Electrical characteristics
SF6 is a medium with high dielectric strength. Under a uniform
electric field, the dielectric strength of SF6 is about 2,5~3 times
that of air at the same pressure, and its dielectric strength is
equivalent to that of transformer oil at 3 atmospheres. Practice
has proved that mixing a small amount of sulfur hexafluoride gas in
the air significantly increases the insulation strength of the air;
on the contrary, adding a small amount of air to the sulfur
hexafluoride gas will significantly reduce the insulation strength
of the sulfur hexafluoride gas. Due to the high dielectric strength
of SF6, for circuit breakers with the same voltage level and
similar breaking current, the number of SF6 series fractures is
less. For example, the LR-220 SF6 circuit breaker developed in my
country has a single fracture voltage of 220KV. ; Another example
is the 500KV oil-less circuit breaker with 6 to 8 fractures, while
the SF6 circuit breaker has only 3 to 4 fractures. The corona onset
voltage of SF6 is much higher than that of air, and the dielectric
strength has nothing to do with the frequency of the applied
voltage. However, attention should be paid to the uniformity of the
electric field, impurities, the shape and irregularity of the
electrode, etc., and the dielectric strength of SF6 The intensity
has a certain intensity. The moisture in SF6 gas will affect the
insulation. When the water content in SF6 exceeds a certain
concentration, SF6 may decompose at a temperature above 200°C. The
decomposition product contains hydrofluoric acid, which is a highly
corrosive and highly toxic acid. In addition, moisture condensation
is also harmful to edge insulation. Therefore, in SF6 electrical
equipment, the moisture content should be strictly controlled.