Grid calculation in transmission networks
Calculation of expansion scenarios and load flow control
The calculation of load flows is an essential part of the planning and operational management of electrical power systems. The basic tasks of a load flow calculation are to determine the node voltages and the resulting load flows via individual operating equipment in a specific generation and consumption situation. With the help of these results, limit violations and critical load situations can be identified and mitigated with appropriate countermeasures.
These critical load conditions can be evaluated over different time horizons. In addition to long-term grid expansion planning with time scales of 10 to 20 years into the future, there is also short-term operational planning for the following day. In both cases, the focus is on identifying grid bottlenecks and eliminating them.
For a well-founded analysis and evaluation of grid expansion measures, time-discrete simulations covering the entire year are carried out, taking into account different generation and load situations as well as the potential integration of new generation plants. The resulting transmission capacity in the existing grid and after implementation of planned expansion measures is quantified, as is the impact on the n-1 security of the grid. Such simulation-based grid development analyses are used to assess the supply reliability, operational safety and economic efficiency of planned infrastructure expansions.
In certain cases, despite ongoing grid expansion, it may be necessary to integrate so-called load flow control elements such as phase-shifting transformers or FACTS (Flexible AC Transmission Systems) into the grid in a targeted manner, thereby enabling further flexibility. It is crucial that these elements are sufficiently dimensioned for the multitude of different load flow situations.
Reactive power balance and voltage stability
While the analysis of active load flows often takes centre stage in grid planning considerations, the consideration of reactive power balance is becoming increasingly important. Reactive power considerations are essential for voltage stability in the grid. A comprehensive analysis of reactive power distribution and provision encompasses various technical measures, including:
• Use of reactive power compensation systems, such as choke coils and capacitor banks, for targeted voltage regulation and load flow control.
• Adjustment of the power factor and feed-in behaviour of decentralised feeders, especially in the case of power electronically coupled generators, for local or regional reactive power provision
• Grid technology structural parameters, such as the proportion of cables or overhead lines, which influence reactive power generation or absorption due to system conditions.
Future challenges and research priorities
A key challenge or opportunity for future considerations lies in the development and application of year-round, time-discrete simulations that map a variety of different generation and load situations. This type of simulation enables a realistic assessment of grid utilisation, identifies potential bottlenecks and allows for a reliable estimation of the effectiveness of planned infrastructure expansions.
In this context, the integration of real measurement data from wide area measurement systems (WAMS) is becoming increasingly important. WAMS provide high-resolution, precisely synchronised, angle-corrected measurements of voltage and current from the transmission grid.
In addition to the structural change in the energy system with regard to decentralised feeders, HVDC (High Voltage Direct Current) technology is increasingly becoming the focus of attention in Europe. Embedded in the AC transmission grid, there are already powerful DC transmission lines, which will be further expanded in the future and will accordingly influence grid planning considerations. By decoupling the physical behaviour of AC transmission (DC transmissions can be specifically controlled by the existing converters), these lines offer greater flexibility and lead to more complex considerations.
Projects
Ring Ktn 2 - HS- Ringplanung Ktn Teil 2
Ring Ktn 1 - HS- Ringplanung Ktn Teil 1
Q-Cable - Studie zur Blindleistungskompensation von Hochspannungskabeln
