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Earth Resistivity in Ireland
J.M.Whelan ESB International B.Hanratty ESB International E.Morgan ESB International
Abstract--Due to the diverse nature of soil and bedrock types in Ireland, the electrical resistivity of the earth varies greatly with location. As part of ESB International’s power system earthing design work a catalogue of apparent earth resistivity measurements has been developed. The measurements have been used to calculate multi-layered earth resistivity models, which form the basis of country-wide topsoil and bedrock resistivity maps. Some analysis of the measurements has been carried out and in particular a more appropriate potential probe position for use in fall-of-potential measurements in Ireland has been calculated. Introduction--There has been a significant expansion of the power system in Ireland in the years 2000-2010 resulting in the construction and/or refurbishment of numerous overhead lines, substations, wind farms, and conventional power plants. As part of the earthing system design for these assets, ESB International has taken measurements of the apparent earth resistivity at many locations. On an individual site basis, these measurements have been used to assess human safety, and protect buried infrastructure, in the vicinity of the assets, during power system earth faults. This paper collates all the measurements taken, develops country-wide maps of the topsoil and bedrock resistivity, and draws some conclusions from the results.
HIFREQ and MALZ models of transferred voltages around a power substation – A proposal for IEEE-367 revision
Jean De Sève, Ing. Hydro-Québec
Introduction--IEEE-367 recommendation covers the areas of GPR, induction and zone of influence (ZOI) calculations. All ZOI calculations examples and guidelines are based on power station grid without taking into account multigrounded line connections. Figure 1 shows an example of one of the proposed graphs recommended for ZOI evaluation. Five graphs are proposed for electrode size ranging from 150 m2 to 87000 m2. The ZOI boundary can be based on contact voltage as defined by IEEE-80 but Telcos usually use a fixed voltage value of 300 V. Even if the aspect of transferred voltage on metallic objects around electrical substation is mentioned in a few clauses of IEEE-367, the subject is barely detailed. Conductive coupling between multigrounded power lines with substation's grid is completely ignored. This paper shows a new model proposed to be added in clause 9.5 of IEEE-367 entitled "Transfer of a GPR". The model shows the effect of mutual resistance between ground connections around substations and the impact on soil and transfer voltage, as well as system grounding impedances. Field tests made by Hydro-Québec between 2004 and 2006 give results similar to those reached by the model. Line models were developed based on field tests information. The proposed model modifies the application of the "zone of influence" concept in multigrounded neutral environments and shows that new guidelines must be added to standards like IEEE-367, 487 and 1590, to cover the case of installations inside the zone of influence. Measuring Footing Resistances using the AEMC 6472 & 6474 MetersWilliam Daily, P.E. Austin Energy
Introduction--For many years the Electric Utility Companies have been looking for a way to measure the footing resistance of transmission and distribution structures without first isolating the structure (i.e., disconnecting the static wires, communication cable messenger wires, distribution neutrals, etc.). This could potentially save the utility or other entity a significant amount of money. A Practical Example of Designing a Sacrificial Anode Cathodic Protection System for Marine Steel Pipe Piling Using MALZDoug Gilroy Bechtel Oil, Gas and Chemicals, Inc., Houston, Texas, U.S.A Winston Ruan Safe Engineering Services & technologies ltd.
Introduction--This article focuses on sacrificial anode cathodic protection design and analysis for near shore steel-fixed piling structures. MALZ was used to model the cathodic protection design as determined by a propriety application, CPOFFSHORE, to closely examine and predict the adequacy of the design. CPOFFSHORE provides an efficient method to perform design calculations for sacrificial anode cathodic protection (CP) for offshore and marine steel structures, including steel pipe piling. This application was written on Microsoft Excel in “visual basic” format, and it is based on industry standards and methodology for marine structure cathodic protection design, including DNV-RP-B401, NACE RP0176 and AS 2832.3, and as covered in a propriety Engineering Design Guide for Sacrificial Anode Design for Offshore Structures . Although CPOFFSHORE is a valuable design tool to determine the anode requirements (e.g., current necessary, initial and final current output, A.hr, kg, type, dimensions, quantity), MALZ was used to model the anode design in detail and to predict the levels and spread of protection throughout the immersed and buried length of the pile. Interesting results were observed.
Grounding Design of Battery Energy Storage UnitWilliam Daily, P.E. Austin Energy Introduction--Distribution Engineering-South of Austin Energy (AE) requested a grounding system design and analysis for a proposed Energy Storage Unit to be located at the South AE Service Center. The design and analysis of the grounding system consisted of computer modeling techniques first to develop a suitable soil model from field measurements and second to design, model and analyze a grounding system for the proposed installation in order to determine its performance during a line-to-ground fault on the transformer high side. The analysis provides the grounding system impedance, ground potential rise (GPR), maximum touch voltage within the boundaries of the Energy Storage Unit perimeter fence enclosure, the maximum reach-touch voltage to the Energy Storage Unit trailer. The safety assessment of the proposed grounding system during fault conditions is based on the criteria established by the ANSI/IEEE Std. 80-2000, “IEEE Guide for Safety in AC Substation Grounding” and input parameters provided by AE personnel. The detailed analysis was carried out using the HIFREQ, MALZ, RESAP and FCDIST Modules of the CDEGS Software. Most of this analysis was performed using the HIFREQ Module of CDEGS. The fault current distribution analysis for this study is determined using the FCDIST Module which determined the actual current injected into the earth through the grounding system during a line-to-ground fault on the transformer high side.
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