Teleprotection with MPLS Ethernet Communications - Development and Testing of Practical Installations
Today’s information technology (IT) advancement is driving both non-operational and operational data communications within a substation towards Ethernet-based communications networks. As a result, protective relay engineers are finding that the telecommunications industry is transitioning from legacy teleprotection channels such as leased circuits, Time Division Multiplexed Synchronous Optical Networks (TDM SONET) multiplexers and rings, over to Ethernet packet-based wide-area networks (WANs). The current, most common WAN packet routing technology is Multi-Protocol Label Switching (MPLS). Traditionally, packet-based routing in an Ethernet WAN has been fundamentally less predictable than the deterministic flow of data bits in a fixed, point to point TDM or serial data communications circuit. Changes in network latency or packet delay variations in the past have raised concerns when considering it for use in protective relaying applications. High latency in any network slows tripping and can result in miscoordination of the protective relay system. Current differential line protection (87L) is particularly sensitive to jitter or variation in latency, in addition to asymmetry or the difference in latencies in the two directions of the protection channel data exchange. To validate the MPLS design and in preparation of migrating substation protective relays from TDM to MPLS within the San Diego Gas & Electric (SDG&E) system, laboratory testing was performed at the SDG&E Integrated Test Facility (ITF). The testing conducted included both fundamental network testing and the Real Time Digital Simulator® or RTDS® system model applied to protective relays, using MPLS routers and proposed MPLS network configuration providing the teleprotection channels. The paper describes the technical requirements developed by SDG&E for critical EHV teleprotection applications, discusses SONET versus MPLS Ethernet communications, and presents the laboratory testing approach and results. The discussion includes impact of channel asymmetry, latency, fail-over, channel availability, and MPLS monitoring tools for troubleshooting and analysis.