Disturbance emission of medium-frequency converter for melting ovens in MV-systems

The connection of medium-frequency converters applied for melting ovens to medium-voltage systems are investigated in this paper. The influence on the voltage quality, especially on harmonics needs special attention in this case. Measurements of harmonic currents and voltages for a time period of one week, determined by the characteristic of the load were carried out. It was recognized, that the harmonic voltage level depends significantly on the configuration of the feeding power system as well. This is due to the fact that parallel and serial resonances exist in the power system with resonance frequencies typically close to significant harmonics. Taking account of the worst conditions, the MF-converters cannot be operated without violating the emission limits and/or the compatibility levels defined in international standards. Solutions were investigated and applied which allowed the operation of the converter ovens without any additional equipment to be installed.