Cable Fault Detection using Refase™
In hybrid circuits containing both overhead lines and underground cable sections, it is advantageous to determine in which section an electrical fault has occurred. This enables an operator to auto-reclose (AR) in the event of a transient OHL fault, or to block auto-reclose in the event of a permanent cable fault. This is not typically possible if simple distance protection schemes are deployed, which will typically result in some ambiguity in identification of the faulted section, rendering auto-reclose prohibitively risky. Ideally, the circuit would be instrumented at every transition point such that robust differential current algorithms may be used to immediately and definitively identify the faulted section in the event of a fault, and so permit or block auto-reclose accordingly.
However, to deploy conventional current measurements at remote transition points is typically very expensive, requiring significant local supporting infrastructure including power supplies, active digital telecoms, and GPS access to obtain reliable measurements. Optical NCITs have fundamental limits on range and environmental withstand and consume multiple fibres per instrumented location, fundamentally limiting their deployment at scale.
A single Refase™ system is uniquely capable of instrumenting multiple hybrid circuit sections with passive, highly-multiplexable current sensors over unprecedented range. This system enables discrete, robust, and scalable differential current monitoring over long-range, with measurements maintaining consistent high accuracy over wide operating temperature ranges when compared to these prior technologies. Discrete AR block signals are output on protection timescales (milliseconds), allowing an operator to cost-effectively manage hybrid circuits in the most efficient manner possible.