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Real-time teleprotection testing using IP/MPLS over xDSL

Blair, Steven Macpherson and Booth, Campbell (2013) Real-time teleprotection testing using IP/MPLS over xDSL. [Report]

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Abstract

Teleprotection for power systems is safety-critical and has demanding requirements for bandwidth, low latency, and low jitter. Traditionally, time-division multiplexing (TDM) using SONET/SDH circuits has been used to provide this quality of service. Modern packet-based networks offer several advantages, such as improved flexibility and greater bandwidth efficiency. With IP/MPLS, packet-based networks can cater for teleprotection functionality. This report demonstrates the potential for commercially-available IP/MPLS hardware to provide teleprotection functionality over two DSL technologies, VDSL and SHDSL. A real-time hardware in the loop environment has been developed to test these schemes under a variety of scenarios, which are indicative of real-world conditions. Commercially-available protection relays were used to implement C37.94-based communications, and the stability of the protection functions were monitored closely during the testing. The results highlight the maximum DSL line distance and the remaining bandwidth (after provisioning for the teleprotection) which can be achieved, whilst observing a 6 ms propagation delay restriction. VDSL is only suitable for links up to approximately 1.4 km, although it can deliver relatively high bandwidth of 4-19 Mbps, depending on the line distance. SHDSL can support up to 4-5 km per span. Distances of approximately 4.3 km offer a good compromise of distance, delay, and remaining bandwidth. Using two serially-connected SHDSL spans is beneficial: it can support either longer distances, or provide greater spare bandwidth. The number of C37.94 slots used for teleprotection should be greater than 4, where possible, to help reduce the propagation delay. Each DSL modem type “favours” particular MPLS payload sizes, and these values provide the best compromises in connection distance, delay, and remaining bandwidth – as well as ensuring that the protection scheme remains stable.