| Integration of large wind farms to bulk power systems presents multiple challenges to system operation and security. One particular challenge to system security is vulnerability to tripping due to transmission system faults. Wind generators may have to be disconnected from the grid once the system has a disturbance, such as a short circuit fault, lightning strike on transmission lines, etc. Tripping generators normally has a negative impact on system stability, especially when wind farms have considerable penetration and this brings a major concern throughout the world. In the early days, the integration of wind power was much, therefore, the sudden disconnection of a wind turbine or a wind farm from the grid causes no significant impact on the stability of the power system. But with the increasing penetration of wind energy, the contribution of power generated by a wind farm is now significant as well as the impact will be significant. If a wind farm with huge capacity is suddenly disconnected at full generation, the system will loss further production capability. Unless the remaining operating power plants have enough "spinning reserve", to replace the loss within very short time, this might lead to a large frequency deviation and voltage drop and possibly followed by a blackout. In order to keep system stability, it is necessary to ensure that the wind turbine restores normal operation in an appropriate way and within appropriate time. Technical constraints in relation to wind power integration in weak grids may be associated with limited thermal capacity in parts of the grid and or the adverse effect wind power can have on voltage quality and stability. In certain situations, however, local constraints regarding development of new transmission or distribution lines or upgrading of existing lines can make it favorable to utilize the existing lines to a level which in worst case may imply operation beyond the normal technical constraints of the system. In this work, challenges and opportunities arising from situations as described above are analyzed, and viable measures to enable secure and acceptable operation of large wind farms in remote areas close to the thermal capacity and stability limits of the power system, are pointed out during loading and analyses have shown that voltage stability problems will occur long before the thermal limits of the regional network are reached. Also, investigation was carried out in case of the sudden disconnection of wind farm from power grid in short circuit fault conditions. In the network calculation, consideration was made for both maximum and minimum short circuit conditions and it is performed according the IEC60909(2001) standards. However, the aim of the analysis was the assessment of the electrical parameters of the Wind Farm during and after a three phase short circuit event at the33/11kV substation at PCC. For completeness of this work, protection coordination was investigated. Furthermore, the study has investigated and calculated the coordination of the protection devices for33kV electrical systems with the new wind farm connection to guarantee a selective clearance of faults in the abnormal operating conditions like overload, three phase faults and ground faults.In conclusion, a case study had been performed according to given information and results were presented. Simulations were performed to analyze the mutual impact of the wind farm technical and operational characteristics of power systems and technical requirements for wind farm-grid connections were analyzed with assessment of issues like flickers calculation, short circuit current, transient stability and protection coordination and various results were presented in this study. |
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