Measurement of the mains frequency
The European grid ranges from Portugal over Poland to Turkey. It is fed with alternating current, which has a frequency of approximately 50.0 Hz. The grid frequency (power frequency) is the same allover the grid, with the exception of local short-term swings.
At every moment the amount of electricity that is generated by the power plants must be equal to the amount von energy that is taken from the grid by the consumers. If the power demand increases beyond the power supplied by the generators, then the power deficit between supplied and removed power is taken from the rotational energy of the generators. They will thus slower, which means the grid frequency decreases.
Various staggered control mechanisms provide the adjustment of the output of the generators to regain the 50.0 Hz when a deviation from the desired frequency occurs. Shown on the left is the current mains frequency. In order to represent the low frequency changes in detail, the scale hat to be set really large. In normal network operation there are regular deviations up to 0,150 Hz, the primary control power is fully used at a deviation of 0.200 Hz.
The primary control is the first step in the mechanism of bringing the frequency back to the 50.0 Hz. If the deviation from the nominal value exceeds ±10 mHz, then the primary control is activated. In a range of ±10 mHz the frequency can flow free, above or underneath this value the primary control is activated linear. This 10 mHz is the same as the allowed measurement error of 10 mHz, to prevent primary control from running with a false sign.
|Utility frequency: ? Hz|
Phase angle to 50.0 Hz: ? °
Date and time (UTC): ?
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.
To grasp the degrees of freedom in the provision of primary control power
presented by the four German TSOs, an accuracy of ±1 mHz is an
advantage over the previously required ±10 mHz, since the difference between
permissible measurement uncertainty and measurement uncertainty of the device,
can be used for example for a charging management of battery storage.
The ENTSO-E member countries should establish a plan until the end of 2015 to retrofit
the dispersed generation to enhance the tolerance band in distributed energy systems
such as wind and PV systems to 47.5 Hz to 51.5 Hz.
To clarify the question "how stable is the mains frequency", data of the last 13 months was
analyzed (July 2011 to July 2012). The greatest fluctuations occurred regularly on the hour change,
which is caused by the use of products of hours. The limits of frequency range allowed in normal operation
(49.8 Hz to 50.2 Hz) were never reached or exceeded in this period.
Forecast errors are caused by unexpected consumer behavior, power outages and loss or reduced supply by
conventional and renewable power plants. If the forecast errors in consumption and production would occur
randomly, then the analysis of the frequency deviations from 50.0 Hz would show a steady noise.
Instead, the Carpet plot
shows systematic frequency variations on the hour change. The greater the
change in load, the greater the deviation.