International audienceThis paper describes the assessment of the resistance to tracking of various polymers after (i) flashover voltage (FOV) and flashover gradient (FOG); and (ii) partial discharges (PDs) measurements in dry, clean and salt fogs on one insulator model using standardised electrodes; the aim being the development of optimised methods based on flashover and PDs to the conception of new generation of piercing connectors. The investigated materials belong to two distinct classes widely used in the electrical industry: thermoplastics (namely polyphenylene sulfide and high density polyethylene) and thermosetting cycloaliphatic epoxy resins namely one unfilled material (UnCEP) and another unfilled and hydrophobic resin (UnHCEP). FOV measurements are based on the electro-geometrical parameters of each specimen and the resistance to tracking, both may be assessed through the slope of FOV curves against the leakage distance as an indicator of surface damages. Regarding PDs, the suggested technique is devoted to clean and salt fogs and provides quicker and more accurate information about PDs effects on materials deteriorations rather than IEC60109 where the exposition time to discharges is much longer at lower voltage levels by using only liquid contaminants such as sulfuric or nitric acids or ammonium chloride as described in IEC60587 or ASTM D2303
International audienceThis work deals with a comparative study of AC breakdown voltage (BDV) of various polymeric samples. The investigated materials cover thermoplastics (namely polyamide 6 (PA6/50), fireproofed polyamide 66 (PA66/50), polyarylamide (PARA/50), polycarbonate (PC/40), polyethylene (HDPE) and polyphenylene sulfide (PPS/65)); and two EPDM based elastomers (namely unfilled EPDM (EPDM) and fireproofed EPDM (EPDM V0)). We mainly analyze: (i) the effect of electrodes shape (namely cylindrical and spherical); (ii) thermal ageing at high temperatures (100, 130 and 150°C); and (iii) hydrothermal ageing in salt fog conditions. It is shown that obtained BDV with spherical electrodes exhibits the highest values because of small surface contact of electrodes with polymeric surfaces; materials such as PEHD and EPDM show the highest BDV. It is found that thermal ageing affects seriously BDV of EPDM based materials. PPS/65 depicts the lowest BDV but is less affected by thermal ageing because of its high thermal stability. Hydrothermal ageing reveals that the moisture absorption is the main reason of the significant decrease of BDV for polyamides
International audienceAbstract:This paper is devoted to the influence of the direction of the applied electric field (namely perpendicular and parallel to the insulator surface) and the type of insulator materials on the propagation of creeping discharges (pattern and stopping length) in presence of air under standard lightning impulse voltage. The investigated materials belong to two distinguished families among the mostly used in electrical industry: (i) thermoplastics (namely polyamide 6 and polyarylamide), and (ii) one cycloaliphatic filled epoxy resin. It is shown that the stopping discharges length on a solid/air interface covers generally 55% of the creeping distance for both polarities under perpendicular E-field right before the flashover. While with parallel E-field, the stopping length is included between 20 to 30% for positive polarity and less than 25% for negative polarity. Also, the application of a perpendicular E-field is more straitened than the tangential one due mainly to the dielectric constant of polymers. Numerical simulations show that the electric field is more reduced for perpendicular E-field inferring that discharges (streamers) lengthen and develop easily at lower voltage levels
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.
In many high voltage equipment, partial discharges are regarded as one of the most widespread pathology whose ignition conditions and effects are studied by scientists and manufacturers to avoid major failures. Actually, those electrical gaseous phenomena generally occur under several constraints such as the electrostatic field level, the nature of insulating surface being polluted or not, and switching or lightning transients. The present paper discusses physical mechanisms related to the creeping discharges propagation growing over insulators subjected to perpendicular electric field and positive lightning impulse voltage. More precisely, the developed discussion attempts to answer some observations especially noticed for main discharges feature namely (i) the discharges morphology, (ii) their velocity and (iii) the space charges effects on electric field computation. Several factors like (i) the influence of the type of a material’s interface, its electric conductivity, permittivity and discharges mobility, (ii) the relationship between the applied electrostatic field, the space charges, the velocity, the propelling pressure and discharges temperature are among numerous parameters that have been addressed in this study which discusses lightning impulse transients phenomena.
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