of synchonous machins is th Citical Claing Tim (CCT). Th citical claing tim is th ability of a synchonous machin to withstand a voltag dip with a ctain dpth and duation and stay in stabl opation. Fo all typ of CHP-plants connctd to th tst systm th CCT is dtmind. In tabl V th simulation figus of th CHP-plants a givn. Authoizd licnsd us limitd to: Eindhovn Univsity of Tchnology. Downloadd on Apil 3,2 at 2:23:7 UTC fom IEEE Xplo. Rstictions apply.

5 5 TABLE V SIMULATION FIGURES OF CHP-PLANTS S MVA P MW H s p.f In nomal opation th CHP-plants a opatd with unity pow facto. In 7 it is dscibd in dtail how th CCT of th CHP-plants is obtaind. In fig. 9 th CCT-cuvs a dpictd u. p.35 i p d U CCT 4.56 MVA CCT MVA CCT MVA CCT 3.3 MVA t s Fig. 9. CCT-cuvs fo th CHP-plants connctd to th tst systm th voltag dip pofil of fig. 5 th dpst voltag dip of a sub-tansmission gid fault is.4 p.u. In tabl IV it is statd that th fault-claing tim of faults in th sub-tansmission gid is 3 ms. Th und-voltag potction will sns th voltag dip but th fault is clad bfo th und-voltag potction tips th CHP-plants. Although switching-off of CHP-plants bcaus of faults in th (sub)-tansmission gid is pvntd by th two dfind lvls, fo dp voltag dips th CHP-plants still can bcom unstabl. Thfo two xta lvls a dfind. Fo faults in th MV-gid dp voltag dips a xpctd. Moov th fault-claing tim in th MV-gid is st to 9 ms. In fig. 9 it is indicatd that fo dp voltag dips th CCT is ath low and cannot mt th fault-claing tim. To pvnt instability of th CHP-plants th two xta lvls of th und-voltag potction a st to.35 p.u.~2 ms and p.u.~ ms. In cas of a fault in th MV-gid ths lvls a xcdd and th CHP-plants a disconnctd. In tabl VI th sttings a summaizd and dpictd gaphically in fig.. TABLE VI PROPOSED SETTINGS OF THE UNDER-VOLTAGE PROTECTION B. Nw potction sttings Now th dynamic bhavio of th CHP-plants and th xpctd voltag dips at th gnato tminals a known th nw sttings fo th und-voltag potction can b dfind. Th goal of th nw sttings is to pvnt disconnction of a lag numb of CHP-plants. Faults in th MV-gid only affct th local distibution gid whil th voltag dip dos not popagat via th sub tansmission gid to nighbouing MVgids. Also th dips in th local MV-gid do not caus disconnction of a lag numb of CHP-plant. To pclud islanding it is vn dsiabl to disconnct th CHP-plants connctd to th faultd MV-gid. Fo th nw sttings th following pincipls has bn chosn: Tansmission gid faults: Fault Rid Though of CHP-plants Sub-tansmission gid faults: Fault Rid Though of CHP-plants Local MV-gid faults: Disconnction of CHP-plants Fo th assssmnt of th nw sttings of th und-voltag potction th possibl oom offd by th wost cas CCTcuv of figu 9 is usd. In this study th CHP-plant of MVA has th most citical CCT-cuv and is takn as a fnc. In figu 5 it has bn shown that most voltag dips a causd by faults in th 5 kv tansmission gid. As statd ali it is assumd that th avag claing tim of ths faults is 9-2 ms. Th disconnction of CHP-plants du to th dips of th tansmission gid can b pvntd by stting th fist pick-up lvl of th und-voltag potction at.8 p.u. ~ 5 ms. Tansmission gid faults a clad fast than 5 ms so th CHP-plants stay connctd. Fo dp voltag dips th tim stting of 5 ms xcds th CCT of th CHP-plants which lad to unstabl opation. Thfo xta sttings hav to b addd to th und-voltag potction. Th scond lvl of th und-voltag potction is st to.5 p.u. ~ 4 ms. This stting pvnts disconnction duing faults in th sub-tansmission gid. In accodanc with s 5 m t Pick-up voltag p.u. Claing tim ms Lvl.8 5 Lvl Lvl Lvl U p.u. Fig. Poposd potction sttings fo th und-voltag potction VI. SIMULATION RESULTS In od to chck th ffct of th poposd lay sttings on th availability of th CHP-plants aft a gid distubanc dynamic simulations a pfomd. Th simulations a caid out with th aid of th tst ntwok as dscibd in sction III. Th cass of intst a: Tansmission gid distubanc Sub-tansmission gid distubanc Distibution gid distubanc Th modl of th CHP-plants is basd on a fifth od synchonous machin modl which is availabl in Pow Factoy. Th modl is quippd with a gnic IEEE typ voltag contoll. Machin and contoll paamts a povidd by th manufactu. Th poposd sttings fo th und-voltag potction a implmntd in th lay modl which is incopoatd in th modl of th CHP-plant. In th simulations th bhavio of th oto angl is takn as a stability indx. Th lin-voltag of vaious busbas in th tst Authoizd licnsd us limitd to: Eindhovn Univsity of Tchnology. Downloadd on Apil 3,2 at 2:23:7 UTC fom IEEE Xplo. Rstictions apply.

6 6 systm is usd to chck if th simulation sults a in complianc with th xpctd bhavio of th nw sttings of th und-voltag potction. A. Tansmission gid faults Th fault in th tansmission gid consists of a lin fault btwn sub 22 and 23. In fig. 2 th simulatd fault location is indicatd. Th simulatd fault typs a a th phas, doubl phas-to-gound and a singl phas-to-gound fault which a simulatd fo 2 ms. In fig. th lin-voltags of sub 23, 26 and 28 a dpictd duing a th phas fault B. Sub-tansmission gid faults Th ffct of th poposd sttings of th und-voltag potction on th CHP-plants is also chckd fo subtansmission gid faults. In fig. 3 th simulatd fault location is givn. Th dfinit ov-cunt potction in th subtansmission gid dtmins th dip duation and is st to 3 ms. In fig. 2 fo a th phas fault th lin-voltag of substation 28 and 29 is shown. Th voltag dip xcds.8 p.u. and th und-voltag potction dos disconnct all CHPplants within ms. Duing th fault, lvl and 2 of th und-voltag potction a xcdd. Aft fault claing th voltag iss abov th pick-up valu of lvl 2 and only lvl stays tiggd. Du to th gid intaction of th CHP-plants th is a dlay in voltag covy. Bcaus of this dlayd voltag covy th sttings of lvl a xcdd and at 5 ms th CHP-plants a switchd off. Simulations hav shown that disconnction of CHP-plants only occus du to a th phas fault at a ctain location. Fo oth locations th CHP-plants do not disconnct. Duing th simulation of all oth typs of faults th CHP-plants stay connctd and in stabl opation. Fo all typs of faults th sults a givn in tabl VIII s Lin voltag p.u.: Sub 28 Lin voltag p.u.: Sub 26 Lin voltag p.u.: Sub 23 Fig.. Voltag dip at vaious busbas du to a th phas fault in th tansmission gid In fig. it can b sn that th voltag of sub 28 dops blow.8 p.u. This mans that fo th convntional stting of th und-voltag potction of.8 p.u.~ ms, it is xpctd that all CHP plants disconnct. Th und-voltag potction with th nw poposd sttings dos not disconnct th CHPplants duing th voltag dip. Fig. also shows th contibution of th CHP-plants to th distubanc. Th CHPplants ty to kp up th voltag of sub 28. Bcaus of th dcaying DC-componnt in th cunt contibution of th gnatos th voltag stats to dop. Aft fault claing th covy of th voltag of sub 26 & 28 is dlayd bcaus of th gid intaction of th CHP-plants. In 8 simila simulations a caid out and th sults also show th dlayd voltag covy but is not mntiond xplicitly. A singl phas-to-gound fault sults in a shallow voltag dip which popagats in th lin-voltag as discussd in sction II. Howv it dos not lad to a disconnction of CHP-plants. In tabl VII fo all fault typs th sults a givn. Fo all fault typs th fault-claing tim and th accompanying voltag dip is such that th CHP-plants stay in stabl opation. TABLE VII SIMULATION RESULTS OF A TRANSMISSION GRID FAULT Fault typ Disconnction of CHP-plants Convntional stting Poposd stting 3 phas Ys No 2 ph-to-gnd Ys No phto-gnd No No s Lin voltag p.u.: Sub 29 Lin voltag p.u.: Sub 28 Fig. 2. Voltag dip at substation 28 & 29 du to a th phas fault in th sub-tansmission gid TABLE VIII SIMULATION RESULTS OF A SUB-TRANSMISSION GRID FAULT Fault typ Disconnction of CHP-plants Convntional stting Poposd stting Sub 28 Sub 29 Sub 28 Sub 29 3 phas Ys Ys Ys Ys 2 ph-to-gnd Ys Ys No No ph-to-gnd No No No No C. Distibution gid faults In this sction th ffct of th poposd sttings a chckd with simulations of a fault in th distibution gid. In fig. 3 th MV-gid of sub 28 is shown in mo dtail. To sub 28 adial MV-fds a connctd including th CHP-plants. Th MV-fds connctd to sub 29 a mo o lss simila to th MV-fds of sub 28. In fig. 3 th simulatd fault location is dpictd. 3. Authoizd licnsd us limitd to: Eindhovn Univsity of Tchnology. Downloadd on Apil 3,2 at 2:23:7 UTC fom IEEE Xplo. Rstictions apply.

7 Th simulations a patd fo th cas with th opn coupling baks. Fig. 5 givs th voltag dips at faultd sction of substation 28 and th busba voltag of substation 29. Du to th opning of th coupling baks only th CHPplants of th faultd sction of substation 28 a disconnctd. Thfo th is no significant jump in th voltag of th faultd sction of substation 28. Fo CHP-plants connctd to substation 29 lvl of th und-voltag potction is not tiggd Fig. 3. Dtails of th MV-gid of substation 28 In fig. 3 in th busba of substation 28 two coupling baks a incopoatd. Fo limitation of th fault lvl th substation is opatd with opn coupling baks. Howv, to study th ffct of th coupling baks th simulations a also caid out fo th situation with closd coupling baks. In fig. 4 th sults of th simulation of a th phas fault is givn fo th cas with th closd coupling baks. Th fault duation is 9 ms which is in accodanc with th fault-claing tim mntiond in tabl IV s Lin voltag p.u.: Sub 29 Lin voltag p.u.: Sub 28 Fig. 4. Voltag dip at substation 28 & 29 du to th phas fault in MV-gid of substation 28 (coupling baks closd) Th voltag dip at substation 28 xcds th convntional stting as wll as th nw poposd stting of th undvoltag potction. Hnc fo both sttings all CHP-plants connctd to substation 28 will b disconnctd. In fig. 4 it can b sn that th CHP-plants of substation 28 a clad aft 2 ms (Lvl 3 of th und-voltag potction). Bcaus th CHP-plants ty to kp up th voltag not all und-voltag potctions a tiggd at th sam tim. Thfo th is a small scatt in fault-claing tim of th individual CHP-plants. Th fault also causs a voltag dip at substation 29. Th voltag dops blow.8 p.u. which tiggs lvl of th und-voltag potction. Bcaus of th fault-claing tim of 9 ms, all CHP-plants connctd to th MV-gid of substation 29 disconnct in 5 ms. In fig. 4 aft 5 ms th busba voltag of substation 29 shows a suddn dcas which is th momnt of th disconnction of all CHP-plants s Lin voltag p.u.: Sub 29 Lin voltag p.u.: Sub 28 Fig. 5. Voltag dip at substation 28 & 29 du to th phas fault in th MVgid of substation 28 (coupling baks opn) In tabl IX fo th cas with th closd coupling baks th sults fo all simulatd fault typs in th MV-gid of substation 28 a shown. Th sults fo th cas with th opn coupling baks a givn in tabl X. Bcaus th MV-gid is opatd with an isolatd nutal th CHP-plants do not disconnct duing singl phas-to gound faults. In systms with an isolatd nutal ths faults do not lad to a voltag dip in th lin-voltag. TABLE IX SIMULATION RESULTS OF A FAULT IN THE MV-GRID OF SUBSTATION 28 (COUPLING BREAKERS CLOSED) Fault typ Disconnction of CHP-plants Convntional stting Poposd stting Sub 28 Sub 29 Sub 28 Sub 29 3 ph Ys Ys Ys Ys 2 ph-to-gnd Ys No Ys No ph-to-gnd No No No No Unncssay disconnction of th CHP-plants of substation 29 can b pvntd by ducing th fault-claing tim in th MV-gid. Th unncssay disconnction of CHP-plants in substation 29 is initiatd by xcding lvl of th poposd sttings which switchs off th CHP-plants in 5 ms. Whn in substation 28 th fault-claing tim is ducd fom 9 ms to 3 ms th CHP-plants of substation 29 stay connctd. Rducing th fault-claing tim to 3 ms ducs th voltag dip duation and unncssay disconnction of CHP-plants is pvntd. Th fault-claing tim can b ducd by applying an xta pick-up lvl in th dfinit ov-cunt potction which is also mntiond in 8. Th sttings a such that th potction only picks up sv fault cunts. 3. Authoizd licnsd us limitd to: Eindhovn Univsity of Tchnology. Downloadd on Apil 3,2 at 2:23:7 UTC fom IEEE Xplo. Rstictions apply.

8 8 TABLE X SIMULATION RESULTS OF A FAULT IN THE MV-GRID OF SUBSTATION 28 (COUPLING BREAKERS OPEN) Fault typ Disconnction of CHP-plants Convntional stting Poposd stting Sub 28 Sub 29 Sub 28 Sub 29 3 ph Ys No Ys No 2 ph-to-gnd Ys No Ys No ph-to-gnd No No No No 6 P. Kundu, Pow systm Stability and Contol, Nw Yok: McGaw- Hill, E.J. Cost, A. Ishchnko, J.M.A. Myzik and W.L. Kling, Compaison of Pactical Fault Rid Though Capabilitis fo MV-connctd DGunits, Psntd at 6 th Pow Systm Computation Conf., Glasgow, Scotland, 28 8 F.M. Gatta, F. Ilicto, S. Lauia and P. Masato, Modlling and Comput simulations of Dispsd Gnation in distibution Ntwoks. Masus to pvnt disconnction duing systm distubancs, psntd at Pow Tch conf. Bologna, Italy, 23 VII. CONCLUSIONS In this pap th fault id though bhavio of MVconnctd CHP-plants is discussd. It is shown that th convntional sttings of th und-voltag potction lad to disconnction of CHP-plants duing gid distubancs. To dfin nw sttings fo th und-voltag potction th appoach of voltag dip pofils is chosn. Th voltag dip pofil shows that most voltag dips a causd du to tansmission gid distubancs. Fo ths dips th is no nd to disconnct th CHP-plants and th sttings of th undvoltag potction a chosn such that this is pvntd. Fo th nw sttings of th und-voltag potction fou lvls a dfind. Th sttings of ths lvls a basd on th xpctd voltag dips at th tminals of th CHP-plants and th CCT of th CHP-plants. With th aid of dynamic simulations th poposd sttings a chckd. It can b concludd that th appoach of th voltag dip pofil is a good stating point but th dynamics of th voltag dip hav also b takn into account. Th simulation sults show that th nw sttings pvnt disconnction of CHP-plants duing faults in th tansmission gid. Fo th sub-tansmission gid most faults do not lad to a disconnction of CHP-plants. Bcaus of th shot fd lngth in th sub-tansmission gid fo som th phas faults th CHP-plants a switchd off. As poposd, fo faults in th distibution gid a limitd numb of CHP-plants disconnct. This numb can b futh ducd by ducing th fault-claing tim fo faults in th MV-gid. In gnal th appoach dscibd in this pap can also b applid to oth tansmission and distibution gids. Diffnt voltag dip pofils can lad to diffnt tigg lvls of th und-voltag potction. Moov, diffnt fault-claing tims of th tansmission and distibution gid potction schms in combination with th citical claing tims of oth typs of otating DG can lad to diffnt claing tims of th und-voltag potction. Howv, th appoach still holds. IX. BIOGRAPHIES Edwad Cost (S' 6) was bon in Lidn, Th Nthlands, in 972. H civd th B.ng dg in lctical ngining fom TH Rijswijk in 997 and th M.Sc. dg in lctical ngining fom Dlft Univsity of Tchnology in 2. Fom 2 h is as a snio spcialist fo ntwok planning with STEDIN. In apil 26 h pat-tim joind th Elctical Pow Systm goup, Eindhovn Univsity of Tchnology to stat a Ph.D. sach pojct. His filds of intst a: Distibutd Gnation, Pow Systm Potction, Dynamic Bhavio and Stability of Pow Systms. Johanna Myzik was bon in Damstadt, Gmany in 966. Sh civd h M.Sc. in Elctical Engining fom th Damstadt Univsity of Tchnology, Gmany in 992. Fom 993 to 995 sh wokd as a sach at th Institut fo Sola Engy Supply Tchnology (ISET.V.) in Kassl, Gmany. In 995 Ms. Myzik joind th Kassl Univsity, wh sh finishd h Ph.D. thsis in th fild of sola invt topologis in 2. Sinc 2, Ms. Myzik is with th Eindhovn Univsity of Tchnology, th Nthlands. In 22, sh bcam an assistant pofsso and in 28 an associat pofsso in th fild of sidntial lctical infastuctus. H filds of intsts a: pow lctonics, nwabl ngy, distibutd gnation, lctical pow supply. Wil Kling (M'95) was bon in Hsch, th Nthlands in 95. H civd th MSc. dg in lctical ngining fom th Tchnical Univsity of Eindhovn, th Nthlands, in 978. Fom 978 to 983 h wokd with KEMA and fom 983 to 998 with Sp. Sinc thn h was with TnnT, th Dutch Tansmission Systm Opato, as a snio ngin fo ntwok planning and ntwok statgy. Sinc 993 h is a pat-tim Pofsso at th Dlft Univsity of Tchnology and sinc 2 h was also a pat-tim Pofsso in th Elctical Pow Systms goup at th Eindhovn Univsity of Tchnology, th Nthlands. At th nd of 28 h is appointd as a fulltim pofsso and chai of th EPS goup at th Eindhovn Univsity of Tchnology. H is lading sach pogams on distibutd gnation, intgation of wind pow, ntwok concpts and liability. M. Kling is involvd in scintific oganizations such as Cig and IEEE. H is th Dutch psntativ in th Cig Study Committ C6 Distibution Systms and Dispsd Gnation. VIII. REFERENCES M.H.J. Bolln, Undstanding Pow Quality Poblms, Voltag Sags and Intuptions, Nw Jsy: IEEE pss, IEEE Standad fo Intconnction Distibutd Rsoucs with Elctic Pow Systms, IEEE Standad 547 July J.F.G. Cobbn, Pow quality, implications at th point of connction Ph.D. disstation, Dpt. Elct. Eng. Univ. Eindhovn, Eindhovn, 27 4 M.T. Aung and J.V. Milanović, Th Influnc of Tansfom Winding Connctions on th Popagation of Voltag Sags, IEEE tans, Pow Dlivy, vol. 2 pp , Jan J.R. Guillén, R. Rodíguz and M.A. Alonso, Influnc of Tansfom Connction Goup and Nutal Eathing on Fault Svity in Wind Fams, psntd at th Nodic Wind Pow conf. Espoo, Finland, 26 Authoizd licnsd us limitd to: Eindhovn Univsity of Tchnology. Downloadd on Apil 3,2 at 2:23:7 UTC fom IEEE Xplo. Rstictions apply.