Analysis and Mitigation of the Interference Between High Voltage Power Line and Buried Pipelines

Transcription

1 Conférence Internatonale des Energes Renouvelables (CIER 3) Sousse, Tunse - 3 Analyss and Mtgaton of the Interference Between Hgh Voltage Power Lne and Bured Ppelnes M hamed Ouadah, Mourad Zergoug Weldng and NDT research centre, BP64 route de Dely Ibrahm Cheraga Alger. Dvson of Corroson, Protecton and Materals Durablty, Tel: m.ouadah@csc.dz Weldng and NDT research centre, BP64 route de Dely Ibrahm Cheraga Alger. Dvson of Electrcal and magnetc methods, Tel: m.zergoug@csc.dz Abstract Analyss of electromagnetc nterference between hgh voltage overhead power transmsson lnes and nearby gas/ol ppelne has been a topc of growng nterest for many years. When ppelnes are located n shared row wth power lnes, the ppelne can ncur hgh nduced voltages and currents due the AC nterference. The nduced voltage on ppelne can be dangerous for operator to touch the ppelne as well as ppe corroson can result from AC dscharge. Ths research evaluates and analyzes the electromagnetc nterference effects on ol and gas bured ppelnes created by the nearby hgh voltage transmsson lnes. The am s to evaluate the AC corroson lkelhoods of ppelnes and suggest proper mtgaton solutons. Keywords AC Interference, Induced Voltages, Electrc Power Transmsson Lnes, ppelne, AC Corroson, cathodc protecton, sol resstvty. I. INTRODUCTION The electromagnetc felds generated by hgh voltage power lnes (HVPL) result n AC nterference to nearby metallc structures [], [], Therefore, n many cases nearby metallc ppelnes (MP) are exposed to the effects of nduced AC currents and voltages [3]. These nduced voltages and currents may be dangerous for both operatng personnel and ppelne structural ntegrty due to corroson effects [4]. The nterference has been tradtonally dvded nto three man categores: capactve, conductve and nductve couplng [5], [6], [7], and [8]. Capactve Couplng: Affects only aeral ppelnes stuated n the proxmty of HVPL. It occurs due to the capactance between the lne and the ppelne. For underground ppelnes the effect of capactve couplng may not to be consdered, because of the screenng effect of earth aganst electrc felds. Inductve Couplng: Voltages are nduced n nearby metallc conductors by magnetc couplng wth hgh voltage lnes, whch results n currents flowng n a conductng ppelne and exstence of voltages between t and the surroundng sol. Tme varyng magnetc feld produced by the transmsson lne nduces voltage on the ppelne. Conductve Couplng: When a ground fault occurs n HVPL the current flowng through the groundng grd produce a potental rse on both the groundng grd and the neghborng sol wth regard to remote earth. If the ppelne goes through the zone of nfluence of ths potental rse, then a hgh dfference n the electrcal potental can appear across the coatng of the ppelne metal. There has been a consderable amount of research nto nterference effects between AC power lne and ppelne ncludng computer modelng and smulaton. [9], []. A general gude on the subject was ssued later by CIGRE [], whle CEOCOR [] publshed a report focusng on the AC corroson of ppelnes due to the nfluence of power lnes. Underground steel ppelnes are n permanent contact wth the electrolyte soluton from the sol, so proper protecton measures are necessary n order to lmt the nduced current denstes, whch are the cause of electrochemcal corroson. There are more than one method appled to power lnes and ppelne to reduce nduced voltage and current on ppelnes. Ths nclude ncreasng the separaton dstance between them, the confguraton of tower, number of the conductor per phase, the dstance between conductors, sol structure, the type of coatng for ppe, and the ppe groundng [3],[4],[5] and [6]. Ths pper evaluates and analyzes the electromagnetc nterference effects on ol and gas bured ppelnes created by the nearby hgh voltage transmsson lnes. Frst we analyze the magnetc feld for horzontal and vertcal confguratons, and then we study the effect of the sol conductvty n the level of the nduced voltage n the ppelne durng both normal condtons on the power lne. Fnally we evaluate the AC corroson lkelhoods of ppelnes and suggest proper mtgaton solutons. I. PHYSICAL APPROACH A. Electrc feld To calculate the electrc feld under the power lne, phase conductors are consdered as nfnte lne charges. The horzontals and vertcals components of the electrc feld due to the three phase conductors at the desred locatons are calculated separately usng equaton () gven below. Fg. shows the components of the electrc feld at the observaton pont M(x,y) due to one phase conductor and ts mage.

2 Conférence Internatonale des Energes Renouvelables (CIER 3) Sousse, Tunse - 3 Q E h = (x-x ) - πε D D Q (y-y) (y+y) E v = - πε D D Q s the charge of the conductor, ε s the relatve permttvty. Resultant of horzontal and vertcal components of the feld gves the total electrc feld at the desred locatons as shown n equaton gven below. () P I= 3U.cosθ P s the actve power carred by the lne, U s the voltage appled; C. Induced Voltage One of the man elements n the study of the nduced voltage as a result of HV lnes s the determnaton of sol resstvty of the surroundng area of ppelne, There are many ways to measure the sol resstvty, The most commonly used method of measurng sol resstvty s the four-pn method (Wenner)[7]. h v E= E + E Fg : Sol Resstvty Calculaton Usng the Four Pn Method Fg.: Components of electrc feld due to HVPL B. Magnetc feld A magnetc feld wll be created by the current gong though the conductors. As n the electrc feld, each pont charge wll produce a magnetc feld havng a horzontal and a vertcal component. h v B= B + B Where B s the magnetc feld, B h and B v are the horzontal and vertcal components respectvely. μi B h = (x-x ) - π D D μi (y-y ) (y+y ) B v = - π D D µ s the ar relatve permeablty, Is the current through the conductor. () Wenner method employs four pns. The two outer electrodes wll used to nject current nto the ground and the two nner electrodes wll used to measure earth potentals. All four electrodes wll placed n a straght lne. The apparent resstance s drectly readable from the nstrument (R = V/I). Approxmatng the current electrodes by hemspheres, the sol resstvty s then obtaned by: ρ=π.a.r [.m] (3) A s the probe spacng n meters, R s the resstance measured n Ohms. By usng ths method, the sol resstvty approxmately at a depth of three quarters of the dstance between two electrodes can be assessed. The nduced voltage on the ppelne s generated by the electromagnetc feld n the sol. The level of nduced voltage from a hgh voltage power transmsson lne on an adjacent ppelne s a functon of geometry, sol resstvty and the transmsson lne operatng parameters. The mage method was used to calculate the nduced voltage n a ppelne, n a sngle sol resstvty layer [8]. ρi V= + (4) 4π x +y + z-h x +y + z+h Where, ρ s the sol resstvty, I s the current n the lne, h s the depth of the ppelne n the sol and x, y, z represent the pont where the voltage potental should be found.

3 Conférence Internatonale des Energes Renouvelables (CIER 3) Sousse, Tunse - 3 II. RESULTS AND DISCUSSION We carred out wthn the context of ths work the calculatons carred out on a hgh voltage power lne havng the followng characterstcs (fgure 3). P = 75 MW under a cos (θ) =.85 and U = 4 KV. Magnetc Feld (T) x -4 m m 3 m 4 m m 3 m Fg.7: Magnetc feld for vertcal confguraton wth varyng heght x -4 Fg.3: Horzontal Vs. vertcal confguratons m Fgs.6 and 7 show the magnetc feld for horzontal and vertcal confguraton respectvely wth varyng heght. As the heght ncreases, the dstance between the charges and the ppe lne ncreases causng a decrease n the magntude of the magnetc feld..9 x -5 Vertcal confguraton Horzontal confguraton Magnetc feld (T) Magnetc feld (T) x -4 Fg.4: Magnetc feld for horzontal confguraton Fg.8: Magnetc Feld for horzontal and vertcal confguratons Magnetc feld (T) Fg.5: Magnetc feld for vertcal confguraton Fgure 4, shows the magnetc feld profle for the horzontal confguraton under one meter of the hgh voltage power lne. Three peaks correspondng to the locaton of the three phase conductors. The peak at the center of the rght of way has a slghtly larger magntude than the two perpheral peaks. The magnetc feld profle n fgure 5, presents a two peak confguraton. m In order to know whch confguraton gves the lowest feld under the transmsson lne, magnetc felds at one meter heght above the ground for varous confguratons have been calculated. In Fg.8, the resultng magnetc felds correspondng to each of the confguratons are shown. In the center of the rght of way, the vertcal confguraton gave the lower magntude, whereas, as we move laterally away from the center, the horzontal confguraton gves the lower magntude. Potental(V) ohm.m 4 ohm.m 5 ohm.m ohm.m Magnetc Feld (T) x Fg.6: Magnetc feld for horzontal confguraton wth varyng heght m m 3 m 4 m 8 m 7 m Fg.9: Induced ppelne potentals under dfferent sol resstvty The nductve nterference effect has been analyzed at dfferent sol resstvty (the sol resstvty vared from 3 to Ω.m). In Fg.9, t s clear that the sol resstvty has an nfluence on the nduced voltage. The ppelne nduce-voltage reduces by reducng the sol resstvty (.e. hgh sol resstvty gves hgh nduced voltage).

4 Conférence Internatonale des Energes Renouvelables (CIER 3) Sousse, Tunse - 3 III. AC CORROSION The rsk of AC corroson of the metallc structures s closely lnked wth the ppelne solaton defects, whch mght occur, for nstance durng constructon work. From an electrcal pont of vew, coatng holdays can be seen as a small, low mpedance AC earthng system connected to the ppelne. If the coatng holday sze for example exceeds a certan dmenson, corroson rsk lkelhood neutralzes accordng to the relevant current densty. We consder a stuaton where a ppelne s bured near a Hgh Voltage Power Lnes, and let us assume that the ppelne coatng has a sngle defect. At the defect pont, the ppelne has a resstance to earth whose approxmate value s [9]: R= ρ 8d. +.D πd (5) Thus the current densty J (A/m) through the coatng defect s: 8.U J= (6) ρ.π(8d+d) U s the nduced voltage, d s the coatng thckness, ρ s the sol resstvely, D s the defect dameter. Based on actual nvestgaton n the feld of AC corroson, as well as to the actual European techncal specfcatons [], the AC corroson rsk can already be expected from current denstes at coatng holdays among 3 A/m. For current denstes between 3 A/m and A/m there exsts medum AC corroson lkelhood. For current denstes upper A/m there s a very hgh A/m corroson lkelhood []. the power lnes, the nterference can be vrtually elmnated. Obvously, ths method of mtgaton s practcal only at the preconstructon stage of ether the power lnes or the structure. Otherwse, the mtgaton must be accomplshed by alternatve methods. One of these methods s groundng ppe usng a metal such as znc, magnesum. On short lnes, ths effect can be remeded by usng dstrbuted sacrfcal anodes on the structure. The anodes wll not only be suffcent to provde cathodc protecton current but wll also smultaneously lower the resstance of the structure wth respect to earth. V. CONCLUSION The nterference problems that affect ppelnes near hgh voltage AC power (HVAC) transmsson lnes have been well defned.the magnetc feld on the ppelne n the vcnty of a hgh voltage power lne have been calculated for horzontal and vertcal confguratons. By comparng the magnetc feld profles for the horzontal and vertcal confguratons, t was found that n the center of the rght of way, the horzontal confguraton gave the lower magntude, whereas, as we move laterally away from the center, the vertcal confguraton gves the lower magntude. The voltage profles for normal operaton condtons have been smulated. Fnally, the AC corroson effect on metals was studed and the method of mtgaton of AC corroson was proposed. The method s groundng ppe usng a sacrfcal anodes such as znc, magnesum. The anodes wll not only be suffcent to provde cathodc protecton current but wll also smultaneously lower the resstance of the structure wth respect to earth. REFERENCES [] Current densty (A/m) 6 [] 4 8 [3] Induced voltage (V) Dameter of the coatng defect (mm) [4] [5] Fg.: Current densty In Fg., the current densty vares lnearly wth nduced voltage and depends on sol characterstcs by ts resstvty,.e. current densty s greater n sol wth low electrcal resstvty. Moreover, current densty ncreases by decreasng the dmenson of the coatng defect. The structures wth a coatng defect of small sze may have a hgher rsk of AC corroson. IV. SUGGESTED SOLUTIONS The close proxmty of structures to power lnes and ther sharng parallel paths for relatvely long dstances s the prncpal cause of stray AC. If the structure s remote from [6] [7] [8] [9] F. P. Dawalb, R. Da. Southey, Analyss of electrcal nterference from power lnes to gas ppelnes, part I - Computaton methods, IEEE Trans. Power Del., vol. 4, no. 3, pp July 989. F. P. Dawalb, R. Da. Southey, Analyss of electrcal nterference from power lnes to gas ppelnes, part II - Parametrc analyss, IEEE Trans. Power Del., vol. 5, no., pp Jan. 99. Hanafy M. Ismal, Effect of Ol Ppelnes Exstng n an HVTL Corrdor on the Electrc-Feld Dstrbuton, IEEE Transactons on Power Delvery, VOL., NO. 4, pp , 7. CIGRE Jont Workng Group C4.., AC Corroson on Metallc Ppelnes due to Interference from AC Power Lnes, CIGRE Techncal Brochure no. 9, 6. G. Chrstofords, D. Labrds, Inductve Interference on ppelnes bured n multlayer sol due to magnetc felds from nearby faulted power lnes, IEEE Transacton on Electromagnetc Compatblty, Vol. 47, No., pp. 54-6, May 5. A. Gupta and M. J. Thomas, "Couplng of Hgh Voltage AC Power Lnes Felds to Metallc Ppelnes," n 9th Internatonal Conference on Electro Magnetc Interference and Compatblty, INCEMIC, Bangalore, Inda, February 3-4, 6. Mohamed M. Saed, The Capactve Couplng Between EHV Lnes and Nearby Ppelnes, IEEE Transactons on Power Delvery, VOL. 9, NO. 3, pp.5-3, 4. R. Braunsten, E. Schmautzer, M. Oelz, Impacts of nductve and conductve nterference due to hgh-voltage lnes on coatng holdays of solated metallc ppelnes, st Internatonal Conference on Electrcty Dstrbuton, June, Frankfurt, Germany, paper 3. George Flppopoulos and Dmt rs Tsanakas, Analytcal Calculaton of the Magnetc Feld Produced by Electrc Power Lnes, IEEE Transactons on Power Delvery, VOL., NO., pp 474, APRIL 5.

5 Conférence Internatonale des Energes Renouvelables (CIER 3) Sousse, Tunse - 3 [] G. M. Amer, Novel technque to calculate the effect of electromagnetc feld of HVTL on the metallc ppelnes by usng EMTP program, The Int. Journal for Computaton and Mathematcs n Electr. and Electron. Eng., vol. 9, no., pp [] CIGRE Workng Group 36., Gude on the Influence of Hgh Voltage AC Power Systems on Metallc Ppelnes, CIGRE Techncal Brochure no. 95, 995. [] AC corroson on cathodcally protected ppelnes Gudelnes for rsk assessment and mtgaton measures, CEOCOR,. [3] L. Bortels, J. Deconnck, C. Munteanu and V. Topa, A General Applcable Model for AC Predctve and Mtgaton Technques for Ppelne Networks Influenced by HV Power Lnes, IEEE Transactons on Power Delvery, Vol., No., 6, pp -7. [4] CIGRE Workng Group C4.4, Mtgaton Technques of Power- Frequency Magnetc Felds Orgnated from Electrc Power Systems, CIGRE Techncal Brochure no. 373, 9. [5] R. D. Southey, F. P. Dawalb and W. Vukonch, Recent advances n the mtgaton of AC voltages occurrng n ppelnes located close to electrc transmsson lnes, IEEE Trans. Power Del., vol. 9, no., pp Apr [6] R. Braunsten, E. Schmautzer, G. Propst, Comparson and Dscusson on Potental Mtgatng Measures Regardng Inductve Interference of Metallc Ppelnes, Proceedngs of ESARS, October, Bologna, Italy. [7] W.Von Baeckmann, W.Schwenk, W.Prnz, Handbook of Cathodc Corroson Protecton - 3Ed, 997. [8] E. Sawma, B. Zetoun, N. Harmouche, S. Georges and M. Hamad Electromagnetc Inducton n Ppelnes Due to Overhead Hgh Voltage Power Lnes IEEE, Internatonal Conference on Power System Technology,. [9] W. von Baeckmann, W. Schwenk, W. Prnz, Handbook of Cathodc Corroson Protecton, Theory and Practce of Electro-chemcal Protecton Processes, 3rd ed., Gulf Publshng Co, Houston, TX, 997 [] CEN/TS58: Evaluaton of a.c. corroson lkelhood of bured ppelnes - Applcaton to cathodcally protected ppelnes, CEN, March 6. [] R. Braunsten, E. Schmautzer, G. Propst, Comparson and Dscusson on Potental Mtgatng Measures Regardng Inductve Interference of Metallc Ppelnes, Proceedngs of ESARS, October, Bologna, Italy.