From the power plant to the plug socket
Electricity is distributed from the power plant to the consumer through the grid at various grid levels. Adaptation of the grid to the new requirements through increased power consumption and the integration of renewable energies are making urgent investments necessary.
Power lines are required to transmit power from the power plant to the consumers. This means that every electricity customer must be connected to the producers via the power grid. The grid are divided into grid levels. They serve various purposes according to their voltage:
- The highest level is the maximum voltage level with voltages from 220 kilovolts (kV, 1 kV = 1000 volts) to 380 kV. Due to the high voltage, large amounts of energy can be transmitted at relatively low currents. Small currents (amperes) mean small losses due to heat on the lines. For this reason, it makes sense to transmit electricity over long distances at this level. Even large power plants feed into the system directly on this level.
- A first rough distribution of the energy to the consumers takes place in the high voltage grid (usually 110 kV). Some large customers, such as industrial companies, are connected to the grid at this level. Medium-sized power plants feed into the system on this level.
- Different cities, for example, are supplied at the medium voltage level. The voltage is 1 kV to 36 kV. Municipal power plants feed energy into the grid on this level, customers at this level are industrial customers.
- Household customers draw electricity from the low voltage level with voltages below 1 kV (in households 230 or 400 V). Power supplies include, for example, private photovoltaic systems.
- These grid levels are connected by substations and transformer stations which transform the current to the respective voltage.
Keep the grid in balance – control energy
The special thing about the electrical energy is that storing it induces high losses. Put simply, the exact amount of electricity being consumed at any moment of the day must be generated at that time. A timetable must be drawn up which details when and how much energy is produced. This is based on consumption estimates, and for solar and wind energy also on estimates of actual generation. If there is a deviation from the timetable, control energy which compensates for the missing or excess energy must be provided. This is provided by power plants that can increase or decrease their power output within a very short time. The power consumption in the grid is monitored by the frequency in the entire European interconnected grid. If too much power is available, the frequency rises above the nominal value of 50 Hz, and conversely, if the power is too low, the frequency decreases. These fluctuations must be balanced for safe operation by the transmission system operators in Europe, who are the operators of the transmission lines of the highest voltage levels.
Investment in power grids – a necessity
The increased use of wind energy and other volatile energy sources leads to increased demand for control energy, as incorrect weather predictions also have an impact on production. In addition, the pipeline capacity for the redistribution of the electricity must exist throughout Europe. This means that if, for example, too much electricity is produced at the large wind farms in northern Germany, the grid must also be efficient enough to distribute this surplus to other countries. At the lowest grid level, on the other hand, private photovoltaic systems are increasingly supplying electricity, a completely new challenge for the distribution system operators, who are responsible for the final distribution of the electricity to the users. The grid in Austria was not designed to meet these requirements when it was built, which is why new concepts in grid operation are needed to meet the new requirements. These new concepts are referred to as smart grids. Furthermore, large investments in grid amplification and grid expansion are absolutely necessary to secure the reliability of Austria's electricity supply in the future.