A Methodology to Develop a Distribution Transformer Model for Transient Studies

Transformers are some of the expensive components of a distribution network. Records from the Ceylon Electricity Board (CEB) indicate that a considerable number of failures of these transformers are caused by lightning surges. Transformer failures incur huge costs to utility suppliers like CEB. Thus the behaviour of distribution transformers under transient conditions needs to be studied and for this a transformer model is very much essential. With the help of such a model, the behaviour of distribution transformers when subjected to lightning surges can be studied. In this paper, a methodology is presented to develop a model to represent a distribution transformer under transient conditions. The validation of the model is illustrated by the calculation of parameters based on a 160 kVA, 33/0.415 kV, three phase distribution transformer. The model is simulated using PSCAD software and the output is obtained when the standard lightning waveform and chopped surge waveforms are input to the model. In order to validate the developed model, the output voltage distribution along the transformer winding is observed and compared with the results of an experiment presented in a research publication [7].