Detection of High Impedance Earth Faults Utilising Metering Assets

Presently, when a high impedance earth fault occurs that is not isolated by protection systems, Energex is reliant on members of the public to report the event. The aim of this research project was to investigate the use of distribution transformer metering assets for the detection of Back Fed Earth Faults (BFEF). A high impedance earth fault typically occurs when an overhead conductor breaks and falls, making contact with the surface of the ground. The fault current that flows may be fed directly from the source feeder, or back-fed via the primary windings of the downstream distribution transformers. In the latter case, the fault current will be influenced by the load side impedance. Data has been collected from metering assets located on the secondary terminals of 11kV/415V distribution transformers, and correlated with known BFEFs within the Energex 11kV network. Theoretical analysis of BFEFs has been performed to assist in the identification and verification of the fault characteristics exhibited by the historical metering data. Theoretical analysis and fault data was used to develop a fault analysis methodology that can identify BFEFs within the Energex 11kV Network, and differentiate between the presence of a BFEF and an open circuit 11kV line or fuse. The proposed fault detection scheme was designed to operate after the existing protection systems have operated to ensure that the 11kV network protection grading is not compromised, whilst also ensuring that any BFEF is disconnected quickly and reliably