HV lines that combine overhead line segments with underground cable segments require a carefully designed protection scheme in order to ensure safety while maximizing the supply KPIs such as SAIDI.
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.