Influence of the rise rate of voltage and leakage distance on flashover gradient and partial discharges level for various polymeric materials under AC stress

Abstract

This paper presents results of investigations on the influence of the rise rate of voltage and the leakage distance (L f ) on flashover gradient (FOG) and partial discharges (PD) activity on insulators issued of different polymers materials in dry conditions; the aim of this study being the development of new generation of high voltage piercing connectors.The investigated polymers are of three distinct classes among the mostly used in electrical industry: thermoplastics, thermosetting and elastomers. The considered thermoplastics are polyamide 6 (PA6/50), fireproofed polyamide 66 (PA66/50), polycarbonate (PC/40) and polyarylamide (PARA/50); the thermosetting are two cycloaliphatic epoxy resins (EP1 and EP2); and as concerns elastomers, two EPDM materials noted EPDM and EPDM V0 (fireproofed) have been tested. It is observed that generally the increase of the rise rate of voltage increases the flashover gradient while the increase of leakage distance leads to the decrease of flashover gradient. The magnitude and time duration of voltage, chemical structure of polymer and leakage distance influence the magnitude of PDs. Small degradations are observed in the vicinity of high voltage electrode for thermoplastics and EPDM elastomers after the occurrence of flashover (arc) especially for PC/40. The surface of cycloaliphatic epoxy resins (EP1 and EP2) appears to be the most resistant to flashover arcs and PD activity making them suitable to be used in high voltage connectors.

Assessment of the resistance to tracking of polymers in clean and salt fogs due to flashover arcs and partial discharges degrading conditions on one insulator model

“…Two groups of polymers are selected to carry out FOV, FOG and PDs measurements: (i) thermoplastics [namely, polyphenylene sulphide (PPS/65) filled with 65 wt% of minerals and glass fibres and unfilled high‐density polyethylene (HDPE)] and (ii) thermosetting resins: namely, unfilled cycloaliphatic epoxy (UnCEP) and unfilled hydrophobic CEP (UnHCEP). The purpose is to pick‐up appropriate polymers to be included in the new generation of high‐voltage piercing connectors [17]. Table 1 shows properties of materials provided by suppliers.…”

“…The influence of the field gradient (kV/mm) as well as the time of polymers exposition to PDs are investigated for L d = 123 mm that is more representative for the PDs activity and allows comparing materials properties [17].…”

“…6 c despite of fields up to ∼0.18 kV/mm that is likely due to the influence of exposition time of polymers to PDs (Fig. 7 c ) by changing the surface resistivity and increasing the PDs level [17].…”