Principles of Current Protection Based on Three Instantaneous-Value Samples

The paper proposes equations for finding the current parametric values and their derivatives based on three samples. These equations reduce the effect of non-periodic components on how accurately their periodic counterparts are isolated from the current samples received by digital power-system protection devices. No calculation errors occur when parameters are sinusoidal. We have developed an algorithm to correct current data when the current transformers have their magnetic cores saturated.