CFD-simulation of high- and low current arcs in a self-blast circuit breaker

The physical phenomena in self-blast circuit breakers at interruption of heavy fault currents strongly differ from that in puffer type devices. The pressure which is generated by the intensive ablating nozzle wall causes a heavy backflow of hot PTFE-vapor with a temperature of about 5000 K. This backflow is accompanied by shock waves which excite Helmholtz-oscillations in the pressure chamber and the backflow channel. Depending on arcing time, fault current, contact velocity and interrupter chamber geometry the blow temperature may rise up to 2000 K. To understand the mixing process of the hot gas cloud with the cold SF ₆, simulations of the high current period have been performed. In earlier investigations the interrupter geometry has been subdivided into several relevant volumina for which the balance equations of mass and energy have been integrated. The gas flow between these volumina has been described by one dimensional Bernoulli flow and the inhomogenous mixing process has been considered by introducing movable boundaries, driven by the pressure difference on both sides, between the hot and the cold gas. CFD-codes facilitate a very fine discretisation of the geometry so that the mixing process can be determined much more accurately. The presented calculations have been performed with the software package FLOW3D, which is commercially available