Wireless measurement system for a large-scale grounding electrode test facility

An evaluation of the impedance of ground electrodes under dc, ac or impulse conditions requires reliable and accurate measurement of the current and earth potential rise (EPR) at the point of injection. This is commonly achieved in wired systems by arranging current-injection and measurement circuits in quadrature, but such wide-area test arrangements are not always possible due to prohibitive environmental conditions or site access restrictions. This problem has been encountered in establishing a large-scale test facility in the lower lake of the Dinorwig pumped-storage power station in Llanberis, North Wales. The geography of the site restricts the location of both current source and data acquisition equipment to a common location on the lake shore, with all wired circuits confined to a narrow corridor along a floating pontoon. Simulations have shown that wired systems arranged in this way lead to significant measurement error due to circuit coupling, increasing with both the frequency and magnitude of the injected current. This paper presents work undertaken to evaluate alternative non-wired measurement systems for application to high current testing of ground electrodes in harsh environments. Technical details of the developed long-range wireless data transmission system are discussed and field data acquired from high-voltage impulse tests at the Cardiff University earthing facility at Llanrumney fields are presented, showing good agreement with both simulation and measured ground resistance data acquired using conventional wired systems.