Interaction of machine and line protection within a coordinated substation control system

Events in the past show that machine protection alone cannot protect a machine against damages (e.g. in the shaft) when certain faults occur in the HV (high-voltage) network near the station. The action of line protection influences the machine protection. The appropriate tripping is also dependent upon 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. This equipment very soon became quite complicated, losing the required flexibility and the necessary reliability. Numerical relays have a serial interface normally. Microprocessor-based substation control provides both global data and communication links. Therefore, the framework of a substation control system coordinating control and protection allows all facilities to solve the problem of machine protection generally. Basic considerations, the concept, and examples are presented