Electricity Quality

Frequency stabilization of large interconnected power systems allow line-operated clocks to keep accurate time. Network operators will regulate the daily average frequency so that clocks stay within a few seconds of correct time. In practice the nominal frequency is raised or lowered by a specific percentage to maintain synchronization. In the continental European UCTE grid, the deviation between network phase time and UTC is calculated at 08:00 each day in a control center in Switzerland, and the target frequency is then adjusted by up to ±0.02% from 50 Hz as needed, to ensure a long-term frequency average of exactly 3600×24×50 cycles per day is maintained.[14] In North America, whenever the error exceeds 2 seconds for the east, 3 seconds for Texas, or 10 seconds for the west, a correction of ±0.02 Hz (0.033%) is applied. Time error corrections start and end either on the hour or on the half hour.[15][16] A real-time frequency meter for power generation in the United Kingdom is available online.[2] Smaller power systems may not maintain frequency with the same degree of accuracy.


The frequency of large interconnected power distribution systems is tightly regulated so that, over the course of a day, the average frequency is maintained at the nominal value within a few hundred parts per million.[17] While this allows simple electric clocks and motors, based on synchronous electric motors, to keep accurate time, the primary reason for accurate frequency control is to allow the flow of alternating current power from multiple generators through the network to be controlled. The trend in system frequency is a measure of mismatch between demand and generation, and so is a necessary parameter for load control in interconnected systems. Regulation of power system frequency for timekeeping accuracy was not commonplace until after 1926 and the invention of the electric clock driven by a synchronous motor.