Convoluted Arc with Flux Concentrator for Current Interruption

Transcription

1 Cnvluted Arc wth Flux Cncentratr fr Current Interruptn Lend M. Shpann, Member, IEEE, Grdn R. Jnes, and Jseph W. Spencer Abstract-- Further cnsderatns are gven t the use f an electrmagnetc flux cncentratr fr plasma cntrl n a rtary current nterrupter. Such flux cncentratrs have been prevusly prpsed fr plasma fusn and ther plasma applcatns. The pssble extensn f the prpsed methd fr enhancng the nterruptn f drect currents wth a rtary nterrupter s dscussed wth the ad f theretcal mdellng f the cncentratr gemetry and wth ts pssble enhancement f ablatn frm the cntanng cylnders. Index Terms--Flux cncentratrs, dscharges, plasma devces, magnetc felds, current nterruptn, ablatn. S I. INTRODUCTION EVERAL evlvng aspects f hgh vltage current nterruptn whch are currently cmmandng attentn nclude the nterruptn f drect currents (D.C.) rather than alternatng currents (A.C.) and the drve twards avdng the use f sulfur hexaflurde (SF6) gas as an quenchng agent because f ts ptental fr causng Glbal Warmng []. Meanwhle, technlgy based upn the evlutn f varus frms f electrmagnetc cntrl f electrc s has been nvestgated ver several years wth ptental fr current nterruptn applcatns [-]. Examples f partcular frms f such devces nclude, as well, an electrc cnvlute rtatng arund a plytetraflurethylene (PTFE) cylnder husng a magnetc feld (B-feld) prducng cl, a smlar arrangement wth an uter PTFE cylnder wth the rtatng n the annular gap between the uter and nner PTFE cylnders etc. [4, 5]. Mre recently the pssblty f ncludng a metal sld cylndrcal shape slug as a B-feld flux cncentratr arund the uter PTFE cylnder (as used n plasma cnfnement [6]) fr enhancng the cmpressng B-feld has been theretcally suggested [7]. Ths cntrbutn cnsders an extensn f the theretcal descrptn fr the effect f the gemetry f the metallc flux cncentratr fr prducng Lrentz frces fr enhancng quenchng fr D.C. nterruptn. In partcular the effect f dfferent rad fr shrt axal length cncentratrs are L. M. Shpann, s wth the Centre fr Mblty and Transprt, Faculty f Engneerng, Envrnment and Cmputng, Cventry Unversty, Cventry CV JH, U.K. (e-mal: len.shpann@cventry.ac.uk). G. R. Jnes, s wth the Centre fr Intellgent Mntrng Systems, Schl f Electrcal Engneerng, Electrncs and Cmputer Scence, Unversty f Lverpl, Lverpl L69 GJ, U.K. (e-mal: G.R.Jnes@lverpl.ac.uk). J. W. Spencer s wth the Centre fr Intellgent Mntrng Systems, Schl f Electrcal Engneerng, Electrncs and Cmputer Scence, Unversty f Lverpl, Lverpl L69 GJ, U.K. (e-mal: je@lverpl.ac.uk). cnsdered fr rectangular crss sectn cncentratrs rather than a cncal crss sectn cncentratr f extended axal length whch has hthert been cnsdered. II. ELECTROMAGNETIC ARC QUENCHING The pssblty f nterruptng A.C. currents by electrmagnetcally rtatng an electrc wth a B-feld prduced by a current carryng cl embedded n a PTFE cylnder arund whch the rtated, has been demnstrated wth the devce arrangement shwn n Fg., but wthut the flux cncentratr used [4, and 5]. Fg.. Rtary nterrupter wth the flux cncentratr and uter PTFE cylnder. Ths fgure shws such an beng rtated n an annular gap between tw cncentrc PTFE cylnders (wdth cm) and wth a metallc flux cncentratr utsde the uter PTFE cylnder. The axal B-feld prduced by a cncal crss sectn flux cncentratr f fxed radus and axal length lnger than the B-feld nducng cl has been cnsdered theretcally [7]. It has been shwn expermentally [8] that at the axal lcatn at whch the axal Lrentz frce (F) s theretcally a maxmum, the radus f the nner PTFE cylnder suffers a maxmum reductn due t ablatn f the PTFE. Such an arrangement wthut the metallc flux cncentratr has been demnstrated fr nterruptng a quas D.C. current [9]. The B-feld prducng cl n such a cncentrc cylnders arrangement (wthut a flux cncentratr) has been ndependently actvated frm the quas-drect current between the ande and cathde usng a resstr-nductrcapactr (RLC) crcut cnnected acrss the gap. Ths prvded a means fr:

2 (a) Encuragng the frmatn f hgh frequency scllatns f the current thrugh the t assst current nterruptn. (b) Investgatng the nfluence f dfferent magntudes f B-felds n the behavr f the plasma carryng a fxed current. An llustratn f the current and vltage varatns frm such tests s shwn n Fg. fr the nterruptn f a quasdrect current f 600A peak wth a B-feld f ~5mT (at current nterruptn) wth khz current scllatns. The results f such tests are shwn n Fg. a,b. It shws hw the Lrentz frce prduced (Fg. (a)) and the tme at whch current nterruptn ccurred (Fg. (b)) vared wth the B-feld prduced by the separately actvated cl current. The results shw that the use f a relatvely lw B- feld (4.4mT) prducng a Lrentz frce f 5N/m nly prvded a small reductn n the tme at whch current nterruptn ccurred (70ms cmpared t 88ms) Hwever, the use f a hgher B-feld (50mT) leads t current nterruptn at a shrter ng tme (ms). Further detals are prvded n Appendx I. As a result there s the pssblty f enhancng such current nterruptn by ncreasng the cmpressng B-feld n a cnvenent and ecnmcal manner usng a flux cncentratr rng n the nterrupter as shwn n Fg.. An nsght nt such a pssblty may be ganed usng a theretcal apprach suggested n [7]. Fg.. Interruptn f a quas-drect current (600A ntal value) wth a cnvluted devce, wthut a flux cncentratr (Fg. ); Operatnal cndtns: Interrupter gas - atmspherc pressure ar, B-feld cl (50mT) energzed separately wth a current f 5.8kA, Outer PTFE cylnder - nserted arund the devce; R, L, C crcut cnnected acrss the gap t prduce current and vltage frequency scllatns f khz [9]). III. THEORETICAL ASSESSMENT OF A FLUX CONCENTRATOR In ths cntrbutn, a theretcal analyss has been made fr a flux cncentratr wth a rectangular (rather than cncal) crss sectn f axal length (cm) less (rather than lnger) than the length f the B-feld prducng cl (5cm). As a result the electrdes regns f the cnvlute wll be less nfluenced by the radal feld f the flux cncentratr nce the cnvlute s frmed. Fg. 4 shws a schematc dagram f the gemetry f the rectangular crss sectn flux cncentratr n a rtary nterrupter wth an nner PTFE cylnder cntanng the B-feld cl f radus R, an uter cncentrc PTFE cylnder f nner radus R, a flux cncentratr f nner radus R, mean radus R4 and axal length b. The flux cncentratr s lcated centrally and unfrmly alng the length f the gap ande and cathde. A current s nduced n the cncentratr due t the B-feld frm the rtatng cl. (a) (b) Fg.. Varatns prduced by a separately actvated B-feld cl, (a) Lrentz Frce vs cl current, (b) Tme f current nterruptn vs cl current. Fg. 4. Schematc dagram f flux cncentratr gemetry; R - Outer radus f nner PTFE cylnder; R - Inner radus f uter PTFE cylnder; R - Inner radus f flux cncentratr; R4 - Mean radus f flux cncentratr; b - Axal length f flux cncentratr cylnder.

3 Als n the present nvestgatn the cncentratr had a rectangular crss sectn rather than a cncal ne f a sngle radus as cnsdered prevusly. The behavr f the flux cncentratr may be descrbed usng the theretcal apprach used by Shpann et al. [7] fr a prelmnary descrptn f the electrmagnetc behavr f sme rtary s. The Lrentz frce prduced n such an arrangement by a flux cncentratr B-feld actng n an carryng a current I s gven by [0] (Equatn AII. 4, Appendx II): F I L L R Where R,,, L, L and are defned n Appendx II. Ths mples that the Lrentz frce s apprxmately prprtnal t the nverse f the nner dameter (R) f the flux cncentratr. Lrentz frces have been calculated wth ths mdel fr an and cl current f 5.8kA peak, an nner PTFE cylnder f uter radus R f 5cm and an uter PTFE cylnder f nner radus R f 6cm. Results fr the varatn f the Lrentz frce (F) prduced by a flux cncentratr as a functn f the cncentratr nner radus (R) are presented n Fg. 5. Fg. 5. Varatn f Lrentz frce prduced by a rectangular crss sectn flux cncentratr (axal length f cm) as a functn f flux cncentratr nner radus (where the and cl current s 5.8kA). Ths shws hw the Lrentz frce ncrease frm 44N/m t 496N/m as the cncentratr radus decreases frm 8.5 t 7.0 cm. These values cmpare wth a Lrentz frce f 4.9kN/m wthn the annular ng space (R and R, Fg. 4) fr the same peak current f 5.8kA reprted by Shpann et al. [] wthut a flux cncentratr. Thus t s theretcally predcted that a flux cncentratr f nner radus 7.0cm wuld prduce a 0% ncrease n the Lrentz frce. () Further detals f the theretcal apprach are gven n Appendx II, and further detals f the calculated parameters are gven n Table I (Appendx II). IV. DISCUSSION OF RESULTS The mplcatns f the expermental results presented n Fg. are that ncreasng the Lrentz frce n a cnvluted carryng a fxed quas-steady current can reduce the tme fr the current t be nterrupted prvded the Lrentz frce s suffcently hgh. A reductn n nterruptn tme frm 88 t ms was shwn t be pssble by ncreasng the Lrentz frce frm 0 t 90N/m. Theretcal calculatns (Sectn III) ndcate that such enhancement f Lrentz frces f ths rder f magntude may be acheved thrugh the ntrductn f a metal cylndrcal flux cncentratr f rectangular crss sectn. Fg. 5 and Table I, Appendx II shw that a flux cncentratr f nternal radus 7cm s capable f prducng an addtnal Lrentz frce f 496N/m fr a 50Hz prmary A.C. peak current f 5.8kA. There are current nterruptn mplcatns whch arse frm the flux cncentratr theretcal results n addtn t affectng nduced flws f the surrundng gas n preparng fr quenchng: (a) (b) The nfluence f the flux cncentratr n the prductn f current scllatns whch lead t quas-steady current nterruptn (Fg. ) warrants further nvestgatn snce t culd prduce hgher ampltude scllatns and hence earler current nterruptn. The prductn f ablated materal frm the uter surface f the cl cntanng PTFE cylnder may be affected by the cncentratr nduced Lrentz frce. An ndcatn f the amunt f such ablated materal can be btaned by measurng the shape f the nner PTFE cylnder surface befre and after ng. Such tests [8] shw that the PTFE materal ersn was manly cncentrated half way axally alng the cl axs where the Lrentz frces were als a maxmum. A Lrentz frce f 5kN/m, wth an half cycle f 50Hz A.C. peak current f 4kA, prduced 5mm ablated materal [8], s that an extra Lrentz frce f 496N/m (Table I, Appendx II) culd ptentally prduce an extra 5.mm f ablated materal. Ths n turn culd reduce the relance upn the quenchng capablty f the surrundng gas. V. CONCLUSIONS Theretcal analyss f the Lrentz frce prduced by a rectangular (rather than cncal) crss sectn flux cncentratr f axal length less (rather than greater) than the length f the B-feld prducng cl has been perfrmed. The results shw that the Lrentz frce n the plasma can be ncreased by abut 0%. Cmparsn wth expermental

4 4 results frm tests wth dfferent B-feld cl exctng currents ndcate that such an ncrease n the Lrentz frce shuld lead t an mprved capablty f drect current nterruptn. Further nvestgatns are needed t valdate such a cnclusn and t nvestgate further the effect f ncreasng the axal extent f the flux cncentratr relatve t the length f the B-feld prducng cl. APPENDIX I: EFFECT OF B-FIELD MAGNITUDE ON THE INTERRUPTION OF A QUASI-DIRECT CURRENT OF 600A INITIAL VALUE L L (AII.) () Where L s the effectve nductance f the flux cncentratr, L s the self-nductance f the central hgh fled regn [7], s a prmary current thrugh the and B-feld cl (whch are cnnected n seres) and s the transfer nductve energy lss between the B-feld prducng cl and the central hgh feld regn (b = 0.0m, Fg. 4) f the flux cncentratr. Substtutng fr and B flux-cncentratr n equatn (AII.) frm equatns (AII.) and (AII.) yelds: F I L L R (AII.4) APPENDIX II: LORENTZ FORCE PRODUCED BY FLUX CONCENTRATORS OF DIFFERENT RADII The prelmnary theretcal cnsderatn f a flux cncentratr fr enhancng rtary s cntrl and quenchng reprted by Shpann et al. [7] may be extended t nvestgate the effect f dfferent flux cncentratr radus and crss sectnal shape. The Lrentz frce prduced by a B-feld flux cncentratr (Fg. 4), actng n an carryng a current I, s gven by [0]: F I B (AII.) () flux_cncentratr Where s defned by equatns (AII.5) and (AII.6), [7]: b R sn b cs () (AII.5) b s the axal length f the flux cncentratr cylnder, n [m], α s a sem-angle f ts cncal ends. (Fr a cncal cncentratr (prevus calculatns [7]) α = 45degrees whlst fr a cylndrcal cncentratr (present calculatns) α = 90 degrees). Where the flux cncentratr B-feld apples thrughut the entre -lp arund the B-feld cl and s apprxmated by [7]: L kl m l (AII.6) l m L l m kl m (0) 0 (AII.) B () flux_cncentratr R Wth the cncentratr nner radus R, maxmum secndary current n the flux cncentratr (Fg. 4), and permeablty f 6 free space (.57 0 H/m) gven by [6 and 7]. k, m and l reflect the cuplng and mutual nductance lsses f the flux cncentratr n relatn t the B-feld prducng cl [6, 7]; and s the transfer lss, whch des nt depend n the gemetry f the flux cncentratr, [6, 7]. The values f k, l, m, L and L are shwn n Table I. Based n an apprxmate thery [6, 7] (.e. gnrng a radal slt (Fg. ) and end effects f the flux cncentratr) the transfer lss f a rectangular crss sectn flux cncentratr s reduced t (Equatn (AII.5)), [6, 7].

5 5 Detals f results btaned wth ths theretcal mdel are shwn n Table I fr rectangular crss sectn (α = 90 degrees) flux cncentratr f three dfferent rad (R) and an nner PTFE cylnder radus R = 5cm, uter PTFE cylnder f nner radus R = 6cm. TABLE I LORENTZ FORCE PRODUCED BY FLUX CONCENTRATORS OF RECTANGULAR CROSS SECTION, AXIAL LENGTH CM AND OF DIFFERENT RADII [9] L. M. Shpann, G. R. Jnes, J. E. Humphres, J. W. Spencer, N. Y. A. Shammas, S. B. Tennakn, R L C - nduced current scllatns n cnvluted s wth ndependently actvated magnetc felds, IEEE Transactns n Plasma Scence, Vl. 4. N.0, pp.86-84, Oct. 0. [0] L.M. Shpann, Electrmagnetc cntrl fr current nterruptn, Ph.D. dssertatn, Unversty f Lverpl, Lverpl, U.K., 006. [] L.M. Shpann, D.R. Turner, J.E. Humphres, J.W. Spencer, G.R. Jnes and B.E. Djakv, Frmatn and prpulsn f an atmspherc pressure plasma rng, Prc. f 6Ith Int. Cnf. n Gas Dscharges and ther Applcatns, X an, Chna, pp.5-8, Sept Lend M. Shpann receved the M.Sc. degree n rad engneerng frm Azerbajan Techncal Unversty, Azerbajan and Ph.D. degree n electrcal engneerng and electrncs frm Unversty f Lverpl, U.K. He s a Lecturer n Aerspace, Electrcal and Electrnc Engneerng, Faculty f Engneerng, Envrnment and Cmputng, Schl f Mechancal, Aerspace and Autmtve Engneerng, Cventry Unversty, UK. He s member f the Hgher Educatn Academy, UK and a member f the Insttute f Electrcal and Electrncs Engneers (IEEE), U.S.A. Nte: Arc and Cl alternatng current = 5.8kA peak, Outer radus f nner PTFE cylnder was 5cm; Inner radus f uter PTFE cylnder was 6cm, k = crrespnds t gd cuplng, [7] (e.g. nductance f the flux cncentratr radal slt far less than the nductance f the B-feld cl ncludng the cnvlute lp (Fg. )) REFERENCES [] H. M. Ryan, Hgh Vltage Engneerng and Testng, rd Edtn, Insttutn f Engneerng and Technlgy, IET Pwer and Energy Seres 66, UK, 0, ch.7, pp. 75-0, ch..7.., pp [] T. Mr, J. W. Spencer, J. E. Humphres, G. R. Jnes, Dagnstc measurements n rtary s n hllw plymerc cylnders, IEEE Transactns n Pwer Delvery, Vl.0, N., pp , 005. [] M.G. Enns, J.K. Wd, J.W. Spencer, D.R. Turner, G.R. Jnes, P. Cventry, Current Lmtng Prpertes f an expandng helcal, IEE Prc-Sc. Meas. Technl., Vl. 4, N., pp.0-05, May I995. [4] L.M. Shpann, G.R. Jnes, J.E. Humphres, and J.W. Spencer, Current nterruptn usng electrmagnetcally cnvlved electrc s n gases, IEEE Transactns n Pwer Delvery, vl. 4, n.4, pp.94-90, Oct [5] L.M. Shpann, G.R. Jnes, J.E. Humphres, J.W. Spencer, Electrmagnetcally cnvluted s cnfned wthn an annular gap between tw PTFE cylnders, Prc. f the 9th Int. Cnf. n Gas Dscharges and ther Applcatns, Chna, pp.4-7, Sept. 0. [6] M.N. Wlsn, K.D. Srvastava, Desgn f effcent flux cncentratrs fr pulsed hgh magnetc felds, The Revew f Scentfc Instruments, Vl. 6, N. 8, Aug [7] L.M. Shpann, G.R. Jnes and J.W. Spencer, Flux cncentratr fr cmpressng an plasma clumn n the current nterrupter, Prc. f the st Int. Cnf. n Gas Dscharges and ther Applcatns, Nagya, Japan, pp.97-00, Sept. 06. [8] L.M. Shpann, G.R. Jnes, J.W. Spencer, B. E. Djakv, Cntrl and prpulsn f an atmspherc pressure plasma rng, IEEE Transactns n Plasma Scence, Vl. 6. N.5, pp , Oct.008. Grdn R. Jnes receved the B.Sc. degree n physcs frm Unversty f Wales, U.K., the Ph.D. degree n physcs frm Unversty f Lverpl, U.K., and the D.Sc. degree frm Unversty f Wales, U.K. He s an Emertus Prfessr and past Drectr f the Centre fr Intellgent and Mntrng Systems at Unversty f Lverpl. He s authr f several bks n the area f Chrmatc mntrng, hgh-pressure s and SF6 swtchgear. He s a member f the Executve Management Cmmttee f the Internatnal Seres f Cnferences n Gas Dscharge and Ther Applcatns and s a member f an nternatnal study grup n swtchgear s, the Current Zer Club. He was awarded the Insttutn f Electrcal Engneerng (IEE) Scence, Educatn and Technlgy Achevements Medal n 999 and a Medal f Dstnctn n 006 by the Academy f Scences, Bulgara. He s a Fellw f the IET, U.K. and member f the Insttute f Physcs, U.K. Jseph W. Spencer receved the B.Eng. and Ph.D. degrees n electrcal engneerng frm Unversty f Lverpl, U.K. He s Prfessr f Electrcal Engneerng, Drectr f the Centre fr Intellgent and Mntrng Systems and Head f Schl f Electrcal Engneerng, Electrncs and Cmputer Scence at Unversty f Lverpl. He s a member f an nternatnal study grup n swtchgear s and Hnrary Treasurer f the Internatnal Seres f Cnferences n Gas Dscharge and Ther Applcatns. He s a member f the Insttutn f Electrcal Engneerng (IET), U.K.