Convoluted Arc With Flux Concentrator for Current Interruption

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1 Cnvluted Arc With Flux Cncentratr fr Current Interruptin Shpanin, L, Jnes, G & Spencer, J Authr pst-print (accepted) depsited by Cventry University s Repsitry Original citatin & hyperlink: Shpanin, L, Jnes, G & Spencer, J 07, Cnvluted Arc With Flux Cncentratr fr Current Interruptin IEEE Transactins n Plasma Science, vl 46, n., pp DOI 0.09/TPS ISSN ESSN Publisher: IEEE 08 IEEE. Persnal use f this material is permitted. Permissin frm IEEE must be btained fr all ther uses, in any current r future media, including reprinting/republishing this material fr advertising r prmtinal purpses, creating new cllective wrks, fr resale r redistributin t servers r lists, r reuse f any cpyrighted cmpnent f this wrk in ther wrks. Cpyright and Mral Rights are retained by the authr(s) and/ r ther cpyright wners. A cpy can be dwnladed fr persnal nn-cmmercial research r study, withut prir permissin r charge. This item cannt be reprduced r quted extensively frm withut first btaining permissin in writing frm the cpyright hlder(s). The cntent must nt be changed in any way r sld cmmercially in any frmat r medium withut the frmal permissin f the cpyright hlders. This dcument is the authr s pst-print versin, incrprating any revisins agreed during the peer-review prcess. Sme differences between the published versin and this versin may remain and yu are advised t cnsult the published versin if yu wish t cite frm it.

2 Cnvluted Arc with Flux Cncentratr fr Current Interruptin Lenid M. Shpanin, Member, IEEE, Grdn R. Jnes, and Jseph W. Spencer Abstract-- Further cnsideratins are given t the use f an electrmagnetic flux cncentratr fr arc plasma cntrl in a rtary arc current interrupter. Such flux cncentratrs have been previusly prpsed fr plasma fusin and ther plasma applicatins. The pssible extensin f the prpsed methd fr enhancing the interruptin f direct currents with a rtary arc interrupter is discussed with the aid f theretical mdelling f the cncentratr gemetry and with its pssible enhancement f ablatin frm the arc cntaining cylinders. Index Terms--Flux cncentratrs, arc discharges, plasma arc devices, magnetic fields, current interruptin, ablatin. S I. INTRODUCTION EVERAL evlving aspects f high vltage current interruptin which are currently cmmanding attentin include the interruptin f direct currents (D.C.) rather than alternating currents (A.C.) and the drive twards aviding the use f sulfur hexafluride (SF6) gas as an arc quenching agent because f its ptential fr causing Glbal Warming []. Meanwhile, technlgy based upn the evlutin f varius frms f electrmagnetic cntrl f electric arcs has been investigated ver several years with ptential fr current interruptin applicatins [-3]. Examples f particular frms f such devices include, as well, an electric arc cnvlute rtating arund a plytetraflurethylene (PTFE) cylinder husing a magnetic field (B-field) prducing cil, a similar arrangement with an uter PTFE cylinder with the arc rtating in the annular gap between the uter and inner PTFE cylinders etc. [4, 5]. Mre recently the pssibility f including a metal slid cylindrical shape slug as a B-field flux cncentratr arund the uter PTFE cylinder (as used in plasma cnfinement [6]) fr enhancing the arc cmpressing B-field has been theretically suggested [7]. This cntributin cnsiders an extensin f the theretical descriptin fr the effect f the gemetry f the metallic flux cncentratr fr prducing Lrentz frces fr enhancing arc quenching fr D.C. interruptin. In particular the effect f different radii fr shrt axial length cncentratrs are L. M. Shpanin, is with the Centre fr Mbility and Transprt, Faculty f Engineering, Envirnment and Cmputing, Cventry University, Cventry CV JH, U.K. ( len.shpanin@cventry.ac.uk). G. R. Jnes, is with the Centre fr Intelligent Mnitring Systems, Schl f Electrical Engineering, Electrnics and Cmputer Science, University f Liverpl, Liverpl L69 3GJ, U.K. ( G.R.Jnes@liverpl.ac.uk). J. W. Spencer is with the Centre fr Intelligent Mnitring Systems, Schl f Electrical Engineering, Electrnics and Cmputer Science, University f Liverpl, Liverpl L69 3GJ, U.K. ( je@liverpl.ac.uk). cnsidered fr rectangular crss sectin cncentratrs rather than a cnical crss sectin cncentratr f extended axial length which has hithert been cnsidered. II. ELECTROMAGNETIC ARC QUENCHING The pssibility f interrupting A.C. currents by electrmagnetically rtating an electric arc with a B-field prduced by a current carrying cil embedded in a PTFE cylinder arund which the arc rtated, has been demnstrated with the device arrangement shwn n Fig., but withut the flux cncentratr used [4, and 5]. Fig.. Rtary arc interrupter with the flux cncentratr and uter PTFE cylinder. This figure shws such an arc being rtated in an annular gap between tw cncentric PTFE cylinders (width cm) and with a metallic flux cncentratr utside the uter PTFE cylinder. The axial B-field prduced by a cnical crss sectin flux cncentratr f fixed radius and axial length lnger than the B-field inducing cil has been cnsidered theretically [7]. It has been shwn experimentally [8] that at the axial lcatin at which the axial Lrentz frce (F) is theretically a maximum, the radius f the inner PTFE cylinder suffers a maximum reductin due t ablatin f the PTFE. Such an arrangement withut the metallic flux cncentratr has been demnstrated fr interrupting a quasi D.C. current [9]. The B-field prducing cil in such a cncentric cylinders arrangement (withut a flux cncentratr) has been independently activated frm the quasi-direct arc current between the ande and cathde using a resistr-inductrcapacitr (RLC) circuit cnnected acrss the arc gap. This prvided a means fr:

3 (a) Encuraging the frmatin f high frequency scillatins f the current thrugh the arc t assist current interruptin. (b) Investigating the influence f different magnitudes f B-fields n the behavir f the arc plasma carrying a fixed current. An illustratin f the current and arc vltage variatins frm such tests is shwn n Fig. fr the interruptin f a quasidirect current f 600A peak with a B-field f ~35mT (at current interruptin) with khz current scillatins. The results f such tests are shwn n Fig. 3a,b. It shws hw the Lrentz frce prduced (Fig. 3(a)) and the time at which current interruptin ccurred (Fig. 3(b)) varied with the B-field prduced by the separately activated cil current. The results shw that the use f a relatively lw B- field (4.4mT) prducing a Lrentz frce f 5N/m nly prvided a small reductin in the time at which current interruptin ccurred (70ms cmpared t 88ms) Hwever, the use f a higher B-field (50mT) leads t current interruptin at a shrter arcing time (3ms). Further details are prvided in Appendix I. As a result there is the pssibility f enhancing such current interruptin by increasing the arc cmpressing B-field in a cnvenient and ecnmical manner using a flux cncentratr ring in the interrupter as shwn n Fig.. An insight int such a pssibility may be gained using a theretical apprach suggested in [7]. Fig.. Interruptin f a quasi-direct current (600A initial value) with a cnvluted arc device, withut a flux cncentratr (Fig. ); Operatinal cnditins: Interrupter gas - atmspheric pressure air, B-field cil (50mT) energized separately with a current f 5.8kA, Outer PTFE cylinder - inserted arund the device; R, L, C circuit cnnected acrss the arc gap t prduce arc current and vltage frequency scillatins f khz [9]). III. THEORETICAL ASSESSMENT OF A FLUX CONCENTRATOR In this cntributin, a theretical analysis has been made fr a flux cncentratr with a rectangular (rather than cnical) crss sectin f axial length (3cm) less (rather than lnger) than the length f the B-field prducing cil (5cm). As a result the electrdes regins f the cnvlute arc will be less influenced by the radial field f the flux cncentratr nce the arc cnvlute is frmed. Fig. 4 shws a schematic diagram f the gemetry f the rectangular crss sectin flux cncentratr in a rtary arc interrupter with an inner PTFE cylinder cntaining the B-field cil f radius R, an uter cncentric PTFE cylinder f inner radius R, a flux cncentratr f inner radius R3, mean radius R4 and axial length b. The flux cncentratr is lcated centrally and unifrmly alng the length f the arc gap ande and cathde. A current i is induced in the cncentratr due t the B-field frm the arc rtating cil. (a) (b) Fig. 3. Variatins prduced by a separately activated B-field cil, (a) Lrentz Frce vs cil current, (b) Time f current interruptin vs cil current. Fig. 4. Schematic diagram f flux cncentratr gemetry; R - Outer radius f inner PTFE cylinder; R - Inner radius f uter PTFE cylinder; R3 - Inner radius f flux cncentratr; R4 - Mean radius f flux cncentratr; b - Axial length f flux cncentratr cylinder.

4 3 Als in the present investigatin the cncentratr had a rectangular crss sectin rather than a cnical ne f a single radius as cnsidered previusly. The behavir f the flux cncentratr may be described using the theretical apprach used by Shpanin et al. [7] fr a preliminary descriptin f the electrmagnetic behavir f sme rtary arcs. The Lrentz frce prduced in such an arrangement by a flux cncentratr B-field acting n an arc carrying a current I arc is given by [0] (Equatin AII. 4, Appendix II): F I arc L i L 3 R3 Where R3,,, L, L 3 and i are defined in Appendix II. This implies that the Lrentz frce is apprximately prprtinal t the inverse f the inner diameter (R3) f the flux cncentratr. Lrentz frces have been calculated with this mdel fr an arc and cil current i f 5.8kA peak, an inner PTFE cylinder f uter radius R f 5cm and an uter PTFE cylinder f inner radius R f 6cm. Results fr the variatin f the Lrentz frce (F) prduced by a flux cncentratr as a functin f the cncentratr inner radius (R3) are presented n Fig. 5. Fig. 5. Variatin f Lrentz frce prduced by a rectangular crss sectin flux cncentratr (axial length f 3cm) as a functin f flux cncentratr inner radius (where the arc and cil current is 5.8kA). This shws hw the Lrentz frce increase frm 44N/m t 496N/m as the cncentratr radius decreases frm 8.5 t 7.0 cm. These values cmpare with a Lrentz frce f 4.9kN/m within the annular arcing space (R and R, Fig. 4) fr the same peak current f 5.8kA reprted by Shpanin et al. [] withut a flux cncentratr. Thus it is theretically predicted that a flux cncentratr f inner radius 7.0cm wuld prduce a 0% increase in the Lrentz frce. () Further details f the theretical apprach are given in Appendix II, and further details f the calculated parameters are given in Table I (Appendix II). IV. DISCUSSION OF RESULTS The implicatins f the experimental results presented n Fig. 3 are that increasing the Lrentz frce n a cnvluted arc carrying a fixed quasi-steady current can reduce the time fr the current t be interrupted prvided the Lrentz frce is sufficiently high. A reductin in interruptin time frm 88 t 3ms was shwn t be pssible by increasing the Lrentz frce frm 0 t 90N/m. Theretical calculatins (Sectin III) indicate that such enhancement f Lrentz frces f this rder f magnitude may be achieved thrugh the intrductin f a metal cylindrical flux cncentratr f rectangular crss sectin. Fig. 5 and Table I, Appendix II shw that a flux cncentratr f internal radius 7cm is capable f prducing an additinal Lrentz frce f 496N/m fr a 50Hz primary A.C. peak current f 5.8kA. There are current interruptin implicatins which arise frm the flux cncentratr theretical results in additin t affecting induced flws f the arc surrunding gas in preparing fr arc quenching: (a) (b) The influence f the flux cncentratr n the prductin f current scillatins which lead t quasi-steady current interruptin (Fig. ) warrants further investigatin since it culd prduce higher amplitude scillatins and hence earlier current interruptin. The prductin f ablated material frm the uter surface f the cil cntaining PTFE cylinder may be affected by the cncentratr induced Lrentz frce. An indicatin f the amunt f such ablated material can be btained by measuring the shape f the inner PTFE cylinder surface befre and after arcing. Such tests [8] shw that the PTFE material ersin was mainly cncentrated half way axially alng the cil axis where the Lrentz frces were als a maximum. A Lrentz frce f 5kN/m, with an half cycle f 50Hz A.C. peak current f 4kA, prduced 53mm 3 ablated material [8], s that an extra Lrentz frce f 496N/m (Table I, Appendix II) culd ptentially prduce an extra 5.3mm 3 f ablated material. This in turn culd reduce the reliance upn the arc quenching capability f the surrunding gas. V. CONCLUSIONS Theretical analysis f the Lrentz frce prduced by a rectangular (rather than cnical) crss sectin flux cncentratr f axial length less (rather than greater) than the length f the B-field prducing cil has been perfrmed. The results shw that the Lrentz frce n the arc plasma can be increased by abut 0%. Cmparisn with experimental

5 4 results frm tests with different B-field cil exciting currents indicate that such an increase in the Lrentz frce shuld lead t an imprved capability f direct current interruptin. Further investigatins are needed t validate such a cnclusin and t investigate further the effect f increasing the axial extent f the flux cncentratr relative t the length f the B-field prducing cil. APPENDIX I: EFFECT OF B-FIELD MAGNITUDE ON THE INTERRUPTION OF A QUASI-DIRECT CURRENT OF 600A INITIAL VALUE i L i L3 (AII.3) (3) Where L is the effective inductance f the flux cncentratr, L 3 is the self-inductance f the central high filed regin [7], i is a primary current thrugh the arc and B-field cil (which are cnnected in series) and is the transfer inductive energy lss between the B-field prducing cil and the central high field regin (b = 0.03m, Fig. 4) f the flux cncentratr. Substituting fr i and B flux-cncentratr in equatin (AII.) frm equatins (AII.) and (AII.3) yields: F I arc L i L 3 R3 (AII.4) APPENDIX II: LORENTZ FORCE PRODUCED BY FLUX CONCENTRATORS OF DIFFERENT RADII The preliminary theretical cnsideratin f a flux cncentratr fr enhancing rtary arcs cntrl and quenching reprted by Shpanin et al. [7] may be extended t investigate the effect f different flux cncentratr radius and crss sectinal shape. The Lrentz frce prduced by a B-field flux cncentratr (Fig. 4), acting n an arc carrying a current I arc, is given by [0]: F I B (AII.) () arc flux_cncentratr Where is defined by equatins (AII.5) and (AII.6), [7]: b R3 sin b cs () (AII.5) b is the axial length f the flux cncentratr cylinder, in [m], α is a semi-angle f its cnical ends. (Fr a cnical cncentratr (previus calculatins [7]) α = 45degrees whilst fr a cylindrical cncentratr (present calculatins) α = 90 degrees). Where the flux cncentratr B-field applies thrughut the entire arc-lp arund the B-field cil and is apprximated by [7]: L i 3 kl m l (AII.6) l m L i l m kl m (0) i 0 (AII.) B () flux_cncentratr R3 With the cncentratr inner radius R3, maximum secndary current i in the flux cncentratr (Fig. 4), and permeability f 6 free space (.57 0 H/m) given by [6 and 7]. k, m and l reflect the cupling and mutual inductance lsses f the flux cncentratr in relatin t the B-field prducing cil [6, 7]; and is the transfer lss, which des nt depend n the gemetry f the flux cncentratr, [6, 7]. The values f k, l, m, L and L 3 are shwn n Table I. Based n an apprximate thery [6, 7] (i.e. ignring a radial slt (Fig. ) and end effects f the flux cncentratr) the transfer lss f a rectangular crss sectin flux cncentratr is reduced t (Equatin (AII.5)), [6, 7].

5 Details f results btained with this theretical mdel are shwn n Table I fr rectangular crss sectin (α = 90 degrees) flux cncentratr f three different radii (R3) and an inner PTFE cylinder radius R =

E. Humphries, J. W. Spencer, N. Y. A. Shammas, S. B. Tennakn, R L C - induced current scillatins in cnvluted arcs with independently activated magnetic fields, IEEE Transactins n Plasma Science, Vl.

W. Spencer, G.R. Jnes and B.E. Djakv, Frmatin and prpulsin f an atmspheric pressure plasma ring, Prc. f 6Ith Int. Cnf. n Gas Discharges and their Applicatins, Xi an, China, pp.5-8, Sept. 006. Lenid M.

6 5 Details f results btained with this theretical mdel are shwn n Table I fr rectangular crss sectin (α = 90 degrees) flux cncentratr f three different radii (R3) and an inner PTFE cylinder radius R = 5cm, uter PTFE cylinder f inner radius R = 6cm. TABLE I LORENTZ FORCE PRODUCED BY FLUX CONCENTRATORS OF RECTANGULAR CROSS SECTION, AXIAL LENGTH 3CM AND OF DIFFERENT RADII [9] L. M. Shpanin, G. R. Jnes, J. E. Humphries, J. W. Spencer, N. Y. A. Shammas, S. B. Tennakn, R L C - induced current scillatins in cnvluted arcs with independently activated magnetic fields, IEEE Transactins n Plasma Science, Vl. 4. N.0, pp , Oct. 03. [0] L.M. Shpanin, Electrmagnetic arc cntrl fr current interruptin, Ph.D. dissertatin, University f Liverpl, Liverpl, U.K., 006. [] L.M. Shpanin, D.R. Turner, J.E. Humphries, J.W. Spencer, G.R. Jnes and B.E. Djakv, Frmatin and prpulsin f an atmspheric pressure plasma ring, Prc. f 6Ith Int. Cnf. n Gas Discharges and their Applicatins, Xi an, China, pp.5-8, Sept Lenid M. Shpanin received the M.Sc. degree in radi engineering frm Azerbaijan Technical University, Azerbaijan and Ph.D. degree in electrical engineering and electrnics frm University f Liverpl, U.K. He is a Lecturer in Aerspace, Electrical and Electrnic Engineering, Faculty f Engineering, Envirnment and Cmputing, Schl f Mechanical, Aerspace and Autmtive Engineering, Cventry University, UK. He is member f the Higher Educatin Academy, UK and a member f the Institute f Electrical and Electrnics Engineers (IEEE), U.S.A. Nte: Arc and Cil alternating current i = 5.8kA peak, Outer radius f inner PTFE cylinder was 5cm; Inner radius f uter PTFE cylinder was 6cm, k = crrespnds t gd cupling, [7] (e.g. inductance f the flux cncentratr radial slt far less than the inductance f the B-field cil including the arc cnvlute lp (Fig. )) REFERENCES [] H. M. Ryan, High Vltage Engineering and Testing, 3 rd Editin, Institutin f Engineering and Technlgy, IET Pwer and Energy Series 66, UK, 03, ch.7, pp , ch..7.., pp [] T. Mri, J. W. Spencer, J. E. Humphries, G. R. Jnes, Diagnstic measurements n rtary arcs in hllw plymeric cylinders, IEEE Transactins n Pwer Delivery, Vl.0, N., pp , 005. [3] M.G. Ennis, J.K. Wd, J.W. Spencer, D.R. Turner, G.R. Jnes, P. Cventry, Current Limiting Prperties f an expanding helical arc, IEE Prc-Sci. Meas. Technl., Vl. 4, N. 3, pp.0-05, May I995. [4] L.M. Shpanin, G.R. Jnes, J.E. Humphries, and J.W. Spencer, Current interruptin using electrmagnetically cnvlved electric arcs in gases, IEEE Transactins n Pwer Delivery, vl. 4, n.4, pp , Oct [5] L.M. Shpanin, G.R. Jnes, J.E. Humphries, J.W. Spencer, Electrmagnetically cnvluted arcs cnfined within an annular gap between tw PTFE cylinders, Prc. f the 9th Int. Cnf. n Gas Discharges and their Applicatins, China, pp.34-37, Sept. 0. [6] M.N. Wilsn, K.D. Srivastava, Design f efficient flux cncentratrs fr pulsed high magnetic fields, The Review f Scientific Instruments, Vl. 36, N. 8, Aug [7] L.M. Shpanin, G.R. Jnes and J.W. Spencer, Flux cncentratr fr cmpressing an arc plasma clumn in the current interrupter, Prc. f the st Int. Cnf. n Gas Discharges and their Applicatins, Nagya, Japan, pp.97-00, Sept. 06. [8] L.M. Shpanin, G.R. Jnes, J.W. Spencer, B. E. Djakv, Cntrl and prpulsin f an atmspheric pressure plasma ring, IEEE Transactins n Plasma Science, Vl. 36. N.5, pp , Oct.008. Grdn R. Jnes received the B.Sc. degree in physics frm University f Wales, U.K., the Ph.D. degree in physics frm University f Liverpl, U.K., and the D.Sc. degree frm University f Wales, U.K. He is an Emeritus Prfessr and past Directr f the Centre fr Intelligent and Mnitring Systems at University f Liverpl. He is authr f several bks in the area f Chrmatic mnitring, high-pressure arcs and SF6 switchgear. He is a member f the Executive Management Cmmittee f the Internatinal Series f Cnferences n Gas Discharge and Their Applicatins and is a member f an internatinal study grup n switchgear arcs, the Current Zer Club. He was awarded the Institutin f Electrical Engineering (IEE) Science, Educatin and Technlgy Achievements Medal in 999 and a Medal f Distinctin in 006 by the Academy f Sciences, Bulgaria. He is a Fellw f the IET, U.K. and member f the Institute f Physics, U.K. Jseph W. Spencer received the B.Eng. and Ph.D. degrees in electrical engineering frm University f Liverpl, U.K. He is Prfessr f Electrical Engineering, Directr f the Centre fr Intelligent and Mnitring Systems and Head f Schl f Electrical Engineering, Electrnics and Cmputer Science at University f Liverpl. He is a member f an internatinal study grup n switchgear arcs and Hnrary Treasurer f the Internatinal Series f Cnferences n Gas Discharge and Their Applicatins. He is a member f the Institutin f Electrical Engineering (IET), U.K.

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