Power system instability — What relay engineers need to know

This tutorial paper discusses what relay engineers need to know about power system stability. The understanding of power system stability has taken on renewed importance because it has played an important role in recent blackouts and power system events investigated by NERC. The paper discusses the four basic types of power system instability: Voltage instability, Steady-state instability, Transient instability and Dynamic instability. The paper relates how these various forms of instability relate to generator and transmission system protection. The paper also discuss system schemes used to address instability including: Generator Fast Valving, Generator Tripping, Generator High speed Excitation Systems, Independent Pole Circuit Breaker applications and various types of Special Protection Schemes (SPS). Recent system instability events have interacted with both transmission and generation protection in ways not always envisioned by the protection engineer.