Transformer magnetic core models for investigating core saturation process during geomagnetic disturbance

Summary

During geomagnetic disturbances, a quasi-DC electric field tends to be generated on the earth surface, which leads to negative impacts on transformers. The aim of this paper is to accurately represent the effects of core saturation of transformers under geomagnetically induced current. The paper looks into the magnetic characterisation of transformers under extreme core saturation operational conditions by establishing transformer equivalent circuit models. The equivalent model incorporates the equivalent magnetic model and the equivalent electric circuit model. In the magnetic model, the leakage flux paths consisting of the oil gaps and the tank wall are taken into account in conjunction with the main paths through the core, allowing the calculation of the flux distribution in each part of the core, the oil gaps and the tank wall. Applying practical transformer geometrical dimensions and core saturation characteristics, the transformer model generates results of the harmonics due to core saturation under certain levels of DC voltage according to the intensity of the geomagnetic disturbance. The process of how the transformer core reaches a full saturation state under an AC+DC voltage injection is analysed in the paper. Furthermore, the model enables the assessment of the performance of 3-phase 3-limb and 3-phase 5-limb cores in high flux density regime to identify design features that need to be taken into account when assessing the capability of a transformer to withstand overexcitation.

Additional informations

Authors

BRAMBILLA, D'ADAMO

Keywords

Geomagnetically induced current, transformer model, core saturation, core flux simulation