Each time a new wind farm is connected to the network, there is a possibility that the harmonic currents generated from turbine might become amplified to an unacceptable level. This is a known issue on wind farm sites that has resulted in considerable breaches of IEC 61000-3-6 standard at MV/HV level and also in some critical cases given rise to a significant impairment of equipment reliability and to expensive equipment failure.
Addressing this harmonic issue at the design stage of wind farm development is vital to sustaining the high reliability of the installation in the future. It can be achieved through detailed software modelling of the network in a dedicated software package (DigSilent, SKM, DesignBase, ETAP), which allows the identification of resonance issues, calculation of harmonic content at the point of common coupling and selection of correct mitigation method if issues are identified. Early identification of the problem will also allow the most cost-efficient implementation.
It should be highlighted that sustaining of low harmonic emissions is required to prevent potential penalties from the utility side. Planning limits, brought in by EirGrid, are much more stringent than the IEC standard compatibility thresholds. It is unavoidable, to allow further uninterrupted expansion of the Irish grid. The same approach was taken in the UK where G5/4-1 engineering recommendation is now in place.
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