CONTROLE DE LINHA DE TRONCO

In a method of and apparatus for obtaining a correction value (KWC) for the deviation between actual power usage and desired target power usage during a time period (CT), the time period is divided into a plurality of time segments. After each time segment, a fraction (FIC) of time into each time period (CT) is measured (43), and the fraction (FIC) is multiplied (41) by the target power usage (KWM) to obtain a value corresponding to the fraction of the total power usage during the cycle. Also after each time segment, the total amount of power usage or energy (KWA) which has actually been used is measured (10, 20, 38) and a difference is taken (51) between the total power usage (KWA) from the beginning of the period (CT) and the fraction (KWM.FIC) of the target power usage from the beginning of the period. This value is then divided (52) by the amount of time (CT-FIC) remaining in the cycle to obtain the correction value (KWC). The correction value (KWC) can be processed and utilised to control an internal generator for a plant or to take other corrective action.