When a slight inter-turn short circuit occurs in the winding of a dry-type transformer, electrical quantities such as phase voltage and phase current change little, and thus cannot be used as a sensitive characteristic quantity to characterize the inter-turn short circuit fault. This results in the lack of corresponding protection measures, and equipment burning accidents occur frequently during operation. In this paper, a 'field-circuit' coupling simulation model of a dry-type transformer is established, and the state parameters obtained by actual test and engineering calculation are used to verify the accuracy of the model. By establishing and analyzing the mathematical model of an inter-turn short circuit fault of a dry-type transformer winding, the difference of per unit value of phase voltage and phase current imbalance is extracted as the characteristic quantity to judge the inter-turn short circuit fault of the winding. Through the simulation analysis of the changes of different electrical quantities when the inter-turn short circuit fault occurs in the dry-type transformer winding under different working conditions, it is demonstrated that the new fault characteristic quantity proposed in this paper can not only perceive the inter-turn short circuit fault of the winding in advance, but also overcome the inherent three-phase asymmetry and unbalanced operation. Effectiveness and sensitivity are taken into account, and this provides a new method for real-time monitoring of the inter-turn insulation state of a dry-type transformer winding.

This work is supported by the National Key Research and Development Program of China (No. 2017YFB0902800).