On the Impact of Grid Harmonics in Transformers: A Case Study

Abstract

With the evolution of solar photovoltaics, the capacity of solar photovoltaic transformers is increasing. The winding conductor succumb to larger dimensions, to be able to withstand the extreme operational condition of solar photovoltaic application. The magnetic flux leakage responsible to produce Eddy currents in windings and other metallic components over and above that also increase. At the same time, the conventional method of estimating the winding Eddy losses result in significant errors when employed for large conductor dimensions at high harmonic orders.This paper conduct an investigation into the computation of the winding Eddy losses of a 300kVA solar photovoltaic transformer. The assumption made in the C57.110-2018 standard about the winding Eddy losses to be increasing in accordance with the non-sinusoidal load current with the exponent 2 is realized to be unsuitable for solar photovoltaic application. There is a shortfall in the C57.110-2018 standard method to take into consideration the tendency of a high- frequency alternating current flowing through only the outer surface of the winding conductor (skin effect) when the oil- immersed transformer is supplying non-sinusoidal current. The frequency response of the winding conductors under non- sinusoidal load current condition is examined by evaluating the dispersal of the magnetic flux leakage in the conductors, from which the skin effect and proximity effect are taken into account. In order to authenticate the soundness of the emendation method, a 2D Finite Element Method model of the transformer under study is developed for the computation of the winding Eddy losses. This method reflect on geometrical properties of the winding conductor and it is revealed some benefit for both the transformer manufacturer and the power utility.