Paper Title
Distribution Transformer External Faults Analysis for Differential protection Modeling of 115/22 KV Tha-Ngone Substation in Laos

Abstract
This research describes the winding short-circuit fault of the 115/22 kV distribution transformer in a high voltage substation. Transformers are always damaged by many reasons, so this research is intended to use the model. The purpose of this study is to simulate the power transformer with exported loads and had faulted (single line to ground, three phases shortcircuit current). By using the PSCAD/EMTDC (Power Systems Computer Aided Design/Electromagnetic Transients including DC) software as tools in the simulation, through simulation using variables input and design equipment of the software, from the results or output, preferred answers can accurately present models, as close to reality as possible. The results of this report such as level short-circuit current, one current transformer (CT) in the primary current and the secondary current, differential current, restrain current and differential relay may also be useful for electrical engineers to have better understanding about the damages which might occurs with a single line to ground, three phases fault and phase to phase fault. Furthermore, the resulting information obtained from modeling is significant for protection plans or upgrading power transformer protection in order to maximize the reliability of the power supply. Keywords - Distribution Transformer, External Fault, Analysis, Modeling, Differential Protection.