Characterization of Electrical Tree Initiation and Growth in XLPE Under Harmonic Waveforms

The electrical treeing growth and initiation of Cross-Linked Polyethylene (XLPE) under the influence of harmonics and frequency are considered in this paper. Constant stress tests and step stress tests were conducted on needle electrode specimens to investigate the effect of harmonic order, Total Harmonic Distortion (THD) and frequency. The field driven tree growth (FDTG) model was utilized to quantitatively explain the effect of THD and harmonic order on electrical tree growth. The variation of tree initiation probability for harmonic and pure frequencies were theoretically explained with the aid of space charge limiting electrical field variation and field limiting space charge cloud formed in the vicinity of the needle electrode. From the average tree length variation and by calculating the FDTG parameters, it was found that under constant voltage, the THD level is the most prominent factor in determining the tree growth rate. From the step stress test, it was concluded THD, harmonic order and frequency can affect the tree initiation.