Fault location on a mixed overhead and underground transmission feeder using a multiple-zone quadrilateral impedance relay and a double-ended travelling wave fault locator

A hybrid relay scheme, which combines the advantages of a quadrilateral impedance relay and a travelling wave fault locator for fault location on a mixed overhead and underground transmission feeder, is described in this paper. A redesigned quadrilateral impedance relay has the ability to determine the fault section and displays good performance to resist the influence of fault resistance on fault location. However, when a fault occurs close to a junction point where an overhead line connects with an underground cable, the impedance relay finds it difficult to determine the fault section. The travelling wave fault locator now takes responsibility for discriminating the fault section, and then the algorithms for the corresponding fault sections will be employed to calculate the accurate fault location. The evaluation of this hybrid relay scheme, based on tests for different fault locations on combined transmission lines, is simulated using the PSCAD/EMTDC simulator.