Rich Multipurpose Substation Automation Using Utility-hardened Ethernet

By Nabeel Sherif, GE

The campus of the Georgia Institute of Technology is a mixture of residential, research, institutional and industrial environments. With students, faculty and staff using the facilities around the clock, safe, reliable power infrastructure is a necessity. That’s why when it came time to renew power distribution infrastructure, Georgia Tech’s Facilities Design and Construction team decided to take a fundamental look at its power distribution facilities and assess how to meet its future needs.


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Upgrade or Replace?

Several reasons for upgrading distribution facilities at Georgia Tech existed. The campus in Atlanta grew considerably in the past 30 years and now serves more than 20,000 students and employees. In addition to the increased population, new buildings, laboratories and student residences meant more demand on the distribution system and increased demand in more places.

“The old [distribution] substation was an electromechanically controlled facility that operated as a stand-alone location–no networks, no remote monitoring, nothing,” said David Chandler, senior electrical engineer for Georgia Tech.

In addition, the area around the substation has developed considerably and now includes new classrooms, residences and other locations. The Georgia Tech team decided that rather than upgrade, they would replace the old substation with a brand-new, unattended and automated distribution substation designed with future needs in mind.

A benefit of starting with a “green-field” facility is that it gave the engineering team a chance to try new options to manage the power system, which included connecting the new substation into a protection and control network, as well as enabling remote control of the substation relays and devices.

Management and Monitoring Infrastructure

The new substation, which would feed power from the upstream utility to a group of buses, was to be controlled by intelligent relays. Relay data would be provided via DNP to the upstream monitoring system. These relays were used to control a tie and two 2,500-amp buses, which were sectionalized using breakers into four-bus zones. Because all of the devices in the station were to be monitored through a SCADA system, the ability to individually monitor and control any individual relay or device in the system was a requirement. The substation would also enable a main-tie-main automatic transfer scheme. This transfer scheme and other automated functions would be implemented through the intelligent electronic devices (IEDs) using IEC 61850 GOOSE messaging.

The Georgia Tech team quickly decided that an Ethernet-based network would allow them to realize all their requirements and more. Prior to this infrastructure upgrade, the Georgia Tech power system had not been heavily networked and many of the devices in the old substation were electromechanically based and were not easily networked. The new substation offered the chance for Georgia Tech to take its first steps toward implementing Ethernet networking as part of the power management system. The key advantages provided by Ethernet in the Georgia Tech substation were the technology’s ability to provide flexibility for multiple applications, overall ease of use and performance reliability. They decided to use General Electric MultiLink switches to implement their new substation network, as these switches offered industrial/substation-specific environmental tolerances and fast recovery to maintain connectivity to end devices at all times.

Flexibility and Ease of use

By using Ethernet, Georgia Tech realized multiple benefits from the new substation. Aside from allowing easy interconnection to the SCADA system, using Ethernet to extend the network to the substation allowed the substation and all its devices to be integrated into Georgia Tech’s existing network and power management systems. This provided unified visibility to issues, alarms and other events in the new facility. It also enabled monitoring and collection of data from the meters on each main, which gave the Georgia Tech team the ability to accurately monitor usage and costs for each part of the power system. Using these features, the team realized that an Ethernet network met their original specified needs and increased visibility to the power system from any location they required. It also made management and control of the power system much easier.

Ethernet networking made it easy for Georgia Tech to set up high-speed connectivity between any two points without excessive network or device set-up or configuration. Unlike serial device connections or other types of networks, Ethernet provided easy interconnection to newer devices such as intelligent relays. It also made it easy to extend the network to older devices by using serial-to-Ethernet converters or Ethernet-enabled serial port servers. One of the Georgia Tech team’s requirements was that the Ethernet platform chosen needed to be a managed Ethernet solution. Managed Ethernet made it even easier to optimize and to future-proof the network. By using functions such as quality of service (QoS) to prioritize critical traffic, and simple network management protocol (SNMP) to integrate into existing network and IT management systems, managed Ethernet made it easy to keep a close eye on network performance and to respond to any issues quickly. The platform they chose also integrated quickly and easily with the relays and IEDs already selected for use in the substation. Additionally, because Ethernet is able to scale speeds from 10Mbps to 1,000Mbps or more as required, Ethernet infrastructure provided the new substation with all the bandwidth it required at the time and any it would need in the foreseeable future.

Hardened and Reliable

The remaining challenge for the Georgia Tech team was to find an Ethernet hardware set suitable for mission-critical applications like the ones running in their new substation. The key to meeting the reliability requirements of the Georgia Tech substation meant managing three concerns. First, the network equipment would need to withstand variations in temperature, electromagnetic fields and power disturbances without affecting network traffic. Next, the equipment needed to be capable of recovering from disturbances or changes in the network quickly and without affecting the mission-critical applications in the substation. Finally, because the main-tie-main transfer scheme would be using IEC 61850 GOOSE messaging to control the relays, compliance to IEC 61850 standards was required. The GE MultiLink system Georgia Tech chose met these requirements: operating temperature of -40 C to 85 C, network recovery of less than 5 milliseconds per switch and compliance with the IEC 61850 standard. With all the network requirements met, the team was ready to begin work on the new facility.

SETUP AND MANAGEMENT

Setup at the new facility started in May 2007. Because interrupting power to the campus to cut over from one station to the other was not an option in a continuously operating environment, the cutover was phased to minimize service interruptions.

“We were able to get everything in and working quickly and simulate events as part of the implementation,” Chandler said.

With the ability to view, manage and control individual relays and devices using the Ethernet network in the new substation, the testing and diagnosing work during cutover was significantly reduced.

The final cutover finished in August 2007, three months after energizing the new substation. Since assuming full operations, the Ethernet network has performed reliably and without failure and has enabled other functions for the Georgia Tech team.

“We also use a GPS clock to do time synch through the network instead of IRIG-B,” Chandler said.

They’ve also set up real-time monitoring of the power system through a Web-based portal, making it easier for the team at Georgia Tech to manage the substation and facilities. By using a well-planned, utility-oriented Ethernet networking platform, Chandler’s team has enabled fast, reliable power that can be managed safely and securely, for the entire community at Georgia Tech.

Nabeel Sherif is the product manager for Ethernet communications products at GE Digital Energy. He holds an MBA from Queen’s University in Canada and has designed and managed dozens of communications products and hundreds of Ethernet networks during the past decade.

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