Contactless and non-invasive determination of the position of an axially blown switching arc in a circuit-breaker model
High voltage gas circuit breakers filled with the insulation gas sulphur hexafluoride are the main safety elements for the interruption of operating and fault currents in today's power grids. In the context of the recent debate on climate change the research on alternative insulation gases is forced. Preceding investigations using carbon dioxide as one of the most promising alternative gases show that a deeper understanding of the physical processes during the interaction of the insulation gas and the switching arc in an insulation nozzle system is necessary if these gases are considered as possible substitutes for sulphur hexafluoride. For this purpose a non-invasive measuring method has been developed which allows the determination of the spatial arc resistance distribution of an axially blown switching arc. This measurement system consists of multiple capacitive field probes placed around the insulation nozzle of a circuit breaker model for measuring the arc potential distribution. In addition, it is possible to determine the arc position during the switching process from the measurement data by using a trilateration algorithm typically applied to communication technologies. As a result, the evaluated measurements yield a three dimensional reconstruction of the arc position which in combination with the results of the spatial arc resistance distribution can be used to analyze the interaction between the arc and the quenching gas during a switching process in the vicinity of current zero.ment of the field sensors along the symmetry axis of the test device allows the resolution of the switching arc position and movement. In total 36 field sensors within nine layers are placed along the symmetry axis of the model. Each layer consists of three identically constructed sensors and an additional fourth sensor which is modified for further investigations of the arc radius. The three so-called position sensors are shifted by the angle of 120°, hence a trilateration method can be used for the reconstruction of the arc position in each layer. The trilateration method is based on multiple independent signals related to the same source. This source injects a signal to the sensors and depending on the signal strength or the signal run-time it is possible to detect and calculate the position of this source. The transfer of this method to the analysis of switching arcs causes new challenges related to the small measurement area of several centimeters and strong electrical and thermal influences of the switching arc. An approximation algorithm is developed so that the calculation of the switching arc position during the process is possible. The arc position is determined by solving circular equations and there intersections. After each step of calculation the quality of the result is validated with the given constraints. Experimentally obtained results are analyzed and the arc behavior is further shown in a 3-D animation for the current zero phase. Hereby a deeper understanding of the physical processes and influencing factors for example on the flow characteristics can be gained to develop and modify circuit-breaker chambers with alternative insulation and quenching gases to improve their interruption capability.