Effect of the pressure on the development of an impulse arc in CO2

The properties of the impulse discharge in carbon dioxide under variable pressure in the range 26.7 kPa - 0.16 MPa (200-1200 Torr) were investigated using fast photography and electrical measurements. In the experiments, fast lightning impulses (70 ns front) were applied to a point/plane gap with gap separation of 6.5 and 11 cm. It was found that the peak current was not affected by pressure; the electric field, on the contrary, did respond to it. The computer simulations and electrical field measurements performed show that the space charge had a dipolar structure. This structure might be responsible for the diminished negative breakdown level observed in CO₂. It was found that the arc expansion in the first 3 μs is very fast and slows down afterwards following a logarithmic curve in time. The pressure of the gas had a small, inverse effect on the arc´s diameter.