The evaluation of frequency properties of digital measuring element reacting to increment vector current values

Abstract

The frequency properties of a digital measuring element can be used as criteria for the selection of operating values of the numerical distance protection starting element of power-swing blocking. The conditions of the selection of the operating values of the starting element of power-swing blocking usually ensure sensitivity to short circuiting. The primary function of the starting element is blocking the distance protection from power swings and out-of-step conditions, based on the fact that the rate of current change and its increment for electromechanical processes are much lower than for a short circuit. Mathematical modeling of the digital measuring element based on filter Fourier and FIR algorithms with confirmation of the results by using a computer-controlled testing system allows criteria to be obtained that reflect the physical nature of the processes that can be used when selecting the settings of the starting element of power-swing blocking. An approach to selection of the settings of a digital measuring element of relay protection that is responsive to the current increment, based on analysis of digital signal processing algorithms, allows one to determine the criteria for the detuning of the emergency operation, taking into account the frequency deviation, the impact of the presence of a transient dc component, and the higher harmonics. The frequency properties of the digital measuring element reacting to increment vector current values can be used to determine the threshold detuning from power swings and out-of-step conditions as additional conditions for selecting settings of the starting element of power-swing blocking, which will increase the sensitivity of the distance protection for short circuits and the reliability of detuning from power swings and out-of-step conditions.