A model to compute the resonance effects in high current instrument transformers

High current instrument transformers (HCTs) are widely used to measure high currents (5 kA and more) in power plants, power grids and special high current applications.These devices are usually designed for operation at power frequency (e. g. 50 Hz or 60 Hz) and have to have a high accuracy (1 % or better). Regarding standard [1], the accuracy of HCTs has to maintain even when using different burden. Due to the rising number of power electronic devices, the amount of harmonic currents in the power grid increases and shall be measured by HCTs, too. These harmonic currents as well as transient currents may cause resonance effects inside HCTs, which results in high measuring errors in thethe affected frequency range [2]. Furthermore, these resonances cause high voltages at the secondary side of the HCT, which may endanger persons and the installed equipment. To estimate and consider resonance effects during the design phase of HCTs, a model is developed to compute the resonance effects of a HCT only by using its production data.