Breakdown sequence in SF₆at pressures up to 8 bar in a geometry representative of a circuit-breaker

Abstract

Breakdown sequence in SF6 of an electrode arrangement which represents the contacts of a circuit-breaker is investigated at pressures up to 8 bar under positive impulse voltages. The Schlieren frames point out the role played by the cathode as a source emitting electrons by field effect emission. Photomultiplier records demonstrated, at Pd = 2 bar, that the discharge's formative time strongly decreases: from 1 µs at pressure lower than Pd, down to 150 ns at pressure higher than Pd. A change in the discharge regime is associated with this transition. An experimental investigation, using photomultipliers and Schlieren devices, allows us to describe both breakdown sequences. At low pressures, there is a critical volume at the anode. Nevertheless, it is a negative discharge which is responsible for the breakdown although the geometrical electrical field at the cathode boundary is about 60 kV cm-1. At high pressures, there is no critical volume. However, a positive discharge develops across the gap. Physical considerations taking into account the electron energy are proposed to explain the mechanisms involved in both types of discharge.

Molecular Dynamic Simulations of the Collision between Copper Ions, SF6 Molecules and a Polyethylene Surface: A Study of Decomposition Products and an Evaluation of the Self‐Diffusion Coefficients

“…In the first simulation, the transfer of energy was not as effective as in the second one and, therefore, the final average temperature of the polymer was lower in the first simulation than in the second. We find similar results for simulations 21 1 and 21 2 . Figure 5 shows the temperature of the polyethylene crystal all along the simulation for which the average velocity of the incoming particles is 17 km Á s…”

“…For the other simulation, the interaction is stronger, and we can point out the large number of atoms or molecules emitted, 18, including 9 atoms of hydrogen. For both simulations, the ratio, as previously defined, is practically the same: 29.6% and 27.0% for simulations 21 1 and 21 2 , respectively.…”

“…Conversely, in the other simulation, the emissions of particles of the first category are more important and the ratio falls down to 2.86%. In simulation 19 2 , there are many long particles, having 5, 7 or 15 carbon atoms, and also we see the degradation of several particles, for example the decomposition of a C 3 H 6 molecule that leads to one C 2 H 4 molecule and one CH 2 molecule. Finally, for the highest initial average velocity, the number of emitted atoms was 21 and 54, respectively, in the two simulations.…”

“…[18,19] This potential is given in Equation (2), where r ij is the inter-nuclear separation distance between atoms i and j, R e is the equilibrium distance between the two atoms, and, D and g are given in Table 1.…”

“…In the field of electrical network protection, the technological challenge is located in the control of the interaction between the plasma and its surrounding material. [1][2][3][4][5] Indeed, the damage induced by the plasma could seriously reduce the life span of electrical devices. It is necessary to understand what happens, especially with respect to the major physical phenomena that must be taken into account.…”