Advanced noise suppression during PD measurements by real-time pulse-waveform analysis of PD pulses and pulse-shaped disturbances

For PD measurements in unscreened laboratories, factory environments, or even during on-site conditions, the measuring result is overlaid and sometimes dominated by numerous disturbances. As common-wave interferences such as radio signals, e.g., can easily be suppressed by frequency-domain filters, pulse-like disturbances cannot be eliminated by filters due to their broad-banded frequency spectrum. As some verifiable differences in the frequency spectrum and therefore differences in the pulse shape do exist, these can be used to distinguish between multiple PD sources and interferences. A real-time data analyzing algorithm, evaluating the spectral energy of the recorded pulses for three selected PD filter settings simultaneously, allows a clustering of different classes of pulse shapes, visualized in a two-dimensional color-coded diagram (3CFRD = 3 Center Frequency Relation Diagram). Multiple clusters are developed in this diagram based upon existing noise sources. By selecting single clusters, the phase-resolved PD pattern of a single PD mechanism can be displayed and therefore analyzed by the PD engineer. As noise pulses are sorted out, this becomes more easy and reliable. Instead of selecting single PD sources for further investigation, single sources of interferences can be selected in order to gate them. PRPD patterns without this disturbance can be created. A time consumptive physical elimination of the disturbance therefore becomes unnecessary. This paper describes the fundamental working principles of this method as well as examples of its practical application.