Analysis of the Influence of Active Parts of the Power Transformer on the Propagation of Signals from Source of Partial Discharges to UHF Sensors

Abstract

Partial discharges caused by initial weaknesses in the insulation system of the power transformer cannot be completely ignored, because they can warn in advance of possible serious deficiencies, which in the worst cases could cause irreversible failure of the power transformer. Monitoring of partial discharge signals using UHF sensors during power transformer operation enables their processing in order to determine the main properties of recorded partial discharge signals (e.g. amplitude, repetition rate, frequency range) to prevent power transformer failure. Using simulations in ANSYS HFSS, this paper investigates the waveforms and delays of UHF electromagnetic signals on UHF sensors mounted at different locations of a small power transformer tank. Electromagnetic waves are emitted by a specially designed model of the source of partial discharges in the insulation of the power transformer. Full-wave electromagnetic simulations are performed on the model of a small power transformer of core construction. The effect of reflections of electromagnetic UHF waves from the walls of the tank is taken into account, then the diffractions of waves around and the reflections of waves from the elements of the three-phase magnetic core and three-phase primary and secondary windings. The simulation is based on finite element method. It is a numerical method that is applied to differential equations with limit values in order to obtain an approximate solution. The source and receiver sensors in the computer simulation are designed with transmitting and receiving UHF antennas, respectively. The advantages and disadvantages of this computer simulation will be described.

Power Transformer Numerical Modeling to Locate Partial Discharge Source Using the UHF Technique

“…The different position I 1 of the PD source was taken into consideration in the article [17], as shown in Figure 8, which, when viewed from the front, is situated in the centre of the second phase of the three-phase copper windings on the right side of the middle limb of the electrical steel core beneath the top yoke. The PD source's real location in this case is I 1 =[893.…”