Arc velocity and cathode erosion rate in a magnetically driven arc burning in nitrogen

Abstract

Measurements of the arc velocity and of the erosion rate are reported for a copper cathode. The 100 A arc, burning in nitrogen, is driven by a magnetic field B, varying from 5.1 to 171.0 mT, between concentric copper electrodes having an inter-electrode gap of 4 mm. The arc velocity varied with B0.60 throughout the range investigated. The erosion rates dropped from 9.0 to 1.0 mu g C-1 as the arc velocity was increased from 15 to 135 m s-1.

SF6 post‐arc recovery characteristics

“…The optimization of this magnetic field, B ¼ 0.1 T, enables the arc to be kept nearly vertical throughout its movement across the plane electrode (Figure 4(b)). The average velocity of the arc column, at the test gap region, under these conditions is about 24 m/s, which is 2.5 times faster than the case without an added external field, reducing considerably contact erosion and metal vapor generation [18].…”

“…During the running phase the arc lengthens due to the anode shape, presenting an angle of 18 with the horizontal axis (see Figure 1). The precise shape of the arc runners was chosen in order to keep the arc as close to the vertical axis of the test gap as possible.…”

Improving GIS Disconnectors for Future HVDC Applications

“…For the scope of this research, however, tests were performed in ambient air exclusively. The use of transverse magnetic fields to continuously move an electric arc on the electrode surface has been studied regularly in the past [32], often with the goal of reducing localized heating and electrode erosion [33]. It has also been suggested as a method to improve switching performance of disconnectors [34].…”

“…The less than linear increase of speed with current can be attributed to the linear increase of Lorentz force with current, which is counteracted by aerodynamic drag growing with the square of the speed. Guile et al [32] give a proportionality of v ∝ I 0.4 , while Szente et al [33] found v ∝ I 0.60 . In the presented data it is also evident that arc speed decreases with opening distance.…”

“…Oxidation of electrodes has been shown to have a measurable influence on arc speed and on erosion (c.f. [17], [33]). When performing test series using the disconnector testbed, exposing electrodes contaminated with erosion products to air for extended periods led to a substantial increase in arc rotation speed.…”