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Preparing and Restoring Power Grids Using Smart Grid Technologies


The growth in frequency and strength of climatic events poses a direct threat to our energy infrastructure, with large-scale power outages becoming more common place. This corresponds to a rise in repair and response costs for utilities to restore electric grids. This trend can be mitigated with the integration of newer, more intelligent technologies.

The Smart Grid is leading innovation efforts in developing and deploying these new technologies to enhance transmission and distribution grid operations and reliability, while also enabling new interactions with customers. Smart Grid can minimize interruptions during an extreme weather event by effectively managing unplanned outages as well as enhancing the restoration of energy infrastructure after a storm, lessening the impact on human life and critical infrastructure.

Smart Distribution Solutions for Restoring Power Grids

The electric industry introduced the term smart distribution to classify some of the growing challenges facing electric distribution utilities. It covers fundamental requirements to maintain grid reliability and enable more efficient restoration from severe storms and other natural disasters. Smart distribution supports the concept of self-healing and autonomous restoration—the ability to restore healthy sections of the network after a fault without manual intervention. Smart distribution also enhances security of supply and power quality—the ability of the distribution grid to maintain supply to customers under abnormal conditions and deliver a quality of power that meets customers’ needs.

Lessons learned from recent restoration efforts have created opportunities for new Smart Grid technologies. Examples from Superstorm Sandy provide important insights into preparing for and recovering from storms. At the core of the entire process was communications; it began within the organization, and continued with field personnel and customers. The ability to keep stakeholders informed helped significantly in saving lives and restoring electric service. Customers with smart phones were able to receive updates from their utilities, and in some cases, were also able to help utilities locate trouble spots. Communication between the utility control room and the field personnel were critical in assessing the damage and understanding the options for reestablishing service. After Sandy, mutual assistance programs brought field personnel from all parts of the U.S. to help with the restoration. Keeping communication infrastructure working is critical to efficient storm recovery efforts.

As part of Smart Grid deployments, utilities have had an opportunity to take a fresh look at how they could benefit from new technologies and simultaneously solve some of the weaknesses in their current operational IT systems. One area that has seen significant growth is in systems designed for control room operations. Integrated distribution management systems (IDMS) include SCADA1, distribution management, and outage management modules on a single IT platform. IDMS provides real-time situational awareness of the electric grid and customer outages, and is accessible by field personnel during the restoration process. IDMS integration with smart meters via automated metering infrastructure (AMI) provides control room operators with real-time information of outages rather than waiting for customers to call in. The ability to connect with these meters from the control room enables operators to check for service restoration and power quality, and notify customers via phone, email, or social media.

IDMS also includes advanced grid optimization applications for locating faults and automatically restoring the distribution grid called Fault location, isolation, and service restoration (FLISR). FLISR is capable of working in tandem with advanced distribution automation (ADA) equipment being deployed as part of the Smart Grid. For sections that do require manual intervention, IDMS provides additional information to help guide field personnel to the approximate location instead of having them locate the fault manually, reducing customer interruptions. Seamless FLISR integration with ADA enables efficient restoration of the grid. Getting it back to normal without IDMS would typically be a tedious and manual process. This significantly reduces field rework required from recovery efforts that involve foreign utility crews that may not be well versed with the local utilities’ procedures.

Another key application is integrated volt/VAR2 control which provides conservation voltage regulation (CVR)—energy efficiently enabling the shifting or reduction of peak load while maintaining grid operations within regulated limits. CVR can be critical for utility restoration efforts when energy supply has been disrupted because of generator outages or loss of critical grid corridors.

Utilities generally conduct extensive training and drills for storm preparations to ensure that their employees, systems, and business processes are ready to react in case of an emergency. IDMS includes a state-of-the-art distribution operations training simulator (DOTS) that is used to prepare control room operators and engineers to manage restoration efforts after severe storms. DOTS is able to recreate scenarios from previous storm events including simulating customer calls and smart meter power-off messages, providing a real-life simulation environment. DOTS can also be used to prepare the distribution grid for a storm by studying switching plans to safely island or disconnect portions of the grid, preventing further degradation during a storm and enabling faster restoration after the storm.

Smart Distribution Equipment for Restoration

New capabilities and functionality of existing devices can provide alternatives for automated system restoration and faster recovery from the impacts of natural disasters. As part of the range of equipment that can optimize Smart Grid deployment, the recloser is a switching device intended to interrupt load and fault currents. By shutting off multiple times in a pre-defined sequence, the recloser can promptly repair service after a temporary fault. Traditionally, their role is to provide overcurrent protection and they are typically installed in the distribution feeder. Recloser locations are optimized to protect portions of the distribution system where faults are more prevalent in order to improve service reliability. Their ability to interrupt the fault and re-energize closer to the fault location allows for continuity of service upstream. They can also be used to configure distribution network in loops when used as a normally-open tie device to increase operational flexibility.

Modern reclosers have increased fault current interrupting ratings, independent-pole operating capability, and shortened dead time during auto reclosing. Because of their higher current interruption capability, reclosers are being installed closer to or at the substation. Dead time is defined as the interval between current interruption in all poles in the opening operation and the first re-establishment of current in the subsequent closing operation. Reclosers are now capable of dead times in the range of 100 ms allowing for very brief service interruptions. Nevertheless, the reclosing time should be long enough to allow for the fault to clear. Reclosers can be three-phase or single-phase operated. Most faults in a distribution network are single-phase faults. The development of single-phase reclosers allows for opening and reclosing of only the faulted phase. Single-phase tripping and reclosing increases service continuity, allowing temporary operation with only two phases. Furthermore, single-pole operated reclosers can perform controlled closing operations. In a controlled closing, each phase in the network is energized at optimum time instants in order to reduce transient voltages and currents. This reduces stresses on network equipment and sensitive loads during service restoration.

In addition, modern reclosers include voltage and current sensors; they incorporate two-way communications and can be equipped with intelligent controllers. These features allow for additional functionality and capabilities. Voltage and current measurements enable the implementation of additional protection schemes including directionality (discrimination of the faulted side) and under/over voltage protection. Also, they enable fault monitoring (success in fault clearing, outcomes of reclosing operations, accumulation of fault history, fault records of current and voltage) and load monitoring. Two-way communication allows remote command transmission, status reporting (open or closed), and transmission of events and data. Communication allows integration of the recloser to the SCADA system. Lastly, intelligent controllers contain operational logic, estimate the remaining life and condition of the device, and can be programmed remotely for flexibility and changing conditions, as well as programmed to store, send, and receive data and commands.

A large storm or other meteorological event can cause multiple faults within a short time in the distribution system. Some of these faults are temporary and can be cleared by reclosers, others are repetitive, and some are permanent. The maximum number of allowable reclosing operations may be exceeded during repetitive or permanent faults. In this situation, multiple reclosers are locked open, leaving feeders and sections of the distribution system without power. During and after a storm, a group of intelligent reclosers can be programmed to operate in a pre-defined sequence to automatically restore service to sections of the distribution system that have not been permanently affected. Information captured by the individual controllers during the event can be transmitted and analyzed at a central location to assess the network condition allowing. This allows for optimization of resources and line crews needed to repair portions of the network affected by permanent faults and reduces the recovery time.

Short-term Investment for Long-term Advantage

Extreme weather events and their associated impacts are causing electric utilities to question their current technological and operational systems. As essential components of a more intelligent power grid, integrated distribution management systems have already proven to support storm preparation and restoration, as well as reduce service interruptions. The initial cost to invest in Smart Grid systems and equipment is offset by the reduction in overall cost implications each time a storm occurs. These technologies can also dramatically lessen the impact on human life and critical infrastructure. Electric utilities that have invested in Smart Grid technologies are able to better prepare their personnel, manage their grids, increase customer satisfaction, and meet their regulatory objectives.

 

1 Supervisory control and data acquisition
2 volt-ampere reactive