Repetitive current limiter based on polymer PTC resistor

Until now, one shot devices as fuses have been used for limitation and interruption of short-circuit currents. A repetitive current l i m i t e r (CL) has been developed using a polymer composite as the functional part of the device. The CL is able to limit and interrupt a fault current flowing through it by a fast increase of its resistance by eight to ten orders of magnitude. Short-circuit tests were carried out on an AC generator circuit with a prospective test current of 16kA,,,, U = 220V,,,, which was limited to 3 kA i n peak. Also further short-circuit tests were performed using a capacitor battery with variable prospective currents between 0.7 and 78 kA,,,. The limitation of the short-circuit current by the CL i s caused by the thermal expansion of the matrix of the polymer composite, which leads to a forced separation of the conducting filler particles. T h i s fast motion in the sub-ms range with amplitudes o n a pm-scale is monitored by using a fast laser distance sensor. The necessary mechanical expansion of the polymer composite for a limitation of the current to a negligible value i s 40 pm within 700 ps.