An Efficient Procedure for Temperature Calculation of High Current Leads in Large Power Transformers

This article presents an efficient methodology for calculating the steady-state temperature of high current busbar leads (HCBL) oil-immersed in large power transformers. The temperature at the surface of the copper HCBL is mainly affected by the Joule effect caused by the passing current, the paper insulation, the top oil temperature rise, and the ambient temperature. The Power Transformer Manufacturers usually follow their proprietary technical specifications for HCBL design in the absence of normalization, and customers would request guidance for temperature calculations independently of proprietary techniques. To date, there is a lack in the literature for this purpose. The method allows calculating the temperature on the HCBL as a function of the parameters already mentioned being flexible because it allows change of the parameters. The method is based on calculating the convection heat transfer coefficient (h), which in turn depends on the geometry factors and cooling system characteristics. The parameter (h) is of major importance and play the primary role during temperature calculation, once the desired temperatures are susceptible to its value and accuracy. Other relevant factors such as the skin and proximity effect are determined by the Finite Element Method (FEM). To validate the proposed method's accuracy, we did measurements using the T2TM Fiber Optic Temperature Sensor from NEOPTIX on a 460 MVA Transformer, running the heating test at 100% of load during 72 hours, yielding satisfactory results. The method is also compared with the winding gradient, which is usually used to estimate the top's conductor temperature. (AU)