Jason LeRoy 2017-04-24 17:42:52
Since 1926, Indianapolis Power & Light Company (IPL) has delivered low-cost electricity with customer service ratings that are among the best. Today, IPL ranks in the top 10% nationally in reliability and is part of AES Corporation, one of the largest global power companies committed to operational excellence to meet the world’s growing power needs. IPL provides retail electric service to more than 480,000 residential, commercial, and industrial customers in Indianapolis and other central Indiana communities. To support reliable power in downtown Indianapolis, IPL operates a complex underground network that serves more than 2,600 critical customers with a peak demand of 114 MW, about 3.6% of the total system load. The network system in Indianapolis supports reliable power to the state capitol building, Indiana State House, Birch Bayh Federal Building, and US Courthouse, Chase Tower, numerous hotels, and other customers with critical power needs. The underground power system provides a secondary redundant network that is designed to meet both the higher reliability requirements and limited space in urban areas. This system delivers electricity through a complicated subsurface network that includes transformers and underground cables that operate in parallel. Power flows in either direction and network protectors are used like large-scale circuit breakers; they are designed to open when they detect power backfeed from a transformer. Challenge The subsurface system dates back to the early part of the 20th century. Many of these systems, including the one in Indianapolis, were installed in the 1930s. Unlike the primary power transmission and distribution system, equipment problems in secondary networks can go unnoticed, as they may not cause an interruption of power. Even if there is no immediate power loss, any equipment failure is problematic because the system serves government agencies, banks, and other downtown-based businesses where failures can result in high-profile events. IPL takes steps year-round to provide safe, reliable service downtown and conducts inspections of transformer vaults every two years. These inspections include a visual inspection of network transformers and network protectors, electrical testing of the network protector, and the physical condition of the vault structure and electrical equipment. In particular, inspections check for corrosive effects of street and sidewalk de-icing chemicals and from other underground utilities such as steam (elevated temperatures) and water. As part of its company-wide commitment to safety, IPL wanted to meet and exceed new arc flash safety requirements mandated by the Occupational Safety and Health Administration (OSHA) and the National Fire Protection Association (NFPA) 70E specifications. The code updates require utilities to conduct arc flash studies to determine the level of arc flash potential present and adhere to personal protective equipment (PPE) requirements. Notably, much of the maintenance work performed on secondary network systems involves live equipment, carrying upward of 480 V. A network system often exceeds Category 4 PPE requirements (+40 calories per square centimeter) if measures are not taken to reduce the energy exposure. To meet the latest requirements, IPL would need to de-energize the vault equipment and customers would experience outages for routine maintenance work. IPL sought to reduce the PPE level requirements to Category 2 (8 calories per square centimeter) to simplify maintenance procedures for personnel while avoiding outages for its customers, as complete downtime is simply not an option for public utility networks. “We needed to reduce the incident arc flash energy in our vaults to help enhance safety for our maintenance teams without impacting service to our customers,” says Mike Holtsclaw, IPL’s director of transmission and distribution engineering. “To help address this challenge, we looked for an organization that would be able to provide the advanced solutions and expert support needed to expedite the project.” The utility approached Eaton. IPL was already familiar with Eaton solutions for secondary power systems and had incorporated Eaton equipment into its network system for decades. The utility had also recently begun to use Eaton’s CM-52 remote racking technology to remotely connect and disconnect the network protector from the energized bus, helping to enhance safety for its maintenance personnel. The utility trusted Eaton to provide a turnkey solution that would streamline the project and help to meet the evolving safety requirements. All in all, IPL sought to replace approximately 135 network protectors in 42 vaults between 2014 and 2018. It relied on Eaton to replace the equipment in a way that allowed its personnel to perform routine maintenance on any of its vaults without power interruptions. Solution IPL took action to support a safer and more reliable power system. As part of that broader effort, the utility maintains and updates its underground network with a focus on: • Enhancing inspections and technology • Inspecting and replacing network protectors and transformers • Improving asset management In 2013, IPL attended Eaton’s annual Electrical Network Systems Conference, featuring expert speakers and engineers, field personnel, and maintenance leads from utilities in the US, Canada, and Brazil. During this conference, another utility discussed a project that involved the replacement of 80 network protectors over two years. IPL was able to tour this utility’s vaults to understand exactly what the project involved. After that experience, updating its network system seemed much less of a theoretical problem. IPL knew it could be done and better understood what the project would involve. IPL selected Eaton’s network protector technology to replace all of its 480 V equipment. Eaton offered expansive solutions for new vault equipment, communications, and automation for underground applications, as well as a host of training programs for IPL maintenance teams. “The solution Eaton developed far exceeded anything else on the market. We gained features beyond our original requirements that allowed us to further enhance personnel safety during routine maintenance on our network system,” says Holtsclaw. This project involved more than just replacing network protector devices. IPL also sought to add communications solutions to enhance maintenance and system reliability, and technology designed to enhance safety and reduce arc flash risks. Overall, the project involved the replacement of approximately 135 network protectors over a four-year period. Eaton’s CM-52 network protectors used on this project incorporate a variety of features to enhance safety and help reduce arc flash risks. The network protectors have one of the highest interrupting ratings in the industry and incorporate a deadfront drawout design. The technology includes an integral Arcflash Reduction Maintenance System, which is designed to sense fault current in either direction. The Arcflash Reduction Maintenance System can be remotely activated before personnel go into the vault. DE Jason LeRoy is a network protector product engineer at Eaton.
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