Power transformer has an important role in a transmission system. One factor that can reduce efficiency in the transmission system is transmission losses. Efficiency can be increased by reducing losses in the power transformer. The biggest influence determining the losses on the transformer is the material characteristic used by the transformer itself. To get maximum efficiency, it is necessary to optimize the materials on the transformer to get the lowest losses. The study is conducted by measuring core losses and copper losses on the 60 MVA 150/20 kV power transformer with the specified specifications. Furthermore, the transformer materials are changed into several types and the losses calculations are done. The calculation results are compared to get the most effective material. The results show that in the calculation of core losses, the core material type with the lowest core loss value is NK E-core of 0,49 Watt/kg. While in the calculation of copper losses, the winding material type with the lowest loss value is Continuously Transposed Conductor.

The activity of partial discharge (PD) is one of the major causes of failure of high voltage transformers. Partial discharge detection is usually used as a preventive technique to avoid large-scale losses in the power system. Suitable and reliable methods to detect and localize PD in equipment winding insulation, such as in a transformer, are still widely researched. Among the methods used are based on the acoustic wave, on the electrical determination of the dominant capacitive region in frequency domain, and on the travelling wave method. After a brief review on current methods, a technique based on the frequency spectra of the measured signals showing the characteristic of the transfer functions is proposed. A Matlab simulation of the proposed technique is then presented. PD signals are injected at various points in a transformer winding to represent PD sources at different location within the winding. The main difficulties encountered in current methods, which is the noise and the limit in the detection frequency range, is overcome. In the frequency spectra of the proposed method, the crests and troughs could be used for locating the source of the discharge activity in a power transformer winding.