A Broadband Model of a Potential Transformer

In this paper, a broadband circuit model of a potential transformer (PT) based on fractional calculus and circuit augmentation method is proposed to improve the high frequency characteristic while providing physical significance of existing traditional equivalent circuit model with simple structure. In order to reflect the characteristics of the hysteresis of the iron core roundly, a fractional model of the magnetic hysteresis loop in iron core measured by a no-load experiment was set up to instead of the single-value magnetization curve of previous model. Besides, the original equivalent circuit model was calculated at low frequencies, and the circuit augmentation method (CAM) was employed to extend the compatibility of the original equivalent circuit model in the wide range of frequency. The element values are calculated by the Brune method of synthesis. For validity, comparisons between the simulation and experiment of a 10 kV single-phase oil-immersed PT with lightning overvoltage and switching overvoltage are conducted, respectively. The results show that the broadband model presented in the paper can provide a good accuracy while reserving the physical significance of original equivalent circuit model.