Abstract: Protective relay apparatus for detecting the direction or distance to a fault from the measuring point on an ac electrical power transmission line using current and voltage deviation signals. The deviation signals represent the changes induced by the fault from the steady-state pre-fault magnitudes. Trajectories are plotted on an X-Y plane using the voltage deviation signal as the X-axis coordinate and the differentiated current deviation signal multiplied by the line reactance to the balance point as the Y-axis coordinate. Due to the use of the differentiated current deviation signal, the trajectories are straight lines. The threshold boundaries for determining the distance to or direction of the fault are time-varying lines of unit slope representing the pre-fault voltage at the fault point.

Abstract: Protective relay apparatus and methods for detecting direction to a fault from a measuring point on an A.C. electrical power transmission line using current and voltage deviation signals which may include traveling wave transients, and for providing both directional and distance information from the same signals after traveling wave transients have been removed. Fault generated current and voltage deviations from the steady-state, prefault magnitudes are used to generate trajectories in one embodiment by differentiating the current deviation and using it as one coordinate, and by using the voltage deviation as the other coordinate. A forward fault produces a straight line trajectory which crosses the origin between the second and fourth quadrants, and the reverse direction fault produces a straight line trajectory which crosses the origin between the first and third quadrants.