High power current limiting with conductor-filled polymer composites

It has generally been assumed that the electrical current limiting properties of conductor-filled polymer composites are based on a positive temperature coefficient of resistance (PTCR) effect where, at a certain switch temperature, the material resistivity increases by orders of magnitude. Here we present studies of the switching behavior at high current densities which demonstrate that, in the high power regime, the observed limiting is not based on the PTCR effect. Instead, we show that this type of limiting appears to be a general feature in conductor-filled polymer composite materials. A qualitative model for the limiting phenomenon is proposed. Key components of the model are the properties of the electrical contact interfaces and polymer ablation. A simple theoretical model for the contact interface is developed which yields scaling predictions for the speed of the current limiting event and it is shown that these are consistent with experiment for current values ranging from 10 to 10,000 A. These results suggest that conductor-filled polymer composite materials can provide a new non-mechanical way of rapidly limiting high power short circuit currents. This should have broad applications in the circuit protection industry.