Protection of Overhead Lines Coupled to a Photovoltaic Generator Against Overvoltage Induced by a Lightning Strike

Transcription

1 3ème conférence Internationale de énergie renouvelable CIER-215 Proceeding of Engineering and Technology - PET Protection of Overhead Line Coupled to a Photovoltaic Generator Againt Overvoltage Induced by a Lightning Strike Bidi Manel #1, Latreche M ed Elhadi #2 # Electrotechnical Laboratory LEC, Department of Electrotechnic, Faculty of Science Technology, Univerity Mentouri of Contantine, Algeria 1 bidi_manel@yahoo.fr Abtract like all electrical equipment photovoltaic ytem can be damaged by both direct and indirect lightning trike and other overvoltage diturbance caued by electrical witching operation, load witching and o on. The purpoe of thi paper i to invetigate the propagation of overvoltage induced by a lightning trike on an overhead line which can be coupled with a photovoltaic array. For reaon of electromagnetic compatibility (EMC), the need for a good quality in power upply along with the widepread ue of enitive device connected to ditribution line make the protection againt lightning induced diturbance of primary importance. In thi paper we invetigate the hielding effect due to the preence of other conductor in a multiconductor overhead line a well a that of the hield wire periodically grounded, and the urge arreter in order to protect an electric network coupled to a photovoltaic generator againt the propagation of overvoltage induced by indirect lightning return troke. Keyword EMC, Lightning-induced voltage, overhead line, hielding, FDTD. I. INTRODUCTION Induced overvoltage i created by either direct or indirect lightning trike hit on olar panel ytem. A cloud to ground lightning flah generate a tranient electromagnetic field which can induce overvoltage of ignificant magnitude on overhead line ituated in the adjacent. Like all electrical equipment photovoltaic ytem can be damaged with both direct and indirect lightning trike and other overvoltage diturbance caued by electrical witching operation, load witching and o on. Thi paper i devoted to the tudy of the induced-voltage on a multiconductor line and to the influence of a hielding wire to reduce the propagation of the phenomena. The electromagnetic field reulting from a patial-temporal ditribution of the return troke current along the lightning channel caue induced voltage in the urrounding device (electric power tranmiion line). The calculation of thee induced voltage require the ue of a uitable coupling model (coupling equation) baed on the tranmiion line theory applied to the problem of interaction between the lightning electromagnetic field and an overhead line. The induced overvoltage on a conductor belong a multiconductor line i affected by the preence of other conductor, and hielding wire. The calculation reult preented in thi paper were obtained by mean of computer program developed by the author uing MATLAB environment. II. CALCULATION OF INDUCED OVERVOLTAGE A. Coupling model between an EM field and multiconductor overhead line Starting from Maxwell equation and adopting the tranmiion line approximation, it i poible to derive a pair of equation decribing the coupling of an external electromagnetic field and multiconductor line. Thee equation can be written in different equivalent formulation. The formulation we adopt in thi paper i the one propoed by Agrawal et al 1], which for the cae of homogeneou lole multiconductor line above a perfectly conducting ground and illuminated by an external field, i given by (ee Fig. 1): Fig.1. Geometry ued to calculate the induced lightning overvoltage on a multiconductor overhead line u ( x, ] + R ] i ( x, ] + L ] i ( x, ] E ( x, h, ] i ij i ij i = xi i x t (1) ii ( x, ] + Gij ] ui ( x, ] + Cij ] ui ( x, ] = ] (2) x t Thee equation will have been olved by mean of the point-centered finite difference technique in time domain (FDTD). Where:

2 E xi ( x, hi, t )] i the vector of the horizontal component of the incident electric field along the x axi at conductor height hi. ] matrice zero. Lij and Cij are repectively the inductance and the ] ] capacitance matrice per unit length of the line. ii ( x, t )] i the line current vector. ] i the cattered voltage vector, related to the voltage vector u ( x, t )] by the following i ] ] ] ] ò (x, z, t ) i the exciting vertical electric field that can be conidered a unvarying in the height < z < hi éhi ù u ie ( x, t ) = - ê E zie ( x, z, t )dz - hi E ze (x,, t ) ê ú ë û The boundary condition for the cattered voltage vector ui ( x, t ) are given by: ] ò ]ii (, t )] + hi E zie (,, t )] e B ]ii (L, t )] + hi E zi ( L,, t )] Z A ] and Z B ] are the matrice A Lii dx Ii(x),, C ijdx x C iidx, Ii(x+dx) C jjdx ZAj (b) Time m] Fig. 4 Typical lightning current over 5 µ Ii(x+dx) Ij(x), ZAi 3 2 Lij dx Ljj dx j, Where of the line termination. The equivalent circuit for infiniteimal ection of a lole line i preented in Fig. 2. i 5 Fig. 3 Power line configuration for the analyi (4, and 5 ground wire), a) 1 conductor in each phae, b) 2 conductor in each phae ] ] ] = -Z ] = -Z i (, t ) i ( L, t ) 4 (a) Where E zie m Current KA] m 1 éhi ù u i ( x, t ) = u i ( x, t ) + u ie ( x, t ) = u i ( x, t ) - ê E zie ( x, z, t )dz ú ê ú ë û ui ( x, t ) total expreion: u u conductor i terminated on it characteritic impedance determined in abence of the other conductor. The adopted channel bae current i the one repreented in Fig. 4. The velocity of the return troke i v = 1,3.18 m/, the channel height i 7.5 km. We note that the ground i alway conidered like a perfect conductor 8, 9]., x+dx ZBi ZBj L Fig.2 Equivalent circuit of Agrawal et al coupling equation for the cae of a lole multiconductor line. III. ANALYSIS OF INDUCED OVERVOLTAGE In the following a three-phae line i analyed. The conidered geometry i repreented in Fig.3. The phae conductor are located at a height of 1 m. The radiu of the conductor i 9.14 mm. The ground wire are located at 3.5 m over the phae conductor and their radiu i 3.96 mm. The line i 1 km long. The troke location i at 5 m from the line centre, at the ame ditance from the two termination. Each A. Multiconductor line without a hielding cable Fig. 5 how induced-voltage calculated at the line extremitie, for the horizontally-configured line, the highet reduction occur for the middle one (conductor 2 in Fig. 3). We alo note that the induced-voltage in conductor 1 and 3 are uperpoed. The hielding effect due to the preence of other conductor i much more important and remarkable when each phae i fractionated in two conductor which i hown in Figure 5-b.

3 6 Induced overvoltage without hielding wire 7 Induced overvoltage without hielding wire hielding wire at 13m hielding wire at 7m a) Time µ ] Induced overvoltage without SW (Phae divided by 2 conductor) Fig. 6 Induced-voltage on a ingle conductor with and without a hielding wire 5 Induced overvoltage with 1 SW Fig. 5 Induced-voltage on horizontal multiconductor overhead line without hielding wire, a) the three phae conductor, b) each phae divided by 2 conductor B. Influence of the hielding wire To illutrate the reducing effect of a hielding conductor, we have conidered both a ingle-wire configuration and the ame three-phae configuration examined previouly with the preence of the hielding wire grounded at line extremitie (conductor 4 and 5 in Fig. 3). For the configuration with a 1 km ingle-conductor, the hielding wire wa placed ucceively above and under a ingle phae-conductor at two different height, namely 7 or 13 m (the ingle-wire height i 1 m). Figure 6 how the induced-voltage at line termination of a ingle phae conductor with and without the preence of the hielding wire. It can be een that the hielding wire i more efficient in mitigating the induced-voltage when it i placed above the phae conductor. Figure 7 how the effect of the ground wire on the induced-voltage on the three conductor. It can be een that the peak value of the induced-voltage i ignificantly reduced. The induced current in the hielding wire i repreented in figure 8. a) b) Induced overvoltage with 2 SW Fig. 7 Induced-voltage on the three line conductor of a multiconductor overhead line with, a) 1 hielding wire, b) 2 hielding wire

4 Courant A] Temp µ] Fig. 8 Induced-current in the end of the hielding wire (Conductor 4 for the horizontal configuration). C. Three-phae line without ground wire and with urge arreter Beide, the line ha been analyed when terminated on non-linear load: each conductor, in thi cae, i terminated at both end on it characteritic impedance R L in parallel to a Zn-O urge-arreter, inerted to protect the load R L (Fig. 9). The nonlinear urge-arreter play a ignificant role in limiting the induced overvoltage. Thi i well remarked in Figure Induced overvoltage without SW and with Surge Arreter Fig. 11 Induced overvoltage on three line conductor terminated on nonlinear load IV. SURGE PROTECTION OF SYSTEMS The photovoltaic ytem coupled with an overhead network i chematized in figure. 12 Fig.9 Non-linear load terminating the phae-conductor The Zn-O urge-arreter ha been modelled by i=k(v/v ref ) n,with k = 2,5 ka, n= 24 and v ref = 4 kv (Fig.1). Fig.1 Characteritic of the Zn-O urge arreter 12] Fig. 12 PV array coupled with overhead network The protection of photovoltaic ytem coupled to the overhead electrical network i performed primarily by limiting induced voltage by the indirect effect of a lightning trike on overhead line (working ection III). The principle of the protection of the photovoltaic ytem ide i carried out a follow 13]: Interconnection of the mae by bare copper cable between the PV array and inverter. Grounding of the mae. Floating photovoltaic generator. Connection PV array / inverter with reinforced protection. Inulation monitoring device generally integrated in the inverter.

5 Fig. 13 protection of the photovoltaic ytem ide 13] Surge arreter on DC Circuit: Bipolar in junction (varitor characteritic of zinc oxide) with integrated thermal diconnection. Bipolar inverter input. Surge arreter on alternative circuit: TT modular type for high flow capacity of ditributor network. V. CONCLUSIONS The knowledge of induced voltage will aid the deigner for the appropriate deign of olar power ytem a well a it et up in a proper way. In our tudy, we have oberved the effect of indirect lightning trike on an overhead line witch coupled with a olar power ytem. Lightning induced-voltage on multiconductor line are computed uing MTL model for the return troke field calculation and the Agrawal et al. coupling model for field-totranmiion line coupling calculation. Voltage induced on 1 km long three phae power line by a ubequent return troke with a triking point cloe to the line equiditant to the line termination have been calculated in order to ae the hielding effect of a multiconductor and the ground wire. It ha been hown that: The induced overvoltage on a phae of a multiconductor line i affected by the preence of other conductor. For the examined cae, the induced-voltage on each of the line conductor are generally 15 to 25% lower than thoe correponding to a ingle phae placed at the ame height. The preence of the hielding wire allow to reduce the peak value of the induced-voltage about 4% (horizontal with two hielding conductor). The preence of non-linear load (Surge arreter) at the termination of the line play a ignificant role in limiting the induced overvoltage. REFERENCES 1] Agrawal.A.K, H.J.Price, S.H.Gurbaxani, Tranient Repone of Multiconductor Tranmiion Line Excited by Nonuniform ectromagnetic Field, IEEE Tranaction on ElectroMagnetic Compatibility (EMC), Vol. 22, N ] Diendorfer.G, and M.A.Uman "An Improved Return Stroke Model with Specified Channel Bae Current", Journal of Geophyical Reearch, Vol 95 (D9), pp , ] Borghetti.A, C.A.Nucci, M.Paolone, E.Petrache, and F.Rachidi "Lightning Induced Voltage on Complex Ditribution Sytem: Model Advanced Software Tool and Experimental Validation, Journal of Electrotatic, Vol. 6(2-4), pp , 24. 4] Heidalen.H.K "Calculation of Lightning Induced Overvoltage in Low Voltage Sytem", PhD Thei, Norwegian Univerity of Science and Technology, ] Ihii.M, K.Michihita, Y.Hongo, and S.Oguma "Lightning Induced Voltage on An Overhead Wire Dependent on Ground Conductivity, IEEE Tranaction on Power Delivery, Vol. 9, No. 1, pp , ] Mater.M.J, M.A.Uman "Lightning Induced Voltage on Power Line: Theory", IEEE Tranaction on Power Apparatu and Sytem, Vol. 9, pp , ] Mater.M.J, M.A.Uman, W.Bealey, and M.Darveniza "Lightning Induced Voltage on Power Line: experiment", IEEE Tranaction on Power Apparatu and Sytem, Vol. 9, pp , ] Nucci.C.A, and F.Rachidi "Lightning Induced Overvoltage", in IEEE Tranmiion and Ditribution Conference, pp. 4, New Orlean, 1999.

6 9] Nucci.C.A, F.Rachidi, M.Lanoz, and C.Mazzetti "Lightning Induced Voltage on Overhead Line", IEEE Tranaction on ElectroMagnetic Compatibility (EMC), Vol. 35, ] Wagner.C.F, and G.D.McCann "Induced Voltage on Tranmiion Line", AIEE Tranaction, Vol. 61, pp , ] Rachidi.F, M.Rubintein, S.Guerrieri, and C.A.Nucci "Voltage Induced on Overhead Line by Dart Leader and Subequent Return Stroke in Natural Rocket-Triggred Lightning", IEEE Tranaction on ElectroMagnetic Compatibility (EMC), Vol. 39, No. 2, pp , ] Renato RIZZO1, Amedeo ANDREOTTI1, Andrea DEL PIZZO1, Luigi VEROLINO1, "Lightning induced effect on loy multiconductor power line with ground wire and non-linear load - Part II: imulation reult and experimental validation", PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN , R. 88 NR 9b/ ] "Protection contre le effet de la foudre dan le intallation faiant appel aux energie renouvelable", Guide ADEME Agence de l Evironnement et de la Métrie de l Energie.