Integrating UCA at the TVA/Tiptonville Switching Station for SCADA and Relay Protection Applications

Introduction

The difficulties and complexities of integrating Intelligent Electronic Devices (IEDs) from different vendors equipped with different communication protocols have bedeviled the electric utility industry since the introduction of IEDs in the 1980’s. In response to this problem, the Tennessee Valley Authority (TVA) began shifting its attention to 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 of 2003 it completed a second UCA project at its Tiptonville switching station site in northwest Tennessee, not far from Reelfoot Lake.

The Tiptonville project broke new ground, integrating both Supervisory Control and Data Acquisition (SCADA) and relay protection applications into a networked, multi-vendor IED product environment. Tiptonville is a two-year old switching station that includes four 161KV 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.

Background

The Tennessee Valley Authority, set up by the U.S. Congress in 1933, is a federal corporation and the nation’s largest public power company. Eleven coal fired plants, three nuclear plants, 29 hydro-electric plants, six combustion turbine plants, and one pumped storage plant make up the bulk of TVA’s generation assets. TVA’s power service area, with 17,000 circuit miles of transmission lines, covers 80,000 square miles in the southeastern United States. It includes almost all of Tennessee and parts of Mississippi, Kentucky, Alabama, Georgia, North Carolina, and Virginia. TVA’s customer base comprises 158 municipal and cooperative power distributors and 62 large directly served industries and government installations.

Project Overview

The overall scope of this project provided additional transmission capacity in the NE Tennessee region of the TVA system by building a new 161kV transmission line and the Tiptonville switching station.

Design Objectives

The decision to use a common, UCA-compliant LAN was perhaps the single most important key for enabling broad use of advanced technologies within the substation environment. This key unlocks the potential to access a wealth of data and functionality from IEDs. It enables the deployment of distributed applications that require peer-to-peer communication among IED devices. It enables centralized control systems to provide strategic guidance to those distributed applications, while receiving continual feedback from them for system-level assessment. Most importantly, the approach offers an abundance of flexibility, in contrast to the rigidly wired systems that precede it, so that systems can continue evolving without undue economic constraint. Clearly, powerful communication capabilities that promote interoperability among connected devices and systems represent a breakthrough toward achieving long-thwarted utility business objectives.

This installation realized multiple goals. Firstly, it provided a test bed to demonstrate how these new technologies can be deployed to advantage in a widespread manner over the TVA system. Secondly, it served as a “proof of concept” demonstration of multi-vendor interoperability. Thirdly, it demonstrated that these new technological approaches can be incrementally melded with traditional practice. This is essential for effective management of system migration; introduction of new technology must be accomplished in ways that avoid operational disruption and avoid the need for wholesale replacement of existing solutions. At Tiptonville, for example, conventional relays and communication techniques (e.g. contact closures) are used alongside UCA-capable relays in transmission line and bus protection schemes designed to minimize project risk and provide redundancy for critical protection functions.

Delving into Tiptonville’s protection implementation a little more deeply, the line protection scheme is implemented with two different methodologies. One set of relays uses a conventional approach, while the other uses UCA Generic Object Oriented Substation Event (GOOSE) messaging. A third relay provides breaker failure and reclosing functions, using only UCA/GOOSE messaging. Two sets of relays are also used to provide bus protection; again, one uses a conventional approach and the other, UCA/GOOSE messaging. All of these relays can be coordinated; those that can exchange UCA/GOOSE messages do so. Otherwise, contact closures are used.

SCADA functions operate over the UCA network as well, using UCA Generic Object Models for Substation & Feeder Equipment (GOMSFE) to represent the structured data and functionality held by the IED device servers and aggregated in the UCA Client/Server repository. Separate network transducers have been installed for line and bus readings, reducing the vulnerability of critical analog data needed by the operations group to relay outages and testing. Although the vast majority of site data is acquired from IEDs, there are some ancillary “hardwired” I/O points that are used to provide access to data not accessible via UCA. This legacy data is seamlessly integrated into the UCA Client/Server repository, just as if it were derived via UCA services. This is another mainstay support for continual system migration.

Network design utilizes a switched Ethernet environment, supported by fiber-optic cable for network connections, to ensure reliable operation. Future addition of a router and other components for enterprise connectivity were also factored into the final system design.

Aside from technical issues, perhaps the most important design goal was to conduct the project and deploy the system in a manner that would effectively impact daily TVA practice. The path here, of course, is to gain acceptance and confidence in these new technologies and practices from affected line groups. These include the O&M organization, which is responsible for the station once the project is completed. It makes all the difference in the world, as time passes, whether a demonstration project is successfully integrated into continuing practice or bypassed, For example, it was helpful to make interaction with the new technology more transparent, by ensuring that existing functional testing and switching procedures could be used. Ideally, we wanted line group personnel to be confronted with few functional differences from TVA’s conventional practice.

System Components

Fourteen IEDs of three different types are used to manage the station via the UCA network. All are UCAserver devices, interconnected via a fiber-optic, Ethernet station LAN. 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). Additionally, one set of non-UCA relays (four SEL-321 relays and one SEL-551 relay) is installed to meet TVA’s redundant system design criteria for transmission line and bus protection. These SEL relays are connected indirectly to the UCA network using a SEL-2030 as a gateway. This configuration allows data from all station IEDs to be accessible via the UCA network for future enterprise connectivity.

Supervisory control at the station is managed by a UCA Client/Server (a StationManager unit provided by Siemens), which is also connected to the station LAN.

RuggedCom RS1600 fiber-optic Ethernet switches and media converters provide the LAN connectivity for the project. A dedicated PC is installed at the station for use with vender configuration software as well as SISCO’s AXS-4-MMS, MMS Object Explorer, and GOOSEMON software for system configuration and testing.

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