变压器拓扑修正暂态模型及其在直流偏磁耐受评估中的应用

Recently, transformer DC bias was on increasing rise with construction and operation of UHV transmission systems in China. It is essentially important to assess the tolerance level of transformer under DC bias. It was a key issue to calculate the exciting current of transformer under DC bias condition. In this paper, a topology-correct transformer transient model taking into account the structural characteristics and nonlinear features of iron core was proposed within duality principle of magnetic and electric circuits to calculate the exciting current of transformer under DC bias. Numerical results demonstrated a good consistency between computed current and measured data. The impact of major parameters, e.g. material type, air gap between core and yoke, zero sequence impedance, and etc. on transformer exciting current under DC bias were verified. It was concluded that the influence of core material type could be neglected, while the air-gap distance and leakage inductance should be carefully chosen and adjusted during computing. The proposed model and conclusions of this paper can provide reference for transformer DC bias assessment in engineering application.