Maximizing the integration of wind power in distribution system

Licentiatavhandling, 2013

The global installed capacity of wind power has shown a significant growth, from just 24 GW in 2001 to 283 GW in 2012. This trend is expected to continue for some years to come. Hence a significant amount of wind power needs to be connected to the electric power system. Usually larger wind farms are connected to transmission systems while smaller wind farms are preferably connected to distribution systems. Such preference arises from comparatively lower connection costs associated with installing wind power in lower voltage networks. But the introduction of wind power into a distribution system poses a number of power quality and reliability concerns such as voltage flicker and harmonics, overvoltage and thermal overloading, and increased fault level. Moreover due to highly fluctuating nature of wind power, some distribution system operators (DSOs) are also concerned about an increase on the frequency of tap changes (FTC) due to the introduction of wind power. Should there be an increase in FTC, in a power system which is already vulnerable to wear and tear due to aging, the DSO may limit the integration of wind power to its network to avoid increased maintenance costs or unexpected tap changer failures. Thus, the thesis discusses these integration issues of wind power and identify the limiting factors. Once identified, the thesis proposes mitigation solutions so as to maximize the hosting capacity of a distribution system. This facilitates the introduction of wind power to the power system in a cost-effective manner. The investigation of the effect of wind power on the FTC shows that the change on the FTC in a distribution system connected to a relatively strong external grid (with X/R≥ 5) is negligible up to a significant level of wind power penetration. But in a distribution system connected to a relatively weak external grid, a significant increase in the FTC has been observed as wind power penetration increases. Hence a further investigation is carried out to limit the FTC by using reactive power from local wind turbines. The results have shown that the methodology is very effective in reducing the FTC. Furthermore, the thesis identifies voltage rise and thermal overloading as the two main limiting factors of wind power integration into distribution systems. Thus, active management strategies (AMSs)--such as wind energy curtailment, reactive power compensation, and coordinated on load tap changer (OLTC) voltage control-- have been investigated in the thesis to increase the wind power hosting capacity of distribution systems. To facilitate the investigation, an optimization model incorporating these AMSs is developed. The output of the model is the optimal wind power hosting capacity of the distribution system which will maximize the profit gained by the DSO and the wind farm owner (WFO). The result of the analysis shows that by using AMSs the wind power hosting capacity of distribution system can be increased up to twice the capacity that would have been installed without AMSs.