Investigating the Frequency Spectrum of Incoming Waveform in the Transformer Terminal Considering the Voltage Distribution Characteristics

Abstract

Transformer is the main equipment in the electricity network which plays an important role because the failure of the transformer can cause seriously power outages. One of the failures of the transformer is breakdown insulation caused by over voltages. Failure of the transformer due to over voltage even still occurs on transformers that are in good condition and also protected by arresters. In this condition, the failures location was located inside the winding caused by turn to turn short circuit. The main issue of this failure is the voltage distribution inside the winding due to the internal winding resonance. The internal winding resonance occur highly depend on the frequency spectrum of incoming waveform. Back flashover in the insulator caused by lightning strike may lead to incoming waveform with higher frequency component. To investigate the spectrum frequency, simulation was made with ATP software to analyze the influence of lightning steepness, strike location and power system network. Based on the simulation results, the expected frequency that have to be considered is the frequency up to 150 kHz. Referring to the frequency characteristics of several transformer winding design, frequency up to 150 kHz still have risk of the resonance and inter-resonance phenomenon. To get a design with optimal voltage distribution characteristics, it is necessary to evaluate the voltage distribution characteristics in the frequency spectrum up to 150 kHz or called sinusoidal voltage distribution (SVD). By performing IVD and SVD, a winding design that has the most optimum voltage distribution characteristics can be obtained.