Análise do desempenho da proteção diferencial sob influência dos transformadores de corrente em condições de saturação

Abstract

The Electric Power System (EPS) has the function of interconnecting the generation of energy and the consuming load with the maximum efficiency and the minimum possible of failures and interruptions. In the EPS the protection is made by relays, which are devices allocated at strategic points of the system that, when they detect anomalies, they act by sending a signal to open a circuit breaker, in order to isolate the system as quickly as possible from the point where it occurred The defect. The operation of the relays takes place from the voltage and current signals in the network. These signals are transmitted to the relays through Potential Transformers (PTs) and Current Transformers (CTs). Referring only to CTs, it can be said that they are fundamental equipment for the correct operation of the protection methods, since its main function is to replicate the high primary currents in a smaller scale in its secondary, ensuring the obtaining of the current signals of the network. The CTs are subject to the saturation of their core, a phenomenon in which the current waveform is distorted at the secondary terminals, damaging the performance of the protection relays, which are based on root mean square values of the quantity in question to determine its performance or not in the protection scheme. In this context, the present work demonstrates the performance of differential relays under the effect of saturation of current transformers, in order to identify possible undue performances for defects outside the protected zone. We have analyzed cases for different types of short circuit and according to the results obtained through the simulations, it can be concluded that the current signal distortions in the secondary of the saturated CT directly influence the operation of the differential protection relays. Preliminarily it was possible to verify that such distortions become more severe according to the magnitude of the short-circuit current.