Abstract
Rate of change of frequency (RoCoF) is a critical parameter in modern power systems, particularly in grids with declining inertia and increasing penetration of inverter-based resources. This chapter provides a summary of RoCoF estimation techniques and their applications in power system operations. The chapter covers three primary RoCoF applications: (i) system inertia estimation, (ii) operational and ride-through limits, and (iii) protection and control systems that use RoCoF as an input. For inertia estimation applications, high-accuracy methods with as little temporal smoothing as possible is desirable to capture instantaneous RoCoF values. Conversely, the monitoring of operational RoCoF limits requires sustained RoCoF measurements over longer defined time windows (such as 500-ms or 1-s) that reflect equipment withstand capabilities. Protection and control applications demand fast, reliable RoCoF detection with appropriate filtering to avoid spurious operation while maintaining security. The selection of appropriate RoCoF estimation methods is shown to be highly application-dependent, with no universal optimal approach existing across all use cases.