193 / 2018-09-05 21:04:06

Method of Determining Compression Set for GIS Seal Ring (O-ring) Based on Directional Section Diameter

GIS,O-ring,Seals,Diameter,Cross-section,Rubber Thickness Gauge,Precision

Gas-insulated metal-enclosed switchgear (GIS) was insulated by SF6 gas. It is compactly installed in aluminum tank, sealed by rubber seal rings, and has the advantages of small footprint, good resistance to electromagnetic interference compared with traditional air-insulated switchgear (AIS). SF6 shows perfect arc extinguishing and insulation performance far superior to air, since it is a kind of gas with strong electronegativity. To keep the electrical properties, high-purity and good sealing are required, which makes high demand on the long-term sealing property to the rubber seal rings. Usually, GIS seals are demanded to work throughout the lifetime of the GIS device(~30a). However, maintenance and management of GIS seals are highlighted currently. On the one hand, it’s hard to predict the lifetime of the GIS seals accurately, nor can we do condition assessment on it, since there is a lack of accelerated aging test considering the operating condition of GIS seals. On the other hand, periods between maintenance stops are longer than before, GIS seals cannot be replaced conveniently without scheduled outage.
In this paper, we first analyzed the degradation mechanism of ethylene propylene diene monomer (EPDM) for sealing rings in GIS sealing application, and analyzes the effects of thermal and mechanical compression aging factors on the compression set. Then, the two-factor of thermo-mechanical artificial accelerated aging test and lifetime prediction platform of GIS seals was proposed, in which the experimental device of flat-plate for compression aging made of steel was designed, the level and combination of heat aging factor and mechanical aging factor were given (the temperature was 25°C, 90°C, 120°C; the compression rates are 0%, 17%, 22%, 30%, and they were combined to form 12 experimental groups), and the test method of the GIS seal rings was proposed (including density and hardness test, mechanical properties test such as permanent compression set rate and tensile strength). The specimens in the shape of arc were prepared from the O-ring product.
Then, we conducted the “heat compression” accelerated aging test in different experimental groups (temperatures, compression rate, durations). The variation law of the permanent compression set value, density, hardness changing with the aging temperature, compression rate, and aging time were analyzed. Residual analysis of the measurement accuracy was performed to compare the effect of parallel samples, test methods, and the influence of testers on the results. The result showed that the subjectivity of the testers and the accuracy of the test device have a great influence on the results.