Air-Gapped Current Transformer simulation and accuracy assessment

The implementation of smart grids makes it necessary to have reliable and efficient measuring devices. Current sensors used for metering purposes in the grid must be accurate enough to overcome new challenges that power networks face such as injection of undesirable Direct Current (DC) in the system. A Current Transformer (CT) is a transformer widely used to measure current in an electrical circuit. This paper describes the modelling and simulation of a CT with a variable air gap, provides different results of cases with different air gap ratios and evaluates the respective primary and secondary currents in each case according to the standard IEC for instrument transformers. Results show that if an air gap is present, the transformer only reached an accuracy class of 0.5 when the air gap ratio is 0.001.