Overhead line monitoring
For a flexible grid
A transmission system that adjusts to the weather
The feed-in of renewable energy is increasing dramatically during the energy transition. In order to transport the high load flows, all capacities of the power line system are needed. However, the transmission capacity fluctuates according to the season and the weather. At colder temperatures and due to the cooling effects of the wind, more electricity can be transported than at other times, such as hot summer days. This is due to the characteristics of the conductor cables: when the cables get hot, they expand and tend to sag more.
Thanks to overhead line monitoring, however, we have been able to significantly increase the load-bearing capacity of our electricity transmission system. This is possible by making exact calculations of the maximum possible load flows at the current weather conditions in order for the amount of slack on the cables to stay within the technical specifications. The parameters needed for these calculations, such as wind speed and ambient temperature, are measured directly at the electricity pylons. Based on the collected data, we then determine whether to transmit more or less electricity. If weather conditions are favourable, we are able to increase the load-bearing capacity of the power lines by up to 50 percent.
Weather-related network overload can be avoided
The feed-in of renewable energy is weather-dependent and thus very volatile. In the electricity transmission system, there are often situations in which the power lines are stretched to the limits of their transmission capacities. For example, there are times when more wind energy is fed in at the north end than the transmission system can transport to the south end. In this case, generation facilities have to be switched off in order to avoid overload (see Redispatch). Innovations such as overhead line monitoring are necessary in order to transmit more electricity and to ensure that the operation of the system remains stable – for the long term.
Keeping an eye on weather conditions
The weather is measured at weather stations mounted on the pylons, which are powered by solar batteries. The measured data is then transmitted via radio to Wendlingen to be displayed on the monitors at the System Control Centre (Hauptschaltleitung). Here, we can respond appropriately and increase the loads on specific lines.
How current load capacity can change
Transmission capacity depends on the wind and temperature
Adapting values to optimise utilization
Until 2002, a standard value of 35 °C and a wind speed of 0.6 m/s = 2.16 km/h was used for calculating the maximum capacity of the transmission system. However, as this condition rarely occurs in Germany, standard values were introduced for summer and winter of 35 °C and 15 °C respectively. As of 2019, temperatures and wind speed will be measured continuously for more effective utilisation of the transmission system’s capacity.
High Practical Relevance
The wind electricity from the north must be transported reliably throughout the entire country to reach the consumption-heavy south. This often pushes the electricity supply system to its limits. The management of weather-dependent overhead lines is thus an important step towards the successful integration of renewable energy. It allows for the more efficient utilisation of the existing system and prevents bottlenecks. At the same time, the expansion of the transmission system will be limited.
Around 340 weather stations have been installed in our transmission zone.
By the end of 2022 at the latest, we will install a comprehensive network of measuring stations throughout our transmission zone. This will enable us to take action when wind speeds or temperatures change, and control our transmission system dynamically and efficiently.
Overhead line monitoring is a measure geared towards the optimisation of the transmission system and thus a component of the NOVA principle, which we take as our guideline for transmission system development.