Optimizing rectifier systems for Zurich’s tramway: assessing harmonic impact on the medium voltage grid

For many years, the city of Zurich’s tramway network has been supplied with DC voltage through solid-state rectifier systems. 6-pulse rectifiers, powered by a medium voltage (MV)/low-voltage (LV) transformer, are used for AC to DC conversion. The combination of two 6-pulse rectifier systems results in a 12-pulse rectifier system, which offers higher power output and lower harmonic emissions, but at increased costs. Both configurations can be found in the distribution grid of the city of Zurich. This study analyses, from a power quality point of view, whether the future concept should be changed towards only 12-pulse rectifiers. Generally, it can be said, that the emission limits of both configurations are not exceeding the limits stipulated in the DACHCZ guidelines. However, especially with the upcoming decarbonization of mobility and heating systems, PQ-monitoring in the MV grids should be intensified as more and more large installations (e.g. heatpumps or charging infrastructure) are expected to be connected.