Downed electrical conductors are a safety and reliability concern for the ComEd distribution system due to short-circuit protection limitations in clearing high-impedance faults. ComEd’s distribution automation (DA) group is piloting the SEL and SDG&E patented falling conductor protection (FCP) solution to bridge the relay protection gap, prevent wire-down faults on utility infrastructure, and mitigate hazardous conditions for customers, first responders, and property. 

Using IEEE C37.118 protocol, synchrophasor data is streamed over ComEd REACTS fiber from the 12kV substation feeder protection relays and DA reclosers to a phasor data concentrator (PDC) with a SEL-3555 RTAC located at the substation. The FCP RTAC analyzes synchrophasors from each of the phasor measurement unit (PMU) enabled relays using five open-phase detection methods, including voltage rate of change and both negative and zero sequence magnitudes and angles to determine a falling conductor event.

During a falling conductor event, the PDC RTAC will analyze the synchrophasor streams and transmit a direct transfer trip (DTT), via IEC 61850 GOOSE, to open the protection devices surrounding the affected segments. The energized conductor is isolated within 500ms of the break before the conductor makes ground contact. The FCP algorithm will block falling conductor DTTs if a short-circuit fault is detected at the start of an event, allowing the existing GOOSE advanced distribution protection (ADP) blocking scheme to clear the fault and avoid upstream momentary customer outages.

The FCP communications architecture presents a unique set of cybersecurity challenges for ComEd because the protection scheme requires IP-connected devices from the separate substation and distribution networks to route information to the FCP RTAC. To maintain isolation between the two networks, the distribution synchrophasor, GOOSE, and DNP3 network traffic is secured by a specially programmed SEL-2741 ethernet switch to prevent unauthorized network traffic back to the substation. Additionally, GOOSE communications to the SEL-351 feeder relay are performed by the SEL-2411 using mirrored bit serial communications.