Abstract: 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).

Abstract: The invention relates to a low impedance excitation system for use in distance relays. In such a system the low impedance check is carried out by comparing the phases of signals (U.sub.D,U.sub.S) which are obtained by forming the sum and the difference from an image voltage signal (U.sub.A) and a line voltage signal (U.sub.K). The triggering characteristic is formed in the complex impedance plane by means of the combination of at least two different triggering characteristics, mainly a circular (K) and a lenticular (L) characteristic, in order to avoid overlapping between the triggering area and the active load area (W) and in order to achieve an adequate arc reserve on the whole length of line to be monitored. The switching over between the different triggering characteristics (K,L) takes place as an operational function of the phase difference (.beta.) between the image voltage signal (U.sub.A) and the line voltage signal (U.sub.K).

Abstract: A process and device useful in the protection of AC current circuits, particularly of parallel lines supplied at both ends, provided with protection relays at both ends of the line against susceptibility to false triggering as a result of transient signal components and signals disturbances, and particularly useful in providing stepped protection upon initial disconnection at one side of a line after occurrence of a short circuit against the change of energy direction with reversal of the fault direction detected in the protection relay of the sound line on crossing the triggering range of the appropriate characteristics curve, which also leads to false triggerings in multi-system protection relays because of transient switching inaccuracies.

Abstract: With heretofore known directional comparison protection systems working with fault direction detectors at both ends of a line section which is to be protected and data transmission between both end stations as well as transmitters and receivers and comparison-evaluation devices for narrowing or sectionalizing the location of the fault site with respect to the line section to be protected, the reliability of such sectionalizing procedure, especially in the case of faults near to an end station, when working with series capacitors or capacitance, is dependent upon the response of the protective gap of such capacitors. With non-response there are produced transient oscillations which can falsify the directional determination. The invention solves this problem by using distance protective relays as the fault direction detectors with line replica or image impedance, which can be switched in the sense of a zone staggering protection.

Abstract: A method and apparatus for fault direction determination is disclosed wherein a capacitor is connected in series in a line or network having a relay arrangement or scheme possessing directional and distance characteristics. To prevent faulty tripping of the relay arrangement, caused by the effect of the series capacitance in the line, the relay arrangement is structured such that the integrity of the directional characteristics thereof is maintained. Positive tripping of the relay is maintained, especially in the event of near faults which usually are most affected by the action of the series capacitance.

Abstract: By switching-in a trip boundary, which excludes the load range in the complex impedance plane, of a directed or non-directed end or final stage of a measuring system of a distance protection apparatus, it is possible to eliminate faulty or spurious triggering of the protection apparatus, notwithstanding a possible improper excitation. The functional reliability of the protection apparatus is thus improved and there is possible monitoring of fault functions where, in each case, there is logically coupled a "yes" or "no"-type output response of the measuring system with a "no" or "yes"-type excitation output by means of appropriate and comparison logic circuitry.

Abstract: A method of, and apparatus for, monitoring faults at electrical lines, wherein there are formed a multiplicity of detection signals, and threshold monitoring the phase angle between timewise successive detection signals. According to a first aspect of the invention none of the detection signals has a magnitude equal to the line voltage signal. As a further aspect one of the detection signals can comprise an external signal. A still further feature contemplates that one of the detection signals is a difference signal formed by the line voltage signal and an external signal.

Abstract: A distance-selective short-circuit monitoring device with a low response time (FIG. 3, FIG. 5) results from sequence detection of first and second monitoring signals (US.sub.1, US.sub.2) which are selectively allotted to the zero cross-overs of detection signals (Ud.sub.1 -Ud.sub.4) which determine a polygonal triggering zone, the selective allocation being in accordance with the sign of the signal change rate, and by counting the alternations between first and second monitoring signals (US.sub.1, US.sub.2) within a predetermined monitoring interval (Tu), the duration of which corresponds at least approximately to a half-period of the mains frequency.

Abstract: Short-circuits are monitored between a measurement point and short-circuit located along an electrical line. Phase detection between voltage and current along the line permits signal value comparison with a threshold value to produce a triggering signal in the event of short-circuit occurance.

Abstract: A method of, and apparatus for, the distance-selective monitoring of faults at electrical lines by means of a quadrilateral trigger or trip region. There are formed at least two reference signals of at least approximately the same phase and from each of these reference signals and the line voltage there is formed a respective difference signal. Each difference signal experiences a separate comparison with a related threshold phase angle in order to determine whether the monitored fault lies within or without the trip region.