Black start
Black start is the capability of a power generation facility or resource to restart itself and begin producing electricity without relying on external power from the grid, enabling the restoration of an electric power system following a total or partial blackout.[1][2] This process typically involves isolated generation units that use on-site auxiliary sources, such as diesel generators, batteries, or hydropower, to energize transmission lines and gradually reconnect loads and other power plants.[1][3] Black start capabilities are a cornerstone of grid reliability, mandated by standards from organizations like the North American Electric Reliability Corporation (NERC) to ensure swift recovery from widespread outages.[4] Historically, black start resources have primarily consisted of hydroelectric plants, which provide about 37% of such capabilities in North America due to their ability to start quickly without external power, and gas turbines, accounting for around 60%.[2] Major events, such as the 2003 Northeast blackout that affected approximately 50 million people across the United States and Canada, underscored the need for robust black start planning to minimize outage durations and economic impacts.[2] Planning for black start involves optimizing the allocation of these resources across the grid to form restoration paths, often using mathematical models to balance costs, timing, and system stability.[5] In recent years, the integration of renewable energy sources and inverter-based resources (IBRs) has introduced new challenges and opportunities for black start.[2] Traditional synchronous generators provide inherent inertia for grid stabilization, but IBRs like solar photovoltaics and wind turbines require advanced controls, such as grid-forming inverters, to support autonomous startup and handle transient loads during restoration.[1][6] Research from institutions like the National Renewable Energy Laboratory (NREL) and Pacific Northwest National Laboratory (PNNL) emphasizes testing distributed energy resources, energy storage systems, and microgrids to enhance resiliency, with projections indicating renewables could comprise 33-57% of generation by 2050, necessitating adaptive black start strategies.[1][2] Ongoing efforts also address cyber threats, aging infrastructure, and coordination with natural gas supplies to improve overall system restoration.[2]Overview
Definition and Purpose
Black start is a generating unit(s) and its associated set of equipment which has the ability to be started without support from the System or is designed to remain energized without connection to the remainder of the System, with the ability to energize a bus, meeting the Transmission Operator’s restoration plan needs for Real and Reactive Power capability, frequency and voltage control, and that has been included in the Transmission Operator’s restoration plan.[7] This capability is provided by designated blackstart resources, which are generating units and associated equipment able to initiate operation using only on-site or self-contained power sources, such as auxiliary diesel generators or batteries, to energize local buses and begin the restoration sequence.[8] The primary purpose of black start is to enable the systematic restoration of generation, transmission, and distribution systems after a blackout, minimizing the duration of outages and preventing further disruptions to critical infrastructure.[2] Unlike normal startup procedures, which assume availability of off-site grid power to drive auxiliary systems like pumps, fans, and controls in power plants, black start addresses scenarios where no such external support exists, breaking the dependency cycle that could otherwise prolong recovery indefinitely.[3] By prioritizing the re-energization of key paths and the synchronization of additional units, it facilitates a controlled rebuild of the bulk electric system while maintaining frequency and voltage stability.[8] In total blackout scenarios, where the entire interconnected system loses power, black start provides the self-sustaining initiation needed to avoid circular dependencies among generation units that require electricity to start. Partial blackouts, involving isolated "islands" of the grid, similarly benefit from targeted black start actions to reconnect and stabilize segments without risking wider collapse.[2] This mechanism is essential for enhancing grid resilience against threats such as cascading failures, cyberattacks, and natural disasters, ensuring rapid recovery and operational reliability.[2] In North America, black start capabilities are mandated under North American Electric Reliability Corporation (NERC) standards, such as EOP-005-3, which require transmission operators to develop, test, and maintain restoration plans incorporating these resources to meet reliability obligations.[8]Historical Significance
The concept of black start in power systems originated in the mid-20th century amid increasing complexity of interconnected grids, but it was formalized following the Northeast blackout of November 9, 1965, which affected approximately 30 million people across eight U.S. states and parts of Ontario, Canada, for up to 13 hours. This event exposed the vulnerability of relying on external power for restarting generators, as many plants lacked self-starting capabilities, leading the Federal Power Commission to recommend provisioning methods for black start services, including the use of auxiliary power sources like diesel engines and hydropower. In the aftermath, surveys of affected utilities revealed that 45% had employed hydropower for rapid restarts due to its ability to generate station service power without external input.[3] Subsequent major blackouts further underscored the need for robust black start protocols. The 1977 New York City blackout, triggered by lightning and affecting 9 million residents for about 26 hours, prompted recommendations to enhance periodic simulations of black start procedures at major generating stations to improve restoration readiness. The August 14, 2003, Northeast blackout in the U.S. and Canada impacted over 50 million people and took several days to fully restore, with black start processes critical for energizing key transmission paths, though challenges arose in coordinating nuclear plant restarts due to off-site power dependencies. More recently, the February 2021 Winter Storm Uri in Texas and the South Central U.S. tested black start resources amid extreme cold, where frozen equipment and fuel supply issues hindered availability, affecting millions and delaying recovery in ERCOT's isolated grid.[9][3][2][10] The evolution of black start practices shifted from ad hoc reliance on fossil fuel-based units like gas turbines toward standardized frameworks, particularly after the deregulation of electricity markets in the late 1990s and early 2000s, which introduced challenges in procuring and compensating these services as ancillary requirements. In the U.S., the North American Electric Reliability Corporation (NERC) formalized black start under standards like EOP-005, which became mandatory in 2013 and was updated to version EOP-005-3, approved by FERC in 2018 and effective in 2019, mandating transmission operators to develop, maintain, and test restoration plans including black start resources. By the 2000s, these standards emphasized coordinated multi-area restoration and annual training, reflecting lessons from events like the 2003 blackout, while post-2010 developments increasingly addressed climate-related resilience, such as extreme weather impacts on resource reliability.[3][2][8] Key milestones include the establishment of black start as a compensable service in major U.S. independent system operators (ISOs) and regional transmission organizations (RTOs) during the early 2000s, with the first requests for proposals (RFPs) issued by PJM Interconnection in 2013 to secure diverse resources. This period also saw a transition from predominantly fossil fuel dependencies to incorporating more reliable options like hydropower, which by the 2010s constituted 35-40% of registered black start units in the U.S. despite representing only about 10% of total generation capacity, due to its quick-response advantages in restoration scenarios.[2][3] A more recent event, the December 2022 Winter Storm Elliott, affected over 1.6 million customers across 13 states in the Eastern Interconnection, particularly in PJM, where black start resources faced challenges from natural gas shortages and extreme cold, leading to load shedding and delays in restoration. This storm prompted NERC to issue recommendations for improved fuel assurance and black start testing to enhance winter preparedness.[11]Technical Fundamentals
Station Service Power
Station service power, also known as house load or auxiliary power, refers to the electricity required to operate a power plant's internal systems, such as pumps, fans, and control mechanisms, prior to synchronization with the external grid during a black start scenario.[3] This power is essential for activating the plant's core functions without relying on an energized transmission system, enabling the initial stages of generation unit startup. In the absence of grid support, station service power must be sourced internally or from dedicated black start resources to initiate these operations.[2] The power demands for station service typically range from 1% to 10% of a generating unit's rated capacity, varying by plant type and size; for instance, coal-fired thermal plants often require 5% to 8% for full auxiliary loads, while hydroelectric units may need only 0.5% to 1%.[12][13][3] This self-supplied power is critical to prevent circular dependencies, where the plant cannot start without auxiliary support, and vice versa. Key components include DC batteries, which provide initial excitation for generators and power control systems, and AC supplies for essential motors, such as boiler feed pumps in thermal plants that circulate water to prevent overheating during startup.[14][15] Unlike normal operations, where station service power is typically drawn from the interconnected grid in parallel mode, black start requires isolated operation without external synchronization, relying on local sources to maintain voltage and frequency stability internally.[3] Black start sources, such as small diesel generators or batteries, fulfill these initial power needs to bootstrap the process.[2]Black Start Sources
Black start sources are essential self-starting generation units capable of providing initial power to restart power plants and energize transmission lines without external grid support. These sources must operate independently, relying on on-site fuel or energy storage to initiate the restoration process. Traditional black start sources primarily include diesel generators, hydropower plants, and gas turbines, which have been the backbone of grid recovery strategies for decades.[2] Diesel generators are widely used as black start sources due to their rapid startup capability, often initiated by onboard batteries, and their ability to provide reliable initial power for auxiliary systems. These units typically feature independent diesel fuel storage, ensuring autonomy during outages, and can achieve full operation in under 10 minutes. With capacities ranging from 0.5 MW to 20 MW, they are particularly suited for energizing small loads or supporting the startup of larger plants, such as providing the necessary power for gas turbine ignition or hydropower gate controls. In surveys of utility practices, diesel generators account for about 26% of black start methods employed after major blackouts.[3][16][2] Hydropower plants serve as highly effective black start sources, leveraging low auxiliary power requirements—typically 0.5-1% of their rated capacity—to operate essential components like spillway gates and excitation systems. They draw on independent water reserves as their energy source, enabling quick restarts in as little as 10 minutes for over 80% of units, and offer capacities from 10 MW to over 100 MW to initially energize transmission networks. Approximately 40% of tested black start units in the U.S. are hydropower facilities, prized for their fast ramping, high inertia, and ability to maintain frequency stability during early restoration phases.[3][2] Gas turbines, particularly simple-cycle combustion turbines, provide robust black start capabilities with onboard batteries or auxiliary diesel support for startup, achieving operational readiness in 30 minutes for hot starts. These units rely on independent natural gas supplies, often from on-site storage or pressurized pipelines, and deliver initial capacities of 10-100 MW, sufficient to crank paths and synchronize additional generation. Examples include GE 7FA models, which require up to 19.5 MW of diesel support for auxiliaries but offer high reliability and ramp rates once running; gas turbines constitute around 20-60% of designated black start resources in regional grids.[16][2][3] Selection of black start sources emphasizes reliability, as mandated by NERC standards requiring periodic testing to verify cranking capabilities; proximity to load centers to minimize transmission losses; and minimal environmental impact, with hydropower favored for its clean operation compared to fossil-based options. These conventional sources form the baseline for initiating the startup sequence in power system restoration, providing the foundational power needed to bring larger units online.[3][2][16]| Source Type | Typical Startup Time | Initial Capacity Range | Key Independence Feature |
|---|---|---|---|
| Diesel Generators | <10 minutes | 0.5-20 MW | On-site diesel fuel storage[3] |
| Hydropower Plants | 10 minutes | 10-100+ MW | Reservoir water supply[3] |
| Gas Turbines (Simple-Cycle) | 30 minutes (hot start) | 10-100 MW | Natural gas pipeline or storage[2] |