Blackouts, electrical systems and common sense

摘要

Before modern computers became available, it was pretty difficult to develop load flow studies. Therefore, "base load" studies were developed and seat of the pants methods were used to operate a "real time" system using "base load" studies. These old time methods recognized that there are only four variables in electrical systems―voltage, current, phase angle and frequency. And, when all possible abnormal power system conditions are evaluated, only three conditions are relieved by instantaneous protective relay action (see table)―namely, short circuits, out of step, and low frequency.