Oncor's broadband-over-power-line (BPL) network, which covers 65 sq miles (168 sq km) in Dallas, Texas, U.S., combines the speed of fiber optics with the unique capabilities of BPL technology to deliver first-rate reliability and service. With 28 substations and 200 distribution lines moving power to homes and businesses in this area, Oncor's BPL network gives unequaled visibility into the performance of the grid and acts as an incubator for new system monitoring tools.

The Dallas BPL system reads meters, monitors network performance, supports automated switching and identifies areas of concern for Oncor operations engineers who use the information to pinpoint potential problems. Because the area has an extensive urban forest and is served primarily by overhead lines, Oncor's BPL network regularly detects transformer trips and tree-related power disturbances. With this advance warning system, Oncor is able to prevent many outages.

In numerous documented cases, the BPL network has identified problems in the field that have been investigated and corrected without customers even realizing there was an issue on Oncor's network.

Fiber Backbone

Fiber-optic cable is the backbone of the BPL project. Oncor currently has fiber connections installed in two substations. In the summer of 2009, Oncor installed fiber-optic cable in a major transmission switching station in the BPL footprint. The fiber will be connected to an adjacent, newly completed static VAR compensator (SVC) station, one of two in Dallas, which has the largest concentration of SVCs in the world. To complete the data connections, an optical switch and routers will be installed at the SVC and switching station in early 2010.

The stations are being used as prototypes for the rollout of a standard North American Electric Reliability Corporation cyber infrastructure protection-compliant substation IP network architecture. The architecture includes a standardized station router design with port management and multiple virtual local area networks for data prioritization and security. High-speed fiber connections enable video monitoring and electronic station access control at substations.

Network Elements

Oncor's BPL network covers approximately 105,000 premises, consists of 560 miles (901 km) of fiber-optic cable and has more than 18,000 network elements. There are three types of network elements: backhaul points, power line bridges and low-voltage repeaters.

Backhaul points transition the data stream from fiber optics to BPL services. The power line bridges, located at single-phase distribution transformers within the BPL footprint, literally bridge around the distribution transformers to transition a BPL signal from medium-voltage distribution primary to low-voltage distribution secondary. There are two bridge configurations: pole mounted and padmounted.

Low-voltage repeaters on distribution secondary repeat the BPL signal to reach meters on longer secondary runs. Both the backhaul points and the bridges use a coupler connected to the network element by a coaxial cable to transfer the BPL signal on and off the medium-voltage primary from the element.

The bridges monitor voltage on both 120-V legs on the distribution secondary, capture readings at 0.1-second resolution and aggregate the data for reporting. Interval measurements are shipped back through the network and processed in the back office through several algorithms to produce actionable alarm information.

Daily Reports

Daily reports are generated for high- and low-voltage excursions outside specific bandwidth parameters, as well as voltage imbalance, incipient secondary neutral failure and transformer failure. Meter loads are accumulated per transformer and included in a transformer loading report.

An example of the level of granularity the system is capable of can be seen in a snapshot of the 1722 data points that represent a day of a voltage observation point. When both 120-V legs are at the same level with only minor fluctuations, the resulting snapshot is fairly smooth. A more erratic voltage secondary plot could reveal characteristics of a loose neutral connection or some other situation that requires investigation.

System Plan

Oncor began installing updated advanced meters in 2008. The goal is to replace every non-interval data recorder meter in the system, a total of 3.4 million, with advanced meters by the end of 2012. The majority of these advanced meters use a 900-MHz spread-spectrum mesh backhaul network. A high percentage of the collectors associated with Oncor's mesh backhaul network are located in substation yards. A collector acts as a central communication node for a specific geographic portion of the mesh network and provides the access point for all of the metering and related smart grid data to enter and leave Oncor's broader IT network.

Three substations now have fiber-optic communications. Ultimately, 26 additional substations within the BPL footprint will have fiber. Several other substations on the fringe of the footprint may have fiber extended to them. Oncor also has 33 S&C Scada-Mate IntelliTEAM II switches linked to the fiber network. The fiber connections, which were installed to test the architecture and ability to connect, have performed superbly.

Currently, cellular modems carry most metering and smart grid-related data from the collectors back to the Oncor IT network. Ultimately, Oncor expects to move as many collectors as possible from cellular to an Oncor-owned network connection. The hybrid fiber BPL infrastructure will provide for or enable many of those network connections in the Dallas area.

Fiber Buildout

Data transport between the BPL fiber hub and Oncor's IT network is handled through a leased dense wavelength divisional multiplexing fiber ring and two points of presence (POPs). Three leased T1 circuits link the POPs to Oncor's data centers. As those leases expire, BPL fiber infrastructure will be integrated into Oncor's existing Dallas/Fort Worth area fiber network.

Extending Oncor fiber to the BPL fiber hub will create a diverse fiber link from the hub to Oncor's data centers and provide sufficient bandwidth for the connection of the remaining substations in the BPL footprint to the fiber rings and other nearby Oncor facilities. Oncor is reviewing high-bandwidth wireless technologies that will allow the extension of the available bandwidth from the fiber-optic network to other area substations and company facilities.

Most of Oncor's substation supervisory control and data acquisition circuits are on analog phone lines. Oncor would prefer to upgrade these analog lines to high-speed digital circuits, a step that would expand system protection options, speed access to equipment like digital fault recorders and support the ability to deploy advanced substation security measures.

Bringing digital (copper) phone circuits into the substations requires expensive fiber-optic isolation equipment to protect the phone system's digital switches from substation ground fault potential. The use of fiber optics and wireless communications avoids that expense and keeps the communication links within Oncor's private network.

Analysis Capability

Oncor has been collaborating with the Science Application International Corp. (SAIC) over the last year to enhance the network's analysis capability. SAIC-designed analysis tools will take data feeds from the existing analysis system and apply additional intelligent filters that will allow finer control over the filter parameters. Currently, engineers use a manual process to sort through alarm entries. With these filters, it will be possible to zero in on information that requires immediate attention.

SAIC-designed Web interfaces will transfer information directly to distribution operation technicians' e-mail accounts. The SAIC interface should remove much of the existing workload of reviewing alarm data and quickly identify field equipment needing repair.

Oncor's BPL network gives operators a detailed view of distribution network operations, information not available with any other technology. This accessibility allows the diagnosis and repair of problems before they become failures and adversely affect customers.

Fiber contained within the network provides backhaul for the BPL-related data and enables high-speed communication to the distribution automation switches. Fiber also brings digital broadband communication links to substations and Oncor facilities within the BPL footprint. In the future, this same fiber will be used to enable broadband extensions to the utility's infrastructure outside the footprint.

Oncor will continue developing and integrating the BPL network into its business practices and communications infrastructure to enhance overall reliability for its customers.

Larry Kohrmann (larry.kohrmann@oncor.com) is the BPL manager for Oncor. In addition to BPL, he has responsibility for the deployment of backhaul infrastructure for Oncor's advanced metering infrastructure network. Other smart grid-related activities include serving as a UCAIug OpenSG Technical Committee member, as a National Institute of Standards and Technology Smart Grid Interoperability Panel voting member and as a member of the ZigBee+HomePlug SE 2.0 MRD team. Kohrmann is a member of IEEE, a registered professional engineer in Texas and a graduate of the University of Missouri - Rolla with a BSEE degree.

Companies mentioned in this article:

North American Electric Reliability Corp. www.nerc.com

Oncor www.oncor.com

S&C Electric Company www.sandc.com

Science Application International Corp. www.saic.com