Inertial Response of an Electric-Power System

With the increasing penetration of converter-interfaced generation in the electric-power systems, the word “inertia” became spoken frequently. System operators tend to monitor system inertia in different ways to be given information on system frequency sensitivity to power imbalances. As a property, inertia can be unambiguously attributed to any physical object. However, in this paper we argue that this is not so straightforward for the electric-power system, especially having in mind a large, continental-wide system with numerous rotating machines. We rather suggest referring to “inertial response” of different machines to a specific incident causing a power imbalance. In fact, what operators are interested in are the frequency changes that follow a particular event, inertia being only a mathematical means to describe the relationship between them. And due to a lot of electro-mechanical dynamics involved, frequency and inertial response are both a time and location varying quantities.