Common Mode Disturbances at Medium Voltage Transformers

In industrial applications, a transformer is the interface between medium and low voltage grid. At this coupling point, disturbances may transmit to the supply grid. Hence, an influence on other electrical loads in the same supply grid may occur. Power electronic components in electric drive systems with high switching frequencies and high voltage slew rates of the switching transitions are able to excite unexpected disturbance currents through parasitic paths. According to legal regulations, the system operator is obliged to keep them in specified limits. In this paper, measurement data recorded at a medium voltage transformer in several typical grid applications with different filters are analysed to show the coupling from low to medium voltage grid and to identify advantages and disadvantages of different commonly used topologies.