Abstract
Due to fault currents occurring in electrical installations, high electromagnetic force values may be induced in current paths of low-voltage electromagnetic relays. This force may lead to an electromagnetic bounce that will further result in an electric arc ignition between contacts, and under some circumstances, it will result in contact welding. For the proper exploitation of relays, the threshold value of the maximum current, and thus the electrodynamic force, should be known. This force depends on several factors, including: contact materials, dimensions of relay current paths, relay electromagnetic coil, etc. This paper presents the results of calculations and an experiment on electromagnetic forces, which cover these factors. A static closing force, acting on the contacts, and the fault current were measured. As a result, values of the force and current threshold were obtained, which inform when an electrodynamic bounce may occur. The obtained result may be used in designing contact rivets and relay current paths together with the selection of adequate fault protection devices.
Highlights
The flow of electric current in apparatus current paths, electric arc, or conductors located in a foreign magnetic field leads to the appearance of electrodynamic forces
The flow of current of a considerable value can lead to the emergence of an electrodynamic force, affecting the contact system, and it can be large enough to cause a dynamic opening of the contacts
The experimental results presented in this paper provide information regarding the electrodynamic contact bounce related to the static contact force of the electromagnetic coil installed in a relay
Summary
The flow of electric current in apparatus current paths, electric arc, or conductors located in a foreign magnetic field leads to the appearance of electrodynamic forces. Other ongoing research focuses on controlling the contact closing process by means of electromagnetic coil energy control [18,19] Another approach is to use FEM methods for non-linear dynamic analysis of electrical machines in the time domain [20]. The experimental results presented in this paper provide information regarding the electrodynamic contact bounce related to the static contact force of the electromagnetic coil installed in a relay. These results can be useful in determining the electrodynamic bounce threshold solely on the dimensions of the relay current path and its rivet contact material. The last and fifth chapter contains a summary and the final conclusions
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