Magnetic Field Around The New 400kV OH Power Transmission Lines In Libya

Transcription

1 ECENT ADVANCES n ENEGY & ENVIONMENT Magnetc Feld Around The New kv OH Power Transmsson Lnes In Lbya JAMAL M. EHTAIBA * SAYEH M. ELHABASHI ** Organzaton for Development of Admnstratve Centers, ODAC MISUATA / LIBYA * EHTAIBA_J@YAHOO.CO.UK ** ELHABASHI_S@YAHOO.COM Abstract:- In ths paper, the magnetc feld produced around a kv over-head power transmsson lnes recently commssoned n Lbya wll be analytcally computed. The approxmate computatons wll be done usng the mage method and applyng Ampere's (Bot-Savart s) law consderng quas-statc felds and an nfnte lne sources parallel to a perfectly conductng flat ground plane. The computaton doman consdered s the D free space n the lateral drectons perpendcular to the lne conductors at 1 and m above ground level. The objectve of ths work s to nvestgate how safe s the transmsson corrdor lmts (±3m, OW edges) set by the Lbyan government and to account for publc awareness. The way of nvestgaton s smply by comparng the feld levels to the electromagnetc felds exposure level lmt standards set by the ICNIP. The resulted feld values consderng dfferent loads are much less than the general publc exposure level lmt (B= μt) recommended by the ICNIP. Keywords: hgh voltage; magnetc feld; transmsson corrdor; rght of way; exposure lmt; ICNIP. 1. Introducton Hgh voltage power transmsson lnes n Lbya covers and extends nearly to the whole places where ndustry growng and people lve. The maxmum hgh voltage used for over-transmsson of power s the -KV 5Hz system wth sngle and double crcuts wth trple bundled conductors. The electromagnetc felds generated around hgh-voltage lnes n general have receved many nvestgatons concernng ther ntenstes and ther nfluence to human bengs. In some places, especally where people lve just under or near by these lnes, the awareness of the effects of the felds produced by these lnes becomes a serous problem. Nether the Lbyan government nor any other nongovernmental local organzaton has set any exposure level lmts to electromagnetc felds. The government has set only the corrdor wdth (ght Of Way, OW) that extends 3 meters from both sdes of the center-lne of a hgh voltage transmsson lnes. The nternatonal standards for publc exposure lmts as set by the ICNIP [7], are 5kV/m for the electrc feld and μt for the magnetc feld. In a prevous work [1], the electrc feld ntensty around the same kv power transmsson lne system was computed analytcally usng statc laws of electromagnetc. In ths work, the statc technque wll also be used to analytcally compute the magnetc flux densty, B, n D usng Ampere's law (Bot-Savart) []. To smplfy the ntegraton of the feld components around the charged lnes, the ϕ- component of the magnetc flux densty wll be decomposed nto two x- and y- components n a Cartesan coordnate system assumng power transmsson s along the z-drecton.. Magnetc Feld Formulaton The dfferental element dl of the lne current shown n Fgure (1), assumng thn wre, makes a dfferental magnetc flux densty db gven by [3][5] oidl a d B (1) ISSN: ISBN:

2 ECENT ADVANCES n ENEGY & ENVIONMENT y y I ay dl pont(x',y',z') db -. xo I + z=-plane az pont(x,y,) ax y o. z Ground a x z y. o x xo. -I (a) (b) Fg.1 Geometry of a thn wre carryng a current I and the dfferental quas-statc magnetc feld produced n the z= plane due to a dfferental element dl. a) 3D vew, b) lne cross-secton vew and ts mage. As shown n the fgure n the computaton space defned by z= plane and the perfectly conductng ground plate n ths paper. Integraton of the overall dfferental contrbutons db's due to the dfferental elements dl's over the lne current and ts mage from to + gves the total magnetc flux densty B, as follows: B Idl o a Where for n conductors: n B x B x 1 B x I (5) & B ax B ay (3) x y n B y B y 1 y y ' y ' () y y ' y ' x ' y ' x ' y ' I B y () The magntude of the magnetc flux densty s then: B B x B y (7) 3. esults and dscusson The magnetc flux densty generated around the 5Hz, kv sngle- and double-crcuts power transmsson lnes descrbed above s analyzed and computed n the aforementoned way. The computatons where done for 1. and.m above ground n the z= plane (md-span) for the two real lne systems shown n Fgure (). The computer program results are shown n Fgure (5a,b,c,d) for the sngle and double crcuts. The feld quanttes were assumed quas-statc felds and computed on ths bass at dscrete tme nstances corresponds to a maxmum value along a full tme perod. The magnetc flux densty was calculated twce for dfferent mnmum possble clearances of the lne conductors,,, 1, 1, and 1 meters for lne currents 15A and A. For the sngle crcut lne confguraton system, the results for lne currents of 15A shows a maxmum magnetc flux densty values wthn the transmsson corrdor of.313μt and μT at 1 and m above ground respectvely. The maxmum values at A lne currents are μT and μT at 1 and m above ground respectvely. The maxmum ISSN: ISBN:

3 ECENT ADVANCES n ENEGY & ENVIONMENT magnetc flux densty outsde the transmsson corrdor (at the OW edges) s less than 1.μT at 15A lne currents, and less than.μt at A lne currents; whch are about 9.% and 93.%, respectvely, below the general publc exposure level lmt, μt, set by the ICNIP. Wthn the transmsson corrdor, and for lne currents of A, the maxmum magnetc flux densty, B, s 9.15% and 9.9%, respectvely, less than the ICNIP exposure level lmt for the 1 and m heghts above ground level respectvely. For lne currents of 15A, these percentages go even hgher those n case of A lne current. e a r t h w r e e a r th w r e e a r th w r e. 7 5 m. 7 5 m S m m T S S m m T 7. 5 m 7. 5 m T h + 3 m h m h + m. 5 m. 5 m h m h 1 h + 1 m h (a) (b) Fg. a) sngle-crcut, kv 3-conductors/phase, -earth wres; b) Double-crcut, kv 3- conductors/phase, 1-earth wre. Bundled conductors are equspaced by s=cm. For the double crcut lne confguraton system, the results for lne currents of 15A shows a maxmum magnetc flux densty values wthn the transmsson corrdor of.37μt and.7735μt at 1 and m above ground respectvely. The maxmum values at A lne currents are 3.39μT and 5.93μT at 1 and m above ground level respectvely. The maxmum magnetc flux densty outsde the transmsson corrdor (at the OW edges) s less than 1.31μT at 15A lne currents, and less than.1μt at A lne currents; whch are about 9.9% and 93.9% below the general publc exposure level lmt set by the ICNIP. Wthn the transmsson corrdor, and for lne currents of A, the magnetc flux densty, B, s 9.7% and 9.9% less than the ICNIP exposure level lmt for the 1 and m heghts above ground respectvely. For lne currents of 15A, these percentages go hgher than those for A lne currents. Outsde the transmsson corrdor, the maxmum average magnetc flux densty s 1.μT and 5.9μT for 15A and A lne currents respectvely. The table below shows the maxmum magnetc flux densty wthn and outsde the transmsson corrdor. Max.Feld Sngle crcut at y(m) Double crcut at y(m) For sngle-crcut at For double-crcut at quantty above ground above ground -3 > x > +3-3 > x > +3 1m m 1m m 1m m 1m m B(μT), Io=15A B(μT), Io=A ISSN: ISBN:

4 ECENT ADVANCES n ENEGY & ENVIONMENT kv Sngle-crcut magnetc flux densty vs lateral dstance x Lne current=io=15a 1.m above ground 1 kv Sngle-crcut magnetc flux densty vs lateral dstance x Lne current=io=15a.m above ground magnetc flux densty, (T) = 1m magnetc flux densty, (T) = 1m Lateral dstance, x (meters) Lateral dstance, x (meters) kv Double-crcut magnetc flux densty vs lateral dstance x Lne current=io=15a 1.m above ground 1 kv Double-crcut magnetc flux densty vs lateral dstance x Lne current=io=15a.m above ground magnetc flux densty, (T) = 1m magnetc flux densty, (T) = 1m Lateral dstance, x (meters) Lateral dstance, x (meters) (a) (b) ISSN: ISBN:

5 ECENT ADVANCES n ENEGY & ENVIONMENT magnetc flux densty, (T) 3 kv Sngle-crcut magnetc flux densty vs lateral dstance x Lne current=io=a 1.m above ground = 1m magnetc flux densty, (T) 5 3 kv Sngle-crcut magnetc flux densty vs lateral dstance x Lne current=io=a.m above ground = 1m Lateral dstance, x (meters) Lateral dstance, x (meters) kv Double-crcut magnetc flux densty vs lateral dstance x Lne current=io=a 1.m above ground kv Double-crcut magnetc flux densty vs lateral dstance x Lne current=io=a.m above ground magnetc flux densty, (T) 3 = 1m magnetc flux densty, (T) 5 3 = 1m Lateral dstance, x (meters) Lateral dstance, x (meters) (c) (d) Fg.(3): a) MF around sngle & double crcuts kv TLs, 1m above ground, Io=15A. b) MF around sngle & double crcuts kv TLs, m above ground, Io=15A. c) MF around sngle & double crcuts kv TLs, 1m above ground, Io=A. d) MF around sngle & double crcuts kv TLs, m above ground, Io=A.. Concluson Analytcal computaton of the magnetc flux densty around kv overhead power transmsson lnes of certan confguraton was the man objectve of ths work. Computer programs have been used to smulate the magnetc flux densty n a D plane space. A comparson of the computed feld values to the ICNIP nternatonal standards was the second step to see whether the magnetc feld consttutes health rsks or not accordng to some specfc magnetc feld reference level. Because magnetc felds produced around overhead power transmsson lnes are decayng as the dstance ncreases after the outer lne conductors, the maxmum magnetc feld values n the general publc area (outsde the transmsson corrdor specfed by the ±3m off the center lne) are those at exactly the OW edges. These feld values as compared to the ICNIP standards for exposure lmts to Mf are too weak to cause any health effects. Consequently, more safe areas are guaranteed as we go far away from the OW edges. For workers n the occupatonal area, the magnetc feld strength ncreases as they go ISSN: ISBN:

6 ECENT ADVANCES n ENEGY & ENVIONMENT closer to the lne conductors where rsk ncreases and the magnetc feld reaches ts maxmum. The results also show a notceable decrease of the feld values by an ncrease n the mnmum clearance of the lne conductors. eferences: [1] S. M. Elhabash, and Jamal E. Ehtaba, Electrc Feld Intensty Around the New kv Power Transmsson Lnes In Lbya, WSEAS Proc. On CSECS 7. [] Walter L. Weeks, "Transmsson And Dstrbuton of Electrcal Energy", Harper & ow, 191. [3]Carl T. A. Johnk,"Engneerng Electromagnetc Felds & Waves", Wley nternatonal edton, [] A. A. Dahab; W. S. Abu-Elhaja and F. K. Amoura; "Acomparatve study of electrc felds beneath compact and non-compact transmsson lnes"; Int. Journal of Electrcal Engneerng Educaton, 7, pt1, pp 7-3. [5] A. Marncu; M. Greconc; and S. Musuro, "The electromagnetc feld around a hgh voltage kv electrcal overhead lnes and the nfluence on the bologcal systems", FACTA Unversty, Department of electrcal engneerng, Aprl 5, pp []LI L; GAO Yougang;"Analyss of magnetc feld envronment near hgh voltage transmsson lnes", Internatonal Conference on Comm. Tech., ICCT'9, Oct.-, 199, Bejng, Chna. [7] ICNIP Gudelnes, "Gudelnes for lmtng exposure to tme-varyng electrc, magnetc, and electromagnetc felds, up to 3GHz", ICNIP, 199. ISSN: ISBN: