Current zero behaviour of a gas-blast arc. Part 1: Nitrogen

The current-zero behaviour of an axisymmetric nitrogen arc burning in a supersonic nozzle has been investigated theoretically by assuming local thermal equilibrium and laminar flow. The approximate radiation model of Zhang et al. [16] has been used to account for the emission and absorption of radiation. The current is ramped down linearly to current-zero from a direct current of 1 kA and a linearly rising voltage is imposed upon the arc after current zero. The relative importance of various energy transport mechanisms (i.e. radiation, radial and axial convection, thermal conduction and Ohmic heating) is discussed and the dominant energy transfer process identified. The thermal interruption capability of such an arc is expressed in terms of the rate of current decay before current zero (di/dt) and the rate of rise of recovery voltage (RRRV) after current zero. The relation between RRRV and the stagnation pressure is also discussed. Finally, a comparison is made between the computed and available experimental results.