System control logic

This chapter discusses system control logic. In an island system, the total MW and MVAR demand is determined by the connected load and the system voltage and frequency, and the total generating load must match these values. To provide a stable system with closely controlled voltage and frequency, it is necessary to ensure that adequate prime mover power is available to meet all steady MW demands plus any MW demands as a result of transient conditions such as accelerating motors and loads. Starting a generator set involves several distinct procedures: monitoring all conditions healthy, starting and accelerating the prime mover, exciting the generator and synchronizing with the supply, and loading the set to the required MW and MVAR values. Most prime movers provided for generators have an automatic start system with inbuilt checks to ensure that safe conditions are being met and operations such as purging or load applications are correctly carried out. When a generator set is started by the PMS, or manually by the operator who then transfers control to the PMS, that system will then control the generated MW and MVAR on the basis of some predetermined criteria.