MF-MV-TrafoISO

To ensure a sustainable energy supply, solutions for the generation, distribution and consumption of electrical energy must be developed, implemented and integrated into existing systems. In contrast to conventional power generation, renewable energy sources also require the use of power electronic converter systems for their integration into the grid. These are usually designed at the low-voltage level (below 1 kV). The subsequent grid connection using a 50 Hz grid transformer takes place at the medium-voltage level (10 kV - 30 kV) for high system outputs in the MVA range. Such system structures are also used to integrate electrical storage systems, "Power-to-X" technologies, large charging infrastructures or hydrogen electrolysers. However, due to the low-frequency load and the use of conventional technology, the volumetric and gravimetric power densities are limited.

In the course of developing a sustainable energy system, reducing the use of limited and non-biodegradable resources is an important focus. Taking these aspects into account, the development of a compact and efficient high-performance converter for the medium-voltage level represents an innovative and forward-looking approach. Solid-state transformers (SST) offer a possible solution for this. SSTs are galvanically isolated high-performance converters that relocate the potential-separating transformer to the converter circuit. This transformer - the medium-frequency medium-voltage transformer (MF-MV transformer) - is operated with medium-frequency voltages in the kHz range, which leads to a significant reduction in the required volume and weight. This reduces the use of resources such as copper, magnetic core materials and insulating materials. However, simultaneous loading with voltages in the medium voltage range leads to critical stress on the component. The application-driven increase in performance also requires an increase in the system voltage in order to reduce current-related losses. The MF MV transformer currently represents a limitation for high-performance converters in terms of system voltage. The research and development of an MF MV transformer for operating voltages in the medium voltage range (> 6 kV) can significantly advance the integration of numerous space-critical applications - such as high-voltage electric battery storage systems, fast-charging systems and DC grids.

The overall objective of the "MF-MV-TrafoISO" research project is to develop and realize a compact and oil-free insulation system for MF-MV transformers for operating voltages above 6 kV and frequencies in the kHz range, which currently does not exist on the market in the configuration for industrial applications. The prevailing technical limitations of today's MF MV transformers are to be overcome as follows:

• Increasing the dielectric strength of oil-free insulation systems for MF-MV windings
• Increasing the thermal load capacity of the MF-MV transformer
• Increasing the volumetric and gravimetric power density of the component by optimizing the insulation system design

• Development of design rules for the design of a "dry" insulation system of MF-MV transformers > 6 kV
• Identification of basic winding designs for MF-MV windings
• Characterization, investigation and optimization of insulation materials and insulation systems for MF MV transformers
• Development of a suitable testing and measuring technique to determine the characteristic material parameters
• Development and testing of a prototype

The project is divided into several work priorities, which are handled by the respective project partners according to their core competencies. Regular exchange is essential to ensure a targeted approach.
The project partners are therefore in close and continuous contact in order to share results and findings from the individual work packages. This ensures rapid processing due to the interdependencies between the tasks. In addition, the current activities and their results are communicated to Project Management Jülich in the form of interim reports.