Automatic Load-Frequency Control (ALFC) Scheme for Sri Lankan Power System

The quality of power in any AC system is primarily determined by system frequency which is a single factor throughout the whole system. The system frequency depends on instantaneous balance between the generated active power and consumed active power. In Sri Lankan system, dynamic changes in demand is tracked by single hydro unit which is operated on fast droop setting (e.g. 1.6 to 2%). All the other connected machines are set on slow droop (e.g. 4 to 6%) which provides dynamic free-governor support for primary regulation controls. The short-term demand change is monitored and the corresponding secondary regulation is triggered by plant operator within the limit of frequency controlling machine. In contrast, the medium- or long-term changes on demand are closely monitored and corresponding secondary regulation is verbally triggered by National System Control Centre (NSCC) on regular intervals. Based on this verbal instruction, the MW set point or speed reference of a turbine is changed by plant operator. Such a human-intervened conventional control scheme adversely affects the quality of the system frequency in large scale. This paper summarizes the research done to adopt ALFC scheme for Sri Lankan power system with dynamic tuning approaches in order to have approximately close control of system frequency.