Spectral Method for Localization of Multiple Partial Discharges in Dielectric Insulation of Hydro-Generator Coils: Simulation and Experimental Results

Novel Features and PRPD Image Denoising Method for Improved Single-Source Partial Discharges Classification in On-Line Hydro-Generators

“…Propagation effects are another issue. From the discharge site, PD pulses are subjected to several electromagnetic phenomena (attenuation, reflections etc), such that its shape, amplitude and rise time change significantly along the propagation path [21,22]. For PD recognition, robust expert systems must be designed in order to cope with these inherent physical phenomena.…”

“…Considering all ANNs (Figure 24), it is observed that when the denoising step is performed by novel filtering, there is a substantial increase in accuracy for surface tracking, mainly because of reduced confusion between this PD source and gap discharges. The accuracy increase is physically associated to the fact that the denoising algorithm reduces the influence of the low-density PD cloud, because the high-density clouds likely correspond to the PD source nearest to the sensor, which is less subjected to distortion effects that happen along the propagation path of the PD pulses to the sensor [22]. Surface tracking patterns are characterized by localized vertical clouds of low-count discharges, which exert little influence on projection features if other spurious PDs are present.…”

Frequency Resolved Partial Discharges Based on Spectral Pulse Counting

“…Corona discharges tend to have higher counting rates distributed over the spectrum because they occur between the energized electrode and the air, with plasma channel length highly dependent on the 50 or 60 Hz instantaneous signal amplitude. In contrast, slot PD counting strongly depends on arcs connecting the circuit poles, producing characteristic resonance frequency, which is associated to the length of the produced ionized electric arcs (which tends to be the distance between the poles) and especially on the total length of the metallic parts shortened by the arcs (the lengths of hydro-generator bars [31], for instance). This behavior explains the fact that slot PDs have, in our test measurements, their highest registered PD repetition rate around 70 MHz.…”

“…An important matter is related to the spectral peaks seen in Figure 5. Although spectra of current PD pulses can be smooth functions, with a certain bandwidth, it is demonstrated in detail in [31], using full-wave simulations (by solving Maxwell's equations numerically), that electromagnetic waves produced by the PD currents resonate inside the winding bar while propagating in the structure, producing resonating electromagnetic fields propagating outwards from the bar. The fundamental resonance frequencies depend on the dimensions of the bar and on the wave propagation velocity inside the structure.…”

“…The fundamental resonance frequencies depend on the dimensions of the bar and on the wave propagation velocity inside the structure. In [31], an analytical formula from [32] is also used to confirm the resonance frequencies obtained from the simulations. Higher harmonics are also seen in simulation results and confirmed using the analytical formula.…”