Avaliação da confiabilidade do sistema de proteção anti-ilhamento de geradores síncronos distribuídos

Abstract

Distributed generators in the distribution system may be disconnected incorrectly due to electrical disturbances from the grid. Similarly, these generators must not operate in an islanded manner from the electrical system. To this end, the anti-islanding protection system is designed to disconnect these distributed generators in situations that characterize islanding. A series of protection functions perform this role; however, they are not always capable of identifying the islanded condition due to the settings adopted. Such settings must comply with current regulations and with the electrical system operator, which impose supportability requirements that characterize an operating range in which the distributed generators must remain connected. In order to fill the gaps in conditions in which islanding is difficult to identify, methods based on quantities other than frequency and voltage are in constant search. However, these methods or quantities do not have the supportability requirements defined as in the case of voltage and frequency. Therefore, the objective of this master’s dissertation is to evaluate the reliability of the distributed generator protection system considering islanding and a series of disturbances from different sources in the electrical grid. This work is carried out using ATPDraw to obtain the results and employs the adjustment map tool to verify the adjustments adopted in these anti-islanding protection methods. The behavior of the quantities of under/overfrequency, under/overvoltage, frequency variation rate, active power variation rate, impedance variation rate, frequency oscillation, vector jump and overcurrent of the electrical grid when islanded under different operating conditions, short circuits with and without fault impedance and switching in the medium and high voltage of the test system were verified. The impact of the change in the grid equivalent and its consequence on the performance of the protection system was also evaluated. The results of this work are conditioned on the test system and the estimators, filters and models of each protection function and may differ depending on different authors, as well as adjustment methods that may allow better performance, and thus, the method of this thesis can be used for in-depth assessments. That being said, the results obtained indicate that the estimation methods of the electrical quantities that govern the operation of the evaluated protection systems have an influence on the performance for the tested events. Furthermore, it is also concluded that the lack of supportability requirements associated with these same quantities causes the protection functions to be incorrectly sensitized to disturbances coming from the transmission grid.