Faults on overhead segments are normally momentary faults (caused by birds, branches, lightnings etc.) that will clear within a very short period of time thus making auto-reclose a sensible option to reduce interruption times. On the contrary, faults on underground cables are usually permanent and auto-reclosing on a faulty underground cable section is not recommended. It is therefore important to implement a protection scheme that can tell with 100% certainty whether a fault occurred on the overhead segment of a mixed line or not.
The conventional approaches to solve this issue are either a distance protection which is cost-effective but not very reliable (i.e., we may make the wrong decision if the fault occurs near the overhead-underground transition) or a line-differential protection which is reliable but expensive (due to the installation of protection devices on every transition point that require power, a building, use of land etc.).
ARTECHE’s Cable Fault Detection system offers a reliable, fully passive, line differential (87L) or Earth Overcurrent (50G) solution to remotely protect these lines.