Monitoring, diagnosis and control systems represent a variant of modern informational technologies used for broadcasting, data acquisition and visualization of primary technical data as well as automated long distance control of dynamic processes from amongst very diverse fields, ranging from metallurgical engineering, chemistry and energy engineering to nuclear engineering. This paper deals with an expert system whose primary purpose is monitoring, diagnosing and operating an AAR (Automatic Activation of Reserve) process. The presented system uses online acquired data and integrates the entire range of needed functions for the monitoring, diagnosis and operation of an AAR system at a software level. This system provides operators with global information, operative suggestions and detailed interpretation of real time operational status of monitored stations.