According to documents filed by ISO New England to the Federal Energy Regulatory Commission, the current restoration plan utilizes a “bottom-up approach” that is dependent upon smaller generators, typically hydroelectric and internal combustion units, to energize the lower-voltage transmission (115 kV and below) and distribution systems, so as to provide cranking power to larger generators.
The larger generators are used, in turn, to energize additional transmission, including portions of the 345 kV transmission system to meet the initial restoration goals of, among other things, providing offsite station service to nuclear power plants, restoration of service to internal load and reconnection with neighboring balancing authority areas.
Under the current bottom-up approach, simulations are being reported in the range of 10 to 12 hours after an event has taken place. With the revised top-down approach reflected in the revised plan, the ISO expects to bring this period to the 4-to-6 hour range.
The current plan is supported by approximately 67 blackstart generators with capacity totaling approximately 2,300 megawatts. Over half of the supporting assets have a capacity of less than 20 MW. Many of the blackstart-capable internal combustion units included in the plan were installed by utilities at large fossil plants with the intention of providing cranking power to the plant. The larger fossil units were then used to proceed with restoration
efforts. Many of these large fossil plants are now much older and are infrequently dispatched, making them more prone to delays during start-up. Further, some of the older blackstart-capable ICUs may retire due to maintenance issues related to aging equipment.
In addition to maintaining approximately 65 percent of the existing blackstart fleet, the revisions to the plan focus on adding larger combustion turbines located on or near the 345 kV transmission system to establish a high-voltage backbone in New England early in the restoration process. Utilizing the high-voltage system is the most efficient way to establish inter-area ties, restore off-site station service to nuclear plants, and enhance the further restoration of load and generation within New England.
Over the past several years, new gas-fired combined-cycle generation facilities have interconnected electrically near or on the 345 kV transmission system in New England. These facilities are routinely dispatched and generally have the ability to come online quickly. Most of these facilities are currently not blackstart-capable and will require retrofitting to make them blackstart-capable.