Calculating discretization step of controlled values in relay protection communication channels

Abstract

In relay protection devices with information digital processing the input controlled values are the currents and voltages of the protected object received from traditional measuring transformers, which are converted into voltage signals using appropriate converters. To limit the frequency spectrum these signals are subjected to preliminary analog filtering, after which they are discretized in time with a desired step Δt and are quantized by level. The difference between adjacent discrete values of the controlled value is proved to depend on its amplitude, and the minimum value of this difference can be observed in the minimum signal mode. When choosing the minimum step Δt the mode with the minimum amplitude of the controlled value is decisive. It has been proved that the difference between adjacent discrete values of the controlled value depends on the frequency and decreases with a decrease in the latter, i.e. when choosing the minimum sampling step Δt it is necessary to take into account the minimum possible value of the frequency. There is shown an example of the dependence of the minimum sampling step of a sinusoidal signal with a frequency of 50 Hz on the ADC bit depth. The analysis of the presented dependences shows that the minimum value of the sampling step Δt is largely determined by the multiplicity of the controlled value and the ADC bit depth. There has been inferred the possibility of using the proposed methods for a rough estimation of the minimum value of a sampling step of input quantities in relay protection devices with information digital processing.