ABSTRACT
In the modern alternating-current electrical grid, electrical current oscillates with a nominal frequency of 60 Hz in North America and parts of South America, or 50 Hz in most of the rest of the world. The grid frequency is constant when the supply of electric power (generation) matches the demand (load), but the frequency falls when generation is lower than load and rises when generation is greater than load. There are a few other technical reasons that cause the frequency to fl uctuate, but the imbalance between generation and load is the main one. If the frequency deviates too far from its nominal value, the grid can become unstable. Grid operators prevent that from happening by adjusting generation to match the changing load – they continuously start up or shut down power plants or adjust their power output.
