Method and a system for analyzing the secondary current in a current transformer, the primary side of which is connected into a line of an electric energy supply network

摘要

The invention relates to a method and a system for analyzing the secondary current (J.sub.2) of a current transformer (20), the primary side of which is connected into a line (10) of an electric energy supply network. When the current transformer (20) is saturated as the result of a short-circuit on the line (10), a saturation signal (X) indicating this saturation and a polarity signal (P) indicating the polarity of the displacement of the short-circuit current (J.sub.1) are generated. The two signals (X, P) are used to select zero transitions of the secondary current (J.sub.2), corresponding to the polarity of the displacement of the short-circuit current (J.sub.1). After the selected zero-transitions, the secondary current (J.sub.2) is extrapolated by a current signal (C), in accordance with its saturation-free curve-shape. The current signal (C) is finally supplied to protective systems, instead of the secondary current (J.sub.2).