Investigation of an Atypical Sixth Harmonic Current Level of a 5 MW Wind Turbine Configuration

Current harmonic production of a 5 MW offshore wind turbine prototype is investigated on an onshore test site. On the PCC an atypical high level of the sixth harmonic current was measured. The evaluation of the existing configuration for future extensions with other wind turbines requires the investigation of this effect. Therefore the existing technical structure with medium voltage cable connection and parallel double-tuned harmonic filter is analyzed. The sixth harmonic generation through asymmetrical loads is shortly introduced. It is shown, that the reason for the high level of sixth current harmonic is not a series-resonance, but an undesired additional effect caused by the double-tuned filter, which damps the uneven harmonics. Measurements confirm the theoretical approach.