A
black start is the process of restoring a
power stationA power station is an industrial facility for the generation of electric power....
to operation without relying on external energy sources.
Normally, the electric power used within the plant is provided from the station's own generators. If all of the plant’s main generators are shut down, station service power is provided by drawing power from the grid through the plant’s transmission line. However, during a wide-area outage, off-site power supply from the grid will not be available.
A
black start is the process of restoring a
power stationA power station is an industrial facility for the generation of electric power....
to operation without relying on external energy sources.
Normally, the electric power used within the plant is provided from the station's own generators. If all of the plant’s main generators are shut down, station service power is provided by drawing power from the grid through the plant’s transmission line. However, during a wide-area outage, off-site power supply from the grid will not be available. In the absence of grid power, a so-called black start needs to be performed to bootstrap the power grid into operation.
To provide a black start, some power stations have small
diesel generatorA diesel generator is the combination of a diesel engine with an electrical generator to generate electric energy. Diesel generating sets are used in places without connection to the power grid or as emergency power-supply if the grid fails...
s which can be used to start larger generators (of several megawatts capacity), which in turn can be used to start the main power station generators. Generating plants using steam turbines require station service power of up to 10% of their capacity for
boiler feedwater pumpA boiler feedwater pump is a specific type of pump used to pump feedwater into a steam boiler. The water may be freshly supplied or returning condensate produced as a result of the condensation of the steam produced by the boiler...
s, boiler forced-draft combustion air blowers, and for fuel preparation. It is uneconomical to provide such a large standby capacity at each station, so black-start power must be provided over the electrical transmission network from other stations. Often
hydroelectricHydroelectricity is electricity generated by hydropower, i.e., the production of power through use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...
power plants are designated as the black-start sources to restore network interconnections. A hydroelectric station needs very little initial power to start (just enough to open the intake gates), and can put a large block of power on line very quickly to allow start-up of fossil-fueled or nuclear stations.
A black start sequence
A typical sequence (based on a real scenario) might be as follows:
- A battery
An electrical battery is a combination of one or more electrochemical cells, used to convert stored chemical energy into electrical energy. Since the invention of the first Voltaic pile in 1800 by Alessandro Volta, the battery has become a common power source for many household and industrial...
starts a small diesel generatorA diesel generator is the combination of a diesel engine with an electrical generator to generate electric energy. Diesel generating sets are used in places without connection to the power grid or as emergency power-supply if the grid fails...
installed in a hydroelectric generating station.
- The power from the diesel generator is used to bring the hydroelectric generating station into operation.
- Key transmission
Electric power transmission is the bulk transfer of electrical energy, a process in the delivery of electricity to consumers. A power transmission network typically connects power plants to multiple substations near a populated area...
lines between the hydro station and other areas are energized.
- The power from the hydro dam is used to start one of the coal-fired base load
Baseload is the minimum amount of power that a utility or distribution company must make available to its customers, or the amount of power required to meet minimum demands based on reasonable expectations of customer requirements...
plants.
- The power from the base load plant is used to restart all of the other power plants in the system including the nuclear power
Nuclear power is power produced from controlled nuclear reactions. Commercial plants in use to date use nuclear fission reactions....
plants.
Power is finally re-applied to the general
electricity distributionFile:Electricity grid simple- North America.svg|thumb|380px|right|Simplified diagram of AC electricity distribution from generation stations to consumersrect 2 243 235 438 Power stationrect 276 317 412 556 Transformer...
network and sent to the consumers. Often this will happen gradually; starting the entire grid at once may be unfeasible. In particular, after a lengthy outage during summer, all buildings will be warm, and if the power were restored at once, the demand from air conditioning units alone would be more than the grid could supply. In colder climates a similar issue can occur in winter with the use of heating devices.
In a larger grid, black start will often involve starting multiple "islands" of generation (each supplying local load areas) and then synchronising and reconnecting these islands to form a complete grid. The power stations involved have to be able to accept large step changes in load as the grid is reconnected.
Procurement of black start services
In the
United KingdomThe United Kingdom of Great Britain and Northern Ireland is a sovereign state located off the northwestern coast of continental Europe. It is an island country, spanning an archipelago including Great Britain, the northeastern part of Ireland, and many small islands...
the grid operator has commercial agreements in place with some generators to provide black start capacity, recognising that black start facilities are often not economic in normal grid operation.
In the North American
Independent System OperatorAn Independent System Operator is an organization formed at the direction or recommendation of the Federal Energy Regulatory Commission...
s the procurement of black start varies somewhat. Traditionally black start was provided by integrated utilities and the costs were rolled into a broad tariff for cost recovery from ratepayers. In those areas which are not part of organized electricity markets this is still the usual procurement mechanism. In the deregulated environment this legacy of cost-based provision has persisted, and even recent overhauls of black start procurement practices, such as that by the
ISO New EnglandISO New England Inc. is a non-profit Regional Transmission Organization , serving Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island and Vermont...
, have not necessarily shifted to competitive procurement, despite the fact that deregulated jurisdictions have a bias for market solutions rather than Cost-of-Service (COS) solutions.
In the United States, there are currently three methods of procuring black start. The most common is Cost of Service, as it is the simplest and is the traditional method. It is currently used by the California Independent System Operator (CAISO), the
PJM InterconnectionPJM Interconnection LLC is a Regional Transmission Organization which is part of the Eastern Interconnection grid operating an electric transmission system serving all or parts of Delaware, Illinois, Indiana, Kentucky, Maryland, Michigan, New Jersey, North Carolina, Ohio, Pennsylvania, Tennessee,...
and the New York Independent System Operator (NYISO). Although the exact mechanisms differ somewhat the same approach is used, namely that units are identified for black start and their documented costs are then funded and rolled into a tariff for cost recovery. The second method is a new method used by the Independent System Operator of New England (ISO-NE). The new methodology is a flat rate payment which increases black start remuneration to encourage provision. The monthly compensation paid to a generator is determined quite simply by multiplying a flat rate (in $/KWyr and referred to as the $Y value) by the unit's Monthly Claimed Capability for that month. The purpose of this change was to simplify procurement and incent provision of black start. The final method of procurement is competitive procurement as used by the Electric Reliability Council of Texas (ERCOT). Under this approach ERCOT runs a market for black start services. Interested participants submit an hourly standby cost in $/hr (e.g. $70 per hour), often termed an availability bid, that is unrelated to the capacity of the unit. Using various criteria ERCOT evaluates these bids and the selected units are paid as bid, presuming an 85% availability. Each black start unit must be able to demonstrate that it can startup another unit in close proximity to begin the islanding and synchronization of the grid.
In other jurisdictions there are differing methods of procurement. The New Zealand System Operator procures the Blackstart capability via competitive tender. It solicits closed tenders from potential providers and enters into contracts with those parties that it identifies. In addition to New Zealand there are a number of other jurisdictions that also appear to have some sort of competitive procurement, although not as structured as ERCOT. These include the
Alberta Electric System OperatorThe Alberta Electric System Operator, abbreviated AESO, is a not-for-profit entity responsible for the planning and operation of the Alberta Interconnected Electric System in a safe, reliable, and economical manner....
, as well as Independent Electric System Operator of Ontario , both of which use a long-term Request For Proposals approach similar to New Zealand and ERCOT.
Limitations on black start sources
Not all generating plants are suitable for black-start capability. For example,
wind turbineA wind turbine is a rotating machine which converts the kinetic energy of wind into mechanical energy. If the mechanical energy is used directly by machinery, such as a pump or grinding stones, the machine is usually called a windmill...
s are usually connected to
induction generatorAn induction generator is a type of electrical generator that is mechanically and electrically similar to a polyphase induction motor. Induction generators produce electrical power when their shaft is rotated faster than the synchronous frequency of the equivalent induction motor...
s which are incapable of providing power to a de-energized network; the same may be true of mini-hydro or micro-hydro plants, which also rely on a power network connection for frequency regulation and reactive power supply. Many large
high-voltage direct currentA high-voltage, direct current electric power transmission system uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance distribution, HVDC systems are less expensive and suffer lower electrical losses...
converter stations cannot operate into a "dead" system, either, since they require
commutationA commutator is a rotary electrical switch in certain types of electric motor or electrical generator that periodically reverses the current direction between the rotor and the external circuit. In a motor, it applies power to the best location on the rotor, and in a generator, picks off power...
power from the system at the load end; this is not true of
PWMPulse-width modulation is a very efficient way of providing intermediate amounts of electrical power between fully on and fully off. A simple power switch with a typical power source provides full power only, when switched on...
-based HVDC schemes.
See also
2007: Isemonger, A.G. “The Viability of the Competitive Procurement of Blackstart: Lessons from the RTOs” The Electricity Journal Volume 20, Issue 8, October 2007, Pages 60-67 doi:10.1016/j.physletb.2003.10.071
Brendan Kirby and Eric Hirst, Maintaining System Black Start In Competitive Bulk-Power Markets, American Power Conference, Chicago, Illinois, April 1999, available online at: http://www.ornl.gov/sci/btc/apps/Restructuring/pub.htm