By David Chiesa, director business development
S&C Electric Company
Grid capability has come a long way in recent years. We are moving past antiquated solutions, such as diesel generation and reclosers, devices that automatically reset a breaker after it has been tripped from a fault. It is now possible to design an electric transmission grid so that the lights stay on during a serious fault. Modern customers need and expect continuous power. Microgrids are stepping in to provide greater electric grid reliability and resiliency.
A microgrid is a smaller group of electricity sources that can operate with or without a larger, centralized electrical grid (macrogrid). A microgrid can also include power from renewable sources, such as wind and solar energy, along with energy storage.
For microgrids to work effectively, however, the developer must configure the system to island safely and securely away from and back to the central utility grid. Islanding occurs when a distributed generator, or microgrid, continues to power a location exclusive of the central electrical grid.
Islanding takes effect once a microgrid has fully kicked in. However, if the operator fails to completely isolate the microgrid’s connection from the larger grid (when running in microgrid mode), it essentially creates a “hole in a gas tank.” This means that when the operator reforms a microgrid, everything is smaller—including generation, loads and protection settings. Islanding is incomplete if the operator fails to fully isolate the microgrid system. This may result in power leaking to the rest of the grid.
Ultimately, this means the microgrid fails to reform because it does not have enough power to handle the loads designated in the microgrid system. In addition, when the microgrid has power (during normal operation or after successfully reforming the microgrid), the operator should be able to switch seamlessly back and forth between microgrid mode and grid-connected mode. Granted, the utility grid was not designed for significant loads switching on and off the grid, but such events should be possible with a microgrid.
In addition, this switching operation should work without triggering an outage. Essentially, it is up to the microgrid integrator’s design process to ensure a smooth transition into and out of microgrid mode or islanding, and with little or no impact to either the micro or macrogrid.
Islanding capabilities are key to a smooth transition between modes. To illustrate the point, imagine that a microgrid has 10 MW of generating capacity. If the system were unable to fully separate or island from the grid, while attempting to operate in microgrid mode, it would leak outside the physical boundaries of the microgrid and through the utility connection. Power would then be insufficient to supply all the connected loads. The 10 MW of generation would eventually shut down.
The ability to island puts a physical and electrical barrier that prevents limited generation from flowing back to the utility. This ensures that a microgrid maintains a stable and consistent flow of power.
Another critical capability of an effective microgrid is the ability to “black start.” Black starting is the process of bringing an electric power station back online. A black start is necessary to regain power after an unexpected loss of utility voltage. In such a case, a developer expects a microgrid to regain operations without utility service—regardless of whether customers are in a residential or commercial and industrial area. This means that if no power is coming from the central electric grid, the operator must be able to black start its microgrid. The system must automatically start and reconfigure to reform its local grid.
Reforming the grid, or changing its settings or power route, is more complicated than it sounds. An integrator must isolate the system, activate its grid-forming generation asset and switch its protections to a new setting suitable for the smaller microgrid system—all in a matter of seconds. This provides the resiliency an operator expects from a microgrid.
A good integrator can smooth such transitions and make the process look easy. One example of poor integration happened at a Midwestern utility that employed a software company to island its microgrid system. The company attempted to do so without factoring in the role of dynamic protection settings, which is a protective device that adjusts to accommodate changing states in the system. As a result, the microgrid simply shut down when switched to island mode.
Of course the developer intended for a smooth transition to island mode, and a skilled integrator can ensure this happens. The microgrid at Ameren Illinois’ Technology Application Center in Champaign, Illinois is an example of a system that has transitioned seamlessly in and out of microgrid mode over 300 times without fail, and while using multiple configurations and multiple generation sources. An integrator’s job is integral to a successful system.
Having a microgrid without efficient black starting or islanding capabilities is similar to having no microgrid at all. If you’re willing to put the time, energy and money into deploying a microgrid, make sure it works reliably.
The who’s who of a microgrid
The developer, integrator and operator of a microgrid are integral to a successful system and provide unique roles.
A developer speculates on the financial viability of a project by provide the financing and business case for why the project will be profitable.
The operator can also be the developer, but in many cases is a third party that has purchased the asset from the developer during the project process or after completion. The operator is responsible for extracting the actual value from the project.
The integrator is the bridge between the developer and operator. The integrator is responsible for making the business case (put together by the developer) and setting the expectations for the project.