148 / 2024-04-14 23:20:17

Research on the Arcing and Breaking Characteristics of C4F7N/CO2 Mixtures with Different Mixing Ratios Under Slightly Positive Pressure

C4F7N/CO2 mixtures, arcing characteristics, breaking performance, ring main unit, SF6 alternative gas, slightly positive pressure.

C₄F₇N/CO₂ mixtures as one of the most likely alternative insulation and arc extinguishing medium of SF₆ gas is attracting more and more attention. Considering the influence of pressure on the liquefaction temperature of the mixed gas, when the operating temperature is limited to -25 °C, the allowable volume mixing ratio of C₄F₇N in the C₄F₇N/CO₂ mixtures under slightly positive pressure can reach 20%. This is significantly higher than the allowable volume mixing ratio under high pressure. However, due to the simple arc extinguishing structure of the medium-voltage ring main unit, it often does not have the gas blowing like that in the high-voltage circuit breakers, resulting in the low breaking performance. Compared with high-voltage circuit breakers, the arcing and breaking characteristics of C₄F₇N/CO₂ mixtures under slightly positive pressure are not studied much. In this paper, the magnetohydrodynamic model of plate arc extinguishing structure of 12 kV gas ring main unit is established. The arcing characteristics of three kinds of C₄F₇N/CO₂ mixed gases with C₄F₇N mixing ratios of 5%, 10% and 20% are studied. It is found that with the increase of C₄F₇N mixing ratio, the arc extinguishing peak of the mixed gas increases, and the voltage drop phenomenon in the arcing process is suppressed. The causes of the differences in arcing characteristics are analyzed from the physical parameters of the three. The breaking characteristics of 20%C₄F₇N/80%CO₂ mixtures then were tested by the synthetic circuit test system, the withstand voltage can reach 3.27 kV after breaking the rated current when the short arcing time is 8ms. This indicates that the C₄F₇N/CO₂ mixtures has the ability to replace SF₆ gas to break the rated current in the medium-voltage gas ring main unit.