The system comprises: a digital data output means for inputting analog ac electrical values and outputting digital data; means of protection and control (23-1) for inputting the data from the digital data output means (28) and for controlling, monitoring and protecting the main circuit components of sub-station (25); Component control and monitoring means (30) for receiving commands from the means of protection and control (23-1) or the control equipment and sub-monitoring station (4) for controlling and monitoring the main circuit components of sub-station; and a communication means (7). Means of digital data output (28), the means of protection and control (23-1) and the means of control and monitoring component (30) are incorporated in their main circuit components of sub-station (25 ) correspondents.