| Over-voltage caused by lightning would cast serious impact on power distribution network considering the level of its layout and insulation. And there are plenty of transformers on unit length of lOkV transmission line. When suffering lightning, caused over-voltage will be conveyed along transmission line inside transformers, resulting in damage on high/low-voltage side of transformers. Operation practice shows that it is not sufficient to protect transformers on power distribution network from being damaged by lightning under existent precautions according to current regulations. As people’s life gets better, the demand on high reliability of power distribution transformers gets stronger, which makes relative measures to maintain such reliability more and more important. Therefore, this thesis aims to develop quantitative study on lightning proof of power distribution transformer.First, this thesis presents broadband equivalent model of power distribution transformer to depict electromagnetic coupling and electrostatic transitive relations, extract parameters of stray capacitance by means of finite element simulation, and verify validity of the model by lightning surge experiment. Secondly, based on verified model, this thesis simulates and analyzes internal over-voltage distribution and damage points caused by lighting when suffering direct and induced lightning. At last, three protection measures of (1)supplementing extra lightning arrester,(2) supplementing induction coil and (3) reducing grounded resistance are derived to arrest over-voltage of transformer, present preferred lightning proof measure of power distribution transformer.The broadband equivalent model presented is an effective way to explore the behavior of lightning over-voltage; relative protection measures based on the model therefore could enhance the level of lightning proof, which contributes to theoretical value and engineering practice of reliability for power distribution network. |
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