Voltage-Current Characteristic of Free Burning Arcs in SF6 Alternative
Gas Mixtures
Abstract
Abstract—Voltage-current characteristics of free burning arcs in SF6
and air have been known for decades. As the demand for an SF6-free
solution is increasing, there is an accompanying need to determine arc
parameters in the alternative gases. An unblown arc experiment has been
established to determine the voltagecurrent characteristics of SF6
alternative gases, which have not yet been thoroughly studied. In this
experiment free burning arc measurements were performed in a number of
gases under consideration of SF6 alternatives, including CO2 and
mixtures of CO2 / O2 with and without C4F7N or C5F10O additives at
concentrations of up to 10 %. Measurements were also performed in air
and SF6 for comparison. Arc voltage was measured in each gas at
pressures ranging from 1 bar to 5 bar absolute, and electrode
separations ranging from 20 mm to 95 mm. Voltagecurrent characteristic
measurements for air and SF6 show good agreement with previously
published results. A linear relationship of the arc voltage to the arc
length is shown, as well as fourth root dependence of the arc voltage on
the gas pressure. It was shown that neither the O2 nor the fluorinated
additives to CO2 have any significant influence on the voltage-current
characteristic. The minimum arc voltage in all measured gases was
slightly higher than in SF6, but the arc in SF6 was the least stable and
had the highest elongations resulting in high voltage peaks. The arc
voltage in air had a similar minimum value to the CO2 based gases, but
the arc was much more stable, resulting in lower effective voltage,
especially at low currents.