580 / 2017-05-15 10:59:24

Experimental and Numerical Investigation of Magnetic Field Distribution Around the Air Arc Plasma of a Simplified Arc Chamber

Magnetic field,Magneto-optical imaging

Widely used in electrical power distribution and control systems, low-voltage switching devices play a significant role in protecting the power systems by detecting faults and interrupting electric circuits. In the case of switching, an air plasma is established between the movable and fixed contacts of the device. After a short stagnation time, the arc column moves towards the quenching area under the action of the Lorentz and gas dynamic forces. Finally, the arc is extinguished and the fault circuit is cut off. The success of the interrupt process is closely linked to the quality of current transfer between the arc and the electrodes. The position and the shape of the average current can be estimated from the magnetic field around the arc based on the numerical inversion of the “Biot and Savarts” relation. So it is of vital importance of measuring the magnetic field distribution around the arc.
In this paper, experimental and numerical methods were used to investigate the magnetic field distribution around the low voltage switching device. To reduce the complexity of the analysis, a simplified geometry (Fig. 1) was used to represent the arc chamber considered in this paper which is a widely used approach. Based on Faraday effect, an magneto-optical imaging system was developed and the diagram was shown as Figure 2. It was composed of a laser driven light source (LDLS), narrow-band filter, polarization beam splitter, analyzer, Faraday indicator with the Verdet constant of -96 rad/(T·m)@632.8 nm and high speed camera. A power station was used to create a half wave of sinusoidal arc current, at a frequency of 50Hz, and thus to simulate a short circuit in an electrical supply network. The motion of arc was captured by the other high speed camera, so that the velocity was deduced from the arc motion. The experiments were replicated twenty times under each current value.
Meanwhile, a 3-D simplified arc chamber model was contrasted and solved by the commercial software COMSOL. The arc current and velocity were consistent with the experiment. By using moving mesh method, the process of arc moving toward quenching chamber was simulated and the magnetic field distribution was obtained.
The results between the experimental and numerical methods were contrasted and the distribution was analyzed with the arc position.