Transformer dynamic loading capability assessment under nonlinear load currents

The portion of the loads which cause harmonic currents is increasing due to the rising prevalence of power electronic components. The use of these loads has increased the awareness of the potential risks due to the transformer overheating. Nowadays, it is well-known that the transformer loading must be restricted for safe operation under non-linear load currents. Conventionally, IEEE C57.110-1998 standard has been applied to give a conservative estimate of loading capability of transformer in this condition. In this paper, the problem of oil-immersed transformer loading capability determination considering nonlinear loads is addressed. A thermal model which considers non-sinusoidal load current is used. Then, the procedure of transformer dynamic and steady state loading capability assessment is described and applied to a power transformer. Comparison of the results of the proposed and conventional methods shows the possibility of transformer loading beyond the limit calculated using conventional method. Finally, an economic analysis is carried out considering two methods.