MOST OF THE ENERGY AND TECHNOLOGY spending provisions of the 2009 U.S. economic stimulus package have been awarded to advance technologies for the smart grid build-out. Although much of the funding involves smart meters, technology to ensure the reliability and resilience of the grid is of equal importance.
Smart grid has a variety of definitions. Regardless of the definition, everybody agrees that the grid must accommodate multidirectional power flow and adapt quickly to changing conditions. And it must be able to establish a balance among renewable energy generation, storage and customer demand fluctuations, while simultaneously being capable of self-healing within a time frame that customers will value.
The term self-healing refers to the introduction of technology to the smart grid, allowing it to automatically detect and respond to faults caused by weather, accidents or equipment failure. Self-healing uses excess capacity available from any alternate conventional, renewable or distributed energy source to restore service to line segments without overloading any part of the system.
Improving the reliability and resilience of electric transmission and distribution systems will reduce the frequency and duration of power interruptions experienced by customers, ultimately improving smart grid users’ productivity and satisfaction. Because end-user adoption of the smart grid is critical to its success, self-healing has taken on an important role in the smart grid build-out.
Significant progress has been made to deploy self-healing technologies. Hundreds of self-healing distribution networks – zones where feeder switching and protective devices communicate in real time to quickly isolate faults and restore service without waiting for supervisory control and data acquisition commands from utility network control centers – have been deployed across the world. Some utilities have reported that automated switching has reduced outage frequency by 40 percent and outage duration by 20 percent.
This basic concept is now advancing to the next level through the integration of distributed energy storage in the form of a sodium-sulfur battery or other local generation source. In the event that service to a feeder is lost, the stored energy is released to serve islanded power grids.
First, intelligent switches operate automatically to sectionalize the faulted section of the feeder. Other switches then operate to restore service to as many sections of the feeder as possible using the stored energy. The switches continue to operate automatically, matching the load to battery capacity as it is depleted over a multi-hour period, or until service is restored. This advanced technique is being tested and refined to improve reliability and increase utilization of smart grid assets.
American Electric Power, in conjunction with the U.S. Department of Energy, NGK Insulators, LTD and S&C Electric, have installed large-scale, sodium-sulfur batteries acting as distributed energy storage systems at five sites to solve a variety of grid-related challenges. The objective was to incorporate stored energy technology as a tool for mediating substation and feeder issues when a permanent fault necessitates islanded operation. These implementations establish a firm foundation for future smart grid initiatives and provide beneficial case studies for the industry at large.
Through the combined efforts of the IEEE Power & Energy Society, the National Institute of Standards and Technology, the U.S. Department of Energy and numerous participating utilities and manufacturers, supporting frameworks for interoperability and security standards are being established and projects are being deployed that are fundamental to realization of the smart grid vision.