For limitation and interruption of short circuit currents in medium voltage (MV) applications, fuses and circuit breakers are widely used today. Fuses exhibit excellent current limitation, but work only for a single shot. Circuit breakers are multi-operation devices, but allow several periods of the short circuit current to pass. Based on new PTC materials (positive temperature coefficient of resistance), we propose a new current limiting device for MV applications, which offers the chance to combine the advantages of fuses with the advantages of circuit breakers: a fast current limitation with a repetitive operation. The active material consists of conducting particles in a polymeric matrix. Its challenging property is a change on resistivity by eight to ten orders of magnitude upon temperature increase. This allows the limitation of available short circuit currents in a stable insulating state for a long period of time. The device consists of a series connection of PTC resistors with varistor elements connected in parallel, which serve for a perfect voltage distribution. Using this principle, repetitive current limitation of prospective currents of 4 to 14 kA within about 1 ms could be demonstrated at circuit voltages up to 12 kV.
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