Maximum interrupting Capacity of CuCr Contacts under the effect of uniform axial magnetic field (AMF)

Maximum interrupting capacity of the butt CuCr 70/30 contacts at external uniform AMF has been experimentally investigated for AMF induction range 0-1.2 T. It has been found that dependency of maximum interrupting current density versus AMF induction has a tendency to saturate when the latter achieves the level of the first characteristic point B1 on Volt-Tesla characteristic. Radial energy losses have been evaluated on the basis of measured anode mass losses. 1D thermal model has been used for evaluation maximum interrupting current density. At the same time radial energy losses have been taken into consideration. Calculated results demonstrate good agreement with the experimental data if critical temperature equal to ~2000 K is considered. This value of critical temperature is supported by several experiments described in literature

I. Introduction

Breakdown of the contact gap just after kA arc extinction occurs in the metal vapour originated by the molten electrode zones. Connection with electrode temperature stimulated different methods of surface heating control: by AMF to keep the arc diffuse and avoid local overheating; by RMF to prevent surface heating by quick rotation of the arc root [1]; equalization of surface temperature by control of the melting contact material flow [2]. Nevertheless the limit of interrupting capability in ideal case of minimal heat flux uniformly distributed on the contact surface – in essence the limit of interrupting capability at all – has not been determined yet. Minimal energy input may be achieved in external AMF providing minimal arc voltages (flat part of Volt-Tesla characteristic (VTC) for the contact of given diameter) [1]. The aim of this paper is to determine the limit interrupting capability in the range 0–1.2T of external AMF, including the range of induction provided minimum arc voltage; to estimate radial loses of arc energy and calculate the limit interrupting capability for the case of uniformly distributed heat flux.