Método para detecção de oscilação de potência no domínio do tempo

Abstract

This work proposes two techniques for the detection of power swings and blocking of distance relays on transmission lines to prevent undue shutdowns. If a fault occurs during power swing, it must be immediately detected and removed. One of the major challenges for the detectors is to distinguish power swing from symmetrical fault near to electrical center (power angle δ near to 180º, since both are balanced phenomena. First technique is inspired by the fact that the frequency with which the signal of active power oscillates is proportional to the swing frequency of power system. Thus, the swing frequency of the active power derivate (dP/dt); the estimated frequency behavior is monitored by the slope angle between samples with the objective of detecting power swing (soft tendency – low angle values) from others events (abrupt tendency – high angle values). This technique was designed to be easy to ajust without extensive studies or evaluations of all possible scenarios in order to get the best setting. A second technique that uses of the asymmetry of the waveform in the stage of detection of short-circuit during power swing is proposed, and its main advantage is the ability to identify three-phase faults during power swing near the electrical center up to δ ≤ 120º. This technique calculates the mean square erros comparing the input signal with periodic functions with the objective of detecting power swing, this technique has predefined settings facilitating the adjustment process. The results show that the approaches provide satisfactory performance for stable power swing, unstable power swing and short-circuit during power swing. The highlights of proposed techniques are the simplicity of mathematical operations used, besides the speed in its operations.