Design and construction of a power electronics based current injection unit to improve the accuracy of earthing system tests

The main method of testing earthing system performance involves the use of an off-frequency injection current produced by a voltage source. While this provides a sufficient testing tool for a number of systems, deficiencies such as noise susceptibility, restricted power capabilities and unstable current present significant challenges to earthing system testers. This paper outlines a novel application of inverter technology to this field. A review of control schemes was undertaken which resulted in the design of a robust method which is stable over a range of system conditions. A hardware prototype design that combined the benefits of a voltage source converter and the aforementioned control scheme was constructed. Furthermore, simulation and testing, in both the laboratory and on-site, demonstrates that the prototype outperforms the existing industry standard.