Something to Bragg About: Army Base Power Distribution System Upgrade

Cooper Power Systems teamed up with Sandhills Utility Services LLC to upgrade the power distribution system at the U.S. Army base at Fort Bragg, NC. Sandhills Utility Services, LLC was awarded the contract for maintaining and updating Fort Bragg’s power distribution system. This included upgrading the relaying system from electromechanical to microprocessorbased relays. Sandhills Utility Services selected the iDP-210 feeder protection Idea™ relay from Cooper Power Systems, in large part because iDP-210 relays with PeerComm™ communication protocol could be used as a basic Supervisory Control And Data Acquisition (SCADA) system for the utility.

A Communications Bridge

This system provides status, load, and voltage information as well as open, close, and tagging command functions. The same communications system can also be used as a ProView™ bridge between each relay and Sandhills Utility Services’ headquarters. This communications bridge enables the operator to individually program and interrogate each relay from the comfort of the office instead of outside at the substation.

The communications system that Sandhills Utility Services installed with the help of Cooper Power Systems is a combination of existing and new technology that meets the base’s objectives while managing costs. The entire system is Ethernet-based, and offers two distinct levels.

Selecting the Switch

The first level, installed at each substation, is a RuggedCom^® RS1600, 100 base fiber optic Ethernet switch. The RuggedCom switch was selected because it is specifically designed to operate reliably in electrically harsh environments. Two features of the RuggedCom switch that are critical to this application are its high electrical immunity, important within substations, and its wide operating temperature range, a key consideration in this application since its location is in a non-temperature regulated enclosure. This switch serves two functions in the overall communications system. The first function is to limit the range of the PeerComm messages, but still provide through access to the relays for other data structures. The second function is to provide electrical isolation between the relays, which is done via the fiber optic cables connecting the relays to the switch.

Linking Substations to Headquarters

The second level of the Ethernet system connects each substation to Sandhills Utility Services headquarters. Ideally, dedicated fiber optic cable would be run from the switches in each substation to headquarters. This would provide ample bandwidth for high speed downloads of ProView schemes. However, running miles of new fiber optic cable between the substation and headquarters was cost-prohibitive. Instead, phone lines that had been previously installed between the substations and the headquarters where utilized.

The phone line usage was made possible with Direct Service Line technologies (DSL). While DSL worked well at reducing the cost of the overall installation, tradeoffs included slower transmission speeds and different transfer rates depending upon the distance the substation is located from the headquarters. The further the distance, the slower the transfer rate, with the physical limitation being 18,000 ft. of conductor distance. Transfer rates between the four substations at the military base ranged between 200kbs and 1Mbs. Ethernet radio communications were considered, but security issues on the base made radios impractical.

Connecting to Each Relay

Once the overall communications backbone was in place, personnel at headquarters could connect to each iDP-210 relay via ProView software. This is possible because each iDP-210 relay can be set up with its own static Internet Protocol (IP) address. ProView application software then seeks out those IP addresses and communications are established. For security reasons, each relay can be set up with a unique connection password that must be entered correctly for the relay to establish communications with the server. With the Ethernet connection established between the server at headquarters and the iDP-210 relay at the substation, full access to the relay is available. Depending upon the established user access levels, access can be limited to simple viewing of status and metering information, or can be as comprehensive as full program uploads, downloads and setting changes. In addition, sequence of events and oscillography data can be downloaded from the relay, just as if the user were next to the relay with an RS232 cable, but at much greater download speeds.

While having the ability to communicate individually to each relay has its benefits, seeing specific information from a group of relays can give operations personnel a better idea of what is happening to the overall system. This factor was especially critical to Army personnel who wanted to have the ability to quickly scan their system to look for tampering of feeders. Also, since the overall base distribution system is relatively small (45 feeders), Sandhills Utility Services didn’t want to incur the expense of installing a full-blown SCADA system that is typically seen at large investor-owned utilities. PeerComm communication protocol addressed this concern.

Gathering and Displaying Information

By segregating the system into substation-size PeerComm protocol sections, all the information from each relay in the substation can be gathered into one relay and displayed in a graphical layout in that relay’s Idea Workbench™ container area. Shown at right is an example of such a graphical layout from the Sandhills Utility Services system at Fort Bragg.

For each iDP-210 feeder relay, PeerComm protocol is transmitting the following information
to the iDP-210 main relay at each substation:

• Phase and Ground Currents
• Line to Ground Voltage
• Open Close Status
• Trip Circuit Fail
• Reclose Block Status
• Ground Trip Block Status
• Any Alarm
• Phase A, B, C, and Ground Targets

From the iDP-210 main relay at each substation, PeerComm can transmit the following command to each iDP-210 feeder relay upon a user-initiated mouse click:

• Breaker Trip
• Breaker Close
• Toggle Reclose Block
• Toggle Ground Trip Block

Broadcasting and Listening to Messages

PeerComm communication protocol Ethernet signals are broadcast-type messages that are sent out by each relay at a fixed interval. Other relays in the same network can be programmed to listen to these messages from none, some, or all of the other relays on the network. The RuggedCommanaged switch is able to limit which ports these PeerComm broadcast messages are allowed on through the use of the VLAN functionality. By limiting the scope of these messages to certain ports, the switches help to keep the PeerComm message traffic manageable and prevent unnecessary bandwidth from being consumed. Other types of messages, such as ProView over Ethernet, are unrestricted and thus can access the entire network to communicate with all of the relays.

Sandhills Utility Services was concerned about future expansion and inter-device compatibility with their system. While PeerComm protocol can be expanded to other substations, at some point investing in a complete SCADA system may make sense. Sandhills Utility Services wanted to make sure that the system they were investing in today would still be useable in the future. While PeerComm itself may not work with non-ProView type devices, the iDP-210 relays and Ethernet communication infrastructure do. When Sandhills Utility Services migrates to a true SCADA system in the future, the hardware installed now will be adaptable. In fact, the iDP-210 relays already have the capability to communicate using a DNP3 protocol via TCP/IP. Sandhills Utility Services only needs to install a DNP master station to their already existing Ethernet network for this functionality to occur.

Flexible Application

PeerComm protocol is very flexible in its application. It is excellent for information sharing between peer devices where no “master” is needed, or where traditional master-slave communications can be
too slow, such as a protection-based communication. Ethernet-based communications are rapidly expanding in the utility industry and Cooper Power Systems continues to develop PeerComm communication protocol options that complement these new technologies.

 

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