Assessment of the Power Balance at a Copper Cathode Submitted to an Electric Arc by Surface Temperature Measurements and Numerical Modelling

The aim of this work is to improve the understanding of the heating of copper cathodes under the action of a nonstationary electric arc in air. An experimental method is proposed for the measurement of the surface temperature distribution just after a very fast arc-controlled arc extinction. The arc current intensity is about 60-70 A, and the arc duration is in the range of 2.5-5 ms. Different kinds of surface temperature distributions have been observed depending on the arc root behavior. The measurement of the temperature decrease after the arc extinction was used to estimate the cathode surface temperature just at the moment of arc extinction. Two-dimensional thermal modeling taking into account phase changes is used to estimate the power balance at the cathode surface and to propose a second estimation of the surface temperature at the point of arc extinction. The comparisons between experimental results and thermal modeling lead in the present experimental conditions to a volt equivalent at the cathode in the range 6.7-10.7 V, to a surface power density in the range0.6 × 10⁹ - 2.5 × 10⁹ W/m² and to a maximum surface temperature in the range 850°C-1300 °C .

I. Introduction

The cathode surface temperature (maximum temperature or temperature distribution) in the case of nonstationary electric arcs in air at atmospheric pressure remains a relatively unknown experimental parameter. This temperature is, however, a very important parameter for the understanding of arc-electrode interaction. Several works have been conducted in order to measure the surface temperature of an electrode submitted to an electric arc. Most of these studies have been done for the case of stationary arcs burning in argon with refractory electrodes (tungsten, thoriated tungsten) [1]–[4].