THE COMPLEXITIES OF INTEGRATING INTELLIGENT ELECTRONIC DEVICES (IEDS) from multiple vendors, using different communication protocols, have bedeviled the electric power industry since their introduction in the 1980s. In response, the Tennessee Valley Authority (TVA; Knoxville, Tennessee, U.S.) began shifting its attention to the Utility Communications Architecture (UCA) in the mid-1990s.

Intent on getting experience with this new technology, TVA completed a demonstration UCA project at its Paradise Power Plant in Kentucky in May 1999. In September 2003, it completed a second UCA project at its Tiptonville switching station site in northwest Tennessee.

The Tiptonville project broke new ground, integrating both supervisory control and data acquisition (SCADA) and relay protection applications into a networked multi-vendor IED system environment. Tiptonville is a three-year-old switching station that includes four 161-kV power circuit breakers in a main-and-transfer bus arrangement that provides for connection to three transmission lines and a customer's local distribution substation. From the very beginning, construction plans focused on UCA networked communications as the basis for station management.

This project provided additional transmission capacity in the northeast Tennessee region of the TVA system by building a new 161-kV transmission line and the Tiptonville switching station.

DESIGN OBJECTIVES

The decision to deploy an Ethernet substation LAN carrying UCA 2.0-compliant communications was key to overcoming traditional roadblocks to substation automation. It unlocks the potential to access a wealth of data and functionality from IEDs. It enables the deployment of distributed applications requiring peer-to-peer IED communication. It enables centralized control systems to provide strategic guidance to those applications, while receiving continual feedback for system-level assessment. Most importantly, the approach offers tremendous flexibility, so that systems can continue to change in response to new requirements, without undue economic constraints. Clearly, communications interoperability among connected devices and systems represents a breakthrough for achieving long-thwarted business objectives.

This installation realized multiple goals. Firstly, it provided a test bed for demonstrating how these new technologies can be deployed advantageously. Secondly, it was a proof-of-concept demonstration of multi-vendor interoperability. Thirdly, it demonstrated that these new technological approaches could be incrementally melded with traditional practice.

This melding with traditional practice is essential for the system migration of existing facilities. New technology must be introduced in ways that avoid operational disruption and wholesale replacement of existing systems. For example, at Tiptonville, conventional relays and communication techniques (contact closures) are integrated with UCA-capable relays and generic object oriented substation event (GOOSE)-messaging techniques to implement transmission line, bus and breaker-failure protection schemes.

SCADA functions operate over the UCA network using UCA generic object models for substation and feeder equipment (GOMSFE) to represent the structured data and functionality within IED device servers and the client/server repository. Some data are acquired from hardwired I/O points, but such legacy data are seamlessly integrated into the repository, just as if they had been derived from UCA sources. This is another mainstay support for continual system migration.

Aside from the technical issues, the most important goal was to gain acceptance from affected line groups, so that these new technologies would be adopted into TVA's standard practice. Where feasible, it was helpful to make interaction with the new technology transparent, allowing existing functional testing and switching procedures to be used. Paying attention to such issues can make all the difference in whether new technology is successfully integrated into practice or bypassed.

SUPERVISORY CONTROL APPLICATION

The UCA client/server gathers data from IEDs via UCA reports and polls, storing that data in its UCA-compliant repository. The repository is locally and remotely browsable as a proxy server. The client/server and all other IEDs use common GOMSFE information models and common application services model (CASM) communications services to exchange data and execute commands. The client/server system acts as a gateway to the station, responding to distributed network protocol (DNP) requests for data and commands issued by TVA's EMS system in Chattanooga, Tennessee.

With few exceptions, the UCA's IEDs provide all the data and control functions needed for real-time supervision of the switchyard and surrounding transmission system. These include power system data, breaker control and status, and recloser control and status. The equivalent of several hundred points of data are implemented.

RELAY-PROTECTION APPLICATIONS

Three protection applications have been implemented: line, bus differential and breaker-failure protection. The nine UCA relays coordinate this distributed protection activity using a combination of GOOSE messages and traditional contact closures. All protection algorithms and coordination are implemented using the devices' native programmable logic.

The relays interact by generating multicast GOOSE messages to transmit discrete state changes, such as the bus differential condition and protective trip/breaker failure initiate. Breaker failure lockout conditions are detected and managed internally by the Cooper EdisonPro relay, eliminating the need for a standalone HEA lockout relay. Lockout reset and breaker failure enable/disable functions are accomplished via front-panel push buttons on the EdisonPro, eliminating other conventional, external components.

Each IED, including relays and client/server, periodically issues a “heartbeat” GOOSE message. Each IED also monitors that activity from its peers. This allows every device to determine which peers are operationally available and which are not. Devices can use information about network abnormalities to complete certain actions via alternate paths.

LESSONS LEARNED

As with any new technology, unexpected circumstances require adjustments to be made to project plans. The Tiptonville demonstration project was no exception. Last-minute firmware changes, functional testing deficiencies, organizational boundaries, knowledge of the technology and design changes challenged TVA and its consultant and vendor partners.

Given the demands of the project, training for personnel turned out to be critically important. Successful rollout of the technology depended heavily on the skill level of the personnel involved in all aspects of the project, as well as long-term O&M support for the Tiptonville system after project completion. Vendor training for IEDs, exposure to UCA basics and networking fundamentals were at the core of this training. It proved essential for those involved in the project to have an understanding of the technology and products involved, and how they were to be used within the system.

Project plans called for testing all schemes in a lab environment and freezing firmware revisions following that activity. However, additional problems were encountered up through the final commissioning phase at the Tiptonville site. These problems were not visible until the fully integrated system was available with all components present on the network. While increased testing in a lab environment may have helped, it is difficult to simulate complete system behavior using only a subset of all devices.

We expected that site commissioning would present some challenges since it was our first opportunity to validate the fully integrated system in its real-world environment. TVA needed to validate the operation of IEDs in support of SCADA and protection applications, test the client/server capabilities, test and validate the customized relay logic, and validate the operation of protection applications. Beyond all this, TVA needed to gain confidence that all these capabilities would operate reliably under various operational scenarios.

Problems encountered in the course of the project had to be individually dissected and solved as they were discovered. Part of the problem involved mental accommodation to the new approaches, but as we gained experience with the system, we were able to make smarter decisions and became better at anticipating problems. In the end, all functional objectives were accomplished by the completion of commissioning, and no design problems have been encountered since. Nevertheless, improved test plans that address network contingencies, validate GOOSE performance, enable safe and acceptable test modes, and enable state-manipulation of data during testing are needed.

Another issue became visible during this undertaking. In conventional substations, protection and SCADA are fairly segregated, and testing activities in the two areas rarely affect each other. However, at Tiptonville this is no longer true. Devices on the network are now so interrelated through the network that the testing of one device may require other devices to be placed off-line as well, for the operational safety of the local system. In other cases, multiple departments share functionality in the same device and so scheduling for testing needs to be coordinated. These examples highlight potential problems that arise when multiple departments share functionality in the same device or even on the same network, and it raises questions for each utility about how to deal with these issues.

DOCUMENTATION

Good project documentation is critically important for smooth project execution. The documents provide a common roadmap for all participants, deal with the resolution of integration issues and show all the details necessary to achieve communications interoperability.

After TVA's commissioning was completed, we updated our documents to create an “as-installed” set. Take note that this project was based on EPRI's UCA 2.0 specifications for substation communications, which preceded the now-released IEC 61850 international standard, Communications Networks and Systems in Substations. As such, there were some unpolished areas that the project had to navigate to realize interoperability among the IEDs. Use of the standard in future projects will undoubtedly result in fewer bumps in the road.

THE FUTURE

TVA's UCA experience at Paradise and Tiptonville has provided the practical knowledge and understanding we need to move forward. TVA is now raising the bar by comprehensively applying IEC 61850 to a new substation site in Tennessee, to be placed into service in 2007. Plans include extensive enterprise access to the site's data and functionality. To be successful, all aspects of substation practice will have to be molded around substation LAN communications.

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Brian Smith is a principle design engineer in TVA's Trans-mission Power Supply/Electric System Projects group. He received his BSEE degree from the University of Tennessee at Chattanooga in 1991. bpsmith@tva.gov

Craig McClure is a principle design engineer in TVA's Trans-mission Power Supply/Electric System Projects group. He received his BSEE degree from the University of Tennessee at Chattanooga in 1991. pcmcclure@tva.gov

Randy Ehlers is a lead consultant with Utility Consulting International (UCI) in Cupertino, California, U.S. He assists utilities with integration and automation projects involving advanced communication technologies. Ehlers received his bachelor's and MSEE degrees from Rice University, and his master's degree in computer science from the University of Southern California. rgehlers@uci-usa.com

SYSTEM COMPONENTS

TVA's network design uses switched Ethernet, implemented over fiber-optic cable to ensure reliable operation. Provisions were made for a future router to support enterprise connectivity.

RuggedComm RS-1600 fiber-optic Ethernet switches and media converters were selected to implement the scheme. An externally powered media converter was installed for each relay, so that its network connection can be interrupted whenever a device is individually tested. An FT test-switch blade is opened to interrupt power to the media converter. These test switches are already installed for all relays to isolate conventional trip outputs during testing. This approach is used in lieu of software interlocks, so that all tripping functions, whether initiated through hardwired contacts or GOOSE messages, can be isolated using the same conventional technique.

Fifteen IEDs of four different types cooperatively manage the station via the UCA network. Four of these are distance-line relays (UR-D60 units provided by GE Power Management), five are line and bus protection relays (EdisonPro units provided by Cooper Power Systems) and five are network transducers (PowerServe units provided by Alstom/Bitronics, now Areva). The last device is the UCA Client/Server unit. There is also a set of non-UCA relays (one SEL-551 and four SEL-321 relays) installed to meet TVA's redundant system design criteria for transmission line and bus protection. They may be connected to the UCA network in the future through a SEL-2030 gateway.

A dedicated PC accommodates vendor configuration software as well as SISCO's AXS-4-MMS, MMS Object Explorer and GOOSEMON software for system configuration and testing.