Sytem Frequency Stabilty in the Pacific Northwest

System frequency in the interconnected power systems of the Pacific Northwest exhibits a random variation overlaying a background oscillatory characteristic with an occasional tendency for oscillations to build up to appreciable magnitudes. These oscillatory buildups, or periods of frequency instability, were familiar occurences which usually lasted only a minute or two; where they lasted for an appreciable period of time, practical methods were developed which enabled powerhouse operators to restore stable frequency conditions. Recent studies, tests, and consequent revisions of the Northwest interconnected system operating methods have apparently eliminated the tendency to excessive frequency oscillations. The program involved all of the major utilities in the Northwest Power Pool, and, eventually, affected the operation of almost all of the generating units in the Pacific Northwest.