MODAL SATURATION DETECTOR FOR DIGITAL DIFFERENTIAL PROTECTION

A new digital method for the rapid and reliable detection of current t ransformer saturation for single and multiple pole short circuits is d escribed. The function principle is independent of the number of phase s envolved ip the short-circuit and independent of the magnetic proper ties of the current transformers including remanence. In order to achi eve this, the secondary currents of the three phases are transformed i nto space phasors with a blocked backward rotating component. In the u nsaturated state their trajectories are circles. The deviation from th is characteristic form and hence the inception of current transformer saturation can be detected in less than 3 milliseconds. One result of quick detection of the current transformer saturation is that the diff erential protection can be adjusted to higher sensitivity than in know n protection devices. This guarantees reliable operation even in case of short circuits with weak short-circuit currents. The new modal satu ration detector is equally suited for the differential protection of l ines as well as busbars and other circuit arrangements.