Partial Discharge Analysis at Arbitrary Voltage Waveform Stimulus

Sammanfattning: Partial discharge (PD) detection is widely used to diagnose the defects and degradation in an electrical insulation system. Generally, PD are measured with 50 Hz AC sinusoidal voltage in the on-line situation, but can also be detected at other voltage stimulus in some off-line situations. In order to investigate the sequence or repetition rate of discharge pulses over time, Pulse Sequence Analysis (PSA) has een used by acquiring data from a time-resolved measurement system.The aim of this work is to investigate other kinds of voltage waveform stimulus which can give a better understanding of the partial discharge behavior and a clearer picture of the physical environment around the defect. Therefore, some PD measurements have been performed by applying three types of arbitrary voltage stimulus. Firstly, the internal discharge was carried out in a narrow dielectric gap between spherical electrodes at half-sine pulse voltage of the alternating or unipolar polarity, and then the linearly ramped pulse voltage was applied. Corona discharge was achieved at the periodic negative step voltage in the needle-plane setup with the ground electrode covered with a layer of insulating material. The results show the effect of different voltage stresses on partial discharge characteristics, which could explain the discharge physical process.A FEM-based numerical model was developed in order to study the in-depth physical process of corona discharge. The model focuses on the decay process of surface charges deposited on the insulation surface after the discharge events. It includes diffusion, bulk and surface conduction processes of surface charge decay. The simulation results have a good agreement with the measurement ones for corona discharge, which indicates the dominant mechanism of surface charge decay at different applied voltage levels.