The Impact of Superimposing Negative HVDC on AC Electrical Tree Growth in LDPE

This paper explores the impact of negative HVDC superimposition on AC electrical tree growth in LDPE by comparing treeing under -60 kV DC superimposed with 7 kV pk AC (denoted ‘N60 ± 7’) and in AC fields at 7 kV pk and 8.4 kV. Trees tended to be limited in propagation at all three applied voltages. Tree lengths and widths at 8.4 kV tended to be larger than those at 7 kV and at ‘N60 ± 7’, while those at 7 kV and ‘N60 ± 7’ share similar lengths and widths. Trees grown at ‘N60 ± 7’ have a slim bouquet structure featuring a dense opaque 2D silhouette, while trees grown at 7 kV and 8.4 kV are dense branch structures with individual channels still evident in 2D images. One exceptional tree at 7 kV pk appeared like a slim bouquet structure but longer and wider. Unlike at ‘N60 ± 7’ which saw fine tree channel development from the existing slim bouquet structure during DC ramp down regardless of AC components, no fine channels were observed during AC voltage ramp down.