Grid Code Frequency Response Working Group
System Inertia
Antony Johnson, System Technical Performance
Overview
 Background to System Inertia
 Transmission System need
 Future Generation Scenarios
 Initial Study Work
 International Experience and Manufacturer Capability
 Transmission System Issues
 Conclusions
Frequency Change
 Under steady state the mechanical and electrical energy must be
balanced
 When the electrical load exceeds the mechanical energy supplied, the
system frequency will fall.
 The rate of change of frequency fall will be dependant upon the initial
Power mismatch and System inertia
 The speed change will continue until the mechanical power supplied to
the transmission system is equal to the electrical demand.
Why is Inertia Important
 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.
 Directly connected synchronous generators and Induction Generators
will contribute directly to System Inertia.
 Modern Generator technologies such as Wind Turbines or wave and
tidal generators which decouple the prime mover from the electrical
generator will not necessarily contribute directly to System Inertia
 Under the NGET Gone Green Scenario, significant volumes of new
generation are unlikely to contribute to System Inertia
What is inertia?
The stored energy is proportional to the speed of rotation squared
3 types of event cause a change in frequency
 Loss of generation (generator, importing HVDC link etc)
 Loss of load
 Normal variations in load and generator output
Loss of Generator
on the system
Frequency Falls as
demand > generation
Stored energy delivered to grid as MW
The maths behind inertia
½Jω2
H=
MVA
H = Inertia constant in MWs / MVA
J = Moment of inertia in kgm2 of the rotating mass
ω = nominal speed of rotation in rad/s
MVA = MVA rating of the machine
Typical H for a synchronous generator can range from 2 to 9 seconds (MWs/MVA)
∂f
∂t
=
∆P
2H
∂f/∂t = Rate of change of frequency
∆P = MW of load or generation lost
2H = Two times the system inertia in MWs / MVA
Strategic Reinforcements
An NGET Future Scenario
TRANSMISSION SYSTEM REINFORCEMENTS
Dounreay
Thurso
REINFORCED NETWORK
Mybster
Cassley
Stornoway
Dunbeath
Lairg
400kV Substations
275kV Substations
400kV CIRCUITS
275kV CIRCUITS
THE SHETLAND ISLANDS
Brora
Shin
‘Gone Green 2020’
Alness
Conon
Deanie
Fraserburgh
Elgin
Orrin
Luichart
Dunvegan
Major Generating Sites Including Pumped Storage
Mossford
Grudie
Bridge
Ardmore
Macduff
Dingwall
Culligran
Aigas
Keith
Nairn
Inverness
Kilmorack
Connected at 400kV
Connected at 275kV
Hydro Generation
St. Fergus
Strichen
Blackhillock
Peterhead
Beauly
Fasnakyle
Dyce
Kintore
Glen
Morrison
Broadford

Redmoss
Fiddes
Fort William
Errochty Power Station
Errochty
Rannoch
Clunie
Taynuilt
Cruachan
Nant
Killin
Dalmally
Lunanhead
Tealing
Dudhope
Arbroath
Milton of Craigie
Inveraray
7.5GW nuclear
Lyndhurst
Charleston
Burghmuir
Finlarig
St. Fillans
SCOTTISH HYDRO-ELECTRIC
TRANSMISSION
Clachan
Glenrothes
Leven
Redhouse
Kincardine
Dunfermline
Longannet
Iverkeithing
Grangemouth
Bonnybridge
Helensburgh
Strathleven
Erskine
Lambhill
Shrubhill
Cockenzie
Portobello
Future requirement, but no strong
need case to commence
at present
Dunbar
Torness
Whitehouse
Kaimes
Currie
Newarthill
Clydes
Mill
Neilston
Hunterston
Farm
Glenniston
Mossmorran
Telford Rd.
Broxburn Gorgie
Bathgate
Cumbernauld
Easterhouse
Livingston
Berwick
Meadowhead
Strathaven
East
Kilbride
South
Blacklaw
Linmill
Eccles
Galashiels
Kilmarnock
South
Ayr
Series Capacitors
Wishaw
Busby
Whitelee
Kilmarnock
Town
Kilwinning
Saltcoats
Carradale
Strong need case
Dudhope
Westfield
Devonside
Stirling
Devol
Moor
Spango
Valley
Inverkip
Hunterston
Glenagnes
Cupar
Sloy
Whistlefield
Port
Ann
Some gas & additional coal
Very strong need case
Bridge of Dun
Tummel
Bridge
Lochay
12GW Coal & oil LCPD
Dunoon

Under Construction or ready to start
Construction subject to consents
Clayhills
Craigiebuckler
Invergarry
Cashlie

Willowdale
Boat of
Garten
Tarland
Plant closures
Persley
Woodhill
Foyers
Fort Augustus
Ceannacroc
Quoich
Coalburn
SP TRANSMISSION LTD.
Coylton
Elvanfoot
Significant new renewable
Hawick
Maybole
NGC
Dumfries
Auchencrosh

Fourstones
Harker
Chapelcross
29 GW wind (2/3 offshore)
Blyth
Gretna
Ecclefechan
Newton
Stewart
Tynemouth
South Shields
West Boldon
Stella
West
Tongland
Glenluce
Offerton
Hawthorne Pit
Hart Moor
Spennymoor

Some tidal, wave, biomass & solar PV

Renewable share of generation grows from 5% to 36%
Norton
Heysham
Significant new non renewable build
Quernmore

3GW of new supercritical coal (some with CCS)

Poppleton Osbaldwick
Bradford
West
Kirkstall
Padiham
Drax
Ferrybridge
Killingholme
Humber Refinery
Eggborough
Keadby
Washway
Templeborough
Thorpe
Whitegate
Kearsley
Farm
West
Marsh
Kirkby
South
Melton
Stalybridge
Lister
Manchester
Stocksbridge Pitsmoor
Rainhill
Drive
Aldwarke
Bredbury Winco Bank
Carrington
Birkenhead
Thurcroft
Neepsend
Daines
Fiddlers
Sheffield City
Ferry
Brinsworth
Jordanthorpe
Frodsham
Capenhurst
Norton Lees
Macclesfield
Chesterfield
Deeside
High
Marnham
Pentir
Dinorwig
South
Humber
Bank
Grimsby
West
West
Burton
Cottam
Staythorpe
Legacy
Ffestiniog
Cellarhead
Bicker
Fenn
Willington
Trawsfynydd
11GW of new gas
Ironbridge
Shrewsbury
Ratcliffe
Walpole
Drakelow
Rugeley
Spalding
North
Norwich
Main
Bushbury
Willenhall Bustleholm
Penn
Enderby
Hams
Hall
Nechells
Bishops
Wood
Coventry
Oldbury
Kitwell
Berkswell
Feckenham
Sizewell
Burwell
Main
Grendon Eaton
Socon
Bramford
Patford
Bridge
Electricity demand remains flat (approx 60 GW)
East
Claydon
Rassau
Upper Boat
Alpha Steel
Walham
Cilfynydd
Uskmouth
Increases from heat pumps & cars
Pelham
Wymondley
Rye House
Brimsdown
Cowley
Whitson
Iron Acton
Amersham Main
Culham
Didcot
Iver
N.Hyde
Minety
Seabank
Cowbridge
Sundon
Leighton
Buzzard
Imperial
Park
Swansea
North
Baglan
Bay
Margam
Pyle
Pembroke
Reductions from energy efficiency measures
Aberthaw

Creyke Beck
Saltend North
Monk
Fryston
Elland
Rochdale
Ocker
Hill

Thornton
Skelton
Grange
Saltend South
Penwortham
Wylfa
3GW of new nuclear
Greystones
Lackenby
Hutton
Stanah

Hartlepool
Tod Point
Grangetown
Saltholme
Laleham
Tremorfa
Cardiff
East
Melksham
Watford
Braintree
Waltham
Cross
Hackney
Elstree
Rayleigh Main
Tottenham Redbridge Warley
Mill Hill
Willesden
Coryton
Barking West Thurrock
Northfleet East
Ealing
Singlewell
Grain
Tilbury
City Rd W.Ham
St Johns
Wood
New Hurst
Cross
Kingsnorth
West
Weybridge Chessington
Bramley
Fleet
Rowdown Littlebrook
Beddington
Wimbledon
Kemsley
Canterbury
North
Hinkley Point
Sellindge
Bridgwater
Alverdiscott
Bolney
Nursling
Taunton
E de F
Ninfield
Dungeness
Marchwood
Axminster
Mannington
Exeter
Chickerell
Langage
ISSUE B 12-02-09 41/177619
C Collins Bartholomew Ltd 1999
Indian
Queens
Landulph
Abham
Fawley
Lovedean
Botley Wood
Quantitative Analysis
 The effect of System Inertia is being quantitatively
analysed through two methods: Energy Balance spread sheet approach
 Utilising simple predictive output models based on an energy
balance
 System Study using a Test Network
 Utilising Dynamic System Models
Energy Balance Spread Sheet Approach
 System Considered
 16.5 GW of Wind, 6.9 GW Nuclear, 1.6 GW Carbon Capture
 Load Response 2% per Hz
 Assumed loss – 1800MW
 System Balanced at t = 0 seconds
 Inertia considered in isolation
 General Conclusion
 The higher the inertia the longer it takes for the steady state
frequency to be reached.
 See subsequent slides
Energy Balance Spread Sheet – Results
Wind Generation with and Without Inertia
Variation in Inertia - Low Resolution
50.5
50
Frequency Hz
49.5
49
48.5
48
47.5
47
46.5
46
0
10
20
30
40
Time (s)
H=0
H=3
50
60
Energy Balance Spread Sheet – Results
Wind Generation with and Without Inertia
Variation in Inertia - High Resolution
50.2
50
Frequency (Hz)
49.8
49.6
49.4
49.2
49
48.8
48.6
48.4
48.2
0
1
2
3
4
Time (s)
H=0
H=3
5
6
Shunt 3
-0.00
-17.75
-1993...
-175.1..
87.43
1
Shunt 2
trf_103_103G
102 GEN
trf_102_102G
1
lne_105_103_C3
21.65
0.00
1999.5..
458.35
87.43 21.95
1.00
26.54
lne_104_101_C5
lne_104_101_C6
10 generators
1.02
18.65
2826.0..
-34.91
85.40
1971.5..
192.88
64.63
102 BUS002 408.69
643.43
-165.8..
66.87
1
lne_105_103_C4
Approx 23GW demand
lod_102_L2
G
~
Shunt 1
643.43
-165.8..
66.87
sym_102_G2
 Basic GB system representation
1
565.21
-6.98
80.11 20.64
0.94
25.69
~
G
-1960...
-35.67
64.63
~
G
604.65
-239.4..
64.29
565.21
-6.98
80.11
604.65
-239.4..
64.29
trf_102_101_T1
1.01
14.11
0.99
17.51 -2816...
440.57
85.40
565.21
-6.98
80.11
0.00
86.98
101 BUS001 278.18
-0.00
-187.6..
103 BUS003 273.26
565.21
-6.98
80.11
-568.3..
246.64
61.25
958.39
287.52
565.21
-6.98
80.11
1319.9..
180.89
571.72
-208.7..
61.25
103 GEN
1999.5..
458.35
82.06
Test network
sym_103_G3_E
sym_103_G3_C
sym_103_G3_A
~
sym_103_G3_D G~ sym_103_G3_B G~
G
1
lod_101_L1
lne_105_104_C2
lne_105_104_C1
5 generators providing frequency response
lod_104_L4
-557.7..
284.52
64.29
-84.70
48.73
11.72
-84.70
48.73
11.72
9.58
-0.00
86.05
-78.88
11.72
86.05
-78.88
11.72
-610.1..
214.05
66.87
-610.1..
214.05
66.87
105 BUS005 273.96
1491.5..
-361.7..
77.03
1
Shunt 4
-1275...
572.77
69.04
-1491...
456.64
77.03
106 BUS006 405.01
trf_106_106G3
trf_106_106G1
1
1
General Load
lod_106_L6
-9380...
1241.6..
92.66
106 GEN3
107 BUS007 408.48
1.02
-2.88
9826.2..
3634.4..
26.53
21.72
0.99
-0.59
9826.2..
3634.4..
52.38
sym_107_G7
107 GEN
-1494...
-195.4..
83.63
lod_105_L5
1
1499.5..
404.73
83.63
105 GEN 21.51
0.98
14.67
1499.5..
404.73
77.66
9380.7..
-168.3..
92.66
lne_106_107_C7
1353.29
0.00
9.71
-0.00
3998.8..
810.20
84.52
21.67
0.99
12.46
3998.8..
810.20
90.67
-3989...
-182.4..
84.52
106 GEN1
~
G
21.97
1.00
11.25
-3987...
-678.6..
85.60
3999.0..
1244.2..
85.60
3999.0..
1244.2..
93.07
~
G
~
G
sym_106_G1
1.01
3.63
1051.6..
286.80
trf_105_105G
trf_106_104_T3
G
~
TEST MACH..
1.00
7.02
-0.00
-150.8..
trf_106_105_T2
1275.3..
-515.5..
69.04
-0.00
0.05
1.42
1.00
5.80
sym_106_G3
(equivalent to loss of a 1320 MW generator)
-557.7..
284.52
64.29
104 BUS004 273.98
-9815...
-3189...
26.53
trf_107_107G
1320 MW load switched in
19196...
1947.8..
1
lod_107_L7
G
~
sym_105_G5
DIgSILENT
lod_103_L3
lne_103_101_C8
DIgSILENT
Base case large disturbance – normal system inertia
X = 10.400 s
50.04
49.86
49.68
49.50
49.32
49.183 Hz
49.14
0.000
12.00
106 BUS006: Electrical Frequency in Hz
24.00
36.00
48.00
[s]
60.00
12.00
24.00
FREQUENCY RESPONSE: Generation, Active Power in MW
36.00
48.00
[s]
60.00
36.00
48.00
[s]
60.00
3027.
2812.
2596.
2381.
2166.
1951.
0.000
2.28E+4
X = 10.400 s
22713 MW
2.24E+4
2.21E+4
2.18E+4
2.14E+4
2.11E+4
0.000
21331.314 MW
12.00
24.00
NON FREQENCY RESPONSE: Generation, Active Power in MW
Decreasing system inertia – large disturbance
DIgSILENT
(½ and ¾ base case inertia)
50.10
49.78
49.46
49.14
Y = 48.800 Hz
48.82
48.50
0.000
12.00
106 BUS006: Frequency (Hz) base case inertia
106 BUS006: Frequency (Hz) 0.5 x base case inertia
106 BUS006: Frequency (Hz) 0.25 x base case inertia
24.00
36.00
48.00
[s]
60.00
12.00
24.00
36.00
FREQUENCY RESPONSE: Total active power from generators providing frequency reponse - base case inertia
FREQUENCY RESPONSE: Total active power from generators providing frequency reponse - 0.5 x base case inertia
FREQUENCY RESPONSE: Total active power from generators providing frequency reponse - 0.25 x base case inertia
48.00
[s]
60.00
12.00
24.00
36.00
NON FREQENCY RESPONSE: Total active power from generators NOT providing frequency reponse - base case inertia
NON FREQENCY RESPONSE: Total active power from generators NOT providing frequency reponse - 0.5 x base case inertia
NON FREQENCY RESPONSE: Total active power from generators NOT providing frequency reponse - 0.25 x base case inertia
48.00
[s]
60.00
3095.
2865.
2636.
2407.
2177.
1948.
0.000
2.28E+4
2.24E+4
2.21E+4
2.18E+4
2.14E+4
2.11E+4
0.000
International Experience and Manufacturer
Capability
 Hydro Quebec requires Generating Units in a Power Plant
to have an inertia constant which is compatible with the
inertia constants of existing Power Plants in the same
region. The minimum inertia for wind power must equate to
3.5s.
 GE Wind advertise a Wind Inertia Control on their Website
 Enercon have completed modelling and field tests on a
wind turbine and published a paper on this subject
 Other manufacturers are believed to be investigating an
inertial capability
Transmission System Issues
 Optimum Performance Capability requirements based on
the minimum needs of the Transmission System.
 Prevention of under and over frequency incidents
 Control System Design and performance
 Filtering requirements if any (Noise Generation?)
 Overall Co-ordination
 Inertial contribution – Delivered from all plant
 Primary Response – FSM – Containment
 Secondary Response – FSM - Correction
Conclusions
 Machine inertia significantly affects the rate and rise and
rate of fall of System Frequency
 It is likely to be cheaper (although some form of
quantitative analysis would be required) to require all
generators to contribute to System Inertia rather than
having no requirement and requiring larger volumes of fast
acting frequency response?
 Non Discrimination
 The inertial delivery requirements needs to be quantified
 Delivery / Capability
 Control System Settings / Filtering