Influência da resposta dos estimadores de frequência no desempenho da proteção contra sobre-excitação do gerador síncrono

Abstract

The growing demand for electricity over the years has made the Power systems (SEP) more complex, since the network must be able to supply such demand. For this, it is necessary to implement new transmission lines, insertion of new generating plants, as well as new technologies, in order to ensure robustness and reliability to the SEP. In this context, the increasing insertion of the relays can be highlighted. In the SEP, which allow for major evolutions in the protection systems, both in relation to the performance in the system and for the coordination and selectivity of the devices. Numerical or digital relays, perform several complex functions, and perform the basic functions of protection, through a microprocessor, which uses algorithms based on the processing of the voltage and current signals. However, new and old problems arising from the various operational conditions of the SEP and their possible adversities persist, making essential studies in the area of signal processing applied to digital protection. I n this context, generators and transformers are subjected to major damage, which occur during failures and improper operations of the system, which must be quickly identified and eliminated. Thus, the ANSI 24 function is used for the protection of transformers and generators against excitement, a phenomenon that occurs due to a magnetic overflow in the core of a machine. Since the magnetic flux is directly proportional to the nominal voltage and inversely proportional to the nominal frequency, the adjustment of this protection function is given by the percentage value of the volts/hertz (V/Hz) ratio of these parameters. It is noteworthy that the function ANSI 24 is necessary to detect situations in which the functions of overvoltage and frequency variation do not detect the defect. Furthermore, it is noteworthy that the adjustment of the relay 24 is based on the damage curve of each equipment, which is normally supplied by the manufacturer. In this way, the specialized literature recommends adjusting the function 24 with a curve of actuation times 20% lower than those verified in the damage curve of the protected equipment. Considering that the frequency is one of the parameters used by function 24, it can be concluded that the computational tool used to estimate the frequency of the system directly influences the performance of this relay. Thus, this work aims to demonstrate the behavior of function 24 in front of the use of different frequency estimation methods recently disclosed in the specialized literature. For this, a test system was implemented in the software DIgSILENT Power Factory ○R , in order to simulate excitement events, from which the voltage signals to be processed by the frequency estivers and the respective logic of the relay 24 were generated. For this purpose, both the frequency estimation logic and the function 24 algorithm were implemented in the MATLAB○R software. Finally, it is noteworthy that the results obtained allowed us to conclude that the frequency estivers directly influence the performance of function 24, which may lead to delays in performance, as well as the non-operation or improper operation of the relays that incorporate this Function.