Influence of the Frequency Estimator Response on Synchronous Generator Overexcitation Protection Performance

Problems arising from the different operating conditions of the Electric Power System make essential the studies in the area of signal processing applied to digital protection. Generators and transformers are subject to extensive damage, which occurs during faults or improper system operations. These conditions must be quickly identified and eliminated. Thus, the ANSI 24 function is used to protect transformers and generators against overexcitation, where its actuation is given by the percentage value of the Volts/Hertz ratio. Considering that the frequency is one of the parameters used by the referred relay, it can be concluded that the computational tool used to estimate the frequency directly influences the performance of this relay. Thus, this work aims to demonstrate the behavior of function 24 using different frequency estimation methods published in the specialized literature. So, a test system was implemented in the ATPDraw software, in order to simulate overexcitation events. The voltage signal generated in the simulations were processed by the frequency estimators and by the Volts/Hz digital relay logic, which were implemented in Matlab® software. Finally, the results obtained allowed to conclude that, as expected, the frequency estimators directly influence the performance of function 24, causing delays in the operation, as well as the non-functioning or inadequate operation of the Volts/Hertz relays.