Governor-responsive units have speed governors with
a droop characteristic and some available headroom (see
“Governor Basics”). These plants increase power output to
support the grid when frequency declines. Other generation
does not. This includes some generation that is operated so
that it cannot increase output for frequency decline but can
decrease output for overfrequency conditions. In the Western
Interconnection, these are referred to as base load units.
Other generators may either lack governors or be operated
with their governors disabled