Abstract: A method for the detection of short circuits in electrical installations, in particular on railway contact wires, comprising generating a measuring signal dependent on the derivative with respect to time of the monitored current, comparing the measuring signal with at least one limit value, determining the time for which the measuring signal exceeds a limit value, comparing the time with a preset time interval, initiating indication of a short circuit when the time for which the measuring signal exceeds the limit value also exceeds the time interval, checking the measuring signal on the occurrence of a decrease following an initial increase and on the occurrence of a subsequent increase, and generating a blocking signal inhibiting indication of a short circuit as a function of the occurrence of such a subsequent increase.

Abstract: A method for the detection of short circuits in electrical installations, in particular on railway contact wires, comprising: generating a signal corresponding to the derivative with respect to time of the monitored current, comparing the generated signal with at least one limit value, indicating a short circuit if the generated signal exceeds a limit value, monitoring the behavior of the monitored current for the occurrence of a criterion indicating the probability of a short circuit, triggering a replica signal corresponding to the behavior of the monitored current from the movement of occurrence onwards as a function of the probability criterion, comparing the replica signal with at least one limit value, and indicating a short circuit if the limit value is exceeded.

Abstract: A circuit which compensates for interference signals when monitoring conditions such as overcurrents and the like in a larger network. The circuit includes a current-signal branch and a compensating branch, the latter fed with an interference voltage and containing a variable gain amplifier. Both branches of the circuit are coupled to a signal superimposing element in the form of a summing amplifier, the output of which is applied to a polarity comparator. The polarity comparator, which is three-state device, forms a portion of a feedback network for controlling the gain of the variable gain amplifier.