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 worst-case 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 plant's 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.