Should one of the GTGs operate in the DLN mode, it is no
longer possible to have identical load sharing among the
machines since it is necessary to ensure that the DLN
machine operate far from its DLN limit. Secondary regulation
is used to prevent operation close to the DLN limit. This is
achieved by considering two different values of minimum
output for the DLN turbine. At low load the DLN turbine
minimum output limit will be set in the PMS to a relatively
small percentage of the turbine’s nominal rating. Operation of
the DLN turbine can then be at the same % output as all other
GTGs and STGs since at light load the output will be far below
the DLN limit shown in Fig. 5. When the plant load is high
however, the DLN turbine must be set to operate well above
the DLN limit. In this case the minimum output limit set in the
PMS is the DLN limit based on the curves of Fig. 5.
Secondary regulation will ensure that the % load within this
new range (DLN limit to maximum output) is the same as the
% load of all other GTGs, their range however, being between
≅0 and Pmax. This is shown in Fig. 6.