Transmission loss
The transmission loss , also called network loss , is the difference between the electrical power generated in the power plant and the electrical power used. The transmission losses in three-phase systems in Central Europe amount to around 6% of the network power, averaged over the various voltage levels. In Germany, around 5.7% of the electrical energy provided in the electricity network is lost due to grid losses . From 2000 to 2012 the transmission loss was reduced by approx. 28% (from 34.1 to 24.6 TWh). Transmission losses arise mainly from the ohmic resistance of the transmission lines. The current flowing through the cables causes the cables to heat up, also known as ohmic loss. In addition, voltage-dependent losses due to corona discharge , losses in the context of reactive power compensation and losses in the power transformers also play a role in the grid losses .
System comparison
In a typical overhead line operated at 380 kV with bundled conductors 4 × 564/72 Al / St , which is designed for the transmission of a maximum of 1.1 GW per three-phase system, current-dependent ohmic losses of 11.6 MW and 245 kW occur over a length of 100 km of voltage-dependent losses, primarily as a result of the corona discharge. At the maximum power, this results in a transmission loss of just over 1% of the power fed in per 100 km. The dominant ohmic losses could apparently be reduced slightly by larger conductor cross-sections, but the weight increases and comes up against economically unacceptable limits in the cost of overhead lines and mast structures in relation to the energy costs.
To reduce the absolute line losses and to fulfill the N-1 rule , double systems with two three-phase systems on a mast are often operated in parallel and only with less than half the maximum power per conductor system. In the event of a short-term failure of a system, for example in the case of an earth fault that frequently occurs on overhead lines, resulting in a line interruption and automatic reconnection , the second transmission system can take over the entire transmission capacity without interrupting the supply.
The relative losses of around 1% over a length of 100 km remain roughly constant with an overhead line even with lower transmission capacities. In the case of underground cables, on the other hand, the load-independent compensation losses are added as a major loss component, while the ohmic losses are reduced because larger conductor cross-sections are selected for underground cable systems. A 380 kV underground cable system similar to the above overhead line has an approx. 15 times higher reactive power requirement due to the higher capacitive coating , which leads to around 25% higher losses with a typical annual load of 30% in the underground cable system compared to the overhead line system.
380 kV lines represent lines with the lowest losses in the power grids common in Central Europe, based on the maximum output. At lower voltage levels such as the 110 kV distribution system and especially in the medium voltage network , greater relative losses occur per 100 km, which is why these voltages are used for regional distributions over shorter distances. Even with the transformation between the different voltage levels, there are primarily thermal losses in the power transformers, which is why there is a total transmission loss of approx. 6% in the power grid with the average distances between consumer and power station common in Central Europe. With greater spatial distances between consumers and power plants, there are higher overall losses, which is why it makes sense to build power plants as close as possible to the consumers.
reduction
In order to keep the effective transmission losses low, the operating voltage is selected as high as possible in order to reduce the dominant ohmic losses with the same transmission power. For example, in Canada, parts of the three-phase network of Hydro-Québec work with voltages of 735 kV.
In addition, high-voltage direct current transmission (HVDC) is used for long distances , which works with direct voltages of up to ± 800 kV. The additional converter losses that occur with HVDC as a result of converting three-phase alternating current into direct current and back again into three-phase alternating current are compensated for by the reduced transmission losses from certain line lengths.
Individual evidence
- ↑ Generation. Balance sheet - monthly report on electricity supply. In: Balance. Federal Statistical Office, 2019, accessed on July 10, 2019 .
- ↑ Energy consumption in Germany in 2012, p. 30 . Website of the AG Energiebilanzen. Retrieved November 7, 2013.
- ↑ a b Loss and energy loss estimate for the 380 kV line construction project Wahle - Mecklar (PDF; 69 kB), BR Oswald, University of Hanover, November 1, 2007.