Black start
Encyclopedia
A black start is the process of restoring a power station
to operation without relying on the external electric power transmission network.
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 generator
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 pump
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 designated tie lines from another station. Often hydroelectric
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 the excitation
of the generator field coils), and can put a large block of power on line very quickly to allow start-up of fossil-fueled or nuclear stations. Certain types of combustion turbine can be configured for black start, providing another option in places without suitable hydroelectric plants.
Power is finally re-applied to the general electricity distribution
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.
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 Operators 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 England
, 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 Interconnection
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 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. Other jurisdictions also appear to have some sort of competitive procurement, although not as structured as ERCOT. These include the Alberta Electric System Operator
, 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.
s, mini-hydro
, or micro-hydro plants, are often connected to induction generator
s which are incapable of providing power to a de-energized network. The black-start unit must also be stable when operated with the large reactive load of a long transmission line. Many high-voltage direct current
converter stations cannot operate into a "dead" system, either, since they require commutation
power from the system at the load end. This is not true of PWM
-based (voltage-source converter) HVDC schemes.
Power station
A power station is an industrial facility for the generation of electric energy....
to operation without relying on the external electric power transmission network.
To provide a black start, some power stations have small diesel generator
Diesel generator
A diesel generator is the combination of a diesel engine with an electrical generator to generate electrical energy....
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 pump
Boiler feedwater pump
A 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 designated tie lines from another station. Often hydroelectric
Hydroelectricity
Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the 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 the excitation
Excitation (magnetic)
An electric generator or electric motor consists of a rotor spinning in a magnetic field. The magnetic field may be produced by permanent magnets or by field coils. In the case of a machine with field coils, a current must flow in the coils to generate the field, otherwise no power is transferred...
of the generator field coils), and can put a large block of power on line very quickly to allow start-up of fossil-fueled or nuclear stations. Certain types of combustion turbine can be configured for black start, providing another option in places without suitable hydroelectric plants.
A black start sequence
A typical sequence (based on a real scenario) might be as follows:- A batteryBattery (electricity)An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
starts a small diesel generatorDiesel generatorA diesel generator is the combination of a diesel engine with an electrical generator to generate electrical energy....
installed in a hydroelectric generating station. - The power from the diesel generator is used to bring the hydroelectric generating station into operation.
- Key transmissionElectric power transmissionElectric-power transmission is the bulk transfer of electrical energy, from generating power plants to Electrical substations located near demand centers...
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 loadBase load power plantBaseload 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 powerNuclear powerNuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provide about 6% of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity...
plants.
Power is finally re-applied to the general electricity distribution
Electricity distribution
File:Electricity grid simple- North America.svg|thumb|380px|right|Simplified diagram of AC electricity distribution from generation stations to consumers...
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 KingdomUnited Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
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 Operators 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 England
ISO New England
ISO New England Inc. is an independent, 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 Interconnection
PJM Interconnection
PJM 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 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. Other jurisdictions also appear to have some sort of competitive procurement, although not as structured as ERCOT. These include the Alberta Electric System Operator
Alberta Electric System Operator
The 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. Wind turbines are not suitable for black start because wind may not be available when needed. Wind turbineWind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
s, mini-hydro
Small hydro
Small hydro is the development of hydroelectric power on a scale serving a small community or industrial plant. The definition of a small hydro project varies but a generating capacity of up to 10 megawatts is generally accepted as the upper limit of what can be termed small hydro. This may be...
, or micro-hydro plants, are often connected to induction generator
Induction generator
An induction generator or asynchronous generator is a type of AC electrical generator that uses the principles of induction motors to produce power. Induction generators operate by mechanically turning their rotor in generator mode, giving negative slip...
s which are incapable of providing power to a de-energized network. The black-start unit must also be stable when operated with the large reactive load of a long transmission line. Many high-voltage direct current
High-voltage direct current
A 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 transmission, HVDC systems may be less expensive and suffer lower electrical losses...
converter stations cannot operate into a "dead" system, either, since they require commutation
Commutator (electric)
A commutator is a rotary electrical switch in certain types of electric motors or electrical generators 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 PWM
Pulse-width modulation
Pulse-width modulation , or pulse-duration modulation , is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches....
-based (voltage-source converter) HVDC schemes.
External reading
- 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