Repetitive current limiter based on polymer PTC resistor

Abstract

Until now, one shot devices as fuses have been used for the limitation and interruption of short-circuit currents. A repetitive current limiter (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 16 kA/sub RMS/, U=220 V/sub RMS/, which was limited to 3 kA in peak. Also further short-circuit tests were performed using a capacitor battery with variable prospective currents between 0.7 and 78 kA/sub RMS/. The limitation of the short-circuit current by the CL is caused by the thermal expansion of the matrix of the polymer composite, which leads to a forced separation of the conducting filler particles. This fast motion in the sub-ms range with amplitudes on a /spl mu/m-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 is 40 /spl mu/m within 700 /spl mu/s.