Menu
Earthing and grounding studies are an essential design requirement for all new HV / EHV electrical systems. These studies are carried out to ENA 41-24, BS En 50522 and sometimes to IEEE-80, and are used to assess the Earth Potential Rise (EPR) and the associated touch and step voltages of a site.
Power system earthing is a complex, iterative design process which needs to determine the soil resistivity, DNO fault levels and metallic return paths back to the upstream source substations. These studies are carried out in either CDEGS or XGSLab allowing creation of complex site models containing localized soil volumes and induced voltages on below ground and above ground systems.
Aurora can undertake a complete earthing design for any power system, with the aim of ensuring that all items of equipment are correctly earthed with the right sized conductor and optimise the earth nest layout to suit the site conditions and reduce costs. Aurora has detailed knowledge of all aspects of power system earthing design and can provide guidance on optimising earthing layouts to help reduce costs and ensure that all equipment, personnel and livestock is fully protected.
Lightning risk assessments are carried out in accordance with IEC 62305, as a way of identifying the probability and impact of a lighting strike hitting a site / asset. Where the risk, or consequence, is non-negligible it is then necessary to provide a lightning protection system, which can range from simple droppers and air finials through to more complex lightning masts and shield wire systems, using techniques such as the rolling sphere method and cones of protection.
More recently, lightning risk assessments have also started including requirements to consider the LEMP requirements of LV systems and simple surge arresters. However, please note that a lighting risk assessment and lightning design is not the same as an insulation coordination / lightning impulse study.
EMF Exposure studies, are a specific method for assessing the risk of exposure to electromagnetic fields (EMFs) emanating from the HV and LV electrical systems. They are carried out to ensure the design is compliant with the Control of Electromagnetic Fields at Work Regulations 2016 (CEMFAW). An EMF exposure study is usually carried out in accordance with the guidance and approach laid out in the ENA document “Compliance of the UK Transmission and Distribution Networks and Generating Equipment with Occupational Exposure Limit”.
Carrying out a soil resistivity survey, is the first step to undertaking an earthing design. At Aurora we have the industry leading Megger Det 2/2 earth tester which we use for all soil resistivity surveys. Surveys are typically carried using the Wenner 4-pin method at 2 to 3 different locations, using spacings in accordance with BS EN 50522, to give a complete indication of the soil configuration, which can then be entered into CDEGS or XGSLab. Depending on the site location.
Once an earthing system has been installed, it is usually necessary to validate that the overall earth grid impedance matches the figure calculated in the CDEGS or XGSLab model. There are various test methods available for carrying out this test, but the preferred method for most sites is known as the Fall Of Potential method. At Aurora we use the Megger Det 2/2 to obtain a series of readings at a suitable distance from the site, until a stable value is confirmed for the site overall earth grid impedance. As with the soil resistivity survey, depending on the site location.
Aurora can undertake a complete earthing survey for any power system, with the aim of checking and investigating to ensure that the earthing system is adequately sized and rated for the required duty, and that all conductors, joints and rods are performing as required. The surveys are usually carried out through a mixture of visual identification, micro-ohmmeter testing of joints and conductors and use of an earth clamp meter to test individual rods. In addition sometimes it is also beneficial to carry out soil resistivity surveys and/or fall of potential tests.
Contact: Dave Reed
Phone: 01305 300 210
Aurora Power Consulting are a leading independent power systems consultancy. We provide specialist power systems analysis services using software such as DIgSILENT, ETAP, PSCAD, EMTP-ATP, CDEGS and XGSLab.
