Protection System Considerations in Networks with Distributed Generation

Abstract

This chapter presents methodologies to assess the impact of distribution generation on electric distribution network protection systems for an integrated network planning. The distributed generation (DG) alternative is seen as a shift in the paradigm of energy generation in the world. The adoption of renewable sources of energy for residential or commercial production brings not only environmental benefits, but also an opportunity to ease the supplying difficulties found in many countries. Despite solving some of the energy suppling problems, this paradigm change caused by the insertion of DG in electric distribution networks can bring some undesired technical impacts. The typical impacts assessed in the electric distribution networks planning involve the expansion of the network, such as losses, power factor, line loading, and voltage profiles, among others. However, a massive insertion of DG may also cause significant problems to the network protection, which involves the protection planning. In this way, it is necessary to identify potential protection issues and design means to model, diagnose and mitigate such issues. This chapter aims at describing the importance of predicting the potential impacts of high penetration of renewable sources on the protection system from electric distribution networks, in order to achieve an integrated network planning. Thus, in the beginning of this chapter it is discussed the main protection system issues that may arise from the high penetration of distributed generation, such as loss of protection coordination, overvoltage, loss of protection sensitivity, directional false tripping, unwanted fuse blowing, beside others. The chapter than demonstrates possible models utilized to assess those impacts, such as network modeling and renewable sources modeling, possible approaches such as the probabilistic and deterministic perspectives, regarding DG allocation algorithms and the possible methodologies for assessment such as scenarios or sensitivity analysis. The methodologies evaluate the protection impacts and are based on several short circuit calculations and for the probabilistic approach, the Monte Carlo Method. The results shown in the chapter may represent the calculation of such impacts for electric distribution networks. Those may contain loss of sensitivity, directional false tripping and unwanted fuse blowing impact calculations for some networks to illustrate the methodologies. To conclude the chapter, there will be more discussions regarding the results presented and the potential benefits of including this analysis on the integrated distribution network planning. In the end, the chapter illustrates the application of the presented methodologies with a case study using a real distribution network.