On EM disturbances over digital equipment used for monitoring and events recording in a power system

Some characteristics of a digital equipment used for parameters monitoring and events recording in a power system are presented. The PC-XX/104 PROCESS CONTROL equipment (PC/104 compatible) refers to modular structures that use a central unit for data acquisition and processing. The basic constructive variants include 8 analogue inputs (4 for voltages, 4 for currents) with (non)unified signals. The equipment can also operate in systems where several equipment are connected in a FB232 compatible network to provide communication between equipment, separated by considerable distances. Synchronization between real-time clocks is required in this case. Specific matters related to the transmission modalities of EM disturbances that might influence data acquisition and processing are presented for these equipment. A special attention is given to the capacitive couplings that allow the transmission of disturbances exceeding the limits imposed by CISPR 11 norms. According to these norms, the solutions proposed for the improvement of the EMC corresponding to the digital equipment used for parameters monitoring and events recording in a power system are correct, certifying the obtaining of measurements which are immune to external EM disturbances.