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