Prompted by recurring severe weather events that cause billions of dollars of damage to the electrical power grid and significant power outage-related costs, Duke Energy decided to implement a microgrid. A microgrid is a group of interconnected loads and distributed generation that acts as a single controllable entity with respect to the grid. This means that it can connect and disconnect from the grid to enable it to operate in both grid-connected mode or island mode. The reliable and resilient power provided by this project enables the adjacent Charlotte Fire Department Station 24 (FS24) to provide critical services during extreme weather events.
Faced with the increasing regulatory goal of incorporating more renewable generation into the electric power grid, Duke Energy decided to integrate their existing renewable resources into their microgrid at their McAlpine Creek Substation and next door at the 50 kW photovoltaic installation and 240 kW battery energy storage system (BESS). A key requirement was that the microgrid use standard utility distribution equipment and off-the-shelf components.
This was a great opportunity to prove what we can accomplish using standard SEL equipment that a lot of utilities already own. The customer had a vision for how they wanted the system to work, and the diverse programming options available in acSELerator RTAC Software allowed us to realize that vision.
Microgrids have low inertia compared to the larger macrogrid, which means they need fast-acting microgrid controllers. Control algorithms and demand response need to operate much more quickly in order to preserve the load and generation energy balance, maintain system stability, and provide good power quality. Because the SEL Real-Time Automation Controller (RTAC) operates at subcyle speeds, it was the ideal microgrid controller. The device’s advanced out-of-the-box capabilities made it an ideal fit for Duke’s desire to use standard utility-grade equipment.
Managing the point-of-interconnection between the microgrid and larger grid can be very challenging. That’s why Duke Energy chose to integrate the SEL-651R Advanced Recloser Control. Working with SEL allowed Duke to implement sophisticated protection algorithms that allow the system to adapt and control the various microgrid operational use cases.
The collaboration also extended to many other phases and components of the project, including layering the RTAC as a SCADA system and creating an intuitive human-machine interface (HMI) for operators.
The McAlpine Creek Substation microgrid has been in service since July 2015. Since then, the microgrid has provided peak shaving and a resilient energy supply, benefiting end users as well as the utility. It has operated manually under operator supervision and also automatically during outages and disturbances. Because the substation can seamlessly island and resynchronize automatically during extreme weather events, it can be relied on to maintain power to mission-critical services for the firehouse.
Duke will use the lessons learned implementing the McAlpine Creek Substation microgrid to develop a process for standardizing and building future microgrids. A key component of this is using standard, off-the-shelf utility-grade control equipment, the SEL-651R Advanced Recloser Control, and the SEL RTAC.
The customer had seen rather complex microgrid control architectures and had a real desire to keep this simple. Using the simple, easy-to-use HMI of the RTAC and the inherent flexibility of SELogic in the SEL-651R and its unique synchronizing abilities, we were able to help them realize that vision.