Factors affecting the behaviour of an electric arc under transient conditions

The paper describes an investigation into the relationship between voltage and current in an arc under transient conditions. It is shown theoretically that the arc resistance is a function of the energy in the arc column, while the power loss from the arc is a function of arc resistance. The relationship between arc resistance and change of arc energy has been obtained by injecting pulses into a static arc. This relationship is valid for periods from 3 ¿s up to at least a millisecond. The relationship between power loss and arc resistance has also been derived experimentally. Measurement of the electrode voltage drop under transient conditions has enabled electrode and arc column effects to be separated. It is shown how the relationship between resistance and energy, as well as between power loss and resistance, is affected by a change of arc length, initial arc current and electrode material. Finally, the experimental results are compared with dynamic arc equations published in the literature.