Electrical Tree Growth Under Very Low Frequency (VLF) Voltage Excitation

Analysis of Partial Discharges in Electrical Tree Growth Under Very Low Frequency (VLF) Excitation Through Pulse Sequence and Nonlinear Time Series Analysis

“…The correlation dimension parameter D 2 has been used to characterize the geometrical structure of electrical trees [4]. Different behavior of D 2 with the progression of electrical trees have been reported [11], [20], [35]. The trend found in this work under VLF excitation, see Fig.…”

“…However, this was not a limitation, due to the use of enough windows or intervals for the study of the parameters' evolution during tree growth. Thus, several intervals of analysis were selected from the entire time series following a similar methodology previously used [11], [36]. Each interval was selected to have at least 10,000 PD events and at least 1,000 and 10 seconds for 0.1 and 50 Hz experiments respectively.…”

“…It is known that with frequency reduction, electrical trees grow slower and their shape is also affected. It has been reported that the time to breakdown at 0.1 Hz was three times longer than at 1 Hz [9] and trees grown at VLF (0.1 Hz) can be almost five times slower than industrial frequency (50 Hz) in test samples at the same high voltage level [11], showing that the tree growth rate is not linear with respect to the frequency. Moreover, electrical trees grown at VLF have a less bushy/dense structure compared to those grown at industrial frequencies [9], [11].…”

“…In this regard, the use of VLF excitation is an interesting choice because these tests require smaller voltage sources than industrial frequency tests and it is less likely to produce harmful accumulation of space charge within the insulation, as it is the case of DC tests [22], [24], [25]. However, there are insufficient data to allow accurate interpretation of PD measurements in VLF testing [16] and new methods of PD analysis are needed for insulation condition assessment under VLF excitation [11], [26].…”

“…A more general approach is to consider the PD phenomenon as a nonlinear dynamic process, and thus, to study it using the mathematical approach of nonlinear time series analysis (NLTSA) and chaos theory in order to characterize the PD behaviour and its sequence of discharges [29], [30]. NLTSA tools have been used in electrical treeing to analyze time series of PD and to describe the growth through nonlinear parameters [4], [11], [20], [35], [36]. In this approach, a similar type of graphical representation can be plotted, normally called "state-space trajectory" or "projection" [29].…”