Structure of the power gridQuality of supply
Besides the permanent availability of electric power, the quality is also an important criterion. Electrical systems do not operate correctly with fluctuating voltages and frequencies and in the worst case can be damaged. The frequency and voltage are therefore strictly limited in the grid. The voltage at the end user may vary within a voltage range of +/- 10%; the frequency should always be between 49.8 Hz and 50.2 Hz. In order to achieve that, the grid operators keep a reserve of balancing power available. If a greater output is required from the grid, this can be provided by the balancing power.