Performance issues in integrated control and protection systems for substations

The integration of control and protection functions into the same terminal devices has been a strong trend of evolution for substations. As a rule, a base platform supporting a large set of protection functions is also shared by a growing number of supervisory, data acquisition and control functions, so that the overall price of such a device becomes very competitive regarding the traditional standalone components. However, protection functions are very computer demanding if high speed and accuracy are desired for timing functions. Such accuracy is a base requirement to keep low the coordination time intervals (CTI) between protective relays in distribution systems, which in turn are detrimental for the time to clear faults close to the substations. On the other hand, control functions demanding a fast exchange of information between distributed relays and local control managers, require safe and still fast protocols. These protocols are also very computer demanding if communication speed is desired. In this paper, a set of performance requirements for both protection and automation are outlined. It is also shown that only a multiprocessor platform can fulfil those requirements for the time being