Reserve power

The power system is continually subjected to
unexpected load changes
The generating units supply about 85-90% of
their capacity maintaining the remainder for
emergencies
Some units are kept in the hot status to be
connected to the network as fast as possible

The need for reserve power arises due to some
abnormal conditions in power system
Sudden unexpected increase in the load demand
Forced outage of generators or other equipments
due to stability problems
Underestimating the load demand due to some
errors in the load forecasting
Local shortage in the generated power (e.g. due
to the outage of a transmission line)

The choice of the operating and standby unit as well
as the distribution of reserve power on different power
plants depends on the following factors:
The start up cost: depends on the start up time “the
time interval between the order of starting to the
moment where the unit delivers power to the network”
Units with high start up cost have not to be frequently
switched on and off. Such units can provide hot
reserve power but not cold reserve power.