Breakdown voltage characteristics in a narrow gap

Static breakdown in most gases is in accordance with the Paschen's law for pressures up to a few atmospheres, at normal temperatures and uniform-field. However, departures from Paschen's law are observed notably for very small spacing or high pressure. Studies have indicated that the deviation is associated with high electric field, usually greater than 105 V/cm.1,2 For gaps of 2–3 mils, the electric field strength at static breakdown is close to 105 V/cm. Under impulse surge conditions, voltage rise rates of ≥ 100 V/μs, the electric field strength can be higher. In the following sections, an experimental arrangement to measure breakdown voltage at different rates of voltage rise (600 V/S and 100 V/μS) in a narrow gap (0.8 to 6 mils) will be described. Studies were made with carbon coated copper electrodes in a gas at pressures from 400 to 1000 torr at room temperature. Data will be presented for argon, argon-neon mixtures, neon, nitrogen and air.