Simulation of the temporal behavior of circuit breakers and motor starters

Low-voltage circuit breakers have to be able to detect and disconnect short circuit currents autonomously. Especially for high-energy applications such as container ships the peak value of the short circuit current has to be limited significantly in order not to overload the downstream parts of the electrical system. That is why the contact system has to open rapidly well before the maximum of the prospective current has been reached. Development and design of these devices faces the challenge of shorter development cycles, smaller volumes and increasing technical requirements making it more crucial to pass the relevant tests in the first try. This work describes a method that enables us to predict the results of short-circuit current tests for single circuit breakers or multiple breakers connected in series before prototypes of the devices are available. Specifically the current, the arc voltage, the position of movable parts, and numerous other data are calculated. We set up a system of coupled differential equations for the subsystems electrical network, contact system of the switching device and the electromagnetic releases. We describe the simulation model and the input data required for the calculations and show results obtained with this method for three-phase circuit breakers and motor starters.