Impacts of Non-Sinusoidal Load Currents on Distribution Transformer Losses-Part I: Theoretical Aspects and Finite Element Based Simulation

摘要

Power quality problems have negative effects on the energy system components. These problems such as voltage sags, voltage harmonics and especially current harmonics can severely impact the loads in electrical systems. Many transformers which installed to supply linear loads with sinusoidal currents have had their loads to be gradually replaced with non-linear loads that inject non-sinusoidal currents into power or distribution networks. These non-sinusoidal currents will increase losses and hence cause abnormal winding temperature rise which will decrease the expected lifetime of transformers. Such conditions require transformer load reduction or upgrading of component with a larger and more economical unit. The transformer loss is a critical problem because with the continuous increase in global electrical energy consumption, there is a necessity to improve the efficiency of transformers. Small reductions in transformer losses produce significant energy savings, since the number of transformers in power and distribution systems is high. Therefore, in today's competitive environment, reduction of transformer losses will give a competitive advantage. Finite Element Analysis consists of a computer model of a material or design that is stressed and analyzed for specific results. It is used in new product design and also, existing product refinement. Especially, this method is using in new electrical machine design procedures, now. In this paper, as a first part of distribution transformer loss study, effects of non-sinusoidal current on distribution transformer have been evaluated and the transformer losses under non-sinusoidal load currents have been investigated using transformer model under non-linear loads. This model has been established and analyzed in PSCAD/EMTDC software package. Then, for validity check of results, the losses have been compared with results of finite element analysis in MAXWELL software.