A Development of Erthing-Resistnce-Estimtion Instrument HITOSHI KIJIMA Abstrct: - Whenever erth construction work is done, the implnted number nd depth of electrodes hve to be estimted in order to obtin the required resistnce vlue. We cll this erth resistnce estimtion. Under conventionl method of erth resistnce estimtion, specil knowledge nd mnpower re needed. And lso, mesurement error of vlues of pprent resistivity cnnot be checked. Furthermore, verticl nd horizontl resistivity sounding cnnot be done simultneously. To overcome these problems, we hve developed new instrument. This instrument does not need n opertion with ny specil knowledge, becuse the entire procedure is utomtic. Tht is, it cn utomticlly mesure the vlues of pprent resistivity t the ground surfce, nlyze the resistivity nd thickness of ech lyer of soil, nd estimte erth resistnce. The instrument effectively reduces the time nd mnpower needed for this type of estimtion. Keywords: - erthing-resistnce, estimtion instrument, soil lyer, resistivity sounding 1 Introduction The erthing-resistnce estimtion is proceeded s follows. First, the vlues of pprent resistivity on the surfce of the ground re mesured [1]. Secondly, the resistivity of ech soil lyer under the ground is nlyzed. Finlly, the erthing resistnce is estimted using the results of soil lyer nlysis [2]~[4]. Under the conventionl method of the erthing-resistnce estimtion, experts hve to proceed these three jobs seprtely by mnul. And the error of mesured vlues of pprent resistivity is not ble to be checked. Also both the verticl nd the horizontl resistivity sounding re not ble to be proceeded simultneously. In this wy, the conventionl erthing resistnce estimtion method needs the time nd mnpower. To void these problems, we hve been developing new instrument. This instrument does not need n opertion with ny specil knowledge, becuse the entire procedure is utomtic. Tht is, it cn utomticlly mesure the vlues of pprent resistivity t the ground surfce, nlyze the resistivity nd thickness of ech lyer of soil, nd estimte erthing resistnce only by touching the strt button of the instrument. In this wy, the instrument effectively reduces the time nd mnpower needed for this type of estimtion. Results from severl field tests with this instrument showed good greement between the estimted vlues before the erth construction nd the mesured results fter the erth construction, which demonstrted the efficiency nd importnce of this instrument 2 Problem Formultions Problems with conventionl method of estimting erth resistnce re s follows. (1) Although the pprent erth resistivity is mesured in the field, the ρ - curve must be mde lter by the huge mount of dt tht must be processed. (2) Verticl nd horizontl resistivity sounding must be done seprtely, which involves chnging the electrode loctions. (3) The mesurement error cnnot be estimted. (4) It is very difficult to nlyze multi-lyered soil. 3 Problem Solution by developing Erth-Resistnce-Estimtion Instrument To overcome these problems mentioned bove, we hve developed new instrument. This instrument cn utomticlly nd ccurtely mesure pprent resistivity t the ground surfce, nlyze the resistivity nd thickness of ech lyer of soil, nd estimte erth resistnce in the field. 3. 1 Outline of Erth Resistnce Estimtion Instrument The outlook of the instrument is shown in Fig.1, nd Fig.2 shows setup exmple. The configurtion of the instrument is shown in Fig.3. The body hs three sections for pprent-erth-resistivity mesurement, erth-resistivity nlysis, nd erth-resistnce estimtion. A specil cble nd electrodes re ttched to the instrument body. The entire procedure is utomtic. Fig.1 Outlook of the Instrument 112
For verticl resistivity sounding, we used the offset Wenner electrode rrngement shown in Fig.5 [5]. Mesurements re mde in five modes with different combintions of current electrodes C 1 nd C 2 nd voltge electrodes P 1 nd P 2. The electrode spns re 0.75, 1.5,3,6,12,24,48,96,192 nd 384 meters. The electrode spn for horizontl resistivity sounding is 3 meters. Some of the electrodes re used for both verticl nd horizontl resistivity sounding, nd others re ttched t 9, 15, 18, nd 21 meters from the edge of the cble. The electrodes re mde of highly rust-proof-stinless-steel rods. Fig.2 The Setup t the Operting Site Fig.3 Configurtion of the Instrument 3.2 Cble nd Electrode The instrument uses specil cble designed so tht verticl nd horizontl resistivity sounding cn be done simultneously. Terminls re ttched to the cble t the electrode connections (Fig.4). Fig.4 Terminls ttched to the Specil Cble Fig.5 Offset Wenner Electrode Arrngement 3.3 Apprent-erth-resistivity Mesurement Section The hert of the pprent-erth-resistivity mesurement section is scnner. It cn mesure ρ by utomticlly choosing electrodes t vrious loctions. With the offset Wenner electrode rrngement shown in Fig.5, the resistivity s ρ d1 nd ρ d2 mesured in modes D 1 nd D 2, respectively. These vlues re obtined by moving the electrodes one spn. By tking the verge of these two vlues, we cn reduce errors. Also, the resistivity sρ,ρ b ndρ c, which re mesured in the positions of mode A, mode B nd mode C, re relted by ρ = ρ + ρ (1) b c Becuse of this, the mesurement error δ is defined s δ={ ρ ( ρ b + ρ c )}/ ρ (2) Through monitoring mesurement error δ, injection current level is utomticlly incresed in the rnge of 5 to 200 ma, nd number of verging time is incresed up to 16 times in order to improve signl-noise rtio until δ becomes less thn 5 %. 113
3.4 Erth-resistivity Anlysis If the resistivity ρ i nd thickness h i of ech lyer shown in Fig. 6 re known, theoreticl pprent resistivityρis clculted by mens of n inversion technique tht uses liner filter method. Once the filter coefficient is clculted considering finite number of soil lyers, the theoreticl vlue for the surfce cn simply be determined from ρ i nd h i [6], [7]. Fig.6 Resistivity nd Thickness of ech Lyer To pply this method, we determine the ρ i nd h i of ech soil lyer by using the lgorithm shown in Fig.7. First, the dt of the mesured pprent resistivity re tken s the initil vlues ρ i nd h i. Becuse true vlues of ρ i nd h i re ssumed to be close to mesured vlues obtined from the sme electrode spn. The theoreticl vlues of ρre clculted from these initil vlues using the liner-filter method. We used the filter coefficient of 4 points/decde by Koefoed [7], nd mximum of five soil lyers. Then, the theoreticlly clculted vlue ρis compred with the mesured vlueρ by mens of the lest squre method. If the difference between them is more thn 5%, ρ i nd h i re mde either lrger or smller to minimize the difference. This process is repeted until the difference is 5% or less. The finl vlues of ρ i nd h i represent the soil resistivity nd thickness of ech lyer, nd the nlysis is finished. 3.5 Erth-resistnce Estimtion If ρ i nd h i of ech soil lyer re known, the erth resistnce of multi-lyered structure cn be found by using the clcultion s delt with in reference [8]. There re two types of erthing method. One is single long erthing electrode buried in the depth direction so tht clled boring method. The other is so tht clled prllel method consisting of severl short electrodes connected in prllel. The erth-resistnce-estimtion section uses the ρ i nd h i of ech lyer to clculte the erth resistnce of either the boring method or the prllel method. 4. Field Test Results 4.1 Improvements mde in the Field When developing the instrument, we mde vrious improvements bsed on our results from field trils. In the Fig. 8(), mrk shows mesured dt, nd solid line shows estimted clcultion result. When electrode spn is incresed, the differences of mesured dt nd clcultion result become obvious. Here, we will discuss the elimintion of the residul chrge. When chnging the electrodes, especilly when the electrode spn is lrge, the effects of the residul chrge become significnt nd distort the dt. Therefore, if the electrode spn is over 24 meters, we strt injecting the current few times to disperse ny residul chrge. As shown in Fig.8(b), this removes lmost ll the distortion, even for lrge electrode spns. 4.2 Response to Estimted nd Actul Vlues of Erth Resistnce After mking these improvements, n experiment ws crried out t Tsukub R&D Center in Jpn to check the ccurcy of this instrument. First, the erth resistnce ws estimted using this instrument. Next, we bored electrodes into the erth to depths of up to 100 meters, nd mesured the erth resistnce t ech depth. We then compred ll the mesurement results. Fig.7 Flowchrt for Erth Resistivity Anlysis 114
Fig.10 Results of the Anlysis Fig.8 Results of Removing Residul Chrge The results of estimting the erth resistnce re shown in Fig.11. The solid line shows the erth resistnce s function of the depth of single erthed electrode implnted verticlly in the erth (the boring method), while the dotted line shows the erth resistnce s function of the number of electrodes when short erth-rod electrodes (2.4 m long, 14 mm dimeter) were connected in prllel. 4.2.1 Estimtion of Erth Resistnce The mesurement vlues of the pprent erth resistivity re shown in Fig.9. Fig.11 Results of Erth-resistnce Estimtion Fig.9 Mesurement vlues of Apprent Erth Resistivity The results of the erth-resistivity nlysis, using the mesured pprent resistivity, clerly show tht erth consisted of four lyers of soil (Fig.10). 4.2.2 Actul Mesurements by Erth Boring The dimeter of the boring hole used for the ctul mesurement ws 66 mm nd it ws bored to depth of 100 meters. The erth resistnce vlues were mesured using YEW 3244. The erth resistnce vlues were estimted using the instrument. The erth resistnce vlues estimted using the instrument nd tht of mesured from the erthed electrodes using YEW 3244 greed closely s shown in Fig 12. We hve done mny other field tests t different loctions, nd hve lso hd good greement between the estimted nd mesured resistnces in those cses. The verge time needed to perform the entire procedure with this instrument is bout 30 minutes. 115
[8] T.Tkhshi, T.Kwse: Proposl of the Grounding Electrode Rods Designing Systems considering the Multi-lyered Ground, J. IEIE Jpn, Vol.9, No.6, 1989 Hitoshi KIJIMA Fig.12 Comprison of the Estimted nd Mesured Erth Resistnces 5 Conclusion We hve developed n erth-resistnce estimtion instrument. This instrument does not need n opertion with ny specil knowledge, becuse the entire procedure is utomtic. Tht is, it cn utomticlly mesure the vlues of pprent resistivity t the ground surfce, nlyze the resistivity nd thickness of ech lyer of soil, nd estimte erth resistnce only by touching the strt button of the instrument within 30 minutes in the field. Our field tests showed good greement between the estimted nd mesured resistnces. Becuse ccurte erth resistnce estimtion cn be quickly obtined, we re sure this instrument will be very useful for estimting erth resistnce. References: [1] G.F.Tgg: Erth Resistnce, London George Newton s Limited, 1964 [2] Toshiyuki Ktym, Reserch on the grounding chrcteristic of the electrode constructed by the perpendiculr disloction ground, Institute of Electricl Instlltion Engineers of Jpn, p265, 2006 [3] T Mkit, H Suzuki, Grounding property of mesh electrode buried ner verticl fult, Nihon University, Report-of-reserch Vol.39, No.2 pp21-27, 2006 [4] Tkehiko Tkhshi, The recent method of grounding electrode design, South Koren Illuminting Engineering Institute, Autumn scientific convention, Specil Lecture 2007 [5] R.D.Brker: The Offset System of Electricl Resistivity Sounding nd Its Use with Multicore Cble, Geophysicl Prospecting, 1981 [6] D.P.Ghosh: The Appliction of Liner Filter Theory to the Direct Interprettion of Geoelectricl Resistivity Sounding Mesurements, Geophysicl Prospecting, 1971 [7] O. Koefoed: Geo-sounding Principles-1, Resistivity Sounding Mesurements, Elsevier,Amsterdm, 1979 He ws born in Ymnshi; Jpn in 1952. He received his BS in Electricl engineering from Ymnshi University (1975), his MS in Electricl engineering from Ymnshi University (1977), nd his Ph.D. from Tokyo University (1999). He is member of IEEJ, IEICE nd IEIEJ. His field is ll EMC spects such s lightning protection, noise reduction, erthing systems. He served 20 yers in R&D center of NTT (Nihon Telegrph nd Telephone public corportion). He ws leder of EMC Deprtment. Then He becme professor of Polytechnic University. He published mny books such s Recent Lightning Protection (ISBN4-542-30397-7) 2006, Electricl Engineering (ISBN4-87563-022-0) 2003, Erthing & Lightning Protection (ISBN4-88552-147-5) 2002. Prof. Dr. Hitoshi KIJIMA. He obtined the best pper wrd for the 9th WSEAS Interntionl Conference (EHAC '10) University of Cmbridge, UK, Februry 20-22, 2010, Electromgnetic Force Anlyzed Results on Switchger of Disconnector for Overevoltge Protector, pp.135-140 Hitoshi Kijim, Tomooki Hsegw. Other recent ppers re s follows. [A] H. Kijim, K. Tkto, K. Murkw, Lightning protection for gs-pipelines instlled under the ground, Interntionl Journl of systems nd pplictions, engineering & development, Issue 1, vol. 5, pp117-126, 2011 [B] H. Kijim, T. Hsegw, Electricl force nlyzed results on switchger of disconnector for overvoltge protector, WSEAS Trnsctions on power systems, Issue 1, vol. 5, pp32-41, 2010 [C] H. Kijim, M. Shibym, Circuit breker type disconnector for overvoltge protector, WSEAS Trnsctions on power systems, Issue 5, vol. 4, pp167-176, 2009 116