The ratio T/B of top to bottom surface salt deposit density (SDD) affects the ac pollution flashover performance of disk insulator strings. The ac pollution flashover stress was established for fifteen different combinations of SDD and T/B in a systematic study, making use of seven-unit suspension strings with six different disk profiles in this paper. Then a comparison was made of pollution performance for glass and porcelain disks with the same profile. The observed relation of ac flashover stress EL to SDD and T/B followed an equation of the form EL=c·SDD-b·(1-A·log(T/B)) . The values of c , b and A were fitted to test results for glass and porcelain disks of identical bottom-rib profile, and to four other bottom-rib and external-rib profiles. A reduction in the ratio T/B from 1/1 to 1/15 gave a median 26% ± 8% increase in flashover strength, corresponding to the calculated increase in overall pollution layer resistance. Extrapolation of results for the seven-unit strings to UHV dimensions suggests that some reduction in leakage distance can be accepted in areas where there is frequent natural washing of the top surfaces of disk insulators.

Study on AC Flashover Performance for Different Types of Porcelain and Glass Insulators With Non-Uniform Pollution

https://iopscience.iop.org/article/10.1088/2053-1591/ab3f0d/pdf

Aging of silicone rubber-based composite insulators under multi-stressed conditions: an overview

Ethylene propylene diene monomer (EPDM) is a polymer widely used for insulation in high voltage outdoor insulators and cables. It is well accepted that appropriate addition of micron particles to form a composite can enhance its insulation performance. This work reports improvement on the dielectric breakdown strength, tracking failure time, mechanical properties and volume resistivity of EPDM composites co-filled with boron nitride (BN) micron and nano–particles. Test specimens were fabricated by melt-blending and hot press techniques. AC breakdown tests were performed as per IEC60243-1 Standard. The tracking test was performed following IEC 60587 Standard and volume resistivity measurement as per ASTM D257. Experimental results show improvement in electrical properties with increasing particle loading up to a certain dosage but enhancement in the mechanical properties is observed up to 30 wt% particles addition. The co-filled composite exhibits considerably higher dielectric breakdown strength (89.24 kV/mm) and volume resistivity (~ 5.0 × 1015 Ω cm) relative to Micro-20 wt%. The tracking failure time of the co-filled is much improved due to excellent resistance against dry band arcing and thermal accumulation in the discharge region. Moreover, co-filled composites show improvement in mechanical properties as compared to the micron–filled counterparts. The improved thermal conductivity, better thermal stability and overall higher surface area of the particles are possible factors which impart better performance to the co-filled composites.

Effect of micro-nano additives on breakdown, surface tracking and mechanical performance of ethylene propylene diene monomer for high voltage insulation

Hydrophobic, dielectric and water immersion performance of 9000 h multi-stresses aged silicone rubber composites for high voltage outdoor insulation

In this paper, surface trap distribution and the affected surface charge transport properties in epoxy/Al2O3 nanocomposites were studied to provide theoretical and experimental basis for improving surface flashover performance in vacuum. Four different contents of nano-Al2O3 particles were doped into epoxy and different trap distribution of samples was calculated from the surface potential decay method. Surface charge injection was identified by a direct current integrated charge [DCIC-Q(t)] method. Secondary electron emission (SEE) coefficient were obtained combing testing and fitting method. Results showed improved charge injection resistance, reduced charge mobility and SEE coefficient at a slight concentration of 0.5 wt% and 1 wt% by introducing deep traps. Continuing to increase nanoparticles in matrix was proved to reduce trap depth and have adverse effects. The surface flashover voltages reached the highest at 1 wt% nano-doping, which was in accordance with the percolate threshold loading content for trap depth, charge injection field and SEE coefficient. Surface charge injection caused the local field enhancement at the counter electrode and increased the possibility of surface flashover. Deep traps over 1 eV contributed to carrier capture, reduced charge injection and had a positive effect on increasing surface flashover voltage.

Surface trap effects on flashover voltages of epoxy/Al2O3 nanocomposites for high voltage insulation

Part of DC arcs may levitate from the insulators' surface to form air-gap arcs in the process of insulator's flashover, especially in the low air pressure The air-gap arcs can cause the bridging between ribs (or sheds) of insulators easily, and the U–I characteristics of air-gap arcs and surface arcs are different Thus, the two aspects should be taken into account when evaluating the DC flashover performance of insulators at low air pressure This study analyses the effect of arc-levitating on the DC flashover voltage of polluted insulators and calculates the insulators' DC flashover voltages with and without considering the effect of air-gap arc The comparisons between calculated and experimental results show that the DC flashover voltages of polluted insulators are overestimated when the air-gap arcs are not taken into account

L. Chen

Papers

Effect of arc-levitating from polluted insulators' surface in the low air pressure on its DC flashover performance