Electromagnetic Transient Calculation and Protective Measures of Transformers under Lightning Overvoltage

Abstract

In order to propose more reasonable protection measures of transformers, the electromagnetic transient of distribution transformers under the lightning strike fault should be given enough attention. In this article, a 35-kV distribution transformer under the lightning strike is taken as the research object. First, the lightning overvoltage model of the transformer is established utilizing the double exponential model. The electromagnetic transient change of the transformer under the rated voltage superposed the lightning overvoltage is analyzed. Second, the magnetic flux distortion of the transformer core and the current distribution law of the transformer windings during the lightning invasion are calculated and summarized, respectively. Finally, on the basis of revealing the whole process that the lightning wave invades the transformer windings, a new type design scheme of transformer lightning protection is proposed. The results show that the additional windings of the lightning protection scheme can greatly reduce the positive and negative overvoltage of lightning wave acting on the transformer. The feasibility of the proposed protective measures is verified, which can provide some scientific references for improving and perfecting the lightning protection measures of the distribution network.