Ensuring Grid Code Harmonic Compliance of Wind Farms

Abstract

The prevalence of cabled infrastructure associated with wind farms, combined with the increase in power-electronic interfaces in wind turbines and reactive power plant, has highlighted the pervasive nature of harmonics on electricity networks. Insufficient consideration is given to the effects of harmonics through the low prioritisation of power quality in the Front-End Engineering and Design stage and a lack of awareness of the obligations of the respective parties involved. The resulting designs are incompatible with the requirements of the relevant Grid Codes. This can lead to delays, commercial exposure, restricted network access and subsequent loss of revenue. The obligations of the Transmission Owner (TO), System Operator (SO) and wind farm developer are discussed with respect to Grid Code requirements and the responsibilities of each party in ensuring compliance. The technical aspects of assessing harmonic compliance are described in the context of the design considerations which are made at the various stages of the project development. These include the shift in resonances within the host network, the modification of existing harmonic distortion and the propagation of injected harmonics into the network and through to the extra high voltage, high voltage and medium voltage substations. The ensuing challenges associated with ensuring compliance through filter design are discussed in the context of relevant international standards, including UK ER G5/4-1, IEEE 519, EN 50160 and IEC 61000-3-6. The results indicate that shifts in resonances are more problematic to resolve, compared to the propagation of injected harmonics: injected harmonics are readily absorbed through local filtering and thus the emissions are typically low; in contrast, the effects of shifts in resonances must be transferred back to the point of common coupling, resulting in complex local filtering. Early selection by the developer of appropriate transmission infrastructure and technology can lower the filtering requirement necessary to meet the harmonic specification issued by the host TO.