METHOD AND PROTECTIVE DEVICE FOR RECOGNISING A SYMMETRICAL SHORT-CIRCUIT IN A MULTI-PHASE ELECTRICAL POWER SUPPLY NETWORK

摘要

The invention relates to a method for recognising a symmetrical short-circuit in a power supply network, wherein with a first protective device (15d) a first section (C) of the power supply network is monitored for a symmetrical short-circuit and with a second protective device (15a) a second section (A) is monitored for a symmetrical short-circuit, wherein the second protective device (15a) is arranged as a reserve protective device so that when a symmetrical short-circuit in the first section (C) is recognised, after a predetermined lag time has elapsed it emits a shut-off command to a power switch (14a), and wherein an oscillation recognition unit (24) is provided which emits an oscillating signal which blocks the emission of the shutoff command by the second protective device (15a) if an oscillation in the power supply network has been recognised. In order to provide a possible means by which external symmetrical short-circuits can be disconnected independently of an occurring oscillation, according to the invention in the case where the second protective device (15a) has recognised a symmetrical short-circuit in the first section (C), before the oscillation recognition unit (24) has recognised an oscillation in the power supply network, the shut-off command is emitted independently of the presence of an oscillating signal if the lag time has elapsed.