Magnetic Field Exposure Assessment of Lineman Brain Model during Live Line Maintenance

Transcription

1 Procdings of th 14 th Intrnational Middl ast Powr Systms Confrnc (MPCON 10), Cairo Univrsity, gypt, Dcmbr 19-1, 010, Papr ID 109 Magntic Fild xposur Assssmnt of Linman rain Modl during Liv Lin Maintnanc M A Abd-Allah Rda Morsi Dpartmnt of lctrical nginring Univrsity of nha Shoubra St 108, Cairo, AR mousa_abdulah@yahoocom Dpartmnt of lctrical nginring Univrsity of nha Shoubra St 108, Cairo, AR rdamorsi@yahoocom Abstract - Liv working lads to considrabl magntic fild xposurs, associatd with acut ffcts on th on hand, and incrasd th dos with th possibl long-trm ffcts on th othr hand This acut xposur rsults in incrasing th inducd voltag, th inducd currnt dnsity, and th spcific absorption rat at th diffrnt sctions in th human body Th magntic fild can b as high as 450 μt in th brain modl nar th lowr phas conductor Th Typical inducd currnt dnsity valus insid th human modl brain can b as high as 55 ma/m at th top of th lft uppr sid of th brain modl nar th lowr phas conductor Typical spcific absorption rats (SAR) valus rach as high as 4x10-9 watts/kg at th top of th lft sid of th brain modl nar th lowr phas conductor Th maximum tmpratur incras ΔT in th brain tissu during on work hour, with considring th maximum valu of th spcific absorption rat, can b 07x10-9 o K nar th lowr phas conductor which is vry low and can b nglctd with powr frquncy filds Indx Trms Magntic fild xposur-linman brain modl- Liv lin maintnanc-inducd currnt dnsity-spcific absorption rats (SAR) I INTRODUCTION Th intraction of vry low frquncy with living tissus is an attractiv subjct in th last fw yars Many studis about th biological ffcts of th lctric powr facilitis hav bn carrid out in various countris throughout th world [1-4] Th analysis of th intraction btwn th magntic filds and th living organisms is on of th main topics in ths rsarch activitis Th xtrmly low frquncy (LF) magntic fild pntrats compltly th tissus of a human body It inducs lctric filds, currnt dnsity within th tissus Th mass-normalizd rats of lctromagntic nrgy absorption and th tmpratur incras in th human organs tissu ar also important factors in quantifying th intraction btwn magntic filds and liv organisms Diffrnt intrnational organizations hav stablishd lvls of rcommndd maximum xposur [5-7], for workrs as wll as for popl that find thmslvs xposd occasionally to lctromagntic filds xposur rcommndations in forc ar givn by th council of th uropan Union and th Intrnational Commission on Non-Ionizing Radiation Protction (ICNIRP) Th rcommndd currnt dnsity valu is ma/m for public xposur For occupational xposur th rcommndd valu is 10mA/m givn by ICNIRP Liv lin work bgan from about 40 yars ago It nabls rpair and maintnanc work to b carrid out on th transmission ntwork without any intrruption of th powr Liv lin work was bgin firstly on low voltag lvl lins, thn aftr 10 yars th work on th high voltag and HV lins wr bgin Thr ar thr basic mthods that ar usd in liv working on transmission lins namly; gloving, stick and bar hand mthods In gloving mthod th linmn us insulating glovs, slvs as thir primary prsonal protctiv quipmnt and this mthod is applicabl to distribution voltags up to 33 kv In stick mthod th linman is at th ground potntial or floating maintain a spcifid distanc from liv parts and carry out thir work using tools that ar attachd to insulating pols or sticks, and this mthod is applicabl to voltags up to 13 kv In bar hand mthod th linman is in dirct contact with nrgizd parts and sparatd from ground by air or insulating quipmnt, th linman uss an insulating laddr, insulating arial dvic or hlicoptr and this mthod is applicabl to voltags from 66 kv and abov On th othr hand, th linmn work vry nar to th lin phass, spcially in th bar hand mthod, so th linmn ar xposd to vry larg amount of th magntic filds which lads to havy amount of th inducd voltags and consquntly incras th inducd currnts in th diffrnt body organs [8, 9] This papr valuats th xposur of th linman brain to magntic filds Som of th carfully prformd xprimntal works show that at last som ffcts dpnd on th inducd lctric filds and currnts in biological systms Th othrs showd that th ris in th human organs tmpraturs, du to th lctromagntic nrgy absorption, hav a grat ffct on ths organs So it is vry ncssary to comput all th paramtrs such as; inducd currnts in diffrnt organs in th living bodis subjctd to ths filds, th distributions of th mass-normalizd rats of lctromagntic nrgy absorption, i, spcific absorption rats, or SAR Also it is ncssary to comput th total powr absorbd and th tmpratur incras in th brain tissu 33

2 II HUMAN RAIN MODLING Magntic filds wr computd in th spac surrounding th lin Th linman body modl with standard 175cm lngth is placd nar th lowr and th cntral phas conductors, Fig1, at which th incidnt magntic filds on th normal cross sction of th human brain wr computd Th human brain is modld by a sphroidal modl Th valus of th man volum, th lctrical conductivity and th mass dnsity of th human brain ar takn as 810 cm 3, 07 S/m and 1700 Kg/m 3 [10] Th human brain is modld by a sphr with a radius 578 cm It is assumd that th brain modl is filld with a homognous biological tissu Th horizontal componnts x and y of th xtrnal magntic filds rlat to th x-axis and y-axis, rspctivly Th vrtical componnt z of xtrnal magntic fild rlat to th z-axis Th linman modl is placd at positions nar th lowr and middl phas conductors Th problm can b considrd as quasi-static, sinc th dimnsions of th human body ar small compard to th wavlngth of th powr-frquncy Two additional simplifications of th problm rsult from th lctrical proprtis of tissus iological matrials ar non-magntic, and as a consqunc th magntic prmability μ is qual to that of th fr spac μ o It can b shown that th scondary magntic fild producd in tissu by th currnt flow inducd by th xtrnal magntic fild can b nglctd for frquncis at which th following condition is satisfid [1]: f μ o σ L << 1 (1) Whr, f is th frquncy, σ is th conductivity, and L is th maximum dimnsion of th body Additionally, at th 50 Hz th prmittivity componnts ε' and σ (whr ε' is th dilctric constant) satisfy th following conditions: σ >> π f ε' () Th intrnal lctric filds vctors in x; y and z-axis rsulting from th thr orintations of th sinusoidal magntic filds ar xprssd as: Whr, is an lctric fild around x-axis inducd by x, is an lctric fild around y-axis inducd by y and z is an lctric fild around z-axis inducd by z Morovr, th angular frquncy =πf whr f is 60 Hz and ϕ is th phas angls of x, y and z Th total inducd lctric fild in th modl can b xprssd as: = + + Th total currnt dnsity inducd by magntic filds is obtaind from J = σ For comparison purposs, a bas human body conductivity of 01 S/m may b assumd, and circulating currnts ar computd accordingly For any givn organ th tru currnt dnsity can b modifid simply by multiplying th bas valus by th ratio of th actual organ conductivity to th bas conductivity Th spcific absorption rat (SAR) is th mass-normalizd rats of lctromagntic nrgy absorption, i th nrgy pr unit mass, and is givn by σ SAR = ρ m z Whr, ρ m is th mass dnsity of th matrial in th human brain and it is takn as 1700 kg/m 3 Th qustion of how much nrgy is absorbd by th humans should b answrd as quantitativly as possibl Th SAR of th fild-xposd organ of th human body indicats th rat of magntic nrgy absorption by that organ This quantity hlps in assssing th nvironmntal impact of th magntic filds Intgrating th avrag powr dnsity (σ / ) ovr th sphrical brain modl volum, givs th total powr absorbd by th human brain xposd to th incidnt magntic fild Th powr absorbd by th human brain modl is givn by: (6) (7) (8) r r z / + ϕ ˆ x = ( zy yzˆ) / + ϕ y = ( xzˆ zxˆ) / + ϕ z ) ˆ z = ( yx xyˆ) ) ) (3) (4) (5) P = σ π R Watt (9) Whr, is th angular vlocity in radians, is th avrag magntic flux dnsity in T As a worst-assssmnt on can stimat th tmpratur incras ΔT in th brain tissu by using: 34

3 SAR t ΔT = C s (10) Whr t is th xposur tim and C s is th spcific hat of th brain tissu which can b takn as 418 J/Kg o K in Fig 3 Th highst valus appar to tak plac on th sid narr to th phas conductor Typical inducd currnt dnsity valus can b as high as 55 ma/m at th top of th lft uppr sid of th brain modl nar th lowr phas conductor III RSULTS AND DISCUSSION Th human body modl usd for th valuation of magntic fild xposur is situatd in clos proximity to a 380 kv transmission lin lowr and middl phas conductors to simulat a liv lin maintnanc positions Th lin is a doubl circuit lin, th phas conductors ar 4x500 mm with a subconductor spacing of 40 cm and a minimum claranc to ground of 10 m, Fig 1 Th lin is fully loadd with 1600A pr phas Fig 3 qui-inducd currnt dnsity (ma/m ) contours insid th brain modl nar lowr phas conductor Th contours of qual spcific absorption rat (SAR) ovr th cross sctional plan of symmtry along a human brain modl nar th lowr phas conductor ar shown in Fig 4 Typical SAR valus can b as high as 4x10-9 watts/kg at th top of th lft sid of th brain modl nar th lowr phas conductor Fig 1 Human body modl nar th lowr phas conductor Th magntic fild is computd in human modl brain; whr th normal cross sction of th brain is dividd into 1400 points at which th magntic fild, th currnt dnsity and th SAR ar computd Th qui-fild contours ar drawn as shown in Fig Th magntic fild nar th lowr phas conductor is varid from about 410 μt to about 450 μt from th lft of th uppr sid to th right of th lowr sid of th human modl brain, i th magntic fild varid by about 10% along th human brain at this situation Fig 4 qui-sar contours (watt/kgx10-9 ) insid th human modl brain nar th lowr phas conductor Fig 5 shows th qui-fild contours in th brain modl nar th middl phas conductor Th magntic fild is varid from about 90 μt to about 35 μt from th lft uppr sid to th right of th lowr sid of th brain modl, i th magntic fild is varid by about 11% Although th human modl brain is small in dimnsions, th magntic fild is varid considrably This considrabl fild variation is du to th nar of th organ from th lin phass Fig Magntic fild contours insid th brain modl at lowr phas conductor Th inducd currnt dnsity in th human modl brain is computd on th cross-sctional plan of symmtry through th sphroidal brain modl and th qui-currnt dnsity contours nar th lowr phas conductor is drw and showd 35

4 Fig 5 Magntic fild contours insid th brain modl at middl phas conductor Fig 6 shows th qui-currnt dnsity in th cross-sctional plan of symmtry of th human modl brain nar th middl phas conductor Th inducd currnt dnsity can b as high as 33 ma/m at th top of th lft sid of th modl nar th middl phas conductor Th distribution is showd a homognous distribution in th uppr brain part and inhomognous distribution in th lowr part Fig 6 qui-inducd currnt dnsity (ma/m ) contours insid th brain modl nar middl phas conductor Fig 7 shows th contours of qual spcific absorption rat (SAR) ovr th cross sctional plan of symmtry along a human brain modl nar th middl phas conductor Typical SAR valus rach as high as 13x10-9 watts/kg at th top of th lft sid of th brain modl nar th middl phas conductor Powr absorbd Th total powr absorbd by th human brain modl nar th lowr phas conductor is about 7x10-9 watt, whil th total powr absorbd by th human brain modl nar th middl phas conductor is about 14x10-9 watt With considring th maximum valu of th spcific absorption rat th tmpratur incras ΔT in th brain tissu during on work hour can b 07x10-9 o K nar th lowr phas conductor, whil nar th middl phas conductor can b 11x10-9 o K IV CONCLUSIONS Th currnt dnsitis, th spcific absorption rat, th powr absorbd and th tmpratur ris ar important factors to valuat th biological ffcts associatd with th xposur to xtrmly low frquncy LF magntic filds Ths factors dpnd on th charactristics of th human body organs tissus and th charactristics of th xtrnal magntic filds Magntic filds in th vicinity of th phas conductors of xtra-high voltag powr lins wr valuatd At th linman position nar th lowr phas conductor th magntic fild is varid by about 10% from th lft of th uppr sid to th right of th lowr sid of th brain modl; whil nar th middl phas conductor it varis by about 11% from th lft of th uppr sid to th right of th lowr sid of th brain modl Th magntic fild can b as high as 450 μt in th brain modl nar th lowr phas conductor Th inducd currnt dnsitis in th human modl brain ar computd nar th lowr and middl phas conductors Th Typical inducd currnt dnsity valus insid th human modl brain can b as high as 55 ma/m at th top of th lft uppr sid of th brain modl nar th lowr phas conductor Th highst valus of th SAR appar to tak plac on th sid narr to th lowr phas conductor Typical SAR valus rach as high as 4x10-9 watts/kg at th top of th lft sid of th brain modl nar th lowr phas conductor Although th human modl brain xposd to high valus of magntic fild, th total absorbd powr by th human modl brain is small This can b rfrrd to th fact that th modl xposd to a low frquncy magntic fild Th highst valu of th total powr absorbd by th human brain modl is about 7x10-9 watt nar th lowr phas conductor Th maximum tmpratur incras ΔT in th brain tissu during on work hour, with considring th maximum valu of th spcific absorption rat, can b 07x10-9 o K nar th lowr phas conductor Fig 7 qui-sar contours (watt/kgx10-9 ) insid th human modl brain nar th middl phas conductor 36

5 RFRNCS [1] M A Abd-Allah, Magntic Fild-Inducd Currnts in Human ody in th Proximity of Powr Lins, I Gnral Mting, Toronto, Canada, July 13-17, 003 [] D L Hnshaw, Dos Our lctricity Distribution systm Pos a Srious Risk to Public Halth, Mdical Hypothss, Vol 59, no 1, pp 39-51, 00 [3] T Kikko, S Kuusiluoma and L Korpinn, xposur to lctric and Magntic Filds of lctric Powr Systms, I, pp35-356, 00 [4] T Matsumoto, N Hayashi and K Isaka, Analysis of Inducd Currnt Dnsity in llipsoidal Human Modl xposd to Concurrnt LF lctric and Magntic Filds with Phas Diffrncs, I, pp , 00 [5] Intrnational Commission of Non Ionizing Radiation Protction (ICNIRP), Guidlins For Limiting xposur to Tim Varying lctric, Magntic and lctromagntic Filds (up to 3000 GHz), Halth Physics, Vol 74, no 4, pp 494-5, April 1998 [6] National Rsarch Council, Possibl Halth ffcts of xposur to Rsidntial lctric and Magntic Filds, National Acadmy Prss, Washington, USA, 1997 [7] Australian Radiation Protction and Nuclar Safty Agncy, lctricity and Halth, 003 [8] M A Abd-Allah, Quantification of Intraction twn LF Magntic Filds and Human ody Organs in Th Proximity of Powr Lins, XIVth Intrnational Symposium on High Voltag nginring, China, Papr C-19, August 5-9, 005 [9] Hutzlr, t al, "xposur to 50 Hz Magntic Filds During Liv Work", CIGR, Papr , Paris, 1994 [10] Hnnry Gray, Anatomy of Th Human ody, Twntith dition, artlbycom, Nw York,