The grid frequency indicates the frequency of the change in the polarity in the AC network. This is measured in hertz (Hz). In Germany and in Europe, there is a constant network frequency of 50 Hertz. Variations in frequency provide information about the relationship between electricity generation and electricity demand.
For a functioning power grid, the grid frequency must always be kept stable. This requires synchrony among all power producers on the one hand and a balance between supply and demand on the other. In order to be able to compensate for fluctuations, a functioning control energy system is also required.
Monitoring the network frequency is important in order to identify voltage drops early on and thus prevent power outages.
The grid frequency results from the AC voltage that prevails in the power grids. AC voltage is a voltage at which the polarity changes continuously and the current periodically changes its correct values. Two poles with different charges generate a voltage field, which forms the basis for the current to flow. The changes in direction cause sinusoidal voltage waves. The frequency is calculated from the frequency with which the alternating current changes its direction per second. In the German power grid, which has a grid frequency of 50 hertz, there are 50 voltage waves in one minute and the voltage changes polarity one hundred times the polarity.
For our European interconnected network to function properly, the network frequency must always be kept constant. To achieve this, there must be a continuous balance between production and consumption of electrical power. If too much or too little electricity is fed into the grid, there may be fluctuations in the frequency and deviations from its target value of 50 Hertz. Slight fluctuations are normal in practice, which is why a tolerance range between 49.8 and 50.2 hertz has been defined.
However, an excessive increase or fall in grid frequency can have the result that the function of numerous electrical devices can be affected and the generators of connected power plants may be damaged. This is because the speed of the rotors of all generators in the network is set to exactly 50 Hertz.
In order to keep the grid frequency stable, it is primarily necessary Control energy. For activation in Germany, the transmission system operator is responsible. If the frequency falls below 50 hertz, additional feeds into the network are necessary; this is known as positive control energy. If there is too much electricity in the grid and the frequency rises above 50 Hertz, this excess power is removed and is referred to as negative control energy.
In order to prevent a grid collapse in the event of excessive fluctuations, power plants automatically disconnect from the grid above the tolerance range. This happens both when the network frequency is too low and too high.
At a frequency lower than 47.5 Hertz, all power plants are disconnected from the grid and there is a complete breakdown of the power supply and thus to nationwide blackouts.
Due to their fast response times and the ability to provide both negative and positive control energy, battery storage systems are particularly suitable for providing primary and secondary control power. If the grid frequency drops below 50 Hertz, battery storage systems feed additional power into the grid. At an increased grid frequency of over 50 Hertz, they draw electricity from the grid. The services requested depend on the amount of fluctuations.
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