A novel approach to testing live earthing systems

During a fault on the power grid, earthing systems operate to contain the energy keeping people and equipment safe. Unfortunately, these systems can fail and create hazards when the resistance is too high, as a result of improper design, installation or maintenance. Regular on-site testing of earthing grids is essential to prevent these situations. The most commonly used method to test earthing grids is accurate and reliable, but only for installations with low background noise, a limited number of feeders and a low system impedance. These limitations have motivated research into improvements in testing equipment. A robust current controlled inverter is introduced for use in high noise earthing system tests. This equipment was tested on-site, demonstrating improvements in noise rejection and stability. These improvements had little impact on the accurate measurement of small test signals elsewhere in the test. For this aspect, a current measurement strategy involving destructive interference, filtering and phase locked loops is also proposed and implemented.