Proteção diferencial baseada nas correntes de sequência zero e de neutro para reatores shunt com núcleo de ar tipo seco
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Data
2021-06-30
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Universidade Federal de Goiás
Resumo
The growing increase in the number of long transmission lines, with high voltage levels, makes necessary the connection of parallel shunt reactors in the lines, as a way to circumvent the consequences of overvoltage, due to the capacitive effect of the lines. The use of shunt reactors enables voltage regulation, by absorbing the excess of capacitive reactive in the line. Considering the important role of shunt reactors for the correct operation of long transmission lines, it is essential to guarantee protection logics that allow the quick identification of short circuits inside this equipment. Therefore, this work presents a differential protection algorithm based on the analysis of zero and neutral sequence currents, which identifies abnormal operating conditions in the shunt reactor and, consequently, allows a safe and selective operation of the protection for turn-to-ground and turn-to-turn faults. This logic is based on the comparison of the zero sequence current, calculated on the basis of the phase currents, measured near the bushing, with the current measured in the neutral winding. The zero sequence and neutral current phases of the reactor are reconstructed in time and, finally, are compared, allowing the identification of the short circuit within the reactor. In addition, the algorithm incorporates a function that detects the occurrence of disturbances of an internal or external nature to the reactor. Simulations were performed using the software Alternative Transient Program (ATP), in which a 230 kV, 380 km transmission line with 50 % of compensation was modeled, such that, in the reactor, different internal short circuits were
applied, of the turn-to-ground and turn-to-turn faults. Furthermore, in order to perform a comparative evaluation, the proposed algorithm was analyzed together with the traditional differential protection
Restricted Earth Fault-(REF), which uses the same input signals. From the results obtained, it was found that the traditional protection did not operate for turn-to-ground with high fault resistance, and was also not able to identify any of the analyzed turn-to-turn faults. On the contrary, it was verified that the proposed algorithm operates correctly for all the turn-to-ground and turn-to-turn faults tested, independently of the variations in the value of the dispersion factor, the number of turns involved and the value of the fault resistance. Futhermore, it is worth to mention the fast speed operation of the proposed protection Also noteworthy was the speed in which the proposed algorithm, which identified all the faults analyzed with an approximate operation time order of 1 ms after their occurrence. It should be noted that in order to guarantee the correct performance of the proposed protection for all external short circuits, it is necessary to use additional logic to guarantee
non-reaction for external faults.
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Citação
SANTOS, G. G. Proteção diferencial baseada nas correntes de sequência zero e de neutro para reatores shunt com núcleo de ar tipo seco. 2021. 91 f. Dissertação (Mestrado em Engenharia Elétrica e da Computação) - Universidade Federal de Goiás, Goiânia, 2021.