Measurement of the utility frequency
The mains frequency is in all countries, which are directly connected to the synchronous grid, the same (exept short-term fluctuations). These are Albania, Belgium, Bosnia-Herzegovina, Bulgaria, Denmark, Germany, Estonia, France, Greece, Italy, Croatia, Latvia, Lithuania, Luxembourg, Macedonia, Montenegro, Netherlands, Austria, Poland, Portugal, Romania, Switzerland, Serbia, Slovakia, Slovenia, Spain, Czech Republic and Hungary. Due to the large east-west extension the sun takes about 3.5 hours to wander over the area, in summer the sun can bee seen about 18 hours a day
Algeria, Morocco, Tunisia, Western Sahara and Turkey are synchronous with the European grid, too. The other members of ENTSO-E are connected via High-voltage direct current (HVDC) power lines to the synchronous grid and have therefore independent frequencies.
The grid frequency in the synchronous grid of Continental Europe has a nominal value of 50.0 Hz. In the short term a change of the nominal value by ± 10 mHz is possible to keep the gridtime of the network low.
If the deviation from the nominal value exceeds ±10 mHz, then the primary control is activated. The 10 mHz is the allowable measurement error of 10 mHz to get a dead zone which prevents primary control from delivering power with the false sign.
From ±10 mHz to ±200 mHz the primary control is activated proportional from 0 % to 100 %. Long-term maximum deviations of ±180 mHz are allowed, for short periodes even ±200 mHz are ok. The allowed mains frequency range in normal operation is thus obtained at 49.8 Hz to 50.2 Hz. (ENTSO-E Operation Handbook Load-Frequency Control and Performance)
In case of the breakdown of generation capacity or large consumers, short term deviations until 800 mHz are allowed (49.200 Hz to 50.800 Hz). With higher deviations a massive grid failure is very likely. Then the first step is dropping some consumers or producers (load shedding), if even this fails, then the network ceased operations (blackout) and the network built up afterwards.
The necessary primary control power depends on the network size and the largest generating units. The continental European Transmission System Operators review annually the primary control power kept available, this is for several years 3,000 MW. This corresponds to approximately 15,000 MW per Hz deviation in the range of ±10 mHz to ±200 mHz. Together with the frequency dependence of the consumers the ENTSO-E experience has shown that there is a of 19,500 MW / Hz.
The primary control is a proportional controller with stationary deviation, it only can stop the frequency from ascending or descending. But it cannot move the frequency back to the nominal value. This is the task of the secondary control, which determines a frequency deviation integral and works against it. By using the secondary control the frequency deviation decreases, and the primary control gets back its performance. So it can be used for its next use (see ENTSO-E Operation Handbook Load-Frequency Control and Performance).
The expression "utility frequency", "grid frequency", "mains frequency", "power frequency" and "line frequency" are synonyms for the frequency of the electric generators, which can be measured in electric supply networks. It is 50 Hz in Europe, USSR, India, China, Australia and Africa, and 60 Hz in USA and the northern parts of south america.