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Grid Code Frequency Response Working GroupRequirements for System InertiaAntony Johnson, System Technical Performance
Overview
Resume’ of System Inertia
Future Transmission System need
System Studies
Requirements and issues for System Inertia
Proposals
Conclusions
Resume’ of System Inertia
Inertia is the stored rotating energy in the system
Following a System loss, the higher the System Inertia (assuming no frequency response) the longer it takes to reach a new steady state operating frequency.
Modern Generation Technologies employing power electronic converters currently do not contribute to System Inertia
ie the equivalent of a vehicle travelling down a hill without engine breaking
Under the Gone Green Scenario in 2020 over half the generation fleet is likely to comprise of such technologies.
Further growth is expected in HVDC which currently does not contribute to System Inertia
The implications of this are a substantial erosion in System Frequency Control and consequent required increases in additional reserve and response
Additional background information is available from the presentation given at the Frequency Response Working Group Meeting of 15 February 2010
The maths behind inertia
∂f/∂t = Rate of change of frequencyΔP = MW of load or generation lost2H = Two times the system inertia in MWs / MVA
∂f∂t
ΔP2H=
∂f/∂t = Rate of change of frequencyΔP = MW of load or generation lost2H = Two times the system inertia in MWs / MVA
∂f∂t
ΔP2H=
H = Inertia constant in MWs / MVAJ = Moment of inertia in kgm2 of the rotating massω = nominal speed of rotation in rad/sMVA = MVA rating of the machine
½Jω2
MVAH =
H = Inertia constant in MWs / MVAJ = Moment of inertia in kgm2 of the rotating massω = nominal speed of rotation in rad/sMVA = MVA rating of the machine
½Jω2
MVAH =
Typical H for a synchronous generator can range from 2 to 9 seconds (MWs/MVA)
An NGET Future Scenario
Plant closures 12GW Coal & oil LCPD
7.5GW nuclear
Some gas & additional coal
Significant new renewable 29 GW wind (2/3 offshore)
Some tidal, wave, biomass & solar PV
Renewable share of generation grows from 5% to 36%
Significant new non renewable build 3GW of new nuclear
3GW of new supercritical coal (some with CCS)
11GW of new gas
Electricity demand remains flat (approx 60 GW) Reductions from energy efficiency measures
Increases from heat pumps & cars
Strategic Reinforcements
Sizewell
Pembroke
Osbaldwick
Rowdown
BeddingtonChessington
West
Landulph
Abham
Exeter
Axminster
Chickerell
Mannington
Taunton
Alverdiscott
Hinkley Point
Bridgwater
Aberthaw
Cowbridge
Pyle
Margam
SwanseaNorth
CardiffEast
Tremorfa
Alpha Steel
UskmouthUpper Boat
Cilfynydd
ImperialPark
Rassau
Whitson
Seabank
Iron Acton
Walham
Melksham
Minety DidcotCulham
Cowley
Bramley
Fleet
Nursling
Fawley Botley Wood
Lovedean
Bolney
Ninfield
Dungeness
Sellindge
Canterbury
E de F
Kemsley
Grain
Kingsnorth
Rayleigh Main
Littlebrook
Tilbury
Warley
Barking
W.HamCity Rd
BrimsdownWaltham
Ealing
Mill HillWillesden
Watford
St Johns
Wimbledon
New Hurst
Elstree
Rye House
N.Hyde
Sundon
Laleham
Iver
Amersham Main
Wymondley
Pelham
Braintree
BurwellMain
Bramford
EatonSocon
Grendon
EastClaydon
Enderby
Walpole
NorwichMain
Coventry
Berkswell
Rugeley
Cellarhead
IronbridgeBushbury
Penn
Willenhall
OckerHill
KitwellOldbury
Bustleholm
NechellsHamsHall
BishopsWood
Feckenham
Legacy
Trawsfynydd
Ffestiniog
Dinorwig
Pentir
Wylfa
Deeside
Capenhurst Frodsham
Fiddlers
Rainhill
KirkbyListerDrive
Birkenhead
WashwayFarm
Penwortham
Carrington
SouthManchester
Daines
Macclesfield
Bredbury
Stalybridge
Rochdale
WhitegateKearsley
Elland
Stocksbridge
WestMelton
Aldwarke
Thurcroft
BrinsworthJordanthorpe
Chesterfield
Sheffield CityNeepsend
Pitsmoor
Templeborough ThorpeMarsh
Keadby
WestBurton
Cottam
HighMarnham
Staythorpe
Stanah
Heysham
Padiham
Hutton
BradfordWest Kirkstall Skelton
Poppleton
Thornton
Quernmore
Monk
EggboroughFerrybridge
Killingholme
SouthHumberBank Grimsby
West
Drax
Lackenby
Greystones
GrangetownSaltholme
Norton
Spennymoor
Tod Point
Hartlepool
Hart Moor
Hawthorne Pit
Offerton
West Boldon
South Shields
Tynemouth
StellaWest
Harker
Eccles
Blyth
IndianQueens
Coryton
RatcliffeWillington
Drakelow
Shrewsbury
Cross
Weybridge
Cross
Wood
North
FrystonGrange
Ferry
Winco Bank
Norton Lees
Creyke Beck
Saltend North
Saltend South
Hackney
BaglanBay
LeightonBuzzard
PatfordBridge
Northfleet EastSinglewell
Fourstones
Humber Refinery
SpaldingNorth
West Thurrock
ISSUE B 12-02-09 41/177619 C Collins Bartholomew Ltd 1999
Dingwall
Dounreay
Newarthill
Cumbernauld
Kincardine
WishawStrathaven
KilmarnockSouth
Ayr
Coylton
Inveraray
HelensburghDunoon
Inverkip
DevolMoor
Hunterston
Sloy
Fort William
Bonnybridge
Neilston
Ceannacroc
Conon
Fort Augustus
Foyers
Inverness
Stornoway
Elvanfoot
Kaimes
Glenrothes
Westfield
Grangemouth
Longannet
Linmill
Bathgate
Errochty Power Station
Torness
Cockenzie
Keith
Thurso
FasnakyleBeauly
Deanie
Lairg
Shin
Nairn
Kintore
Blackhillock
Elgin
Keith
Peterhead
Persley
Fraserburgh
InvergarryQuoich
CulligranAigas
Kilmorack
GrudieBridge
Mossford
OrrinLuichart
Alness
Brora
Cassley
Dunbeath
Mybster
St. Fergus
Strichen
Macduff
Boat ofGarten
Redmoss
Willowdale
Clayhills
Dyce
Craigiebuckler
Woodhill
Tarland
DalmallyKillin
Errochty
Tealing
GlenagnesDudhope
Milton of Craigie
Dudhope
Lyndhurst
CharlestonBurghmuir
Arbroath
Fiddes
Bridge of Dun
Lunanhead
St. Fillans
Finlarig
Lochay
Cashlie
Rannoch
TummelBridge
Clunie
Taynuilt
Nant
Cruachan
PortAnn
Carradale
Auchencrosh
Lambhill
ClydesMill
Glenluce
NewtonStewart
Maybole
Dumfries Ecclefechan
Berwick
Hawick
Galashiels
Dunbar
Meadowhead
Saltcoats
HunterstonFarm
SP TRANSMISSION LTD.
Kilwinning
Currie
Cupar
Leven
Redhouse
Glenniston
SCOTTISH HYDRO-ELECTRICTRANSMISSION
Telford Rd.Gorgie
KilmarnockTown
Busby
Erskine
Strathleven
MossmorranDunfermline
Broxburn
Livingston
Whitehouse
ShrubhillPortobello
Devonside
StirlingWhistlefield
SpangoValley
Ardmore
Broadford
Dunvegan
NGC
Easterhouse
EastKilbrideSouth
Gretna
Chapelcross
THE SHETLAND ISLANDS
Tongland
GlenMorrison
Clachan
400kV Substations275kV Substations400kV CIRCUITS275kV CIRCUITS
Major Generating Sites Including Pumped Storage
Connected at 400kVConnected at 275kVHydro Generation
TRANSMISSION SYSTEM REINFORCEMENTS
Langage
BlacklawWhitelee
Iverkeithing
Marchwood
BickerFenn
Coalburn
REINFORCED NETWORK
Under Construction or ready to startConstruction subject to consents
Very strong need case
Series Capacitors
RedbridgeTottenham
Strong need case
Future requirement, but no strongneed case to commenceat present
‘Gone Green 2020’
Test Network
Simplified GB system representation
25GW demand
11 generators
Frequency Response selected between 3 – 6 Generators depending upon Inertia - Green
1320 MW Loss - Red
No Load Response
Additional Reserve Calculated Depending upon System inertia
1320MW Loss – Effect of Inertia and FR
Full H – Three Machines selected for FR to achieve 49.19 Hz (approx 49.2Hz)
F = 49.19 Hz
H/2 – Three Machines selected for FR as in Red Curve
H/2 – Six Machines selected for FR to achieve 49.19 Hz (approx 49.2Hz)
1320MW Loss – Effect of Inertia and FR
Full H – Three Machines selected for FR to achieve 49.19 Hz (approx 49.2Hz) - Red
H/2 – Three Machines selected for FR as in Red Curve - Green
H/2 – Six Machines selected for FR to achieve 49.19 Hz (approx 49.2Hz) – Blue
Frequency Insensitive Plant
Frequency Sensitive Plant
Test Network
Simplified GB system representation
25GW demand
11 generators
Frequency Response selected between 3 – 6 Generators depending upon Inertia - Green
1320 MW Loss - Red
Load Response Both Frequency and Voltage
Additional Reserve Calculated Depending upon System inertia
1320MW Loss – Effect of Inertia alone with V/F Load Response
Full H, No Frequency Response and Load Response
H/2, No Frequency Response and Load Response
Full H, No Frequency Response and Load Response
H/2, No Frequency Response and Load Response
1320MW Loss – Effect of Inertia and Frequency Response with Load Response
Full H – Two Machines selected for FR to achieve 49.235 Hz
H/2 – Two Machines selected for FR as in Base Case – Minimum Frequency 49.124Hz
H/2 – Three Machines selected for FR to achieve 49.215 Hz
1320MW Loss – Effect of Inertia and Frequency Response with Load Response
Full H – Two Machines selected for FR to achieve 49.235 Hz - Red
H/2 – Two Machines selected for FR as in Base Case – Minimum Frequency 49.124Hz - Green
H/2 – Three Machines selected for FR to achieve 49.215 Hz - Blue
Frequency Insensitive Plant
Frequency Sensitive Plant
Test Network
Simplified GB system representation
25GW demand
15 generators
1800 MW Loss - Red
Load Response Both Frequency and Voltage
Frequency Response selected between 3 – 10 Generators depending upon Inertia – Green
Load Reduction introduced for comparison purposes
1800MW Loss – Effect of Inertia alone with V/F Load Response
Full H, No Frequency Response and Load Response
H/2, No Frequency Response and Load Response
Full H, No Frequency Response and Load Response
H/2, No Frequency Response and Load Response
1800MW Loss – Effect of Inertia, Frequency Response and Load Reduction with V/F Load Response
Full H, 10 Machines providing Frequency Response f = 49.107Hz
Full H, No Frequency Response and Load Response
H/2, No Frequency Response and Load Response
Full H, 3 Machines Providing Frequency Response (in 1320 MW case frequency above 49.2Hz)
2H, 10 Machines providing Frequency Response f = 49.289Hz
Full H, 6 Machines providing Frequency Response, 480 MW of load reduction at 4 seconds f = 49.203Hz
Assessment of Study Work
Inertia has a significant effect on System Frequency
Increased rate of change of frequency (Hz/s) for a lower system inertia
With Frequency response included, the minimum recorded system frequency is increased
If System Inertia is allowed to drop substantially additional fast acting Reserve / Response will need to be scheduled at additional cost to ensure standards of security are maintained.
Fast Acting Load Reduction (ie block tripping) is more effective than that provided by Generators in containing a frequency fall
There needs to be co-ordination between requirements for inertia, delivery of primary response and delivery of secondary response – 10% P, 10% S and 10% H is only adequate if Generators / loads adequately contribute towards system inertia
Under an 1800 MW loss scenario the need for system inertia becomes even more critical
Analysis undertaken to date demonstrates the need for Generators and HVDC Converter Owners to contribute towards System Inertia unless additional reserve is scheduled at considerable cost
Requirements for Inertia
Contribution towards System Inertia can be achieved by a modification to the Control System in order to control df/dt
Three wind turbine manufacturers have published information on systems to contribute towards system inertia (Enercon, Vestas and GE).
Discussions are ongoing with other manufactures
The Costs of installing such a requirement is believed to be negligible – certainly against the cost of installing additional fast acting frequency response (Volumes double)
Hydro Quebec have introduced Inertial requirements in their Grid Code
Analysis suggests that an inertial requirement would be applicable to all forms of generation where there is decoupling between the Generator and System
Additional Issues for Inertia
Since the Control Systems would rely on a df/dt control, which is a noise amplifying process some consideration will need to be given to adequate filtering
In order to reduce complexity and following discussions with manufacturers it is suggested that such a facility would only be applicable to plant in Limited Frequency Sensitive Mode of operation.
The ability of Generators to recover following contribution to System Inertia needs to be examined in more detail.
To minimise wear on the generator, it is suggested a dead band is introduced to the df/dt term.
A static dead band value still requires evaluation but a value in the range of 0.003 Hz/s
is thought to be adequate based on the current experience – see attached slide
Deadband
High Level Proposals (1)
In order to limit the rate of change of frequency following a generation loss or load loss, each Generating Unit, Power Park Module or DC Converter shall be required to contribute towards System Inertia.
For Generating Units, DC Converters and Power Park Modules (including Power Park Units thereof) which do not inherently have a capability to provide inertia to the Transmission System, then each Generating Unit, DC Converter and Power Park Module shall be fitted with a Control System to contribute towards system inertia.
Any such Control System should aim to control df/dt in order to reduce the rate of change of active power and hence rate of change of system frequency. Such a Control System would need to reflect and maximise the synthetic value of the Inertia Constant H.
High Level Proposals (2)
In addition, the Inertial Control System fitted to each Generating Unit, Power Park Module and DC Converter shall:-
operate whenever the Generating Unit, DC Converter and Power Park Module (including the Power Park Unit thereof) is selected to Limited Frequency Sensitive Mode of operation.
have an adjustable dead band of between 0.001 Hz/s – 0.01Hz /s. The initial dead band shall be set to 0.003 Hz/s
Include elements to limit the bandwidth of the output signal. The bandwidth limiting must be consistent with the speed of response requirements and ensure that the highest frequency of response cannot excite torsional oscillations on other plant connected to the network. A bandwidth of 0-5Hz would be judged acceptable for this application. All other control systems employed within the Generating Unit, Power Park Module (including the Power Park Unit thereof) and DC Converter should also meet this requirement.
For the avoidance of doubt there is no requirement for the Inertial Control System to be active when the Generating Unit, Power Park Module (including the Power Park Unit thereof) or DC Converter is operating in Frequency Sensitive Mode.
Conclusions
Machine inertia significantly affects the rate of change of System Frequency
In a System containing dynamic frequency response, a low system inertia will result in a lower minimum system frequency
There needs to be co-ordination between requirements for inertia, delivery of primary response and delivery of secondary response – is 10% P, 10% S and 10% H still adequate especially in an 1800MW scenario
It would be significantly more expensive to allow system inertia to be eroded (as new Generation Technologies are introduced) and hold more fast acting response than mandating the need for a control system to contribute towards system inertia.
The cost of fitting an inertial control is believed to be insignificant in comparison with holding additional response.
Requirements for an inertial control need to reflect issues such as control system dynamics, dead band and complexity
Some additional study work is required in respect of exact control system performance.
The Control System would only be required to be active when the Generator is operating in Limited Frequency Sensitive Mode of operation.
National Grid has already started discussion with several turbine manufacturers to determine settings.
References / Further Information
Contribution of Wind Energy Converters with Inertia Emulation to frequency control and frequency stability in Power Systems – Stephan Wachtel and Alfred Beekmann – Enercon – Presented at the 8th International Workshop on Large Scale Integration of Wind Power into Power Systems as well as on Offshore Wind Farms, Bremen Germany, 14 – 15 October 2009.
Variable Speed Wind Turbines Capability for Temporary Over-Production – German Claudio Tarnowski, Philip Carne Kjaer, Poul E Sorensen and Jacob Ostergaard
Study on Variable Speed Wind Turbine Capability for Frequency Response - German Claudio Tarnowski, Philip Carne Kjaer, Poul E Sorensen and Jacob Ostergaard
GE Energy – WindINERTIATM Control fact sheet – Available on GE Website at :- http://www.ge-
energy.com/businesses/ge_wind_energy/en/downloads/GEA17210.pdf
Transmission Provider Technical Requirements for the Connection of Power Plants to the Hydro-Quebec Transmission System – February 2006
Amendment Report SQSS Review Request GSR007 Review of Infeed Loss limits – Prepared by the SQSS Review Group for Submission to the Authority – 10 th September 2009 available at:- http://www.nationalgrid.com/NR/rdonlyres/EF5C0829-1C5E-4258-8F73-70DC62C43F49/36936/SQSS1320Reportv10_final.pdf