In the RaMagNostic research project, a diagnostic method for low-voltage switchgear is being developed that is based upon magnetic field measurement. The project is being sponsored by the German Federal Ministry of Education and Research (BMBF). The aim is to be able to non-reactively determine the arcing movement inside a switching device during a switching process.
In a first step, a magnetic field camera was developed that can record the arc’s magnetic field in a spatially and temporally resolved manner. For this purpose, 3D Hall Effect sensor ICs were used, each of which can locally detect all three components of the magnetic field vector up to 25,000 times per second in one point. In order to locally resolve the magnetic field, 288 of these sensor ICs were arranged in an array of 12 x 24 ICs. This sensor array forms the main component of the sensor board, which is shown in Fig. 1. An FPGA developer board was used to control the sensors and record the measured values. The use of an FPGA, which is very well suited for the parallel processing of data, enables this large number of sensors to be implemented. Together with the sensor board and two adapter boards, the FPGA board forms the first version of the magnetic field camera. The further development towards a compact camera head and the production of five such heads enables the simultaneous recording of the magnetic field on five measuring planes.
The functionality of the magnetic field camera could be demonstrated by initial measurements on a circuit breaker (see measurement arrangement in Fig. 2). The temporal and local changes in the magnetic field could be recorded during the burning process of the arc, which lasted approx. 5 milliseconds. Fig. 3 shows an example of the measured field distribution at four different points in time.
In the second step, this project is working upon an algorithm approach with which a back-calculation of the measured magnetic field on the movement of the arc should be possible. Together with the camera system, a diagnostic process for switching devices is to be created.