Ungrad - ABB Relays AG, CH-۵۴۰۱ Baden/Switzerland
IEEE - ABB Relays AG, CH-۵۴۰۱ Baden/Switzerland

Events in the past show that some protection problems are hard to solve with the information only available on the relay location. One of these cases are the unit protection which alone cannot protect a machine against damage (e.g. in the shaft) when certain faults occur in the HV etwork near the station. The action of line protection influences the machine protection, the appropriate tripping is also dependent on other machines and lines and also on the actual network situation. Not only local data but global data are needed. Dedicated protection and programmable logics were proposed and implemented for this task. Such equipment very soon becomes quite complicated, losing the required flexibility and the necessary reliability. Normally, numerical relays have a serial interface. Microprocessor based substation control provides both global data and communication links. Therefore, the framework of a substation control system coordinating the control and the protection provides all facilities to solve the problem of machine protection generally. Basic considerations, the concept and examples are presented.