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| {{Use dmy dates|date=July 2013}}
| | In a most real identification, the domain name registrars are now organizations that register domain names for many who love to own a domain name. And for everybody to grasp the true character of domain name r... <br><br>Would you like to have a domain name? O-r, do you wish to register for your domain name? Well, that"s not too much though. Together with the pres-ence of the domain name registrars, your desire for domain names will soon be made possible. To discover more, please consider checking out: [http://stir.sourceforge.net/wiki/index.php?title=The_ABC_Of_Dating_Profile_Preparation_98713 flickr.com/people/rolandfrasier]. But what actually are area registrars? <br><br>In a most real identification, the domain name registrars are now organizations that register domain names for individuals who love to own a domain name. And for everyone to grasp the nature of their work and the actual nature of domain name registrars and their function in domain name registration, one should then learn about the ICANN or the International Corporation for Assigned Names and Numbers. <br><br>Therefore these are the ICANN that represents an important component in the domain name registrars, it is required to know that it"s two main tasks. One of these is to manage the Domain Name System or DNS for the purpose of validating the department of the IP Addresses and domain names, verifying that each one is distinct. Such party then coordinates the mapping and distribution with each one of the registry. Subsequently, the ICANN is responsible of accrediting the domain name registrars. <br><br>Broadly speaking, the ICANN has particular criteria for the domain name registrars accreditation. It is generally known that once the domain name registrars are approved, it"s then a duty of the domain name registrars to sign a contract and agree to keep from the ICANNs guidelines and procedures. Discover further on [http://doc.froza.ru/index.php?title=DicksBurgin159 check my source] by going to our lovely essay. <br><br>The next position of the domain name registrars that"s associated with the process is the Registries. The domain name registrars then acquire areas from the Registries while the consumer requests them. It is interesting to know that the people might not register a domain name right from the Registry, they have to achieve this by the domain name registrars. The Registries only cost the domain name registrars for registration. And along side such responsibility, the domain name registrars also update the domain name in the corresponding Registry whenever a contact o-r DNS change is created. <br><br>In case if you will find requests for domain names, such groups then talk to the Registry to make certain whether the requested domain name is available for purchase or already owned by still another party. So it is clear when the requested domain name is available, the client can register the domain. To check up additional info, please view at: [http://dg.imp.kiev.ua/slinca/team_display.php?teamid=4745 click reference]. <br><br>Such is the character and the position of the domain name registrars on the planet of domain names. So if you wish to own a name, then you know now where to request it and where to get it..<br><br>For more information on health insurances ([http://www.kiwibox.com/kaputgestu603/blog simply click the up coming document]) review the internet site. |
| '''Soil [[resistivity]]''' is a measure of how much the soil resists the flow of electricity. It is a critical factor in design of systems that rely on passing current through the Earth's surface. An understanding of the soil resitivity and how it varies with depth in the soil is necessary to design the grounding system in an [[electrical substation]], or for lightning conductors. It is needed for design of grounding (earthing) electrodes for [[High-voltage direct current]] transmission systems. In [[single wire earth return]] power transmission systems, the earth itself is used as the path of conduction from the end customers (the power consumers) back to the transmission facility.
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| In general there is some value above which the impedance of the earth connection must not rise, and some maximum step voltage which must not be exceeded to avoid endangering people and livestock.
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| The soil resistivity value is subject to great variation, due to moisture, temperature and chemical content. Typical values are:
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| * Usual values: from 10 up to 1000 (Ωm)
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| * Exceptional values: from 1 up to 10000 (Ωm)
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| The [[SI]] unit of resistivity is the Ohm-meter (Ωm); in the [[United States]] the Ohm-centimeter (Ωcm) is often used instead.{{citation needed|date=October 2011}}
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| A wide range typical soil [[resistivity]] values can be found in literature. Military Handbook 419 (MIL-HDBK-419A) contains reference tables and formulae for the resistance of various patterns of rods and wires buried in soil of known resistivity. Being copyright free, these numbers are widely copied, sometimes without acknowledgement.
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| ==Measurement==
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| Because soil quality may vary greatly with depth and over a wide lateral area, estimation of soil resistivity based on soil classification provide only a rough approximation. Actual resistivity measurements are required to fully qualify the resistivity and its effects on the overall transmission system.
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| Several methods of resistivity measurement are frequently employed:
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| ===Wenner method===
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| [[File:4 pins.jpg|4 pins]]
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| The Wenner four-pin method, as shown in figure above, is the most commonly used technique for soil resistivity measurements.<ref name=Dias2010>
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| {{cite journal
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| |title=Two-dimensional Simulation of the Wenner Method with the Boundary Element Method - Influence of the Layering Discretization
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| |first1=Rodrigo|last1=Dias
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| |first2=Simone|last2=dos S. Hoefel
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| |first3=Edmondo G.|last3=de A. Costa
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| |first4=Jose A. M.|last4=Carrer
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| |first5=Luiz A.|last5=de Lacerda
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| |journal=Mecánica Computacional
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| |volume=XXIX
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| |pages=2255–2266
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| |date=15 November 2010
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| }}</ref><ref name=Metodi>
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| {{cite web
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| |url=http://www.csgi.unifi.it/~restauro/Prospezione%20geofisica_12.pdf
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| |title=Metodi di prospezione Geofisica
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| |publisher=[[University of Florence]]
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| }}</ref><ref name=Voltimum>
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| {{cite web
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| |url=http://www.voltimum.it/techarea.php?dyntype=hs&hsid=153&hpid=375
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| |title=Guida alla realizzazione dell'impianto di terra
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| |publisher=Voltimum
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| }}</ref><ref name=Tutorial>
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| {{cite web
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| |url=http://pangea.stanford.edu/research/groups/sfmf/docs/DCResistivity_Notes.pdf
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| |title=Tutorial : 2-D and 3-D electrical imaging survey
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| |first=M. H.|last=Loke
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| |publisher=[[Stanford University]]
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| }}</ref>
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| Using the Wenner method, the apparent soil resistivity value is:
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| :<math>\rho_E=\frac{4\cdot {\pi}\cdot a\cdot R_W}{1+\frac{2\cdot a}{\sqrt{a^2+4\cdot b^2}}-\frac{a}{\sqrt{a^2+b^2}}}\,</math> <ref name=Andolfato1997>
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| {{cite journal
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| |title = Analisi di impianti di terra a frequenza industriale: confronto tra indagine sperimentale e simulazione numerica
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| |first1 = Roberto|last1 = Andolfato
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| |first2 = Lorenzo|last2 = Fellin
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| |first3 = Roberto|last3 = Turri
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| |journal = Energia Elettrica
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| |location = Milan
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| |volume=74|number=2|pages=123–134
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| |url = http://webcache.googleusercontent.com/search?q=cache:EBYk5ipwnvUJ:www.sintingegneria.com/index.php%3Foption%3Dcom_phocadownload%26view%3Dcategory%26download%3D5%253Al-energia-elettrica%26id%3D5%253Apublications%26Itemid%3D40%26lang%3Dit+andolfato+wenner+metodo&cd=3&hl=en&ct=clnk&gl=uk
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| |date = 4 March 1997
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| }}</ref>
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| where
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| '''''ρ<sub>E</sub>''''' = measured apparent soil resistivity (Ωm)
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| '''''a''''' = electrode spacing (m)
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| '''''b''''' = depth of the electrodes (m)
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| '''''R<sub>W</sub>''''' = Wenner resistance measured as "V/I" in Figure (Ω)
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| If '''''b''''' is small compared to '''''a''''', as is the case of probes penetrating the ground only for a short distance (as normally happens), the previous equation can be reduced to:
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| :<math>\rho_E=2\cdot \pi\cdot a\cdot R_W\,</math><ref name=Andolfato1997/>
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| ===Schlumberger method===
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| [[File:Schl 4 pins.jpg|Schl 4 pins]]
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| In the Schlumberger method<ref name=Dias2010/><ref name=Voltimum/><ref name=Tutorial/> the distance between the voltages probe is '''''a''''' and the distances from voltages probe and currents probe are '''''c''''' (see figure above).
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| Using the Schlumberger method, if '''''b''''' is small compared to '''''a''''' and '''''c''''', and '''''c'''''>'''''2a''''', the apparent soil resistivity value is:
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| :<math>\rho_E={\pi}\frac{c\cdot (c+a)}{a}R_S\,</math>
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| where
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| '''''ρ<sub>E</sub>''''' = measured apparent soil resistivity (Ωm)
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| '''''a''''' = electrode spacing (m)
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| '''''b''''' = depth of the electrodes (m)
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| '''''c''''' = electrode spacing (m)
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| '''''R<sub>S</sub>''''' = Schlumberger resistance measured as "V/I" in Figure (Ω)
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| ===Conversion between measures using Schlumberger and Wenner===
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| [[File:Measured volume.jpg|thumb|left|400px|Measured volume]]
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| The conversion between values measured using the Schlumberger and Wenner methods is possible only in an approximate way.<ref name=Tutorial/> In any cases, for both Wenner and Schlumberger methods the electrode spacing between the currents probe corresponds to the depth of soil investigation and the measured apparent soil resistivity is referred to a soil volume as in figure aside.
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| The current tends to flow near the surface for small probe spacing, whereas more current penetrates deeper soils for large spacing. Thus, it is usually a reasonable approximation to assume that the resistivity measured for a given current probe spacing represents the apparent resistivity of the soil to a depth of when soil layer resistivity contrasts are not excessive.
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| If the apparent soil resistivity measured with Schlumberger method '''''ρ<sub>E</sub>''''' (with the corresponding electrode spacing '''''a<sub>S</sub>''''' and '''''c''''') is given, assuming that the soil resistivity are referred to a volume as in the figure aside with '''''a=L/3''''' follows:
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| :<math>R_W=\frac{\rho_E}{2\cdot \pi\cdot a_W}\,</math>
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| with
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| :<math>a_W=\frac{a_S+2c}{3}\,</math>
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| where:
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| '''''R<sub>W</sub>''''' = equivalent Wenner [[Electrical resistance|resistance]] (Ω)
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| '''''a<sub>W</sub>''''' = equivalent electrode spacing with Wenner method (m)
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| '''''a<sub>S</sub>''''' = [[electrode]] spacing between voltages probe with Schlumberger method (m)
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| '''''c''''' = [[electrode]] spacing between voltages and currents probe with Schlumberger method (m)
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| If the measured Schlumberger [[Electrical resistance|resistance]] is given, before to the calculate the and values, the apparent soil [[resistivity]] has to be calculate as follows:
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| :<math>\rho_E={\pi}\frac{c\cdot (c+a_S)}{a_S}R_S\,</math>
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| The Wenner method is more laborious than the Schlumberger method because it requires many time, long measure cables, large free space, and for big electrode spacing one person per electrode is necessary to complete the survey in a reasonable time. However, the Wenner four-pin method is the most efficient in terms of the ratio of received voltage per unit of transmitted current. | |
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| The soil [[resistivity]] measurements have not to be affected by existing grounded electrodes. Buried conductive objects in contact with the soil can invalidate readings made by the methods described if they are close enough to alter the test [[Electric current|current]] flow pattern. This is particularly true for large or long objects.
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| ==Soil resistivity variability==
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| [[File:Effetto salinità.jpg|thumb|right|400px|Effects of moisture, temperature, and salt upon soil resistivity]]
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| Electrical conduction in soil is essentially electrolytic and for this reason the soil resistivity depends on:
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| * moisture content
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| * salt content
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| * temperature (above the freezing point 0 °C)
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| Because of the variability of soil resistivity, [[International Electrotechnical Commission|IEC]] standards require that the seasonal variation in resistivity be accounted for in transmission system design.<ref>[[International Electrotechnical Commission|IEC]] Std 61936-1 "Power Installations Exceeding 1 kV ac – Part 1: Common Rules" Section 10.3.1 General Clause b.</ref> For practical purposes, when there are no other available information, in very cold regions, during the winter, a [[resistivity]] scale factor of 5 to 6 times the "summer" value would be an adequate average.
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| ==Corrosion==
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| Soil resistivity is one of the driving factors determining the corrosiveness of soil. The soil corrosiveness is classified based on soil electrical [[resistivity]] by the [[British Standard]] BS-1377 as follow:
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| * '''''ρ<sub>E</sub>''''' > 100 Ωm: slightly corrosive
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| * 50 < '''''ρ<sub>E</sub>''''' < 100 Ωm: moderately corrosive
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| * 10 < '''''ρ<sub>E</sub>''''' < 50 Ωm: corrosive
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| * '''''ρ<sub>E</sub>''''' < 10 Ωm: severe
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| ==References==
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| {{reflist}}
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| [[Category:Electric power distribution]]
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| [[Category:Electrical engineering]]
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| [[Category:Electrical safety]]
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| [[de:Erdungswiderstand]]
| |
In a most real identification, the domain name registrars are now organizations that register domain names for many who love to own a domain name. And for everybody to grasp the true character of domain name r...
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Therefore these are the ICANN that represents an important component in the domain name registrars, it is required to know that it"s two main tasks. One of these is to manage the Domain Name System or DNS for the purpose of validating the department of the IP Addresses and domain names, verifying that each one is distinct. Such party then coordinates the mapping and distribution with each one of the registry. Subsequently, the ICANN is responsible of accrediting the domain name registrars.
Broadly speaking, the ICANN has particular criteria for the domain name registrars accreditation. It is generally known that once the domain name registrars are approved, it"s then a duty of the domain name registrars to sign a contract and agree to keep from the ICANNs guidelines and procedures. Discover further on check my source by going to our lovely essay.
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In case if you will find requests for domain names, such groups then talk to the Registry to make certain whether the requested domain name is available for purchase or already owned by still another party. So it is clear when the requested domain name is available, the client can register the domain. To check up additional info, please view at: click reference.
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