TESL CASE STUDY HALLBURN WINDFARM EARTHING DESIGN
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PROJECT OUTCOMES One of the main functions of an earthing system is to ensure personnel safety during earth fault situations. When an earth fault occurs, the earth return fault current, in conjunction with the resistance to earth of the earthing system, results in an Earth Potential Rise (EPR) at the site. This EPR reflects the voltage rise on the earthing system where hazardous touch, reach- touch and step voltages, can arise due to the voltage differences between the items of plant and the surrounding soil. It is essential that each item of plant is sufficiently earthed and the below ground conductors are effectively arranged so that safety to personnel is ensured. The project involved designing the earthing system for both the contestable (combined DNO Metering and Customer Substation) and private installations. The respective wind turbines are bonded together via an earthing conductor installed in the HV cable trenches. Once constructed, TESL measured the site resistance by means of a Fall of Potential (FOP) test, to compare the site resistance against the design. FOP tests were also performed on each of the individual wind turbine units to confirm their standalone resistance. PERFORMANCE The soil resistivity measurements were provided by the client as part of the geo technical report. The results were modelled in the CDEGS-RESAP software suite, to obtain a soil model at each of the turbine locations and an overall soil model for the entire site. This enabled the standalone resistance of each turbine to be modelled, as well as the site as a whole. The earthing system was designed to ensure touch and step voltages are safe across the site. This model also included verification of nose to legs and forelegs to hind legs voltage limits for sheep. This confirmed that the area is safe for sheep, so that they can be farmed across the site. The FOP confirmed that the individual turbine and overall site resistances as a whole, aligned with the designed values. The overall installed site resistance was measured to be lower than the design, therefore confirming the touch and step voltage are safe across the site. SPECIFIC REQUIREMENTS It is important consider what the land surrounding the installation will be used for. The land owner in this instance wanted to ensure that it would be safe to farm sheep across the site. Therefore, the site EPR was controlled so that the nose to legs and forelegs to hind legs voltage limits for sheep were not exceeded. HALLBURN WINDFARM EARTHING DESIGN TESL CASE STUDY THE PROJECT Hallburn Windfarm is a 13.2MW wind farm, consisting of six 2200kW wind turbines sited on an abandoned WWII airstrip at Hallburn Farm, Longtown, Carlisle, CA6 5TW. The Wind Farm is connected via a looped connection to the ENWL 33kV distribution network where both underground 33kV cable circuits terminate onto overhead lines (OHL) at the site boundary. TESL INVOLVEMENT We were contracted to undertake the earthing system design for the whole Hallburn Windfarm. PROJECT DATES Project Start Date: May 2017 Submission Date: Jul 2017 CLIENT REG Power Management Modelled Voltage Rise of Earthed Rebar Inside Wind Turbine Foundation THE EARTHING SPECIALISTS LIMITED Cardiff House Cardiff Road Vale of Glamorgan CF63 2AW 07376 375 629 www.tesl-ltd.co.uk If you have any issues with your installed earthing system or require a new earthing design, please get in touch with our experts at TESL.
Transcript of TESL CASE STUDY HALLBURN WINDFARM EARTHING DESIGN
PROJECT OUTCOMESOne of the main functions of an earthing system is toensure personnel safety during earth fault situations.When an earth fault occurs, the earth return faultcurrent, in conjunction with the resistance to earth ofthe earthing system, results in an Earth Potential Rise(EPR) at the site. This EPR reflects the voltage rise onthe earthing system where hazardous touch, reach-touch and step voltages, can arise due to the voltagedifferences between the items of plant and thesurrounding soil. It is essential that each item of plantis sufficiently earthed and the below ground conductorsare effectively arranged so that safety to personnel isensured.The project involved designing the earthing system forboth the contestable (combined DNO Metering andCustomer Substation) and private installations. Therespective wind turbines are bonded together via anearthing conductor installed in the HV cable trenches. Once constructed, TESL measured the site resistanceby means of a Fall of Potential (FOP) test, to comparethe site resistance against the design. FOP tests werealso performed on each of the individual wind turbineunits to confirm their standalone resistance.
PERFORMANCEThe soil resistivity measurements were provided by theclient as part of the geo technical report. The results were modelled in the CDEGS-RESAPsoftware suite, to obtain a soil model at each of theturbine locations and an overall soil model for the entiresite. This enabled the standalone resistance of eachturbine to be modelled, as well as the site as a whole. The earthing system was designed to ensure touch andstep voltages are safe across the site. This model alsoincluded verification of nose to legs and forelegs tohind legs voltage limits for sheep. This confirmed that
the area is safe for sheep, so that they can be farmedacross the site. The FOP confirmed that the individual turbine andoverall site resistances as a whole, aligned with thedesigned values. The overall installed site resistancewas measured to be lower than the design, thereforeconfirming the touch and step voltage are safe acrossthe site.
SPECIFIC REQUIREMENTSIt is important consider what the land surrounding theinstallation will be used for. The land owner in this instance wanted to ensure that itwould be safe to farm sheep across the site. Therefore,the site EPR was controlled so that the nose to legs andforelegs to hind legs voltage limits for sheep were notexceeded.
HALLBURN WINDFARM EARTHING DESIGNTESL CASE STUDY
THE PROJECTHallburn Windfarm is a 13.2MW wind farm,consisting of six 2200kW wind turbinessited on an abandoned WWII airstrip atHallburn Farm, Longtown, Carlisle, CA6 5TW.The Wind Farm is connected via a loopedconnection to the ENWL 33kV distributionnetwork where both underground 33kVcable circuits terminate onto overhead lines(OHL) at the site boundary.
TESL INVOLVEMENTWe were contracted to undertake theearthing system design for the wholeHallburn Windfarm.
PROJECT DATESProject Start Date: May 2017Submission Date: Jul 2017
CLIENTREG Power Management
Modelled Voltage Rise of Earthed Rebar Inside Wind Turbine Foundation
THE EARTHINGSPECIALISTSLIMITED
Cardiff HouseCardiff RoadVale of GlamorganCF63 2AW
07376 375 629www.tesl-ltd.co.uk
If you have any issues with your installed earthingsystem or require a new earthing design, please get intouch with our experts at TESL.
