Fault location in combined transmission lines using PMUs for recloser control

In general, there is a growing trend towards the installation of underground cable to replace overhead lines, completely or in certain sections, resulting in combined transmission lines. The present protection practice for faults in the underground section of these lines is based on protecting the cable with a line differential relay, which blocks the reclose order issued by the protections installed in each line end. This paper discusses the replacement of the line differential relay by a fault location algorithm added to the line end relays. The algorithm is based on the measurement of synchrophasors at each end of the line to allow or cancel the reclose order, depending on the faulted section. The new algorithm has been validated by extensive simulations using Matlab and by laboratory tests.