Hartwig Stammberger

Low-Voltage Arc Simulation with Out-Gassing Polymers

Polymer walls and inserts are an important design criterion in low-voltage switching devices. Besides their good insulation properties they are used to influence the switching arc. An important part of the energy dissipated in the arc is absorbed by the walls of the arc chamber. This leads to degradation and evaporation of the polymer and subsequent impact on and interaction with the switching arc. This contribution explains the enhancements of an existing simulation model for the interaction between the low-voltage switching arc and walls composed of polyamide PA 66. This includes a model of plastic ablation, the influence of the plastic vapor on the transport properties of the arc as well as on its radiation. Calculations and comparisons with experimental results show the applicability of the model in arc chambers that are close to reality.

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.

Two Different Experimental Approaches to Investigate the Influence of Gassing Polymer Walls on Switching Arcs in Miniature Circuit Breakers

Experiments with high current arcs confined in gassing polymer walls for two different experimental setups and characteristics of the current source were carried out. The first setup consists of a rotationally symmetric electrode configuration with the arc burning inside a small polymer tube. For the second setup conventional 16 A miniature circuit breakers were slightly modified by changing the geometry of the polymer gassing inserts and by drilling a small channel for the measurement of pressure inside the arc chamber. The signals of arc current and voltage and pressure inside the arc chamber using 9 different polymers and a not gassing ceramic were measured and compared. The paper presents the results of the different experimental approaches and evaluates the differences due to the corresponding setup. The influence of the polymers on the interrupting performance of the breakers is described.