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Prioritizing Necessary Upgrades: The Graceful Degradation Principle


What should guide future upgrades?

A “well thought-out system.” Something that “improves and grows over time.” Something that can “build out and improve upon our existing system, but does not risk reliability for our most critical infrastructures and services.”

In today’s IT-driven world, this concept is called “graceful degradation” and in the context of upgrading our electric grid, it can be viewed as an approach for prioritizing necessary upgrades.

It would work off of a concentric network of normal configurations that successively decrease into circles of priority until reaching a central core that must operate at all times. This smallest circle would have the highest reliability requirements. Many could view this circular map as starting at the utility feeder, then defining micro-grid areas, then limited campuses, and ending at individual buildings.

This calls for a paradigm shift away from standard interconnected designs to delivery models that do not primarily depend on a single source of energy. Restorative automation is one aspect of this design, but it extends further to a grid design that has layered levels of supply loss under emergency conditions.

A Smarter Grid

Before proceeding with anything, an implementation of basic, cost-effective elements of a “smarter grid” needs to take place to ensure more resilience in the current system. Such elements include:

  • increased network redundancy supporting multiple supply paths
  • distribution automation reconnecting customers
  • remote SCADA monitoring and control to better assess the current conditions and manage safety
  • outage management to efficiently guide restoration
  • load and voltage restoration analysis to avoid restoration problems

A key concept at this phase is interoperability. Optimum effectiveness and efficiency will not be attained unless there is integration between the operations technology and information technologies used for systems monitoring, controlling, analyzing, and managing key aspects of day-to-day and emergency operations. Fortunately, there are systems today that are more “open” and allow integration from existing systems into newer ones.

It would be beneficial for utilities with more than 50,000 connected customers to have a geospatial information system to locate assets, a distribution management system to visualize and control the network, and an outage management system for automatic handling and response to trouble calls. This would speed assessment and response to issues in the network and facilitate communication with consumers.

Infrastructure: Working Toward Self-sustaining Electrical Islands

Maintaining critical infrastructure such as hospitals, prisons, police and fire stations, and street lights requires more than just backup generation for isolated buildings or systems; it requires self-sustaining power infrastructures such as embedded microgrids. Essentially, in a major storm or event, the availability of electric service should “degrade gracefully” into self-sustained areas according to layered priorities assigned to different load areas.

Local generation and storage allow sections of the power grid to operate independently in an intentional island mode during a major grid disturbance, such as the recent widespread outages caused by Superstorm Sandy. Efficiency is increased by locating generation close to the consumption which reduces costs and losses associated with transmission.

A microgrid will utilize distributed energy resources (power generation) throughout its system to provide power when disconnected from the main grid. This typically includes a combination of thermal generation and renewable generation. Importantly, the microgrid can be scaled for different applications and implemented at military bases, critical care facilities, hospital complexes, assisted care campuses, and other designated high priority areas or cells, which essentially aggregate and coordinate load and supply in a defined area. When implementing these microgrids, designs should include important modernizing technologies including alternative generation sources, grid stabilization equipment, grid management software, energy storage, and a communications network.

New microgrids will utilize multiple renewable and alternative fuel generation sources (wind, solar, fuel cells, and natural gas) that can provide power to multiple loads. These alternative power sources will not only allow redundancy, but also reduce dependency on fossil fuel generation.

Gas Insulated Switchgear: Protecting Power Sources from Water

Medium-voltage (MV) switchgear, especially for electrical substations, is available in gas-insulated form. Gas-insulated switchgear (GIS) is contained in a fully sealed vessel, which means that all electrical conductors and vacuum interrupters are protected from the environment. This type of containment makes MV switchgear conductors resistant to water contamination. Furthermore, the insulated cables that connect the GIS use a type of connector that is resistant to temporary submersion. While GIS is not normally designed to be operated in a submerged condition, it is likely that it would withstand a major interruption if temporarily immersed in water.

Reliability Enabled with Communications Capabilities

Today’s advanced reliability improvement technologies offer advanced protection for overhead radial lines. They are capable of almost completely removing the impacts of temporary fault currents on radial lines and when applied with unique fault-clearing speed (one-half cycle), it can also protect the fuse in the case of temporary faults. This technology is usually designed to be installed in a series to the fuse. When it senses a fault current, it will open and stay open for a pre-determined time (dead time). Then it will close again and remain closed. If the fault is temporary, then the radial line is re-energized. If the fault is permanent, then the fuse will blow, protecting the system.

In order to minimize installation and operating costs, this technology is often offered as part of an integrated system of tools and accessories. One of the most important of these is the communications module which allows the crew to interface with the technology from ground level using a laptop or handheld device. All of the different system components, when working together, permit easy installation, fast commissioning, and reliable operation in all conditions.

Feeder Distribution Systems Locate, Isolate, Restore

To be most effective immediately, today’s distribution automation solutions should be instantly implementable with a focus on being model-based according to existing national standards, including those of the Department of Energy and the National Institute of Standards and Technology.

Automation controllers should easily mount in new or existing reclosers, switches, and substation circuit breakers. The purpose of these automation controllers is to detect and locate faults in the feeder circuit, isolate the faulted section, then restore power to the unfaulted sections up to the rated capacity of the alternate power source. Sensing is provided via current transformer and potential informer inputs. Automation controllers can be installed inside any manufacturers’ switchgear and can be configured to work with the feeder’s existing protection logic.

Quicker Restoration: Reliable Power via Modular Energy Storage

The power distribution market is shifting. Today’s increasing utilization of distributed generation and renewables leads to new challenges which result from the unpredictable generation capacity of renewable energy, especially during unforeseeable outages.

Modular energy storage systems are a viable solution for a sustainable and reliable supply of power in the future, whether for the integration of fluctuating renewable energy sources in the grid, self-sufficient power for microgrids, or as reliable reserve during outages.

These systems combine cutting-edge power electronics for grid applications and the latest high-performance lithium-ion batteries. Importantly, their modular design enables power and capacity to be adapted to specific demands and ensures high availability and reliability.

Roadmap Recommendations

  • Make existing grid smarter with easily implementable, open, drop-in technologies that allow a graceful degradation of the entire system.
  • Enhance critical infrastructure sites with protected, self-sustaining islands of power in the form of embedded microgrids.
  • Improve the resiliency, notification, and restoration time for less critical areas with drop-in, flexible, expandable solutions that allow future integration into a broader, smarter system.