Assessment of the Dynamic Overload Capability of Distribution Transformers

Summary

In this paper, a dynamic thermal model for calculation of the top oil temperature in distribution transformer is presented. In the modelling process, the heat transfer phenomena from the transformer winding to oil in the radiator, from radiator to the transformer station and from the transformer station to the ambient are modelled. All electrical losses are considered as an input of equally distributed heat and assumed to be the sum of the short circuit and no load losses. Furthermore, the material properties and the temperature gradients in oil and air are taken into account. To determine the thermal behaviour of a specific transformer, the model uses several empiric factors which are estimated based on measurements during the normal operation of the transformer. In order to validate the model, the calculated top oil temperature is compared with the measured top oil temperature during the normal operation of transformer. The transformer which is used in this paper is a 400kVA, 10kV/0.4kV distribution transformer with ONAN cooling system. The performance of the model is compared with the IEC 60076-7 loading guide. It is worthwhile to note that the inputs of the model are the load of transformer, temperature of the transformer station and ambient temperature. Due to the simplicity and accuracy of the model, it can be used in an online monitoring system in a smart grid for managing the load of the network.

Additional informations

Authors

Miyazaki Satoru, Mizutani Yoshinobu, Viereck Karsten