In the first few seconds following the loss of a large
generating plant, the frequency dynamics of the system are
dominated by the inertial response of the online generation.
Synchronous machines inherently contribute some of
their stored inertial energy to the grid, reducing the initial
rate of frequency decline. In synchronous machines, the
inertial response is inherent to the machine physics and is
not controllable. Slower initial rate of frequency decline
can be helpful, allowing slower governor actions to nonetheless
stabilize grid frequency. In some smaller systems,
the initial rate of frequency decline is quite important. This
does not appear to be as much of a concern in the major
U.S. interconnections.