Segment Routing for Differential Protection: Transport Network Evolution and Field Validation for C37.94 Applications in High Power Substations

(IP/MPLS) to Segment Routing (SR) to support differential protection (87L) traffic (using

C37.94 interfaces), a highly latency, path asymmetry-sensitive and synchronization-critical application used between high voltage substations.

This paper discusses the analysis of a complete real use case implemented by a distribution utility, which previously operated a mission-critical IP/MPLS network configured in a ring topology using OPGW links over 115 kV high-voltage lines. This setup provided dual active communication paths between substations, leveraging the benefits of a Traffic-Engineering capable converged protocol with symmetrical transport tunnel using RSVP-TE (Resource

Reservation Protocol for Traffic Engineering) and support for multipurpose traffic types over

LDP (Label Distribution Protocol).

In the tested scenario, two Segment Routing MPLS-capable edge routers were integrated at each substation, directly connected to current differential protection relays, using C37.94 interfaces, as well as to other substation devices such as RTUs, energy loggers, HMIs, and L2 switches (station and process bus).

A field test campaign was conducted over a three-month period, during a controlled testing window on the operational network. The study measured latency, relay response behavior, and failover performance scenarios under path switching conditions. It also validated the system’s ability to handle active-active 87L messaging using an Active Multipath feature, combined with end-to-end Quality of Service (QoS) enforcement, and group-based MPLS encryption for secure differential protection 87L packets delivery.

This paper discusses the results of the tests demonstrating Segment Routing’s potential as a future-proof, resilient and efficient transport solution for differential protection, meeting modern IEC 61850 requirements while ensuring service continuity under dynamic network conditions.

ELFEC is the electric distribution company of Cochabamba, Bolivia, playing a critical role in the National Interconnected Electric System. It operates a 115 kV high-voltage backbone ring that carries around 80 percent of the regional electrical load.