Measurement of the densities of Cu and Ag vapours in a low-voltage switch using the hook method

作者：Lins Guenter^*

来源：Journal of Physics D: Applied Physics , 2012, 45(20): 205202.

DOI：10.1088/0022-3727/45/20/205202

In a research model of a low-voltage circuit breaker with fixed contacts and windows for optical access, arcs powered by either a high-current transformer or a capacitor bank were initiated by the explosion of tungsten wires. Air at atmospheric pressure was the switching medium. The number densities of neutral silver and copper vapours from contacts and arc runners were measured simultaneously by the hook method using a Mach-Zehnder interferometer combined with a 1 m spectrograph and a gated intensified CCD camera. When an arc current was flowing, a substantial fraction of the metal vapour was ionized, and thus not amenable to a density measurement with the technique chosen. To nevertheless obtain approximate density values, the arc current was forced to zero within 8 to 10 mu s at a preset time and measurements were carried out 100 mu s after extinction of the arc. At that time the metal vapour was expected to have recombined to a large extent but not yet diffused to the walls in significant amounts. Depending on the current amplitude reached within the arc duration the arc remained anchored to the silver contacts or commutated to the copper arc runners. At a maximum current amplitude of 650A Ag vapour densities of the order of 10(22) m(-3) were observed near the anode outweighing the Cu vapour density by a factor of 20. When at 1600A the arc commutated to the arc runners a Cu vapour density of 8 x 10(21) m(-3) was reached while the Ag density remained limited to 2 x 10(21) m(-3).

• 出版日期2012-5-23