Transmission of protection commands to a remote tripping device

The present invention is concerned with the transmission of protection commands to a remote tripping device over an analog signal link with a limited number of tones or frequencies (F 1 , F 2 , F 3 , F 4 ). Different operating principles involve a number of frequency detectors ( 41, 42, 43, 44 ) depending on the number of commands (A, B, C, D) that are to be transmitted either alone or in combination. In order to transmit a maximum number of protection commands with a minimum number of tones/detectors, two of the abovementioned distinct operating principles are assigned at least one common tone. A prioritizing mechanism is established for preferring certain related protection commands belonging to a common application. Upon reception of a signal coding a combination of protection commands, it is possible to detect individual protection commands in accordance with different minimum safety and/or security values. A protection command can thus always be transmitted optimally for the intended application, i.e. the parameters of safety and/or security, dependability and transmission time are individually configurable for the protection command.