Method and apparatus for monitoring an ac transmission line

Abstract

The invention is directed to an improved method and apparatus for monitoring the status of an AC electrical transmission line connected between first and second locations. In a disclosed embodiment of the method of the invention, first signal parameter values are generated, for the first location, by time integrating between zero-crossings of an AC signal parameter measured at the first location. Second signal parameter values are generated, for the second location, by time integrating between zero-crossings of the AC signal parameter measured at the second location. The second signal parameter values are transmitted to the first location. In a form of this embodiment, the second signal parameter values transmitted for each of the three phases are transmitted only for time periods between successive zero-crossings beginning with a zero-crossing of one sense (e.g. positive-going zero-crossings), and the second signal parameter value for the ground reference return is transmitted only for time periods between successive zero-crossings beginning with a zero-crossing of an opposite sense (e.g. negative-going zero-crossings) to said one sense. This technique can provide a further saving of bandwidth without substantial compromise of tripping response time.