Energy Reports (Nov 2022)
Analysis of excitation characteristics of transformers with different core shapes under severe DC bias
Abstract
When a transformer is in the DC bias state, a series of consequences will occur. Mainly including excitation current distortion, losses increase, hot spot temperature rise and vibration and noise increase, these consequences are not conducive to the safe operation of the power grid. The relevant DC bias studies mainly focus on the case of several hundred amps of DC. In some special conditions like the HEMP E3 period, the bias DC is about several thousand amps. So, it is important to get the changing trend of relevant physical quantities when the transformer is at severe DC bias saturation. To obtain the excitation characteristics of transformers in the case of severe DC bias up to several thousand amperes, this paper established 3D finite element models of a single-phase three-limb transformer, a three-phase three-limb transformer, and a three-phase five-limb transformer. The graph of the variation of the harmonics within the 10th order of the excitation current with the direct current is obtained. And through the magnetic field distribution change of the iron core in the DC bias simulation, the reasons for the changing trend of the excitation current distortion characteristics can be analyzed.
