The upgrade concerns the drive system and in particular replacing the traction converter and integrating the relevant control technology. These are special-purpose vehicles that play an important part in rail network maintenance and conservation.Their job is to grind and clean the rail head and they are designed for operation on meter gauge and standard gauge tracks. The two Windhoff SF 60 railgrinders first entered service in 1999/2000. The power converters have become obsolete and need replacing as the availability of the vehicles can no longer be assured. Replacing the traction converters calls for an integrated design. The design of the new power converters will be based on the DPU 103. To ensure compatibility and functionality, the converters need to fit the existing installation envelope, taking account of the mechanical and electrical interfaces.