Investigation of Stray Losses in Converter Transformer Using Parametric Analysis of Wall Shunt Thickness

In High Voltage Direct Current Transmission (HVDC) system, converter transformer is an integral part of the system. Generally, core loss, copper loss and stray losses occur in the transformer.  In which stray losses are produced in the transformers metallic parts such as transformer tank which can be 10\% to 15\% of the total loss. Experimentally, stray losses are difficult to measure. So, it is essential to use numerical modelling to predict the stray loss. The secondary winding of the converter transformer is directly linked to the rectifier or inverter. As a result, the converter transformer winding’s current is non-sinusoidal. Due to non-sinusoidal current, losses are more in converter transformer than in~the power transformer. This article analyses the stray loss reduction techniques by applying wall shunt on the transformer tank surface. These stray losses are estimated for different wall shunt thickness values by varying the thickness of wall shunt using parametric analysis in 3-D finite-element analysis (FEA). Two types of wall shunts is used:-horizontal and vertical. In which horizontal wall shunt results are compared with the vertical wall shunt for non-sinusoidal and sinusoidal current excitation, where sinusoidal excitation is a fundamental component of non-sinusoidal excitation. For a case study, 315 MVA converter transformer is used to estimate stray losses on this transformer. The results obtained by the numerical method are also compared with the analytical method. Result shows that the stray losses are decreased with an increase in wall shunt thickness. Also, these losses are less for sinusoidal excitation than the non-sinusoidal excitation.