Lighting Grounding System of a Tall-mast for Human Safety

Electric Elect ric Powe Powerr Syste Systems ms Res Research153 earch153 (201 (2017) 7) 119 119–127 –127

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Lightning grounding system of a of a tall-mast for human safety John J. John J. Pantoja ∗ , Francisco Roman, Francisco Amortegui, Carlos Rivera Depart Departame amento nto de Ingenie Ingeniería ría Eléctr Eléctrica ica y Electr Electróni ónica, ca, Facult Facultad ad de Ingeni Ingenierí ería, a, Univer Universid sidad ad Nacion Nacional al de Colomb Colombia–S ia–Sede ede Bogotá Bogotá,, Carrer Carrera a 30 # 45-03, 45-03, Edifici Edificio o 411, Bogotá, Bogotá, Colombia Colombia

a r t i c l e

i n f o

Article history: Recei Receive ved d 29 April April 2016 2016 Recei Receive ved d in revise revised d form form 24 Janua January ry 2017 2017 Accepted Accepted 16 February February 2017 2017 Avail Availab able le online online 6 March March 2017 2017 Keywords: Lightning Lightning Lightning earthing earthing system system Frequenc Frequency y dependen dependence ce of soil Grounding Human Human safety safety Lightning protection

a b s t r a c t

Numerical techniques enable realistic analysis of lightning currents effects on tall tall structures including actual installation conditions. Characteristics such as the frequency dependence of soil of soil parameters, parameters, inductances and capacitances due due to nearby metallic elements, and the actual geometry of the of the structure and its grounding system are commonly neglected or simplified in lightning grounding system design. In this this paper, the impact of neglecting of neglecting these characteristics on a tall tall-m -mas astt lightning grounding system design is discussed. discussed. The effects are determined using three risk assessment approaches based on energy calculation, voltage thresholds, and current integration, which allows comparing the performance of the the grounding system under different conditions. Results obtained from numerical simulations and then verified by measuremen measurements ts show that a metall metallic ic protecting fence not connected to the earthing mesh produces lower human safety risks to lightning currents than when when it is connected. This result is in opposition to common design practices and shows the need to assess each specific grounding design under true conditions to guarantee human safety requirements. © 2017 2017 Elsevier B.V. All rights reserved.

1. Intr Introd oduc ucti tion on

The The adeq dequate uate desi design gn of light ightni ning ng prot protec ecti tio on syst system emss of tall tall stru struct ctur ures es is a basi basicc requ requir irem emen entt to guar guaran ante tee e the the huma human n safe safety ty andto avoid avoid cultur cultural,econo al,economic mic,, or sociallosse sociallosses. s. Protect Protectionsystem ionsystemss shou should ld guar guaran ante tee e that that volta voltage ges, s, curr curren ents ts,, and and ener energy gy indu induce ced d by a lightni lightning ng strike strike are lower lower than than well-d well-defin efined ed thresho thresholds. lds. Curren Currently tly,, comp comput utat atio iona nall tool toolss can can be used used for for this this task task;; howe howeve ver, r, model modelin ing g induce induced d voltag voltages es dueto lightn lightning ing curren currents ts inject injected ed intonatural intonatural soil soil prese resent ntss diff differ eren entt chal challe leng nges es.. On one one hand hand,, ther there e is not not a modmodelin eling g tech techni niqu que e tha that rep reprodu roduce cess the the impu impuls lsiv ive e respo espons nse e of the the curr curren ents ts and and mate materi rial als, s, the the ioni ioniza zati tion on proc proces ess, s, and and nonnon-li line near arit ity y [1,2].. On the other [1,2] other hand, hand, the availa available ble models models and charac character teriza izatio tion n tech techni niqu ques es of the the dyna dynami micc beha behavi vior or of elec electr trom omag agne neti ticc para parammeter eterss of soil soilss pres presen entt inco incons nsis iste tenc ncie iess [3] [3].. Usua Usuall assu assump mptio tions ns of freq freque uenc ncy y inde indepe pend nden entt soil soil para parame meter terss are are far far from from actua actuall valu values es for most most soils soils and produc produce e import important ant deviati deviations ons in the calcul calculati ation on of induce induced d voltage voltagess [1,4] [1,4].. For For thes these e reas reason ons, s, the the perf perfor orma manc nce e of eart earthi hing ng syst systems ems is comcommonl monly y asse assess ssed ed using sing cal calcula culati tio ons and simu simula lati tio ons base based d on a pure pure resi resist stiv ive e grou ground nd beha behavi vior or.. When When this this happ happen ens, s, most most simu simu--

∗ Corresponding Corresponding author.

E-mail addresses: addresses: jjpantoja [email protected] [email protected] .co (J.J. Pantoja), [email protected] (F. Roman), Roman), [email protected] [email protected](F. (F. Amortegui), [email protected] (C. Rivera). Rivera).

http://dx.doi.org/10.1016/j.epsr.2017.02.013 0378-77 0378-7796/© 96/© 2017 2017 Elsevier Elsevier B.V. All rights rights reserved reserved..

lati lation onss are are perf perfor orme med d with with elec electr tros osta tatic tic simu simula lati tion onss tool tools. s. This This is main mainly ly tru true due due to the the fact fact tha that subs substa tati tion onss grou ground ndin ing g syst system emss are are almo almost st alwa always ys calc calcul ulat ated ed for for rela relati tive vely ly low low freq freque uenc ncy y faul faultt curr curren ents ts.. Howe Howeve ver, r, in some some case casess ligh lightn tnin ing g curr curren ents ts,, with with high high freq freque uenc ncy y comp compon onen ents ts,, coul could d impa impact ct stru struct ctur ures es such such as mast mastss or protecting protecting fences. fences. Theeffect Theeffect of thefrequenc thefrequency y depend dependenc ency y ofsoil parame parameter terss on the groundpotentialrise (GPR)of groundingelectrodesdue groundingelectrodesdue to lightning lightning curren currents ts has been been analyz analyzed ed by differ different ent author authorss using using experi experimen men-tal result resultss [1,5,6] [1,5,6],, numerical numerical simulations simulations [2,3] and electromagne electromagnetic tic models [7] [7].. Thes These e studie studiess reve reveal aled ed that that negl neglec ecti ting ng the freq freque uenc ncy y depen dependen dence ce of the soil soil para parame meter terss prod produc uces es an over overes esti tima mati tion on of the indu induce ced d volt voltag ages es.. This This over overest estim imat atio ion n is more more pron pronou ounc nced ed in low conduc conductiv tivity ity soils, soils, due to their their strong strong freque frequency ncy depende dependence nce;; andin short short impuls impulses,such es,such as associ associate ated d with with lightni lightning ng subseq subsequen uentt return return stroke strokes, s, due to their their higher higher freque frequency ncy conten content. t. These These effect effectss become become releva relevant nt for soil soil resisti resistivity vity above above 1000 1000 m [8] [8].. Rece Recent ntly ly,, nume numeri rica call simu simula lati tion onss have have been been used used to stud study, y, in more more detai detail, l, the the effe effects cts prod produc uced ed by light lightni ning ng strik strikes es taki taking ng into into accoun accountt realis realistic tic earthi earthing ng system system charac character terist istics ics [3,9] [3,9].. In Ref. Ref. [9] [9],, the step step and and touc touch h volta voltage ge distr distribu ibutio tion n arou around nd a GSM GSM base base stati station on are are used used to asse assess ss the the eart earthi hing ng desi design gn usin using g a full full-w -wav ave e elec electr troomagn magneti eticc simu simula latio tion n in time time doma domain in.. Simi Simila larr anal analys yses es have have been been perfor performed med for wind wind turbin turbines es [3,10] [3,10].. These These studie studiess have have shown shown that that the the incl inclus usio ion n in the the simu simula lati tion on of deta detail ilss and and near nearby by stru struct ctur ures es,, usuall usually y neglec neglected ted in ground grounding ing system system analys analyses, es, produc produces es signifi signifi--

120

J.J. Pantoja et al. / Electric Power Systems Research 153 (2017) 119–127

Risk Riskss caus caused ed by trans transie ient nt elec electr tric ic sign signal alss in huma human n beings beings are are still still bein being g studie studied d [12] [12].. Dang Danger erou ouss effe effects cts of curr curren ents ts on pers person onss have have being being widely widely studie studied d since since the beginni beginnings ngs of the cities cities electri electri-ficat ficatio ion. n. A refe refere renc nce e stud study y is the the publ publis ishe hed d by Dalz Dalzie iell in Ref. Ref. [13] [13],, wher where e leth lethal al leve levels ls for for both both AC elec electr tric ic curr curren ents ts and and capa capaci cito torr disdischar charge gess are are pres presen ente ted. d. In Ref. Ref. [13] [13],, Dalz Dalzie iell prop propos osed ed the the ener energy gy criter criterion ion to calcul calculate ate the maximu maximum m curren currentt levels levels I and exposition exposition times t before before ventri ventricul cular ar fibrilla fibrillatio tion n occurs occurs,, by using using the relati relation on where e K is the the ener energy gy cons consta tant nt that that depe depend ndss on the the body body K 2 = I 2 t , wher weight.In weight.In Ref. Ref. [14] [14],, the study study of physio physiolog logica icall effect effectss of electr electric ic curcurrents rents is extende extended d to DC and impuls impulse e shocks shocks,, while while voltag voltage, e, curren current, t, and and ener energy gy thre thresh shol olds ds are are disc discus usse sed. d. This This stud study y refe refers rs to 25J and and 10J as letha lethall and and dange dangero rous us ener energy gy leve levels ls,, resp respec ecti tive vely ly;; howe howeve ver, r, it also also conc conclu ludes des that that more more rese resear arch ch is requ requir ired. ed. Here Here,, the the desi design gned ed prot protec ecti tion on syst system em is asse assess ssed ed by mean meanss of three three para parame meter terss comm common only ly used used:: the the ener energy gy deli delive vere red d to a perperson, son, the step step volt voltag age, e, and and the the seve severi rity ty para parame meter ter.. To obta obtain in thes these e para parame mete ters rs,, both both step step-- and and touc touch h volt voltag ages es gene genera rate ted d by a ligh lighttning ning curr curren entt inje inject cted ed in the eart earthi hing ng syst system em are are calc calcul ulat ated ed usin using g numerical numerical simulations. simulations.

2.1. Numerical simulation

Fig. Fig. 1. Insta Installa llatio tion n of the 30m high high Coronacurre Coronacurrent nt measur measuring ing mast mast in the campu campuss

of the of the Universid Universidad ad Nacional Nacional de Colombia Colombia..

cant cant chan change gess in its its resp respon onse se to indu induce ced d volt voltag ages es due due to ligh lightn tnin ing g currents [11] [11].. In the the pres presen entt work work,, the the grou groundi nding ng syst system em of the the 30m tall tall mast mast shown shown in Fi Fig. g. 1 is analyzed analyzed using numerical numerical simulations simulations.. This structure ture was was inst insta alled lled in a quite uite dese desert rted ed stre street et at the the Univ Univer ersi sida dad d Naci Nacion onal al de Colo Colomb mbia ia camp campus us to inve invest stig igat ate e Coro Corona na curr curren ents ts in high high mast masts. s. The The mast mast base base is isol isolat ated ed by a 2 m high high squa square re meta metall llic ic fence, fence, called called here here “metallic enclosure”, sepa separa rate ted d 2 m from from the the mast mast cent centre re.. Howe Howeve ver, r, due due to its its loca locati tion on and and to prot protec ectt peop people le walk walkin ing g orstayingin orstayingin thevicinityof thevicinityof themetallicencl themetallicenclosu osure,ligh re,lightnin tning g induce induced d over over volt voltag ages es arou around nd the the struc structu ture re are are calc calcul ulat ated ed.. The The effe effect ct of the the meta metall llic ic encl enclos osur ure e is inve invest stig igat ated ed in orde orderr to eval evalua uate te a poss possib ible le volta voltage ge indu inducti ction on due due to indu induct ctiv ive e or capa capaci citi tive ve effe effects cts,, inst instea ead d of the pure pure resisti resistive ve ones. ones. This This paper paper is organi organizedas zedas follow follows: s: In Sectio Section n 2, the methodology methodology used used for for the the ligh lightni tning ng prot protec ecti tion on syst system em asse assess ssme ment nt is pres presen ente ted. d. Then Then,, in Sect Sectio ion n 3, the the nume numeri rica call appr approa oach ch to calc calcul ulat ate e indu induce ced d volt voltag ages es due due to ligh lightn tnin ing g curr curren ents ts is vali valida date ted. d. In Sect Sectio ion n 4, the earthi earthing ng system system design design is describ described ed and numeri numerical cal result resultss are prepresented. Finally, Finally, Section Section 5 presents resents the conclusions conclusions.. 2. Risk Risk assess assessmen mentt method methodolo ology gy

The The main main purpo urpose se of the the mast mast is to meas measur ure e coro corona na cur current rentss and and loca locall atmo atmosp sphe heri ricc cond condit itio ions ns in its its top. top. Howe Howeve ver, r, the the mast mast is prone rone to be imp impacte acted d by ligh lightn tnin ing g and touc touch h and step step vol voltage tagess coul could d be expe expect cted ed in the the meta metall llic ic encl enclos osur ure. e. Ther Theref efor ore, e, a spec specia iall risk risk assess assessmen mentt was perfor performed med..

2.1.1. Simulation setup Theinduced Theinduced over over voltag voltages es were were calcul calculate ated d bysimulatinga bysimulatinga direct direct ligh lightn tniing stri strike ke on the the top top of the the mast mast.. A nume numeri rica call simu simula lati tio on in CST CST Micr Microw owav ave e Studio Studio usin using g a tran transi sien entt solv solver er was was perf perfor orme med. d. The ligh lightn tnin ing g curr curren entt is repr repres esen ented ted by an idea ideall curr curren entt sour source ce at the the tow tower’s top top. To characterize a level III or IV scenario of the inte intern rnat atio iona nall stan standa dard rd IEC IEC 6230 623055-1, 1, a 100 100 kA, kA, 10/3 10/350 50 s doub double le expone exponenti ntial al impuls impulse e curren currentt source source was used used to repr repres esen entt a first first posi positi tive ve curr curren entt impu impuls lse. e. In addi additi tion on,, to maxi maximi mize ze indu induct ctiv ive e and and capa capaci citi tive ve effe effect ctss in the the indu induce ced d volt voltag ages es,, a shor shorter ter wave wavefo form rm of 100kA,1/50 s was was cons consid ider ered ed.. This This wave wavefo form rm is base based d onthe first first negativ negative e lightn lightning ing curren currentt impuls impulse e accord according ing to IEC 62305-1 62305-1.. The The simu simula lati tion on volu volume me has has a 30m side side leng length th and and is cent center ered ed at the mast. mast. To repres represent ent the fact fact that that locall locally y the curren currents ts spread spread in all directi directionsinto onsinto thesoil, thesimulatio thesimulation n volumewas volumewas setconsidera setconsiderably bly larg larger er than than the the simu simula late ted d stru struct ctur ure. e. Whil While e the the side side leng length th of the the grou ground ndin ing g mesh mesh is 5 m, the the side side lengt length h of the the simu simula lati tion on volu volume me is 30m. In full-w full-wave ave lightn lightning ing phenom phenomena ena simulat simulation ions, s, the report reported ed bounda boundary ry conditi conditions ons are the follow following ing:: – Absorb Absorbing ing bounda boundary ry conconditions ditions (ABC) (ABC) in all the bounda boundarie riess [15] [15],, – ABC ABC with with perf perfec ectt elec electr tric ic conduc conductor tor (PEC) (PEC) ground ground [16] [16],, or – fully PEC [17] [17].. ABC are are used used to trunca truncate te the comput computati ation on domainby domainby reduci reducing ng the amplit amplitude ude of the reflecti reflections ons of the electr electroma omagne gnetic tic waves waves imping impinging ing the simula simulatio tion n borde borders rs whil while e PEC PEC is used used to prov provid ide e a clos closed ed path path for for thelightn thelightnin ing g current [17] [17].. In the perfor performed med simulat simulation ion,, absorb absorbing ing wave wave boundboundary ary cond conditi ition onss were were used used on all all the face facess of the simu simula lati tion on volu volume me as report reported ed in [18] [18].. In this this simu simula lati tion on setu setup, p, it was was verifie verified d that that the effe effect ct of the the refle reflect cted ed wave wavess from from the the boun bounda dari ries es on the the vari variab able less of inte intere rest st is negl neglig igib ible le sinc since e an erro errorr of 2.6% 2.6% was was obtaine obtained d when when resu result ltss were ere comp compar ared ed with with a simu simula lati tion on volu volume me of a 40m side side length.

2.1.2. Soil parameter frequency dependency Diff Differ erent ent mode models ls to calc calcul ulat ate e the freq freque uenc ncy y depe depend nden ence ce of soil soil para parame mete ters rs are are avai availa labl ble. e. A comp compar aris ison on betw betwee een n some some of thes these e model modelss is pres present ented ed in Refs Refs.. [3,19] [3,19].. Rece Recent ntly ly,, a caus causal al mode modell with with stro strong ng expe experi rime ment ntal al supp suppor ortt has has been been prop propos osed ed to addr addres esss this this effect [6] [6].. In this this pape paper, r, the the Mess Messie ierr mode model, l, whic which h prov provid ides es resu result ltss in good good agre agreem emen entt with with expe experi rime ment ntal al data data for for soil soilss with with mode moderrate ate and and low low resi resist stiv ivit ity y and and whic which h sati satisfi sfies es caus causal alit ity y [3] [3],, is used used..


121

Fig. Fig. 2. Classifica Classification tion of alternat alternating ing currents currents of 15Hz–100Hz in current– current–time time areas areas

acco accord rdin ing g to thei theirr effe effect cts. s. Effe Effect cts: s: 1 – None None,, 2 – None None phys physio iopa path thol olog ogic ical al effe effect ct,, 3 – Non Non fibri fibrill llat atio ion n risk risk,, 4 – Fibr Fibril illa lati tion on risk risk (5%) (5%),, 5 – Fibr Fibril illa lati tion on risk risk (<50 (<50%) %),, 6 – Hearth Hearth attack, attack, burns, burns, fibrillati fibrillation on risk (>50%). (>50%). Based Based in the internat internationa ionall standardIEC standardIEC 60479-2.

Z Th V Th

+

~0 Ω

R B

-

1 kΩ

Step or Contact or Contact Voltage Fig. Fig. 3. Theven Thevenin in equiva equivalen lentt circui circuitt used used to calcul calculat ate e the curren currentt and energy energy delivdeliv-

ered ered to a human human being being..

Usin Using g this this mode model, l, the freq freque uenc ncy y resp respon onse se of the the soil soil perm permit ittiv tivit ity y and conduc conductivi tivity ty can be calcul calculate ated d as [20] εr (ω ( ω) =

 +     

ε∞ ε0

 (ω) =  0

1

 0 fε∞

1+

4fε∞  0

(1)

[S/ [S/m], m],

(2)

where ε0 is the the free free-s -spa pace ce perm permitt ittiv ivit ity, y,  0 i s the DC or low frequency quency conductivity conductivity,, ε∞ = 8ε0 , and and f is the the freq freque uenc ncy. y. The The comp comple lex x  − jεr  ), wher perm permit itti tivi vity ty in a mate materi rial al is give given n by ε = ε0 (εr − where e εr = / (ωε0 ). Theref Therefore ore,, a soil soil can be charac character terized ized using using just just  0 , which which canbe calcul calculate ated d as the invers inverse e of the low-fr low-frequ equencysoil encysoil resist resistivi ivity ty LF . 2.2. Assessment Assessment parameters

Fig. Fi g. 2 is based based on altern alternati ating ng curren currents ts below below 100Hz, extrap extrapola olatio tions ns to tran transi sien entt curr curren ents ts are are used used.. In Ref. Ref. [22] [22],, for for exam exampl ple, e, a curr curren entt impuls impulse e of199 A and340 nsof timeto half half value,whic value,which h corres correspon ponds ds to 13.5J, 13.5J, is used used as a refe refere renc nce e valu value e to asse assess ss grou ground ndin ing g syst system emss against against lightning. lightning. To calc calcul ulat ate e the the ener energy gy give given n by the ligh lightni tning ng indu induce ced d step step and and touch touch voltag voltages, es, the method methodolo ology gy of the Theven Thevenin in equiva equivalen lentt circui circuitt propos proposed ed in Ref. Ref. [21] and show shown n in Fi Fig. g. 3 was used. used. In the the calc calcul ulaations, tions, the Theven Thevenin in voltag voltage, e, V Th , corr corres espo pond nded ed to the the step step or touc touch h voltage, voltage, the Thevenin Thevenin impedance, impedance, Z Th , wasneglected wasneglected,, assumi assuming ng that that the feet feet cont contac actt resi resist stan ance ce was was zero, zero, and and the the body body resi resist stan ance ce,, Rb , . Fina was was assu assume med d to be 1000 1000 Finall lly, y, the the ener energy gy was was calc calcul ulat ated ed as W

2.2.1. Energy calculation The first first estimate estimated d parame parameter ter is the amount amount of energydelive energydelivered red to a per person son by a light ightni ning ng indu induce ced d over overvo volt ltag age. e. The The limit imit of the the amoun mountt of ener energy gy W in Joule oules, s, which hich a perso erson n cou could with withst stan and d with withou outt fibri fibrill llat atio ion n risk risk,, can can be calc calcul ulat ated ed usin using g both both the the Dalz Dalzie iell curv curve e show shown n in Fi Fig. g. 4 and Eq. Eq. (3) (3)::

W = I 2 · R · t [ J] J] ,

Fig. Fig. 4. Setup Setup fora direct direct lightn lightning ing strike strike simula simulatio tion. n. (a)Lateral (a)Lateral and and (b) (b) persp perspect ective ive

views.

(3)

where I and t are the pair of current and time values along the Dalzie Dalziell curve curve in Fi Fig. g. 4 and R is the human human body body resist resistanc ance e estima estimated ted , as spec in 1000 1000 speciified fied in the the IEE IEEE Std. Std. 80 [21] [21].. When When the ener energy gy that that a pers person on coul could d with withsta stand nd is calc calcul ulat ated ed usin using g Dalzi Dalziel el’s ’s char charac ac-teri terist stic ic curv curve, e, a cons consta tant nt ener energy gy valu value e of 10J is obta obtain ined. ed. Altho Althoug ugh h

 =

P (t ) dt

 =

V 2 (t ) dt, Rb

(4)

where V ( the step step or touc touch h volt voltag age e calc calcul ulat ated ed as a func functi tion on of ( t ) is the time time and and P (t ) is the the diss dissip ipat ated ed powe powerr as a func functi tion on of time time.. 2.2.2. Step voltage threshold The The seco second nd meth metho od used used to asses ssesss the the ligh lightn tniing prote rotect ctiion syst system em was was to comp compar are e the the indu induce ced d step step volt volta age with with a volt volta age thresho threshold ld calcul calculate ated d as [23] [23]::

= U st st =

250) +  g (165∼250) , √ T

(5)

where  g is the soil soil resisti resistivit vity y and T is the lightni lightning ng durati duration. on. Using Using  g = 70 m and T =1ms, a 10.12kV 10.12kV thre thresh shol old d volt voltag age e is obta obtain ined ed..


122

Fig. Fig. 5. Calcul Calculate ated d step step volta voltage ge induce induced d at 2.83m 2.83m from from a direct direct lightn lightning ing strike strike on a soil soil with with  = 70 m. Simu Simula lati tion on resu result ltss are are obta obtain ined ed usin using g a resi resist stiv ive e soil soil with with constant constant paramete parameters rs  = 70 m and εr =1 and and usin using g the the Mess Messie ierr mode modell for for a soil soil with LF = = 70 m.

This This expres expressio sion n is restri restricte cted d to long long durati duration on lightni lightning ng strike strikes, s, such such as the the first first posi positiv tive e impu impuls lse. e. 2.2.3. Severity parameter Si1.4 The thi third metho thod is to use a parameter for safety condit dition for ventri ventricul cular ar fibrill fibrillati ation on when when short short durati duration on impuls impulsive ive curren currents ts flow flow in the the huma human n body body.. The The crit criter erio ion n appl applie iess for for heal health thy y adul adults ts and and curr curren ents ts due due to touc touch, h, trans transfe fer, r, and and step step volt voltag ages es.. The The seve severi rity ty parame parameter ter Si1.4 is give given n by [24,25]

 = |

Si1.4

ib (t ) |1.4 dt

(6)

where ib (t ) is thecurrent thecurrent throughthe throughthe body. body. Thelimitof theseverity theseverity para parame mete terr is 1.52A 1.52A 1.4 ms for negligi negligible ble probab probabili ility ty of ventri ventricul cular ar 1.4 fibrill fibrillati ation on and 2.96A ms for for a prob probab abil ilit ity y of 5% [24,25] [24,25].. 3. Vali Valida dati tion on of the the simu simula lati tion on

Firs First, t, a vali valida dati tion on of the the nume numeri rica call simu simula latio tion n was was performed. The The vali valida dati tion on cons consis iste ted d in the the comp compar aris ison on of nume numeri rica call resu result ltss with with theo theore reti tica call and and expe experi rime ment ntal al data data for for simp simpli lifie fied d case cases. s. The The step step volt voltag age e indu induce ced d due due to a dire direct ct ligh lightn tnin ing g stri strike ke to eart earth h was was conside considered red for this this purpos purpose. e. 3.1. Theoretical Theoretical comparison

The The step step volt voltag age e give given n on the the gro ground und sur surface face at a dist dista ance nce r 0 from from the the ligh lightni tning ng strik strike, e, with with a step step leng length th l, soil soil conduc conductiv tivity ity  , and a lightni lightning ng curren currentt I (t ) as a func functi tion on of time time,, can can be calc calcul ulat ated ed as [11] U p (t ) =

I ( I (t ) 1 2 r 0



− r 1+ l 0



.

Fig. Fig. 6. Step Step voltag voltage e induce induced d dueto an impuls impulsivecurre ivecurrent nt at 0.23m 0.23m from from thecurrent thecurrent

inje inject ctio ion n and and with with a step step of 0.7m. 0.7m. Measu Measurem rement ent result resultss are taken taken from from Ref. Ref. [1] [1].. Simulatio Simulation n results results are obtained obtained using using a 2nd order order fit of the soil paramet parameters ers reported reported in Ref. [1] and usin using g the the Mess Messie ierr mode modell for for a soil soil with with LF = = 2700 2700 m.

Fig. 5 show showss the comp compar aris ison on betwe between en step step volt voltag ages es obta obtain ined ed from from theo theore reti tica call and and simu simula lati tion on resu resullts. ts. A good good agree greeme ment nt is observed observed betweenboth approaches,validatin approaches,validating g the numerical numerical simulation. lation. In Fig.5 is alsoshown the calculated calculated step voltage voltage considering considering the the freq freque uenc ncy y depe depend nden ency cy of the the soil soil para parame mete ters rs.. To incl includ ude e the the soil soil Mess Messie ierr model model in the the elec electr trom omag agnet netic ic simu simula lato tor, r, a diel dielec ectr tric ic dispe dispers rsio ion n fit with with an erro errorr of 3.7% 3.7% with with resp respec ectt to the the para parame meter terss prod produc uced ed by the the mode modell was was used used.. As prev previo ious usly ly repo report rted ed [1,3,8] [1,3,8],, the effe effect ct of this this freq freque uenc ncy y depe depend nden ency cy is to redu reduce ce the the peak peak valu value e of the the indu induce ced d volt voltag ages es,, as it is confi confirm rmed ed in Fi Fig. g. 5. 3.2. Experimental results comparison

In Ref. Ref. [1] [1],, impulsi mpulsive ve curren currents ts areimpresse areimpressed d from from a hemisp hemispher heric ic elec electr trod ode e to a dist distan antt auxi auxili liar ary y grid grid whil while e the the indu induce ced d step step volt volt-age age at the the soil soil surf surfa ace is meas measur ured ed.. Usin Using g the the simu simula lati tio on setu setup p pres presen ente ted d in prev previo ious us para paragr grap aph, h, the the deve develo lope ped d step step volta voltage ge was was calc calcul ulat ated ed.. In this this case case,, the the soil soil para parame mete ters rs with ith the the frequ requen ency cy depend dependen ence ce betwe between en 100 100 Hz and and 4 MHz MHz are are used, used, sinc since e they they were were calc calcul ulat ated ed in Ref. Ref. [1] f rom r om impu impuls lsiv ive e curr curren entt meas measur urem emen ents. ts. In the the simu simula lati tion on,, an extr extrap apol olat atio ion n of thes these e data data up to 100 100 MHz MHz was used. For comparison comparison,, another another simulation simulation using the soil parameters parameters obta obtain ined ed with with the Mess Messie ierr model model was was performed. Fig. Fi g. 6 shows hows the induced induced voltag voltage e obtaine obtained d from from measur measureme ements nts and simula simulatio tions.This ns.This figure figure shows shows that that the voltag voltage e simula simulated ted using using both both sets sets of soil soil para parame mete ters rs,, pred predic icts ts well well the the wave wavefo form rm expe experi ri-mentally mentally obtained. obtained. Although Although the voltage voltage obtained obtained usingthe Messier Messier model model pres presen ents ts a high higher er peak peak valu value, e, this this resu result lt descr describe ibess the gengeneral eral behavio behaviorr of theinduced theinduced voltag voltage e only only withthe lowest lowest freque frequency ncy resistivityreportedinRef. [1] [1].. This This canbe conside consideredas redas anadequate anadequate resp respon onse se due due to the high high depe depend nden ence ce of the the volt voltag age e wave wavefo form rm on the resp respon onse se of the the soil soil para parame meter ters. s.

(7)

For the numeri numerical cal simula simulatio tion, n, the lightn lightning ing channe channell was represent sented ed usin using g a 15m long long cyli cylindr ndric ical al perf perfect ect condu conducto ctorr conn connec ecte ted d to a curr curren entt sour source ce buri buried ed 0.5 0.5 m, as show shown n in Fig ig.. 4. A soil with a low freque frequency ncy resist resistivi ivity ty of 70 m was was used. used. The The step step volta voltage ge was was meas measur ured ed by inte integr grat atin ing g the the elec electr tric ic field field calc calcul ulat ated ed in the the simu simu-lation lationss using using the integr integrati ation on line line shown shown in Fi Fig. g. 4a. The step length, length, repr repres esen ente ted d asthe arro arrow w numbe numberr 2 inthisfigure,was inthisfigure,was 1.4 1.4 m and and the the dist distan ance ce to the the ligh lightni tning ng chan channe nell was was 2.83m. 2.83m.

4. Lightn Lightning ing earthi earthing ng system system assess assessmen mentt

4.1. 4.1. Eart Earthi hing ng syst system em desi design gn

The The ligh lightn tnin ing g prot protec ecti tion on desi design gn cons consis iste ted d of two two conc concen entr tric ic squa square red d eart earth h loop loopss arou around nd the the towe tower, r, as show shown n in Fi Fig. g. 7. To avoid avoid unau unauth thor orize ized d pers person onne nell acce access ss,, the the mast mast base base is prot protec ected ted with with a 2 m high high squa square re metal metalli licc encl enclos osur ure. e. This This meta metall llic ic encl enclos osur ure e is not not bond bonded ed to the the eart earthi hing ng mesh mesh and and it is sepa separa rate ted d 2 m from from the the mast mast


123

Fig. Fig. 7. Simula Simulatio tion n Setup.(a) Setup.(a) Persp Perspect ective ive,, (b) (b) latera lateral, l, and and (c)top views. views.

cent center er.. Due Due to the the meta metall lliic encl enclos osur ure e geo geometr metry y incl includ uded ed in the the design design,, high high electr electric ic field field intensi intensitiesare tiesare present presented ed at its corner cornerss [9] [9].. Forthis reason reason,, the protec protectio tion n assess assessmen mentt wasbased on calcul calculati ating ng the the stepstep- and and cont contac actt- indu induce ced d volt voltag ages es at the meta metall llic ic encl enclos osur ure e corner corners. s. These These voltag voltages es were were calcul calculate ated d by integra integratin ting g the electri electricc field field in the the pathsshow pathsshown n in Fi Fig. g. 7a; wher where e the the steplen steplengt gth h is1 m and and the the touc touch h path path is form formed ed by two two stra straig ight ht lines lines,, one one hori horizo zont ntal al and and one one vert vertic ical al with with resp respect ectiv ive e lengt lengths hs of 1 m and and 1.5 1.5 m. Thre Three e poss possib ible le situ situat atio ions ns of the the meta metall llic ic encl enclos osur ure e were were conconside sidere red. d. In the the first first one, one, the the meta metall llic ic encl enclos osur ure e is remo remove ved, d, in the the

seco second nd case case,, the the corn corner erss of the meta metall llic ic encl enclos osur ure e are are boun bounde ded d to the eart earthi hing ng mesh mesh,, whil while e in the the thir third d case case the the meta metall llic ic encl enclos osur ure e is not not conn connec ected ted to the eart earthi hing ng mesh mesh.. 4.2. 4.2. Effe Effect ct of the the meta metall llic ic encl enclos osur uree

Figs. 8 and 9 show show the the resp respec ectiv tive e indu induce ced d volt voltag ages es due to first first posi positiv tive e and and first first nega negati tive ve light lightni ning ng impu impuls lses es.. Thes These e figure figuress show show that that the earthin earthing g conditi condition on of the metalli metallicc enclos enclosure ure has an imporimportant tant effect effect on the wavefo waveform rm and amplit amplitude ude of the induced induced voltag voltages. es.

Table 1

Risk assessme assessment nt paramet parameters ers calculate calculated d from simulate simulated d voltages voltages.. Excitation

Metallic enclosure

Delivered energy (J)

Step voltage (kV)

Touch to the Touch metallic enclosure

Step

Severity Seve rity par paramet ameter er Si1.4 (A 1.4 ms) Touch to the metallic enclosure

Step

First positive impulse 100 kA 10/350

Without Bonded to the earthing mesh Not bonded to the earthing mesh

– 7.4 9.7

18.0 61 0.8

8.4 15.5 3.8

– 3.3 3.9

6.7 15.8 0.8

First negative impulse 100 kA 1/50

Without Bonded to the earthing mesh Not bonded to the earthing mesh

– 2.3 2.1

2.7 6.8 0.2

– – –

– 0.6 0.7

0.9 1.7 0.07

124


Fig. Fi g. 9. Ma Magn gnit itud ude e of th the e st step ep an and d to touc uch h vo volt ltag ages es pr prod oduc uced ed by th the e 10 100kA, 0kA, 1/ 1/50 50 s Fig.. 8. Ma Fig Magni gnitud tude e of the ste step p an and d tou touch ch vol voltag tages es pro produc duced ed by a 10 100kA, 0kA, 10 10/3 /350 50 s

lightningstrikeat thetowertop, cons lightningstrikeat consideri ideringthe ngthe eart earthingsyste hingsystem:(a) m:(a) witho withoutmetalutmetallic encl enclosur osure, e, (b)with a meta metallicenclosur llicenclosure e bond bondedto edto theearthin theearthing g mesh mesh,, and(c) with a met metall allic ic enc enclos losur ure e not bo bonde nded d to theearth theearthingmesh. ingmesh.

lightningstrik lightn ingstrike e at thetop of thetowerconsi thetowerconsider deringthe ingthe ear earthi thing ng sys system(a) tem(a) wit withou houtt metall met allic ic enc enclos losure ure,, (b) wit with h a met metall allic ic enc enclos losurebonde urebonded d to theearth theearthing ing mes mesh, h, an and d (c) wit with h a met metall allic ic enc enclos losurenot urenot bon bonded ded to theearth theearthingmesh. ingmesh.


125

Fig. Fi g. 10 10.. Ex Expe peri rime ment ntal al se setu tup p us used ed to me meas asur ure e th the e to touc uch h vo volt ltag age e pr prod oduc uced ed by an

impulsiv impu lsive e curre current nt inje injected cted into the mast bas base. e.

4.3.. Lig 4.3 Light htnin ning g ea earth rthing ing sys system tem des design ign ass assess essmen ment t

Usin Us ing g th the e ca calc lcul ula ate ted d vo volt ltag ages es,, th the e pr prop opo ose sed d li ligh ghtn tnin ing g ri risk sk assess asse ssmen mentt me metho thodo dolo logy gy wa wass ap appl plie ied d to th the e ea eart rthi hing ng sy syst stem em.. Th The e ener en ergy gy le leve vels ls fo forr ea each ch ca case se we were re ca calc lcul ulat ated ed ap appl plyi ying ng Eq Eq.. (4) to the voltag voltage e wavefo waveforms rms presen presented ted in Figs. 8 and 9. Ta Tabl ble e 1 shows hows that that removi removing ng themetallicenclos themetallicenclosurefromthe urefromthe simula simulatio tions ns yieldsto yieldsto very very high high ener energy gy valu values es deli delive vere red d by the the step step path path.. For For the the othe otherr conconside sidere red d case cases, s, with with the meta metall llic ic encl enclos osur ure e bonde bonded d and and not not bond bonded ed to the the earth earthin ing g mesh, mesh, thedelive thedelivere red d ener energy gy leve levels ls are are below below the the 10J limi limitt for for the the touc touchi hing ng integ integra ratio tion n line line.. Howe Howeve ver, r, for for the the step step path, path, the the not not bond bonded ed cond condit itio ion n is the the only only one that that is belo below w the the limit imit.. For For both both impu impuls lses es,, thedesign thedesign with with theenclos theenclosur ure e not not bond bonded ed to the the eart earthi hing ng mesh mesh deli delive vers rs less less ener energy gy than than the the eart earthe hed d one. one. Peak Peak step step volt voltag ages es are are also also pres presen ented ted in Ta Tabl ble e 1, which which shows shows that that the designwith designwith the enclos enclosurenot urenot bonded bonded to the earthin earthing g mesh mesh has has lowe lowerr volt voltag age e leve levels ls than than the the step step volt voltag age e thre thresh shol old d of 10kV determ determine ined d by using using Eq. (5) (5).. The The seve severi rity ty para parame meter ter Si1.4 was calcul calculate ated d applyi applying ng Eq. (6) to the the cur current rent pro produce duced d in a body body resi resist stan ance ce of 1k 1k  by the the volt voltag age e waveforms waveforms presented presented in Figs.8and9 Figs.8and9.. Table1 shows hows that that thelimitof 2.96A1.4 ms is not not surp surpas asse sed d in any any case case for for the the 1/50 1/50 s wavefo waveform. rm. For For the the 10/3 10/350 50 s wave wavefo form rm,, both both simu simula lati tion ons: s: with with and and witho without ut the the meta metall llic ic encl enclos osur ure e bond bonded ed to the the eart earthi hing ng mesh mesh surp surpas asss the the 2.96A1.4 ms limit. limit. The best perfor performan mance ce accord according ing to this this parame parame--

Fig. Fig. 12. 12. Measured Measured injected injected current current produced produced by the impulse impulse generato generator. r.

ter was was obta obtain ined ed when when the encl enclos osur ure e is not not bonde bonded d to the the eart earthi hing ng mesh mesh sinc since e it does does not not surp surpas asss the the step step-v -vol olta tage ge limi limitt and and slig slight htly ly surpas surpasss the touchtouch-vol voltag tage e limit. limit. It is import importantto antto note note that that the three three calcul calculate ated d approa approache chess indiindicate cate tha that the the lowe lowest st risk risk to perso ersons ns in the the vici vicini nity ty of the the mast mast is obta obtain ined ed for for the the case case when when the the meta metall llic ic encl enclos osur ure e is not not bond bonded ed to the the eart earthi hing ng mesh mesh.. Alth Althou ough gh the the 1/50 1/50 s wave wavefo form rm is shor shorte terr than than the the maxi maximu mum m valu values es of ligh lightni tning ng para paramet meter erss define defined d by the the stan standa dard rd IEC IEC 6230 623055-1 1 for for the the first first nega negati tive ve impu impuls lse e (i.e (i.e.. 100 100 kA, kA, 1/100 s), s), the the obta obtain ined ed ener energy gy leve levels ls are are cons consid ider erab able le belo below w the the thres thresho hold ld of 10J for for the not not bonde bonded d desi design gn.. The The calc calcul ulat ated ed resu result ltss indic indicat ate e that that there there is an influ influen ence ce of the the impuls impulse e wavefo waveform rm on the risk risk assess assessment ment parame parameter ters. s. 4.4. 4.4. Experi Experime menta ntall test test

An expe experi rime ment ntal al test test was was perf perfor orme med d to veri verify fy that that the the desi design gn with with the the encl enclos osu ure not not bond bonded ed to the the ear earthin thing g mesh mesh provi rovide dess a lowe lowerr risk risk when when the mast mast carr carrie iess impu impuls lsiv ive e curr curren ents. ts. An impu impuls lse e current current of −1.1kA, 17/62.5 17/62.5 s was was injec injecte ted d intothe intothe baseof baseof themast themast

Fig. Fig. 11. 11. Schema Schematic tic of thesetupused to gener generat ate e andmeasure andmeasure the impuls impulsivecurre ivecurrent nt inject injected ed in themast base. base.

126


metalli metallicc enclos enclosure ure not bonded bonded to the earthi earthing ng mesh. mesh. It is import important ant to note note that that thes these e resu result ltss hold hold for for soil soilss with with high higher er resi resist stiv ivity ity than than the here here consid considere ered d since since as the soil soil resist resistivi ivity ty become becomess higher higher,, the resisti resistive ve coupli coupling ng yields yields less less determi determinan nant. t. Differences Differences between between measured measured and simulated simulated results results are probaprobablydue to simpli simplifica ficatio tions ns in themodel,such as tempora temporall invari invarianc ance e in the the soi soil resis esisti tivi vity ty,, soil soil homo homoge gene neit ity, y, and syst system em iso isolati latio on. Addi Additio tiona nall lly, y, duri during ng the the expe experi rime menta ntall camp campai aign gn,, the the conn connec ectio tion n betwe between en the the mast mast and and the the meta metall llic ic encl enclos osur ure e was was perf perfor orme med d with with a single single conduc conductor tor.. This This connec connectio tion n could could involv involve e parasi parasitic tic inducinductance tancess that that were were not not easi easily ly repr repres esen ented ted in the simu simula lati tion on.. 5. Conc Conclu lusi sion onss

Fig. Fig. 13. 13. Meas Measur ured ed touc touch h volt voltag ages es indu induce ced d due due to a −1.1 1.1 kA impuls impulsive ive curren currentt inject injected ed in themastwiththe metall metallic ic enclou enclousein sein twoconfig two configurat urations ions:: (a) bonded bonded to the earth earthingmesh ingmesh and and (b) (b) not not bonde bonded d to the earth earthingmesh. ingmesh.

as show shown n in Fi Fig. g. 10 10.. Deta Detail ilss of the expe experi rime ment ntal al setu setup p are are show shown n in the equiva equivalen lentt circui circuitt presen presented ted in Fi Fig. g. 11 11.. Two capaci capacitor torss in series series were were disc discha harg rged ed thro throug ugh h a spar spark k gap gap to prod produc uce e an impu impuls lsiv ive e curcurrent rent.. The The curr curren entt wave wavefo form rm was was meas measur ured ed with with a 618  coaxial resi resista stanc nce e and and the touc touch h volt voltag age e was was meas measur ured ed usin using g a high high volt volt-age age prob probe. e. Resi Resist stiv ive e matc matchi hing ng imped impedan ance ce in para parall llel el was was used used in the the 50 50  measu measure reme ment nt cabl cable e to redu reduce ce high high freq freque uenc ncy y nois noise. e. The The termin terminallocate allocated d at 20 m from from themetallic themetallic enclos enclosureconsi ureconsistsof stsof two . post postss buri buried ed 1.5 1.5 m with with an equi equiva vale lent nt resi resist stan ance ce to eart earth h of 7.45 7.45 Fig. Fi g. 12 shows hows the the measu measure red d injec injecte ted d curr curren ent. t. This This wave wavefo form rm is impu impuls lsiv ive e as expe expect cted ed and and pres presen ents ts some some osci oscill llat atio ions ns in the wave wave fron frontt due due to theresona theresonanc nce e of thecircui thecircuitt indu induct ctan ance ce and and the the coax coaxia iall capa capaci cito torr forme ormed d by the the encl enclos osu ure and the the mast mast and due due to the the refle reflecti ction onss of in the the mast mast and and the the meas measur urem emen entt wiri wiring ng.. Fig.. 13 shows Fig hows themeasuredinduce themeasuredinduced d touch touch voltag voltages es betweenthe betweenthe meta metall lliic encl enclos osu ure and a term termin ina al place laced d on the the grou ground nd at a disdistanc tance e of 1 m from from the the encl enclos osur ure. e. It is show shown n that that the the magn magnit itud ude e of the measur measured ed peak peak induce induced d voltag voltage e with with the metall metallic ic enclos enclosurenot urenot bondedto bondedto theearthing theearthing meshis almostthreetimes almostthreetimes lower lower than than in the case case when when the the encl enclos osur ure e is bond bonded ed to the the eart earthi hing ng mesh mesh.. In addi addi-tion, tion, Figs. Figs. 12 and 13 show how that that the the touc touch h volta voltage ge for for the the grou ground nded ed encl enclos osur ure e case case foll follow owss the the injec injecte ted d curr curren entt wave wavefo form rm,, indic indicat atin ing g that that the the coup coupli ling ng is main mainly ly resi resist stiv ive. e. This This is not not the the case case for the the

Diff Differ erent ent techn techniq ique uess to asse assess ss the the risk risk perf perfor orma mance nce of a ligh lighttning ning protec protectio tion n system system agains againstt transi transient ent curren currents, ts, based based in energy energy,, voltag voltage e thresh threshold olds, s, and curren currentt integr integral, al, were were used used in the earthi earthing ng syst system em of a high high mast. mast. By usin using g thes these e metho methods ds simi simila larr conc conclu lusi sion onss were were obta obtain ined ed,, sinc since e the the desig design n with with the best best perf perfor orma manc nce e yiel yields ds lowe lowerr leve levels ls than than the sugg sugges ested ted thre thresh shol olds ds for for each each metho method. d. Partic Particula ularly rly,, it is shown shown that that a metalli metallicc enclos enclosure ure placed placed around around themast in thecondit theconditio ion n of notnot-bo bonde nded d to the the eart earthi hing ng mesh mesh comcompare pared d with with the the eart earthe hed d one, one, prod produc uces es lowe lowerr ener energy gy and and volt voltag age e leve levels ls to a pers person on touc touchi hing ng it. it. This This resu result lt was was corr corrob obor orat ated ed durin during g an expe experi rime ment ntal al camp campai aign gn,, when when curr curren entt impu impuls lses es were were inje injecte cted d to the actu actual al mast mast.. This This paper paper shows shows theimportan theimportance ce ofincludingboth ofincludingboth accura accurate te repreprese resent ntat atio ions ns of the the actu actual al eart earthi hing ng syst system em of high high mast mastss and and the the expe expect cted ed fast fast chan changi ging ng light lightni ning ng curr curren entt impu impuls lses es.. A risk risk asse assess ss-ment ment meth method odol olog ogy y is prop propos osed ed and and full full wave wave elec electr trom omag agne neti ticc simu simula lati tion onss are are incl includ uded ed in the the proc proced edur ure e to cons consid ider er poss possib ible le indu inducti ctive ve or capa capaci citi tive ve effe effects cts when when a ligh lightni tning ng curr curren entt impa impact ctss the structure. structure. Work Work in the use use of rece recent nt comp comput utat atio iona nall tool toolss to incl includ ude e diff differ er-ent lightn lightning ing phenom phenomena ena in the protec protectio tion n system system analys analysis,such is,such as the soil soil ioniza ionizatio tion n andnon-linea andnon-linearit rity, y, is in progre progress.Parti ss.Particul cularl arly, y, the possib possibili ility ty ofa groundflasho groundflashoverbetwe verbetweenthe enthe earthi earthing ng mesh mesh andthe not-bon not-bonded ded metall metallic ic enclos enclosurewill urewill be analyz analyzed ed using using detail detailed ed simsimulatio ulations, ns, in which which specifi specificc materia materials ls and dimens dimension ionss are includ included. ed. Acknowledgments

This This work work was was devel develop oped ed unde underr the rese resear arch ch proj projec ectt “Sis “Siste tema ma para para la Capt Captur ura a y Alma Almace cena nami mien ento to de la Ener Energí gía a Prov Proven enie ient nte e de Nubes Nubes de Torm Tormen enta ta”” and and financ financia iall lly y supp suppor orted ted by the the Colo Colombi mbian an Administrati Administrative ve Department Department of Science, Science, Technology Technology and Innovation Innovation Colcie Colcienci ncias as under under the contra contract ct No.795No.795-201 2011. 1. Author Authorss would would like like to than thank k to PhD. PhD. Nico Nicolá láss Mora Mora Parr Parra a from from Mont Monten ena a Tech Techno nolo logy gy S.A. S.A. for the valuab valuable le contri contribut bution ionss about about the numeri numerical cal simula simulatio tions. ns. References [1] S. Vis Visacr acro, o, R. Ali Alipio pio,, M.H M.H.. Mu MurtaVale,C. rtaVale,C. Pe Perei reira,The ra,The res respon ponse se of gro groun undin ding g electrodes elect rodes to ligh lightning tning curr currents ents:: the effe effect ct of freq frequenc uency-dep y-depende endent nt soil resistivi resi stivity ty and perm permittiv ittivity, ity, IEEE Tran Trans. s. Elec Electroma tromagn. gn. Comp Compat. at. 53 (2) (201 (2011) 1) 401– 401 –406. [2] M. Akb Akbari ari,, K. She Sheshy shyeka ekani, ni, M. M.R. R. Ale Alemi, mi, The eff effectof ectof fre freque quency ncy dep depend endenc ence e of soil elect electrical rical para paramete meters rs on the ligh lightning tning perf performa ormance nce of grou groundin nding g syst systems, ems, IEEE IEE E Tra Trans. ns. Ele Electr ctroma omagn.Comp gn.Compat.55 at.55 (4)(201 (4)(2013) 3) 73 739 9 –746. [3] D. Ca Cavka vka,, N. Mor Mora, a, F. Ra Rachi chidi, di, A com compa paris rison on of fre freque quency ncy-de -depen penden dentt soi soill models: mode ls: app applicat lication ion to the anal analysis ysis of grou grounding nding syst systems, ems, IEEE Tran Trans. s. Electroma Elect romagn. gn. Comp Compat. at. 56 (1) (201 (2014) 4) 177– 177–187. 187. [4] C. Por Portel tela, a, M. Tava Tavares, res, J. Pisc Piscolato olato,, Influ Influence ence of eart earth h condu conductivi ctivity ty and permittiv perm ittivity ity freq frequenc uency y depe dependen ndence ce in elect electroma romagnet gnetic ic tran transien sientt phen phenomen omena, a, in: Inter Internati national onal Conf Conferen erence ce on Powe Powerr Syst Systems ems Tran Transien sients ts– –IP IPST ST 20 2003,New 03,New Orleans, Orle ans, USA USA,, 200 2003. 3. [5] S. Visa Visacro, cro, R. Alip Alipio, io, Freq Frequenc uency y depe dependen ndence ce of soil para paramete meters: rs: expe experime rimental ntal results, resu lts, pred predictin icting g form formula ula and influ influence ence on the light lightning ning resp response onse of ground gro undingelect ingelectrod rodes, es, IEE IEEE E Tra Trans. ns. Po PowerDeliv werDeliv.. 27 (2)(201 (2)(2012) 2) 92 927 7 –935.


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Lighting Grounding System of a Tall-mast for Human Safety

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