GPS synchronised current differential protection

A new technique for current differential feeder protection employing measurement synchronisation is described in this paper. The application of current differential protection to feeders can present several difficulties due to the distance between the relays at the line ends. These problems are briefly described together with how their effects can be reduced by the use of synchronised measurements. The second part of the paper discusses the practical implementation of synchronisation with reference to the design and ongoing development of a new prototype differential relay, including a brief description of the Global Positioning System, time tagging of synchronised data, synchronised sampling and phase angle compensation synchronisation. Finally, measurement data from the prototype synchronised differential relay system, employing phase angle compensation synchronisation is presented. This demonstrates the level of synchronisation accuracy that is attainable.