Online-measurement of the mains frequency

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2021-05-26 14:00:10

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.