to cope with all scenarios the system operator must have a range of ancillary reserves in the generation portfolio to maintain system stability regulation load following and to prepare for the worstcase scenario scheduling and dispatch of ancillary reserves is a complicated exercise ancillary reserves are generally divided into three categories according to how quickly they can ramp up or down its production to meet the demand they can ramp up or down production very quickly within a few seconds to minutes to respond to frequency disturbances it compares the plants actual production over a given period of time with the amount of power the plant would have produced if it had run at full capacity for the same amount of time