The interaction of consumers and generators in the UCTE grid leads to deviations of the grid frequency from its set point of 50 Hz. The positive and negative frequency deviations not always achieve equilibrium resulting in significant long term average deviations from the set point frequency. A long term balance is important for historical reasons, since mains-operated clocks (e.g. oven clocks, many radio alarm clocks, etc.) use the grid as clock and timer. How do consumers use the network time and how does the network time work?

The grid time is based on the base frequency of our electricity grid in Europe. In the nominal state, the voltage in the power grid oscillates 50 times per second. These fifty oscillations are the time keeping pulse for mains controlled clocks. Assuming, that the grid frequency would be higher than the target frequency, the grid time would run faster than the coordinated world time (UTC). Conversely, if the grid were to slow below the target frequency of 50 Hz, the grid time would run slower than the standard time. Within the 24 hours of a day fluctuations may amount to several tens of seconds, but the long-term average of the mains time matches the coordinated world time quite precisely.

Mains time steering

The specifications for controlling the UCTE grid time come from the Swiss electricity grid operator Swissgrid. In order to be able to readjust the grid time in the event of deviations, the following rules are applied:

If the mains time differs compared to UTC by more than +20 s at the end of the day, the frequency set point is reduced by -10 mHz to 49.990 Hz.
In case of a negative mains time deviation of -20 s compared to UTC, the set point frequency is increased by +10 mHz to 50.010 Hz.