First IEEE PSRC WG H7 Sub C7 1588 Plug-fest

by Galina Antonova , GE Digital Energy, Canada

Synchronization plays an important role for many power system applications. Some applications require relative synchronization (synchronization of merging units), others need traceability to UTC either locally or over a wide area (event recorders, synchrophasors). Synchronization of samples and various measurements is critical for protection applications, which demand high security and dependability.

To address power industry and Smart Grid needs for accurate timing and synchronization over Ethernet networks, the Relaying Communications Subcommittee (H Subcommittee) of the IEEE Power System Relaying Committee (PSRC) and the Data Acquisition, Processing, and Control Systems Subcommittee (C0 Subcommittee) of the IEEE Substations Committee (SUB) established a joint Working Group, PSRC H7/Sub C7, tasked to develop IEEE Standard PC37.238 titled “IEEE Standard Profile for Use of IEEE 1588 Precision Time Protocol in Power System Applications”.  The joint Working Group coordinates its work with IEC TC57 WG10 to enable adoption of the standard profile into IEC 61850.  To speed up standard profile development and ensure that the most appropriate and interoperable options are selected, the WG established an interoperability testing program called plug-fest. The first plug-fest took place on September 14, 2009 in Arlington, TX, where 6 vendors with 15 devices were able to demonstrate interoperation achieving 200-400 ns timing accuracy over 4-5 network hops. The second plug-fest took place on January 11, 2010 at the IEEE Power and Energy Society meeting in Orlando, FL. Five vendors (Hirschmann, IXXAT, Meinberg, RuggedCom and Tekron) with 11 devices (grandmaster clocks, transparent clocks and ordinary clocks) successfully performed detailed testing and statistically analyzed the data. For the first time two vendors’ teams were represented locally and participated from overseas using an intercontinental audio-video bridge.

The devices were connected over 100Mb/s Ethernet (copper) links into various star and ring network topologies. The network grandmaster was locked to UTC using a GPS receiver and antenna placed outside for adequate sky coverage. All devices were configured per profile IEEE PC37.238 Draft 1.6, which specifies Layer 2 Ethernet mapping, use of IEEE 802.1Q tagged frames, peer-to-peer delay measurements, 1s Sync and Announce Intervals, etc. Initial baseline testing covered establishing master-slave hierarchy using the IEEE 1588 Best Master Clock Algorithm, measuring slave-to-master offset, per-link peer delay, etc.

As power substation networks are expected to fall into isolated islands and reconnect without causing unexpected behavior, special attention was given to measuring convergence time after different events. Series of tests were performed to measure master failover and master recovery time. Slave convergence time following slave power down/up and disconnect/reconnect events was also measured. For the plug-fest demonstration, a ring configuration was set up with one Ethernet link blocked by Rapid Spanning Tree protocol. For more strenuous testing Omicron IEC 61850 traffic generator was added. It emulated and fed to the network IEC 61850-9-2 sampled values traffic from one merging unit. Most devices were able to keep the same quality of synchronization with such traffic load.

The plug-fest demonstrated the expected quality of time synchronization (normally within 1 microsecond) and convergence time (around 20s). It showed that IEEE PC37.238 Draft 1.6 specifies implementable and interoperable options, which could lead to desirable performance. Plug-fest results were presented and discussed at PSRC WG H7/SUB C7 meeting on January 13, 2010.  WG will consider including plug-fest recommendations, such as adding a specification of holdover, into the final standard draft. 

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