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The arc behaviour of short, low current switching arcs is not well understood and lacks a reliable model. In this work, the behaviour of an arc in the air is studied during contact separation at low DC currents (0.5 A to 20 A) and for small gap lengths (0 mm to 6 mm). The experiments are performed on a low voltage relay with two different electrode configurations. The arc voltage is measured during the opening of the contacts at constant current. The arc length is determined optically by tracing the mean path of the arc over time from a series of high-speed images. From the synchronised data of voltage vs. distance, first a sudden jump of the voltage at the start of contact opening is observed. Secondly, a sudden change in the voltage gradient occurs as the arc is elongated. Short arcs with a length up to approximately 1.25 mm show an intense radiation in the overall gap region and high voltage gradients. An unexpected behaviour never reported before was observed for longer arcs at low current: Two characteristic regions occur, a region in front of the cathode, with a length of approximately 1.25 mm, having an intense radiation and a high voltage gradient as well as a region of much lower radiation intensity and a comparatively lower voltage gradient in the remaining gap area despite a small anode spot region. The characteristic border of approximately 1.25 mm is almost independent of the current. A generalised arc voltage model is proposed based on the assumption that a constant sheath voltage and two discrete field regions exist, which are modelled as two independent linear functions of voltage vs. length. The data for various currents is combined to yield a general non-linear function for predicting the arc voltage vs. arc length and current.

Electrical exploding wires have found many applications in industry and research. Some of the most promising applications include high-speed sheet metal forming and explosive welding. Most research to date has been conducted using thin highly conductive, pure metal wires at relatively low energies. In contrast, experimental trials are performed in air, on relatively thick AISI 304 stainless steel wires with diameters 600-800 µm and lengths ranging from 40 to 160 mm. The test wire produces circuit damping in a series RLC circuit with C = 150 µF and L = 4.36 µH, which yields a maximum theoretical discharge energy of 2.7 kJ at 6 kV. The energy absorbed in the wire and the wire plasma respectively, is calculated to determine the fraction of absorbed energy, i.e. the energy transfer efficiency, for each case and the optimum wire dimensions for the circuit. Longer wires attain a lower action integral and absorb more energy with respect to short wires resulting in a higher energy transfer efficiency to the wire. Thicker wires attain a lower final action integral despite lower initial resistance and absorb more energy with respect to thin wires resulting in a higher energy transfer efficiency to the wire. The total efficiency of dissipated energy in the wire is analysed depending on the wire length and diameter, together with an introduction of the time-averaged wire resistance.

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