Device for monitoring current failure in at least one phase of a three-phase load

摘要

A device for monitoring current failure in at least one phase of a three-phase load contains a signal generator circuit which is connected to the phases and derives measurement signals from the phase voltages which measurement signals are compared with a reference voltage in a comparator circuit which is connected to the signal generator circuit. A switching stage is controlled by the comparator circuit, by means of which switching stage the voltage supply to the three-phase load is switched off when a current failure is detected in one phase. In order also to be able to monitor three-phase loads which induce an e.m.f. in one phase in the event of a current failure, the signal generator circuit contains at least one filter device which produces measurement signals corresponding to the frequency spectra of the phase voltages.