Effect of harmonics on Pulse Sequence Analysis plots from electrical trees

This paper investigates the effect of harmonic pollution on the Pulse Sequence Analysis (PSA) pattern. Partial discharge data was captured from electrical trees growing in epoxy resin in the presence of different harmonic regimes. These regimes included 50Hz waveforms polluted with 3^rd, 5^th, 7^th, 11^th, 13^th, 23^rd and 25^th order harmonics, at varying levels of Total Harmonic Distortion (THD) and waveshape factor (KS). In this paper, the data has been analyzed using PSA by plotting the external voltage of consecutive PD pulses (u_n vs u_n-1). Under pure 50 Hz conditions, four clusters of data points can be identified in the plot and the formation of the clusters is discussed. Further investigation was performed by running the samples to breakdown. The results show that even in the presence of harmonics, an increase of PD occurrence and phase distribution translates into the expected PSA pattern, where clusters of data points merge to form a 45° straight line. Therefore, PSA is relatively immune to the effects of harmonic distortion when considering it only as an indicator of breakdown.