Wireless Connectivity for a Reliable Smart Grid

by Jason Wilson, On-Ramp Wireless

The Department of Energy (DOE) has aggressively sought emerging products, systems and networks capable of realizing a cost-effective solution that would provide seamless coverage to every corner of the grid.

According to the IEEE Distribution Reliability Working Group 2012, homes and businesses experience an average of more than 120 minutes of electricity outage each year (see Figure 1).

IEEE Distribution Reliability Working Group 2012

This costs billions of dollars annually, and the Systems Average Interruption Duration Index (SAIDI) is on an upward trend. The need to improve grid reliability is clear, and the DOE has set a goal to improve SAIDI by 20 percent by 2020. The DOE’s work with industry, national labs, universities and other groups to research, develop and demonstrate commercially viable solutions is beginning to pay off as new systems are commercially available.

More Sensors Provide More Intelligence

Reaching these reliability goals requires that utilities can predict grid maintenance requirements accurately and rapidly detect, locate and remediate electricity outages.

Today’s utility outage management tools provide the intelligence required to manage maintenance and outage remediation efforts, but pervasive monitoring of grid control devices is still lacking in many areas of the grid.

Placement of grid control and monitoring devices typically is determined first by the functional requirements for the devices and second by the availability of communications with the device. Many devices installed do not have a reliable communications link, but as improvements in the reliability and cost of such communications technologies evolve, existing devices are being connected and the list of high-value, feasible grid-monitoring points is expanding, thus improving utilities’ intelligence base for predictive and reactive outage management.

Smart Grid Communications That Meet the Challenge

A communications network capable of cost-effectively providing blanket coverage over a utility’s geographic service area will allow utilities to install devices based solely on grid infrastructure needs and no longer be constrained by limited availability of a communications link. Such a coverage model needs to consider above-ground and below-ground assets to accommodate for electric utilities’ increasingly moving larger portions of their distribution grids underground, with some utilities’ having 65 percent or more of their circuit miles below ground. As utilities take advantage of increased monitoring intelligence, the range of device types needed in their networks expands. The connectivity solution must scale seamlessly and service line-powered and battery-powered devices, support industry-standard protocols for data exchange, and easily integrate with the outage management tools utilities have implemented. Utilities see the value from expanding monitoring points, and some are working to correlate information across distribution automation, advance metering and demand response solutions. A single communications network that can service the total smart grid-monitoring challenge provides a simple, cost-effective approach to solving the grid reliability challenge.

General underground communications
General underground communications
General underground communications
General underground communications

Proof Beyond the Brochure

The DOE is aware that achieving the stated 2020 reliability goals requires a significant technology breakthrough to monitor all assets on the grid. With a focus on cost-effective and commercially viable technologies, the DOE recently set out to tackle some of the most challenging communications requirements of smart grid monitoring with a project focused on wireless connectivity for previously unconnected grid assets.

Network versatility. Many utilities have implemented hybrid communications networks to address different needs of advanced metering, demand response and distribution automation monitoring adequately. While possibly sufficient to serve connectivity requirements, a hybrid solution might result in higher complexity and cost than a utility should have to manage. A single network technology that interoperates with all types of endpoints (e.g., electric meters, water meters, gas meters, load control devices, faulted circuit indicators (FCIs), smart transformers, cap bank controllers) and that has support for main line-powered and battery-powered devices greatly simplifies the implementation and operational burden on a utility. This also is a tremendous cost advantage.

Underground Coverage Map 2
Underground Coverage MaP

Underground coverage. If the technology reliably and repeatedly works in reaching underground, then the same system easily will cover above-ground assets. Most continuous underground distribution lines are accessible every 500 feet via vaults, manholes, handholes or padmounts. These circuit access points are most often where the equipment to be monitored is located. A wireless network must be able to accommodate all above-ground radio frequency (RF) challenges such as clutter, interference, multipath, etc., and then still compensate for 30 dB or more of additional signal loss to penetrate into the underground vault.

Accurate prediction. The ability to predict network coverage accurately is critical in understanding the total cost of ownership of a prospective wireless smart grid solution. Coverage prediction is statistical, but a good model is unbiased and has a small standard deviation when compared to actual measurements. RF propagation software cannot model every building, tree, shrub, etc., so the goal is to continue improving such models with real-world measurements.

Schweitzer Engineering<br />Laboratories underground FCI
Schweitzer Engineering
Laboratories underground FCI

An industry project team was formed to deploy and manage a smart grid-monitoring network solution that meets these challenges. The industry team includes:

  • On-Ramp Wireless, which managed the project and supplied the On-Ramp Total Reach Network, which provides secure, reliable communications for assets in hard-to-reach distribution circuit locations;
  • Schweitzer Engineering Laboratories (SEL) provided the wireless analog interface to the underground FCIs;
  • GridSense provided the underground smart transformer monitors;
  • Partner utilities San Diego Gas & Electric Co. (SDG&E) and Southern California Edison are working to expand their communications networks to address their padmount and underground grid assets.

The project team designed a technical demonstration to address the key study objectives:

  • Based on potential asset locations (e.g., underground vaults two stories below grade, underground manholes and handholes, pad-mounted structures), design and build a single wireless network to provide reliable, two-way communications for all selected assets with minimal field infrastructure;
  • Remotely and reliably monitor underground grid assets, collecting periodic status reports and immediate alerts if a device detects an alarm condition;
  • Demonstrate this monitoring for various devices, including battery-powered and line-powered endpoints, as well as endpoints’ demonstrating standard antenna configurations and antenna diversity;
  • Validate network plans against actual coverage obtained, analyze deviations and upgrade planning models to improve prediction results; and
  • Track and document device monitoring results over six months and, given the results, develop full-scale network planning and solution deployment recommendations.
A smart transformer
A smart transformer

DOE Study Results

The project team met all of the DOE’s objectives for a fully commercial solution that can be deployed by any utility to address reliability of its underground grid:

  • The On-Ramp Total Reach Network was proven to provide cost-effective, reliable monitoring coverage for underground assets in vaults, manholes, handholes, padmounts and other hard-to-reach locations.
  • The SEL and GridSense devices provided data that helped SDG&E and SEL predict reductions of underground line outage durations by an average of 90 minutes for a commercial deployment, lining them up to achieve the DOE reduction targets.
  • The wireless communications reliability of 99.8 percent of data packets received far surpassed other wireless communications technologies deployed to monitor underground assets.
  • Network planning methodologies adapted for the challenges of covering static assets, hard-to-reach assets or both, such as those installed underground, proved highly accurate when validated against actual field measurements.

Conclusion

The DOE-funded study achieved its objectives with the demonstration of a cost-effective commercial solution for monitoring underground grid assets. The solutions were demonstrated to exceed the DOE’s 2015/2016 SAIDI reduction targets and fully position utilities to meet 2020 targets, and the benefits extend beyond reduced outage time. The rich data collected during the project contributed to the generation of the first highly accurate network planning model designed specifically for statically deployed assets, applicable to designing above-ground and below-ground monitoring solutions.

All partners involved in the study are actively expanding the networks used for the demonstration and are working with other utility partners to evaluate use of the solution in their networks.

Jason Wilson is the senior vice president of product and program management at On-Ramp Wireless. Reach him at info@onrampwireless.com.

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