Análise do desempenho dos dispositivos de proteção sob efeito de correntes geomagneticamente induzidas

Abstract

Solar eruptions cause the discharge of ionized particles in space, and part of this ejection is toward the Earth, causing the called solar storms. When ionized charges interact with the Earth's magnetosphere and enter into motion, they alter Earth's magnetic field, inducing mirrored currents on the planet surface. Such currents are known as Geomagnetically Induced Currents (GICs) and ow through parallel paths to the ground, such as electric power transmission lines, in which they penetrate through the grounding of the associated equipment, such as transformers in the substations. The GICs have very low frequencies (near DC) with average magnitudes ranging from 0 to 15 A, with peaks of up to 100 A and durations ranging from a few milliseconds to a few minutes. However, GICs are dificult to predict and detect. For a long time South American electrical engineers were trained under the paradigm that GICs were only problems of high-latitude electrical systems. However, it is speculated that GICs are the cause for several undue and unexplained disconnections occurring in Brazil, due to a deformation in the Earth's magnetic field known as the South Atlantic Anomaly. The objective of this work is to investigate the impact of GICs on the performance of current transformers (CTs) and Mho type distance relays, in order to determine if protection operates for these currents. For that, a transmission line (TL) was modeled, as well as the saturable CT of one of its terminals. A circuit involving these equipments was implemented in the EMTP-ATP Software for the simulation of events involving the circulation of GICs in the TL. These simulations were performed with the purpose of analyzing the performance of CT in situations involving GICs, allowing to conclude that CT saturates in a few cycles for low frequency currents. Finally, situations were simulated in which the GICs circulated through the grounding of the relays. From these simulations, it is concluded that, depending on their intensities, the GICs can cause the instantaneous actuation of the distance relays.