SIMULATION OF THREE PHASE THREE LEG TRANSFORMER BEHAVIOR UNDER DIFFERENT VOLTAGE SAG TYPES

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1 SIMULATION OF THREE PHASE THREE LEG TRANSFORMER BEHAVIOR UNDER DIFFERENT VOLTAGE SAG TYPES Mhammadreza Dlatan Alreza Jallan Department f Electrcal Engneerng, Iran Unversty f scence & Technlgy (IUST) e-mal: mhammadreza_dlatan@yah.cm e-mal: Jallan@ust.ac.r Key wrds: Vltage Sag, Three phase three leg transfrmer, Inrush current ABSTRACT Vltage sags are usually caused by energzng heavy lads such as arc furnaces, startng f large mtrs, sngle lne t grund (SLG) faults, lad transferrng frm ne pwer surce t anther etc. Vltage sags can cause prblems n sme electrcal equpment such as transfrmers, nductn mtrs etc. Smulatn shws that transfrmer saturatn s prduced when the vltage sag s recvered. It prduces dc magnetc flux and causes transfrmer saturatn. Inrush current smlar t that f transfrmer energzng s als created. In ths paper the effects f vltage sag type, depth and duratn are nvestgated by smulatn f a three phase transfrmer n Matlab envrnment. It s shwn that the current pea has a perdcal dependence n sag duratn n symmetrcal vltage sags. The lnear nfluence f sag depth s bserved n the nrush current pea value. It s als shwn that unsymmetrcal sags can prduce current pea as hgh as thse f symmetrcal vltage sags. 1. INTRODUCTION Pwer qualty prblems have sgnfcant nfluences n dfferent equpments such as transfrmers. Vltage sag s a majr cause f mal-functn f electrcal devces and equpment n electrcal systems, ndustral prcess, etc [1. It s reprted that the ttal damages due t vltage sags are hgher than ther pwer qualty prblems [2. Recently, behavur f three phase three leg transfrmer under dfferent vltage sag cndtns s nvestgated. One mdel fr three phase three leg transfrmer n PSPICE s ntrduced n [3. The transfrmer was mdelled wth varable characterzatn f ts nnlnear magnetc behavur. Each leg was vewed as a separate magnetc crcut and a functn was prpsed t represent cre nnlnear behavur. There was a functnal relatnshp between the magnetc ptental n the leg and the flux thrugh t. The mdel was mplemented and the transfrmer behavur under dfferent sag depth, duratn and ntal pnt n wave n symmetrcal vltage sag was reprted [4. Mdellng f three phase three leg transfrmer peratng under dfferent types f vltage sag n PSPICE was mplemented and reprted n [5. Unsymmetrcal vltage sag effect n transfrmer and current pea relatn wth type f vltage sags, duratn and depth was nvestgated. In ths paper a three phase three leg transfrmer and all type f vltage sags are mdelled n MATLAB/SIMULINK envrnment fr smulatn purpses. Fr prducng dfferent types f vltage sag a blc s created n MATLAB/SIMULINK t tae the parameters f vltage sag such as sag duratn ( t), depth (h) and ntal pnt n wave. In the next step the prduced vltages are appled t the transfrmer mdel separately n rder t evaluate the transfrmer behavur. The transfrmer mdel whch was mplemented n MATLAB/SIMULINK s based n the prevusly develped mdel [3. 2. CHARACTERIZATION AND SIMULATION OF VOLTAGE SAGS There are dfferent types f vltage sags whch are characterzed by ts magntude, duratn and phase angle jump. Phase angle jump depends n X/R rat f the surce and feeder. Anther reasn fr phase angle jump s the changng f the vltage t lwer level [2. Vltage sags are dvded n t 7 grups as types A t G [3. Three phase faults cause type A whch s symmetrcal vltage sag. Unsymmetrcal vltage sags are due t sngle phase and phase t phase faults [4. T clear these faults crcut breaers usually act at zer crssng pnt f current. The number f sequences fr vltage recvery depends n the fault type and can prduce 14 sub-grups as descrbed n [3. Fg.1 shws the blc that s mplemented n MATLAB/SIMULINK fr smulatn dfferent types f vltage sag. All type f vltage sag are prduced wth changng vltage sag characterstcs (sag duratn ( t), sag duratn (h) and ntal pnt n wave ( ) ).

2 vltage sag characterstcs s peratn f transfrmer s cnsdered under dfferent characterstcs f vltage sags. 4. TRANSFORMER OPERATION UNDER VOLTAGE SAG Transfrmer s smulated under symmetrcal vltage sag frst. Effects f vltage sag duratn, vltage sag depth and ntal pnt n wave n transfrmer has been nvestgated where the transfrmer lad s 0.8 p.u. Fg.1. MATLAB/SIMULINK Blc fr smulatn f dfferent types f vltage sags 3. SIMULATION OF THREE PHASE THREE LEG TRANSFORMER A 60VA-380/220V-WyeG-WyeG three phase three leg transfrmer s used fr smulatn purpses n MATLAB/SIMULINK. Functn (1) s used fr presentng cre nnlnear behavr between magnetc ptental n the leg and the flux thrugh t [3. R 1 1 ( f ) p p f 1 + f 0 f R ( f ) φ (1) where 1, 2,p and f 0 are expermental parameters wch allw ths sngle-valued functn t be ftted t the ( φ f ) transfrmer saturatn curve SYMMETRICAL VOLTAGE SAG (TYPE A) Fg.3 shws ntal vltage, current and fluxes n a vltage sag wth fllwng characterstcs: v( h 0.4, 5T 0). In ths case n pea current s ccurred. Ths fgure shws that n saturatn s ccurred when ntal and fnal fluxes are equal ( φ φ f ). Fg.4 shws that saturatn s ccurred when ( φ φf ). Fg.5 shws nrush current that s ccurred n lng term vltage sag wth characterstcs v( h 0.4, 150.5T 0). The current pea has a perdcal dependence n sag duratn n symmetrcal vltage sags. It means that pea t, ) pea + nt ). Shrt term vltage sag wth fllwng characterstc v( h 0.4, 5.5T 0) s als shwn n Fg.6 whch s smlar t Fg 5. It shws that the current pea has a perdcal dependence n sag duratn. Fg.2. Internal Vew f Smulated Three-phase Three leg Transfrmer Insde vew f smulated three phase three leg transfrmer s shwn n Fg.2. Further detal abut magnetc and electrc crcut are descrbed n [4. Tw mprtant effects f vltage sag are saturatn and nrush current n transfrmers. Inrush current s depended n dfferent Fg.3. Three phase vltage, current and flux fr a sag type v( h 0.4, 5T 0)

3 nfluence n transfrmer s cnsdered here. Each seres has cnstant ntal pnt n wave and vltage sag depth and dfferent vltage sag duratn as: v1 ( h 0.4,, wt 0 ),...6T v2 ( h 0.4,, 90 ),...6T v3 ( h 0.4,, 180 ),...6T v4 ( h 0.4,, 270 ), [ 5T...6T Fg.7 shws clearly that maxmum nrush current s ccured when 0 r 180 and ( nt +1/ 2) when n1, 2, 3 and etc. Fg.4. Three phase vltage, current and flux fr a sag type v ( h 0.4, 5.5T 0) Fg.5. Three phase current fr a sag type v( h 0.4, 150.5T 0) Fg.7. Maxmum nrush current versus dfferent vltage sag duratn n vltage sag type A wth h VOLTAGE SAG DEPTH INFLUENCE İnfluence f vltage sag depth s cnsdered here wth the fllwng characterstcs : v1 5.5T 0 ), h [ v2 5.4T 0 ), h [ v3 5.3T 0 ), h [ v4 5.2T 0 ), h [ v (, 5.1, 0 ), [ h t T h v6 5T 0 ), h [ Fg.6. Three phase current fr a sag type v( h 0.4, 5.5T 0) VOLTAGE SAG DURATION INFLUENCE 4 seres f vltage sags wth dfferent ntal pnt n wave ( 0_ 270) and vltage sag duratn Fg.8. Maxmum nrush current versus dfferent vltage sag depth (h0-0.9) Ths fgure shws that vltage sag depth nfluence n maxmum nrush current s lnear.

4 4-2. UNSYMMETRICAL VOLTAGE SAGS All type f vltage sags are smulated and vltage sag parameters varatn nfluence n transfrmer s nrush current s studed. Effect f tw examples f vltage sag types (A 3 & E 1 ) n transfrmer s nrush current s shwn frst. Results f thers type f vltage sag effects n nrush curent are studed n the next step. ncreases. The current peas prduced when vltage recvers fr these sag types are drawn wth bren lne n Fg VOLTAGE SAG TYPE A 3 Fgure 9 shws nrush currents when vltage sag type A3 wth characterstcs (h0.4, t 5. 5T ) s ccured. Vltage sag has three step fr clearng. Avearge dc flux s mved frm zer value when vltage s recvered. Inrush current s prduced when saturatn s ccured t. Fg.11. Sag duratn nfluence n the current pea fr sag type B wth h0.4 Fg.9. Three phase current fr a sag type A 3 : h0.4, 5. 5T VOLTAGE SAG TYPE E 1 Fgure 10 shws the transfrmer behavur under vltage sag type E 1 wth characterstcs (h0.4, t 5. 4T ). It shws a case where ne current pea s ccured when the vltage drps and anther current pea s prduced when the vltage recveres. Fg.12. Sag duratn nfluence n the current pea fr sag type E 1 and E 2 wth h0.4 Fg.10. Three phase current fr a sag type E 1 : h0.4, 5. 4T VOLTAGE SAG DURATION INFLUENCE Fg.11 shws three phase current when duratn f sag type B s vared. It shws that saturatn s ccurred when nt and n1, 2,... whle n vltage sag type A n current pea was ccurred. In ppste manner f type A maxmum current pea s ccurred when nt +1/ 4. The transfrmer behavr caused by type E sags (E1 and E2) s dfferent snce sme f the current pea values n Fg.12 are prduced when vltage drps, and the remanng current pea values are prduced when vltage Fg.13. Sag duratn nfluence n the current pea fr sag type C and F 2 wth h0.4

5 Current pea fr type C and D (Fg 13) are prduced when vltage recvers and ther values are lwer than thse f type A sags VOLTAGE SAG DEPTH INFLUENCE Vltage sag depth nfluence n the current peas have been cnsdered. Almst a lnear nfluence can be bserved fr all sag types (Fg.14). saturatn s ccurred when t nt and maxmum current pea s prduced when t nt + T / 2. Accrdng t the smulatn results, vltage sag depth nfluence n nrush current pea s almst lnear. REFERENCES [1 Bllen, M. H. J., Styvatas, E, "Sgnatures f Vltage Dps: Transfrmer Saturatn and Multstage Dps", IEEE Transactns n Pwer Delvery, Vl.18, N.1, Jan [2 Bllen, M. H. J., "Vltage Recvery after Unbalanced and Balanced Vltage Dps n Three-Phase System", IEEE Transactns n Pwer Delvery, Vl.18, N.4, Oct Fg.14. Vltage sag depth nfluence n the current pea fr unsymmetrcal sag types. 5. CONCLUSION The behavur three phase three leg transfrmers under dfferent type f vltage sag s nvestgated n ths paper. Symmetrcal and unsymmetrcal vltage sags are smulated and appled t the transfrmer mdel whch was mplemented n MATLAB_SIMULINK envrnment. In rder t prduce dfferent types f vltage sag a blc s created whch taes the vltage sag parameters related t the dfferent vltage sags. Transfrmer saturatn, dc magnetc flux varatns, nrush current pea etc are studed usng varus smulatns. It s shwn that the vltage sag depth has drect rle n ncreasng the current pea when the vltage recvers. Hwever, the current pea and saturatn are hghly depended n the ntal pnt n wave durng recvery prcess. It s shwn that n [3 Bllen, M. H. J., "Understandng Pwer Qualty Prblems: Vltage Sags and Interruptns", NewYr: IEEE Press, [4 Pedra, J., Crcles, F., Sanz, L., Lpez, R., and Salchs, M.,"PSPICE Cmputer Mdel f a Nnlnear Three-Phase Three-Legged Transfrmer", IEEE Transactns n Pwer Delvery, Vlume 19, Issue: 1, Jan. 2004, pp [5 Pedra, J., Crcles, F., Guasch, L., "Effects f Symmetrcal Vltage Sag n Three Phase Three- Legged Transfrmers ", IEEE Transactns n Pwer Delvery, Vlume 19, N. 2, Aprl 2004, pp [6 Pedra, J., Crcles, F., Sanz, L.,"Symmetrcal and Unsymmetrcal Vltage Sag Effects n Three Phase Transfrmers", IEEE Transactns n Pwer Delvery, Vlume 20, N. 2, Aprl 2005, pp