Tyndall Centre Working Paper 32
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Integrating Renewables and CHP into the UK Electricity System: Investigation of the impact of network faults on the stability of large offshore wind farms
Xueguang Wu, Lee Holdsworth, Nick Jenkins and Goran Strbac
April 2003
Tyndall Centre for Climate Change Research
Working Paper 32
Integrating Renewables and CHP into the UK Electricity System: Investigation of the impact of network faults on the stability of large offshore wind farms
Xueguang Wu Lee Holdsworth Nick Jenkins Goran Strbac The Manchester Centre for Electrical Energy (MCEE) UMIST UK Email: [email protected] [email protected] [email protected] [email protected] Tyndall Centre Working Paper no. 32 April 2003
SUMMARY Simulations have been performed to investigate the impact of network faults on the stability of large offshore wind farms. Results are presented for balanced 3-phase faults applied on the GB 400 kV transmission system. The studies indicate that faults on the GB transmission system (close to the wind farm) may cause instability of the large offshore wind farms. The voltage drop investigations show that for a 100% voltage drop at a 400 kV connection point (such as Norwich Main), a very fast clearance time (less than 90 ms) is required to maintain stable operation of a 120MW offshore wind farm. However, when the voltage drops are less than or equal to 60%, the critical clearance times are longer than 140ms. The contours of voltage drop for the GB transmission system illustrate that for a 60% voltage drop the 3-phase fault would have to occur close to the connection point. Therefore the stability of the offshore wind farms may only be effected by relatively local faults. Possible remedial measures include the use of fast acting reactive power support, e.g. a Static Reactive Power Compensator (STATCOM).
SUMMARY Simulations have been performed to investigate the impact of network faults on the stability of large offshore wind farms. Results are presented for balanced 3-phase faults applied on the GB 400 kV transmission system. The studies indicate that faults on the GB transmission system (close to the wind farm) may cause instability of the large offshore wind farms. The voltage drop investigations show that for a 100% voltage drop at a 400 kV connection point (such as Norwich Main), a very fast clearance time (less than 90 ms) is required to maintain stable operation of a 120MW offshore wind farm. However, when the voltage drops are less than or equal to 60%, the critical clearance times are longer than 140ms. The contours of voltage drop for the GB transmission system illustrate that for a 60% voltage drop the 3-phase fault would have to occur close to the connection point. Therefore the stability of the offshore wind farms may only be effected by relatively local faults. Possible remedial measures include the use of fast acting reactive power support, e.g. a Static Reactive Power Compensator (STATCOM).
CONTENTS 1. Introduction ......................................................................................................... 3 2. Studies and assumptions ...................................................................................... 4 2.1 Assumptions of the voltage drop calculations................................................ 4 2.2 Assumptions of the dynamic stability calculations ........................................ 4 3. Zones of voltage drop influence of faults............................................................. 5 4. Dynamic stability of large offshore wind farms ................................................ 11 4.1 Dynamic performance of large offshore wind farms................................... 11 4.2 Critical clearing times of large offshore wind farms ................................... 12 5. Conclusions ........................................................................................................ 14 6. References........................................................................................................... 15
2
1. Introduction The generation of electrical power using sustainable sources of energy is developing rapidly with the worldwide installed capacity of wind generation now exceeding 25 GW. For the UK, a target of 10% of electrical energy to be supplied by renewables by 2010 implies a capacity of renewable generating plant of up to 8 – 10 GW, of which some 60 % might be wind turbines. In the UK the Crown Estate has granted licenses to 18 consortia to investigate large offshore wind farm sites with a potential of at least 1500 MW [1]. There are also suggestions that a target as high as 20 % of UK electricity from renewables might be achievable by 2020 [2], with similar ambitious targets existing in many European countries. Until recently, wind farms connected within the UK network had been limited to small sized installations, connected at distribution voltage levels. The connection standards [3] do not currently require wind farms to support the power system during a network disturbance. During a network fault the wind turbines were disconnected from the system and then subsequently reconnected when the fault has been cleared. However, the network design grid codes are now being revised for the increased penetration of wind generators. The wind farms will now have to continue to operate during system disturbances. A fixed speed wind turbine consists of a squirrel cage induction generator coupled to the wind turbine rotor via a gearbox. The induction generator consumes reactive power and requires compensation capacitors at the terminals in order to achieve unity power factor. The growth in fixed speed wind farms with large MW capacity connected to the UK transmission network will have a significance impact on the technical and operational characteristics of the electricity system. The connection requirements of large wind farms therefore require reviewing to ensure continuing network security. The objective of this work was to investigate network faults and stability issues that need to be taken into account in order for high penetrations of large offshore wind farms to be connected to the network. These must be investigated and resolved in order to build the required confidence that a high penetration of wind generators connected to the network is both feasible and safe. The methods used in this study are based on modelling of the Great Britain (GB) network and the dynamic stability of a typical large offshore fixed speed wind farm. The aim of the study was firstly to assess zone influence of faults in the GB network and secondly to explore potential dynamic impacts of the faults on the large offshore wind farms. This report presents the main results of this work. The main areas of focus for this work are as follows: (1) Studies and assumptions (2) Zones of voltage drop influence of faults (2) Dynamic stability of large offshore wind farms 3
A detailed description of the work performed under each of the above headings is provided below. 2. Studies and assumptions For high penetrations of the large offshore, fixed speed, wind farms to be connected to the network, the effect of voltage drops at their 400 kV connection points and the dynamic stability of the wind farms have been investigated. The results shown in this study were based on the following assumptions. 2.1 Assumptions of the voltage drop calculations (1) The study case was the GB network operating under the winter-peak load of 2002. (2) The offshore wind farms were connected to the 400 kV transmission system at Deeside, Penwortham, Walpole, and Norwich Main substations [4]. (3) The sub-transient reactances of all synchronous generators were 0.2 per-unit. (4) The type of fault was a balanced three-phase short circuit. (5) The fault levels at the 400 kV substations were calculated from the three-phase short circuit currents using PowerWorld. (6) PowerWorld was also used to calculate the voltage drops at the connection points for faults in the network. 2.2 Assumptions of the dynamic stability calculations (1) The study cases were based on the network shown in Figures 1 and 2. The shortcircuit ratios (SCR) at the 33 kV busbars of the offshore wind farm substations were 6. (2) The 400 kV system was represented for the dynamic stability simulation by a voltage source in series with an impedance. The voltage of the source was 1 p.u. The impedance was calculated from PowerWorld and is shown in Table 1. (3) The offshore wind farm consisted of the same type of wind turbines, each of 2 MW. These were represented by a single equivalent coherent fixed-speed induction generator. The data of the 2 MW wind turbine induction generator is shown in Table 2 [5]. (4) The distance from the offshore wind turbines to shore was 5 km. (5) A lumped 33kV/0.69kV wind turbine terminal transformer with 5% impedance was used to connect the offshore wind farm to the 132kV/33kV onshore substation through the 33 kV submarine cables. (6) Each of the 33 kV submarine cables was 185 mm2, multicore copper, and paper insulated distribution cable with rated current 360 A, resistance 0.118 ohms/km, reactance 0.101 ohms/km and capacitance 0.4 µF/km [6]. (7) The number of parallel submarine cables was 4 for the 60 MW offshore wind farm and 8 for the 120 MW. (8) An earthing zigzag transformer with rated current 1000 A was used to provide an earthed point on the 33 kV network. (9) A 132kV/33kV transformer with 15% impedance was connected to the 400kV/132kV system substation through the 132 kV overhead lines. (10) Each of the 132 kV overhead lines was 20 km long and 258 mm2 aluminum conductor steel reinforced (ACSR) conductor with rated capacity 115 MVA, 4
resistance 0.068 ohms/km, and reactance 0.404 ohms/km [7]. (11) The number of parallel overhead lines was 1 for the 60 MW offshore wind farm and 2 for the 120 MW. (12) The 400kV/132kV system substation had a transformer with 15% impedance [8]. (13) The computer program, PSCAD/EMTDC, was used to simulate dynamic stability. 400kV 400kV/132kV
30*2MW, 0.69kV 132kV/33kV 20km, 132kV 5km, 33kV SCR = 6 large offshore wind farm 300MVA, 15% 100MVA, 15% one overhead line four submarine cables WT
G
132kV
system impedance
33kV 60MW earthing 33kV/0.69kV capacitor transformer 80MVA, 5% banks
fault resistance
Figure 1 A 60MW offshore wind farm connected to the 400 kV busbar 400kV 400kV/132kV 132kV/33kV 60*2MW, 0.69kV 5km, 33kV SCR = 6 large offshore wind farm 1000MVA, 15% 20km, 132kV 150MVA, 15% two overhead lines eight submarine cables WT
G 132kV
system impedance
earthing transformer
33kV 120MW 33kV/0.69kV capacitor 150MVA, 5% banks
fault resistance
Figure 2 A 120MW offshore wind farm connected to the 400 kV busbar Table 1 System data 400kV Short-circuit level substation (MVA) Deeside 19,514 Penwortham 18,785 Walpole 19,142 Norwich Main 12,006
Impedance (ohms) 8.20 8.52 8.36 13.33
X/R 10.2 10.6 10.4 11.9
Table 2 Wind turbine induction generator data (on its own base) Capacity Vol. f R1 X1 Xm R2 X2 (MW) (kV) (Hz) (p.u) (p.u) (p.u) (p.u) (p.u) 2 0.69 50 0.0049 0.0924 3.9528 0.0055 0.0995
Frequency (Hz) 50 50 50 50
Lumped inertia constant (sec.) 3.5
3. Zones of voltage drop influence of faults Voltage drops at the 400 kV busbars at substations (Deeside, Penwortham, Walpole and Norwich Main) were calculated. The results are shown in Figures 3, 4, 5 and 6. The retained voltage is shown at the location of the fault. For example, when a three5
phase fault was applied at Harker, the retained voltage at Deeside 400 kV busbar was 0.88 as shown at Harker. Figure 3 shows the retained voltages at Deeside for faults on each busbar in the GB network. Contours of the voltage drop were drawn from the retained voltages. The 30% voltage drop contour only extends over North Wales, the West Midlands, and the Manchester area. Figures 4-6 show similar results for Penwortham, Walpole and Norwich Main substations.
6
Figure 3 Retained voltages at Deeside 400kV substation for faults in the GB network NORTH WEST-SSE
BEAULY
KEITH
1.00
PETERHEAD
KINTORE
FOYERS
1.00
CRUACHAN
ABERDEEN
1.00 NORTH SOUTH-SSE TEALING INVERKIP
WINDYHILL BONNYBRIDGE
0.99
400kV SSE & SP
LONGANNET
275kV
NEILSTON
0.98
Power flow boundary
COCKENZIE
0.99
HUNTERSTON
STRATHHAVEN
KILMARNOCK SOUTH
TORNESS
0.95
0.97
5%
Voltage drop range
ECCLES
0.98 SP & NGC STELLA WEST
0.98
HARKER
0.88
HAWTHORN PIT NORTON
HUTTON
10 %
0.85
0.95
0.93
B1-NGC
THORNTON PENWORTHAM
DRAX EGGBORO UGH0.81 MACCLESFIELD COTTAM 0.66
30 %
WYLFA
0.63 PENTIR
DEESIDE
0.91
50 CELLARHEA 0.67 D 0.00 %
0.49 TRAWSFYNYDD
0.53 30 % 10 %
0.88
0.81
0.65
CREYKE BECK
0.87 0.90
WEST BURTON
0.89
RATCLIFFE ON SOAR 0.89
LEAGCY
DRAKELOW
0.30
0.76
B2-NGC
KEADBY
B3-NGC WALPOLE
NORWICH MAIN
0.94
0.98
IRONBRIDGE
0.61
FECKENHAM
0.81
ENDERB 0.92 Y WYMONDL SUNDON EAST EY 0.95 CLAYDON 0.94
0.94
WALHAM
BRAMFOR D 0.99
SIZEWELL
0.98
B9-NGC BRAINTREE
0.94
RAYLEIGH0.99 MAIN
COWLEY
0.94
5%
PELHAM
0.94
0.98
CITY ROAD
1.00 SWANSEA
0.99 PEMBROKE
0.99
MELKSHAM
CILFYNYDD
0.97
0.94
LOVEDEAN
1.00
EXETER
1.01
LANDULPH
1.01
1.00
0.99
MANNINGTON
1.00 INDIAN QUEENS
CANTERBURY BOLNEY
0.99 1.01
0.99
0.96
HINKLEY POINT
ALVERDISCOTT
KEMSLEY
LONDON AREA BRAMLEY
FAWLEY NORTH
CHICKERELL
1.00
1.01
B7-NGC
7
DUNGENESS
1.00 NINFIELD
1.00
0.99 SELLIN 1.00 DGE E de F (France)
Figure 4 Retained voltages at Penwortham 400kV substation for faults in the GB network BEAULY
NORTH WEST-SSE
KEITH
0.99
PETERHEAD
KINTORE
FOYERS
0.97
CRUACHAN
ABERDEEN
0.97 NORTH SOUTH-SSE
5%
TEALING INVERKIP
WINDYHILL BONNYBRIDGE
0.95
400kV
SSE & SP
LONGANNET
275kV
NEILSTON
0.92
Power flow boundary
COCKENZIE
0.95
HUNTERSTON
STRATHHAVEN
KILMARNOCK SOUTH
TORNESS
0.86
0.90
10 %
Voltage drop range
ECCLES
0.94 SP & NGC STELLA WEST
0.93
HARKER
0.67 30 %
HUTTON
0.57
HAWTHORN PIT
NORTON
0.90
0.86
40 %
PENWORTHAM
B1-NGC
THORNTON DRAX
0.81
CREYKE BECK
0.71
0.00
EGGBOROUGH
WYLFA
0.83 KEADBY
0.70
B2-NGC
0.88 MACCLESFIELD 30 COTTAM WEST BURTON 0.66 PENTIR % DEESIDE 0.91 0.88 CELLARHEAD 0.78 RATCLIFFE 0.70 ON SOAR 0.91 0.64 WALPOLE LEAGCY TRAWSFYNYDD DRAKELOW 0.69 0.93 0.84 0.80 IRONBRIDGE 10 0.81 FECKENHAM ENDERBY % 0.94 0.90 WYMONDL 5% SUNDON PELHAM EAST EY 0.95 CLAYDON 0.95 0.95 0.95 WALHAM COWLEY 0.97 CITY ROAD 0.96 1.00 0.84
SWANSEA
1.00 PEMBROKE
1.00
MELKSHAM
CILFYNYDD
0.99
0.98
LOVEDEAN
1.01 1.01
INDIAN QUEENS
1.01
LANDULPH
1.01
1.01
1.00
MANNINGTON
FAWLEY NORTH
CHICKERELL
1.01
1.01
B7-NGC
8
SIZEWELL
BRAMFOR D 0.98
0.98
B9-NGC BRAINTREE
0.99
RAYLEIGH MAIN
0.99 0.99 CANTERBURY
BOLNEY
EXETER
0.97
0.98
1.00 1.01
NORWICH MAIN
KEMSLEY
LONDON AREA BRAMLEY
HINKLEY POINT
ALVERDISCOTT
B3-NGC
DUNGENESS
1.00 NINFIELD
1.01
1.00 SELLIND 1.00 GE E de F (France)
Figure 5 Retained voltages at Walpole 400kV substation for faults in the GB network NORTH WEST-SSE
BEAULY
KEITH
1.01
PETERHEAD
KINTORE
FOYERS
1.01
CRUACHAN
ABERDEEN
1.01 NORTH SOUTH-SSE TEALING INVERKIP
WINDYHILL BONNYBRIDGE
1.00
400kV SSE & SP
LONGANNET
275kV
NEILSTON
1.00
Power flow boundary
COCKENZIE
1.00
HUNTERSTON
STRATHHAVEN
KILMARNOCK SOUTH
TORNESS
0.99
0.99
Voltage drop range
ECCLES
1.00 SP & NGC STELLA WEST
0.99
HARKER
0.97
5%
HAWTHORN PIT NORTON
HUTTON
0.95
0.91
0.96
B1-NGC
10 %
THORNTON PENWORTHAM
0.85
DRAX
0.75
0.90
EGGBOROUGH
WYLFA
KEADB Y 0.76 WEST BURTON
0.79
0.97
MACCLESFIELD
DEESIDE PENTIR
0.91 CELLARHEAD 0.87
0.95
LEAGCY TRAWSFYNYDD
0.76
B3-NGC WALPOLE
IRONBRIDGE ENDERB 0.85 Y 0.92 WYMONDL SUNDON EAST EY 0.63 CLAYDON 0.68
0.54
50 %
FECKENHAM
PELHAM
0.76
WALHAM
NORWICH MAIN
0.00
0.92
0.92
30 %
0.61
RATCLIFFE ON SOAR 0.85 DRAKELOW
0.92
0.95
COTTAM
0.88
CREYKE BECK 0.75 B2-NGC
SIZEWELL
0.67 30 %
B9-NGC BRAINTREE
0.41
0.76
COWLEY
0.94
BRAMFOR D 0.67
RAYLEIGH MAIN
0.79
0.72
CITY ROAD
0.86 SWANSEA
0.98 PEMBROKE
0.98
CILFYNYDD
0.96
LOVEDEAN
0.96
INDIAN QUEENS
CANTERBURY BOLNEY
0.96 EXETER
LANDULPH
0.93
0.91
MANNINGTON
0.98 1.00
0.85
HINKLEY POINT
1.00
0.79
BRAMLEY
0.90
ALVERDISCOTT
KEMSLEY
LONDON AREA
MELKSHAM
0.99
0.94 B7-NGC
1.00 9
0.90 NINFIELD
FAWLEY NORTH
CHICKERELL
DUNGENESS
5%
0.92
10 %
0.85 SELLIN 0.88 DGE E de F (France)
Figure 6 Retained voltages at Norwich Main 400kV substation for faults in the GB network BEAULY
NORTH WEST-SSE
KEITH
1.00
PETERHEAD
KINTORE
FOYERS
1.00
CRUACHAN
ABERDEEN
1.00 NORTH SOUTH-SSE TEALING WINDYHILL BONNYBRIDGE
INVERKIP
1.00
400kV SSE & SP
LONGANNET
275kV
NEILSTON
0.99
Power flow boundary
COCKENZIE
0.99
HUNTERSTON
STRATHHAVEN
KILMARNOCK SOUTH
TORNESS
0.98
0.99
Voltage drop range
ECCLES
0.99 SP & NGC STELLA WEST
5%
0.99
HARKER
0.96
HAWTHORN PIT
NORTON
HUTTON
0.95
0.92
0.96
B1-NGC
10 %
THORNTON PENWORTHAM
DRAX
0.80
0.91
EGGBOROUGH
WYLFA
0.83
0.97 PENTIR
MACCLESFIELD
DEESIDE
0.92
0.95
LEAGCY TRAWSFYNYDD
CREYKE BECK 0.78 B2-NGC
KEADBY
30 %
0.78
COTTAM
0.89
0.76 CELLARHEA RATCLIFFE 0.88 D ON SOAR 0.85
WEST BURTON
0.67
B3-NGC
50
WALPOLE
DRAKELOW
0.92
0.95
0.87
NORWICH MAIN %
0.23
0.92
0.00
IRONBRIDGE
0.92
FECKENHAM
0.91
ENDERB 0.85 Y WYMONDL SUNDON EAST EY 0.61 CLAYDON 0.67
BRAMFORD
0.74
WALHAM
B9-NGC BRAINTREE
0.39
0.58
COWLEY
0.93
RAYLEIGH MAIN
0.77
0.59
CITY ROAD
0.81 SWANSEA
0.97 PEMBROKE
MELKSHAM
CILFYNYDD
0.94
0.99
LOVEDEAN
0.95 EXETER
0.98
LANDULPH
0.90
0.89
MANNINGTON
0.96 INDIAN QUEENS
CANTERBURY BOLNEY
0.95
ALVERDISCOTT
DUNGENESS
0.86 NINFIELD
FAWLEY NORTH
CHICKERELL
0.89
0.91
0.97
B7-NGC
0.99 10
30 %
0.71
0.82
HINKLEY POINT
0.97
KEMSLEY
LONDON AREA BRAMLEY
0.89
SIZEWELL
0.38
0.36
PELHAM
5%
10 %
0.79 SELLIN 0.83 DGE E de F (France)
4. Dynamic stability of large offshore wind farms 4.1 Dynamic performance of large offshore wind farms The dynamic performance of a 60 MW offshore wind farm connected to 400 kV substations at Deeside and Norwich Main was simulated. The results are shown in Figures 7 and 8. Figure 7 shows the dynamic performance of the wind farm at Deeside for a fault on the 400 kV busbar. The fault was applied at 2 second and cleared after 110 ms (the critical clearing time). During the fault, the 400 kV busbar voltage approaches zero. The terminal voltage of the wind turbines goes from 1p.u to 0.32 p.u. When the fault is cleared, the voltage and speed of the wind turbines return to their initial values in about 1.8 seconds. During this period, the wind farm absorbs a significant amount of reactive power from the network. Figure 8 shows a similar result for Norwich Main. The short-circuit levels on the 400 kV busbars at Penwortham and Walpole are almost the same as that at Deeside (see Table 1). Hence, the dynamic performance of a wind farm connected to Penwortham and Walpole will be similar to one connected to Deeside.
Figure 7 Dynamic performance of a 60 MW offshore wind farm connected to Deeside 400 kV busbar
11
Figure 8 Dynamic performance of a 60 MW offshore wind farm connected to Norwich Main 400 kV busbar
4.2 Critical clearing times of large offshore wind farms Figures 9 and 10 show the variations of critical clearing time with voltage drops on the 400 kV busbars for 60 MW and 120 MW offshore wind farms at Deeside and Norwich Main. The voltage drop is defined as: voltage drop = [1 − retained voltage ( p.u.)]× 100% . The different voltage drops on the 400 kV busbar were obtained by changing the fault resistance.
12
Figure 9 Variations of the critical clearing time with voltage drop at Deeside
Figure 10 Variations of the critical clearing time with voltage drop at Norwich Main
13
From the “Technical and Operational Characteristics of the NGC Transmission System” [9], the normal clearance time for faults on the 400 kV transmission system is between 60-120 ms. Figure 9 shows the critical clearing times for the 60 MW and 120 MW offshore wind farms at Deeside. The critical clearing times are less than 120 ms when the voltage drops are larger than 90% for the 60 MW and 82% for the 120 MW. Hence for the 100% voltage drop, a fast clearing time (less than 100 ms) is required to maintain stable operation of a wind farm connected to Deeside. Figure 10 shows the critical clearing times of the offshore wind farm at Norwich Main. The critical clearing times are much lower than at Deeside due to the smaller short-circuit capacity at Norwich Main. The critical clearing times are less than 120 ms if the voltage drops are larger than 90% for the 60 MW wind farm and 75% for the 120 MW wind farm. So for a 100% voltage drop, a very fast clearing time (less than 90 ms) is required to prevent instability of the large offshore wind farm at Norwich Main.
5. Conclusions Simulations have been performed to investigate the impact of network faults on the stability of large offshore wind farms. Results are presented for balanced 3-phase faults applied on the GB 400 kV transmission system. This investigates a worst case scenario as the fraction of this type of fault occurring on the 400 kV transmission system is less than 5% of all faults [9]. The number of incidents of overhead-line faults, on the British system 132kV and above, is typically about 1 fault per 100km per year. The most common fault is the single line to earth fault which accounts for 75-85 % of all faults [9]. The impact of 1-phase faults upon the stability of fixed speed wind farms will be much less severe. The studies indicate that faults on the GB transmission system (close to the wind farm) may cause instability. The voltage drop investigations at Norwich Main (Figure 10) show that for a 100% voltage drop at the 400 kV connection point, a very fast clearance time (less than 90 ms) is required to maintain stable operation of a 120MW offshore wind farm. However, when the voltage drops are less than or equal to 60% on the 400 kV busbar at Norwich Main, the critical clearance times are longer than 140ms. The contours given in Figure 6 for the GB transmission system illustrate that for a 60% voltage drop the 3-phase fault would have to occur close to Norwich Main. Therefore the stability of the offshore wind farms may only be effected by relatively local faults. Possible remedial measures include the use of fast acting reactive power support as discussed in [10].
14
6. References 1. The Crown Estate, Potential Offshore Wind Farm Sites Announced by the Crown Estate, 5 April 2001, http://www.crownestate.co.uk/news/pr20010405.shtml. 2. PIU, The Energy Review, 14 February 2002, http://www.piu.gov.uk 3. EA, Engineering Recommendation G.59/1, Recommendations for the Connection of Embedded Generating Plant to the Regional Electricity Companies’ Distribution Systems, 1991. 4. BWEA, Offshore Wind Farm Developers and Locations of Sites, http://www.offshorewindfarms.co.uk/sites.html. 5. Vestas, Generator data 2MW- 690V-50Hz. 6. Bungay E.W.G., McAllister D., Electric Cables Handbook (second edition), BSP Professional Books, 1990. 7. Weedy B.M., Electric Power System (book), John Wiley & Sons Ltd, 1992. 8. Alstom, Protective Relays Application Guide, GEC Alstom T&D, Protection & Control Limited. 9. NGC, Technical and Operational Characteristics of the Transmission System, April 2000. 10. Wu X. Arulampalam A., Zhan C. Jenkins N., Application of a Static Reactive Power Compensator (STATCOM) and a Dynamic Braking Resistor (DBR) to Stability Enhancement of a Large Wind Farm, Accepted for publication in Wind Engineering, Vol.27, Issue 2, 2003.
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The trans-disciplinary Tyndall Centre for Climate Change Research undertakes integrated research into the long-term consequences of climate change for society and into the development of sustainable responses that governments, business-leaders and decisionmakers can evaluate and implement. Achieving these objectives brings together UK climate scientists, social scientists, engineers and economists in a unique collaborative research effort. Research at the Tyndall Centre is organised into four research themes that collectively contribute to all aspects of the climate change issue: Integrating Frameworks; Decarbonising Modern Societies; Adapting to Climate Change; and Sustaining the Coastal Zone. All thematic fields address a clear problem posed to society by climate change, and will generate results to guide the strategic development of climate change mitigation and adaptation policies at local, national and global scales. The Tyndall Centre is named after the 19th century UK scientist John Tyndall, who was the first to prove the Earth’s natural greenhouse effect and suggested that slight changes in atmospheric composition could bring about climate variations. In addition, he was committed to improving the quality of science education and knowledge. The Tyndall Centre is a partnership of the following institutions: University of East Anglia UMIST Southampton Oceanography Centre University of Southampton University of Cambridge Centre for Ecology and Hydrology SPRU – Science and Technology Policy Research (University of Sussex) Institute for Transport Studies (University of Leeds) Complex Systems Management Centre (Cranfield University) Energy Research Unit (CLRC Rutherford Appleton Laboratory) The Centre is core funded by the following organisations: Natural Environmental Research Council (NERC) Economic and Social Research Council (ESRC) Engineering and Physical Sciences Research Council (EPSRC) UK Government Department of Trade and Industry (DTI) For more information, visit the Tyndall Centre Web site (www .tyndall.ac.uk) or contact: External Communications Manager Tyndall Centre for Climate Change Research University of East Anglia, Norwich NR4 7TJ, UK Phone: +44 (0) 1603 59 3906; Fax: +44 (0) 1603 59 3901 Email: [email protected]
Recent Working Papers Tyndall Working Papers are available online at http://www.tyndall.ac.uk/publications/working_papers/working_papers.shtml Mitchell, T. and Hulme, M. (2000). A Country-by-Country Analysis of Past and Future Warming Rates, Tyndall Centre Working Paper 1. Hulme, M. (2001). Integrated Assessment Models, Tyndall Centre Working Paper 2. Berkhout, F, Hertin, J. and Jordan, A. J. (2001). Socio-economic futures in climate change impact assessment: using scenarios as 'learning machines', Tyndall Centre Working Paper 3. Barker, T. and Ekins, P. (2001). How High are the Costs of Kyoto for the US Economy?, Tyndall Centre Working Paper 4. Barnett, J. (2001). The issue of 'Adverse Effects and the Impacts of Response Measures' in the UNFCCC, Tyndall Centre Working Paper 5. Goodess, C.M., Hulme, M. and Osborn, T. (2001). The identification and evaluation of suitable scenario development methods for the estimation of future probabilities of extreme weather events, Tyndall Centre Working Paper 6. Barnett, J. (2001). Security and Climate Change , Tyndall Centre Working Paper 7. Adger, W. N. (2001). Social Capital and Climate Change , Tyndall Centre Working Paper 8. Barnett, J. and Adger, W. N. (2001). Climate Dangers and Atoll Countries, Tyndall Centre Working Paper 9.
Gough, C., Taylor, I. and Shackley, S. (2001). Burying Carbon under the Sea: An Initial Exploration of Public Opinions, Tyndall Centre Working Paper 10. Barker, T. (2001). Representing the Integrated Assessment of Climate Change, Adaptation and Mitigation, Tyndall Centre Working Paper 11. Dessai, S., (2001). The climate regime from The Hague to Marrakech: Saving or sinking the Kyoto Protocol?, Tyndall Centre Working Paper 12. Dewick, P., Green K., Miozzo, M., (2002). Technological Change, Industry Structure and the Environment, Tyndall Centre Working Paper 13. Shackley, S. and Gough, C., (2002). The Use of Integrated Assessment: An Institutional Analysis Perspective , Tyndall Centre Working Paper 14. Köhler, J.H., (2002). Long run technical change in an energyenvironment-economy (E3) model for an IA system: A model of Kondratiev waves, Tyndall Centre Working Paper 15. Adger, W.N., Huq, S., Brown, K., Conway, D. and Hulme, M. (2002). Adaptation to climate change: Setting the Agenda for Development Policy and Research, Tyndall Centre Working Paper 16. Dutton, G., (2002). Hydrogen Energy Technology, Tyndall Centre Working Paper 17.
Watson, J. (2002). The development of large technical systems: implications for hydrogen, Tyndall Centre Working Paper 18. Pridmore, A. and Bristow, A., (2002). The role of hydrogen in powering road transport , Tyndall Centre Working Paper 19. Turnpenny, J. (2002). Reviewing organisational use of scenarios: Case study - evaluating UK energy policy options, Tyndall Centre Working Paper 20. Watson, W. J. (2002). Renewables and CHP Deployment in the UK to 2020, Tyndall Centre Working Paper 21. Watson, W.J., Hertin, J., Randall, T., Gough, C. (2002). Renewable Energy and Combined Heat and Power Resources in the UK, Tyndall Centre Working Paper 22. Paavola, J. and Adger, W.N. (2002). Justice and adaptation to climate change , Tyndall Centre Working Paper 23. Xueguang Wu, Jenkins, N. and Strbac, G. (2002). Impact of Integrating Renewables and CHP into the UK Transmission Network, Tyndall Centre Working Paper 24 Xueguang Wu, Mutale, J., Jenkins, N. and Strbac, G. (2003). An investigation of Network Splitting for Fault Level Reduction, Tyndall Centre Working Paper 25 Brooks, N. and Adger W.N. (2003). Country level risk measures of climate-related natural disasters and implications for adaptation to climate change , Tyndall Centre Working Paper 26
Tompkins, E.L. and Adger, W.N. (2003). Building resilience to climate change through adaptive management of natural resources, Tyndall Centre Working Paper 27 Dessai, S., Adger, W.N., Hulme, M., Köhler, J.H., Turnpenny, J. and Warren, R. (2003). Defining and experiencing dangerous climate change, Tyndall Centre Working Paper 28 Brown, K. and Corbera, E. (2003). A Multi-Criteria Assessment Framework for Carbon-Mitigation Projects: Putting “development” in the centre of decision-making, Tyndall Centre Working Paper 29 Hulme, M. (2003). Abrupt climate change: can society cope?, Tyndall Centre Working Paper 30 Turnpenny, J., Haxeltine A. and O’Riordan, T. A scoping study of UK user needs for managing climate futures. Part 1 of the pilot-phase interactive integrated assessment process (Aurion Project). Tyndall Centre Working Paper 31 Xueguang Wu, Jenkins, N. and Strbac, G. (2003). Integrating Renewables and CHP into the UK Electricity System: Investigation of the impact of network faults on the stability of large offshore wind farms, Tyndall Centre Working Paper 32
Xueguang Wu, Lee Holdsworth, Nick Jenkins and Goran Strbac
April 2003
Tyndall Centre for Climate Change Research
Working Paper 32
Integrating Renewables and CHP into the UK Electricity System: Investigation of the impact of network faults on the stability of large offshore wind farms
Xueguang Wu Lee Holdsworth Nick Jenkins Goran Strbac The Manchester Centre for Electrical Energy (MCEE) UMIST UK Email: [email protected] [email protected] [email protected] [email protected] Tyndall Centre Working Paper no. 32 April 2003
SUMMARY Simulations have been performed to investigate the impact of network faults on the stability of large offshore wind farms. Results are presented for balanced 3-phase faults applied on the GB 400 kV transmission system. The studies indicate that faults on the GB transmission system (close to the wind farm) may cause instability of the large offshore wind farms. The voltage drop investigations show that for a 100% voltage drop at a 400 kV connection point (such as Norwich Main), a very fast clearance time (less than 90 ms) is required to maintain stable operation of a 120MW offshore wind farm. However, when the voltage drops are less than or equal to 60%, the critical clearance times are longer than 140ms. The contours of voltage drop for the GB transmission system illustrate that for a 60% voltage drop the 3-phase fault would have to occur close to the connection point. Therefore the stability of the offshore wind farms may only be effected by relatively local faults. Possible remedial measures include the use of fast acting reactive power support, e.g. a Static Reactive Power Compensator (STATCOM).
SUMMARY Simulations have been performed to investigate the impact of network faults on the stability of large offshore wind farms. Results are presented for balanced 3-phase faults applied on the GB 400 kV transmission system. The studies indicate that faults on the GB transmission system (close to the wind farm) may cause instability of the large offshore wind farms. The voltage drop investigations show that for a 100% voltage drop at a 400 kV connection point (such as Norwich Main), a very fast clearance time (less than 90 ms) is required to maintain stable operation of a 120MW offshore wind farm. However, when the voltage drops are less than or equal to 60%, the critical clearance times are longer than 140ms. The contours of voltage drop for the GB transmission system illustrate that for a 60% voltage drop the 3-phase fault would have to occur close to the connection point. Therefore the stability of the offshore wind farms may only be effected by relatively local faults. Possible remedial measures include the use of fast acting reactive power support, e.g. a Static Reactive Power Compensator (STATCOM).
CONTENTS 1. Introduction ......................................................................................................... 3 2. Studies and assumptions ...................................................................................... 4 2.1 Assumptions of the voltage drop calculations................................................ 4 2.2 Assumptions of the dynamic stability calculations ........................................ 4 3. Zones of voltage drop influence of faults............................................................. 5 4. Dynamic stability of large offshore wind farms ................................................ 11 4.1 Dynamic performance of large offshore wind farms................................... 11 4.2 Critical clearing times of large offshore wind farms ................................... 12 5. Conclusions ........................................................................................................ 14 6. References........................................................................................................... 15
2
1. Introduction The generation of electrical power using sustainable sources of energy is developing rapidly with the worldwide installed capacity of wind generation now exceeding 25 GW. For the UK, a target of 10% of electrical energy to be supplied by renewables by 2010 implies a capacity of renewable generating plant of up to 8 – 10 GW, of which some 60 % might be wind turbines. In the UK the Crown Estate has granted licenses to 18 consortia to investigate large offshore wind farm sites with a potential of at least 1500 MW [1]. There are also suggestions that a target as high as 20 % of UK electricity from renewables might be achievable by 2020 [2], with similar ambitious targets existing in many European countries. Until recently, wind farms connected within the UK network had been limited to small sized installations, connected at distribution voltage levels. The connection standards [3] do not currently require wind farms to support the power system during a network disturbance. During a network fault the wind turbines were disconnected from the system and then subsequently reconnected when the fault has been cleared. However, the network design grid codes are now being revised for the increased penetration of wind generators. The wind farms will now have to continue to operate during system disturbances. A fixed speed wind turbine consists of a squirrel cage induction generator coupled to the wind turbine rotor via a gearbox. The induction generator consumes reactive power and requires compensation capacitors at the terminals in order to achieve unity power factor. The growth in fixed speed wind farms with large MW capacity connected to the UK transmission network will have a significance impact on the technical and operational characteristics of the electricity system. The connection requirements of large wind farms therefore require reviewing to ensure continuing network security. The objective of this work was to investigate network faults and stability issues that need to be taken into account in order for high penetrations of large offshore wind farms to be connected to the network. These must be investigated and resolved in order to build the required confidence that a high penetration of wind generators connected to the network is both feasible and safe. The methods used in this study are based on modelling of the Great Britain (GB) network and the dynamic stability of a typical large offshore fixed speed wind farm. The aim of the study was firstly to assess zone influence of faults in the GB network and secondly to explore potential dynamic impacts of the faults on the large offshore wind farms. This report presents the main results of this work. The main areas of focus for this work are as follows: (1) Studies and assumptions (2) Zones of voltage drop influence of faults (2) Dynamic stability of large offshore wind farms 3
A detailed description of the work performed under each of the above headings is provided below. 2. Studies and assumptions For high penetrations of the large offshore, fixed speed, wind farms to be connected to the network, the effect of voltage drops at their 400 kV connection points and the dynamic stability of the wind farms have been investigated. The results shown in this study were based on the following assumptions. 2.1 Assumptions of the voltage drop calculations (1) The study case was the GB network operating under the winter-peak load of 2002. (2) The offshore wind farms were connected to the 400 kV transmission system at Deeside, Penwortham, Walpole, and Norwich Main substations [4]. (3) The sub-transient reactances of all synchronous generators were 0.2 per-unit. (4) The type of fault was a balanced three-phase short circuit. (5) The fault levels at the 400 kV substations were calculated from the three-phase short circuit currents using PowerWorld. (6) PowerWorld was also used to calculate the voltage drops at the connection points for faults in the network. 2.2 Assumptions of the dynamic stability calculations (1) The study cases were based on the network shown in Figures 1 and 2. The shortcircuit ratios (SCR) at the 33 kV busbars of the offshore wind farm substations were 6. (2) The 400 kV system was represented for the dynamic stability simulation by a voltage source in series with an impedance. The voltage of the source was 1 p.u. The impedance was calculated from PowerWorld and is shown in Table 1. (3) The offshore wind farm consisted of the same type of wind turbines, each of 2 MW. These were represented by a single equivalent coherent fixed-speed induction generator. The data of the 2 MW wind turbine induction generator is shown in Table 2 [5]. (4) The distance from the offshore wind turbines to shore was 5 km. (5) A lumped 33kV/0.69kV wind turbine terminal transformer with 5% impedance was used to connect the offshore wind farm to the 132kV/33kV onshore substation through the 33 kV submarine cables. (6) Each of the 33 kV submarine cables was 185 mm2, multicore copper, and paper insulated distribution cable with rated current 360 A, resistance 0.118 ohms/km, reactance 0.101 ohms/km and capacitance 0.4 µF/km [6]. (7) The number of parallel submarine cables was 4 for the 60 MW offshore wind farm and 8 for the 120 MW. (8) An earthing zigzag transformer with rated current 1000 A was used to provide an earthed point on the 33 kV network. (9) A 132kV/33kV transformer with 15% impedance was connected to the 400kV/132kV system substation through the 132 kV overhead lines. (10) Each of the 132 kV overhead lines was 20 km long and 258 mm2 aluminum conductor steel reinforced (ACSR) conductor with rated capacity 115 MVA, 4
resistance 0.068 ohms/km, and reactance 0.404 ohms/km [7]. (11) The number of parallel overhead lines was 1 for the 60 MW offshore wind farm and 2 for the 120 MW. (12) The 400kV/132kV system substation had a transformer with 15% impedance [8]. (13) The computer program, PSCAD/EMTDC, was used to simulate dynamic stability. 400kV 400kV/132kV
30*2MW, 0.69kV 132kV/33kV 20km, 132kV 5km, 33kV SCR = 6 large offshore wind farm 300MVA, 15% 100MVA, 15% one overhead line four submarine cables WT
G
132kV
system impedance
33kV 60MW earthing 33kV/0.69kV capacitor transformer 80MVA, 5% banks
fault resistance
Figure 1 A 60MW offshore wind farm connected to the 400 kV busbar 400kV 400kV/132kV 132kV/33kV 60*2MW, 0.69kV 5km, 33kV SCR = 6 large offshore wind farm 1000MVA, 15% 20km, 132kV 150MVA, 15% two overhead lines eight submarine cables WT
G 132kV
system impedance
earthing transformer
33kV 120MW 33kV/0.69kV capacitor 150MVA, 5% banks
fault resistance
Figure 2 A 120MW offshore wind farm connected to the 400 kV busbar Table 1 System data 400kV Short-circuit level substation (MVA) Deeside 19,514 Penwortham 18,785 Walpole 19,142 Norwich Main 12,006
Impedance (ohms) 8.20 8.52 8.36 13.33
X/R 10.2 10.6 10.4 11.9
Table 2 Wind turbine induction generator data (on its own base) Capacity Vol. f R1 X1 Xm R2 X2 (MW) (kV) (Hz) (p.u) (p.u) (p.u) (p.u) (p.u) 2 0.69 50 0.0049 0.0924 3.9528 0.0055 0.0995
Frequency (Hz) 50 50 50 50
Lumped inertia constant (sec.) 3.5
3. Zones of voltage drop influence of faults Voltage drops at the 400 kV busbars at substations (Deeside, Penwortham, Walpole and Norwich Main) were calculated. The results are shown in Figures 3, 4, 5 and 6. The retained voltage is shown at the location of the fault. For example, when a three5
phase fault was applied at Harker, the retained voltage at Deeside 400 kV busbar was 0.88 as shown at Harker. Figure 3 shows the retained voltages at Deeside for faults on each busbar in the GB network. Contours of the voltage drop were drawn from the retained voltages. The 30% voltage drop contour only extends over North Wales, the West Midlands, and the Manchester area. Figures 4-6 show similar results for Penwortham, Walpole and Norwich Main substations.
6
Figure 3 Retained voltages at Deeside 400kV substation for faults in the GB network NORTH WEST-SSE
BEAULY
KEITH
1.00
PETERHEAD
KINTORE
FOYERS
1.00
CRUACHAN
ABERDEEN
1.00 NORTH SOUTH-SSE TEALING INVERKIP
WINDYHILL BONNYBRIDGE
0.99
400kV SSE & SP
LONGANNET
275kV
NEILSTON
0.98
Power flow boundary
COCKENZIE
0.99
HUNTERSTON
STRATHHAVEN
KILMARNOCK SOUTH
TORNESS
0.95
0.97
5%
Voltage drop range
ECCLES
0.98 SP & NGC STELLA WEST
0.98
HARKER
0.88
HAWTHORN PIT NORTON
HUTTON
10 %
0.85
0.95
0.93
B1-NGC
THORNTON PENWORTHAM
DRAX EGGBORO UGH0.81 MACCLESFIELD COTTAM 0.66
30 %
WYLFA
0.63 PENTIR
DEESIDE
0.91
50 CELLARHEA 0.67 D 0.00 %
0.49 TRAWSFYNYDD
0.53 30 % 10 %
0.88
0.81
0.65
CREYKE BECK
0.87 0.90
WEST BURTON
0.89
RATCLIFFE ON SOAR 0.89
LEAGCY
DRAKELOW
0.30
0.76
B2-NGC
KEADBY
B3-NGC WALPOLE
NORWICH MAIN
0.94
0.98
IRONBRIDGE
0.61
FECKENHAM
0.81
ENDERB 0.92 Y WYMONDL SUNDON EAST EY 0.95 CLAYDON 0.94
0.94
WALHAM
BRAMFOR D 0.99
SIZEWELL
0.98
B9-NGC BRAINTREE
0.94
RAYLEIGH0.99 MAIN
COWLEY
0.94
5%
PELHAM
0.94
0.98
CITY ROAD
1.00 SWANSEA
0.99 PEMBROKE
0.99
MELKSHAM
CILFYNYDD
0.97
0.94
LOVEDEAN
1.00
EXETER
1.01
LANDULPH
1.01
1.00
0.99
MANNINGTON
1.00 INDIAN QUEENS
CANTERBURY BOLNEY
0.99 1.01
0.99
0.96
HINKLEY POINT
ALVERDISCOTT
KEMSLEY
LONDON AREA BRAMLEY
FAWLEY NORTH
CHICKERELL
1.00
1.01
B7-NGC
7
DUNGENESS
1.00 NINFIELD
1.00
0.99 SELLIN 1.00 DGE E de F (France)
Figure 4 Retained voltages at Penwortham 400kV substation for faults in the GB network BEAULY
NORTH WEST-SSE
KEITH
0.99
PETERHEAD
KINTORE
FOYERS
0.97
CRUACHAN
ABERDEEN
0.97 NORTH SOUTH-SSE
5%
TEALING INVERKIP
WINDYHILL BONNYBRIDGE
0.95
400kV
SSE & SP
LONGANNET
275kV
NEILSTON
0.92
Power flow boundary
COCKENZIE
0.95
HUNTERSTON
STRATHHAVEN
KILMARNOCK SOUTH
TORNESS
0.86
0.90
10 %
Voltage drop range
ECCLES
0.94 SP & NGC STELLA WEST
0.93
HARKER
0.67 30 %
HUTTON
0.57
HAWTHORN PIT
NORTON
0.90
0.86
40 %
PENWORTHAM
B1-NGC
THORNTON DRAX
0.81
CREYKE BECK
0.71
0.00
EGGBOROUGH
WYLFA
0.83 KEADBY
0.70
B2-NGC
0.88 MACCLESFIELD 30 COTTAM WEST BURTON 0.66 PENTIR % DEESIDE 0.91 0.88 CELLARHEAD 0.78 RATCLIFFE 0.70 ON SOAR 0.91 0.64 WALPOLE LEAGCY TRAWSFYNYDD DRAKELOW 0.69 0.93 0.84 0.80 IRONBRIDGE 10 0.81 FECKENHAM ENDERBY % 0.94 0.90 WYMONDL 5% SUNDON PELHAM EAST EY 0.95 CLAYDON 0.95 0.95 0.95 WALHAM COWLEY 0.97 CITY ROAD 0.96 1.00 0.84
SWANSEA
1.00 PEMBROKE
1.00
MELKSHAM
CILFYNYDD
0.99
0.98
LOVEDEAN
1.01 1.01
INDIAN QUEENS
1.01
LANDULPH
1.01
1.01
1.00
MANNINGTON
FAWLEY NORTH
CHICKERELL
1.01
1.01
B7-NGC
8
SIZEWELL
BRAMFOR D 0.98
0.98
B9-NGC BRAINTREE
0.99
RAYLEIGH MAIN
0.99 0.99 CANTERBURY
BOLNEY
EXETER
0.97
0.98
1.00 1.01
NORWICH MAIN
KEMSLEY
LONDON AREA BRAMLEY
HINKLEY POINT
ALVERDISCOTT
B3-NGC
DUNGENESS
1.00 NINFIELD
1.01
1.00 SELLIND 1.00 GE E de F (France)
Figure 5 Retained voltages at Walpole 400kV substation for faults in the GB network NORTH WEST-SSE
BEAULY
KEITH
1.01
PETERHEAD
KINTORE
FOYERS
1.01
CRUACHAN
ABERDEEN
1.01 NORTH SOUTH-SSE TEALING INVERKIP
WINDYHILL BONNYBRIDGE
1.00
400kV SSE & SP
LONGANNET
275kV
NEILSTON
1.00
Power flow boundary
COCKENZIE
1.00
HUNTERSTON
STRATHHAVEN
KILMARNOCK SOUTH
TORNESS
0.99
0.99
Voltage drop range
ECCLES
1.00 SP & NGC STELLA WEST
0.99
HARKER
0.97
5%
HAWTHORN PIT NORTON
HUTTON
0.95
0.91
0.96
B1-NGC
10 %
THORNTON PENWORTHAM
0.85
DRAX
0.75
0.90
EGGBOROUGH
WYLFA
KEADB Y 0.76 WEST BURTON
0.79
0.97
MACCLESFIELD
DEESIDE PENTIR
0.91 CELLARHEAD 0.87
0.95
LEAGCY TRAWSFYNYDD
0.76
B3-NGC WALPOLE
IRONBRIDGE ENDERB 0.85 Y 0.92 WYMONDL SUNDON EAST EY 0.63 CLAYDON 0.68
0.54
50 %
FECKENHAM
PELHAM
0.76
WALHAM
NORWICH MAIN
0.00
0.92
0.92
30 %
0.61
RATCLIFFE ON SOAR 0.85 DRAKELOW
0.92
0.95
COTTAM
0.88
CREYKE BECK 0.75 B2-NGC
SIZEWELL
0.67 30 %
B9-NGC BRAINTREE
0.41
0.76
COWLEY
0.94
BRAMFOR D 0.67
RAYLEIGH MAIN
0.79
0.72
CITY ROAD
0.86 SWANSEA
0.98 PEMBROKE
0.98
CILFYNYDD
0.96
LOVEDEAN
0.96
INDIAN QUEENS
CANTERBURY BOLNEY
0.96 EXETER
LANDULPH
0.93
0.91
MANNINGTON
0.98 1.00
0.85
HINKLEY POINT
1.00
0.79
BRAMLEY
0.90
ALVERDISCOTT
KEMSLEY
LONDON AREA
MELKSHAM
0.99
0.94 B7-NGC
1.00 9
0.90 NINFIELD
FAWLEY NORTH
CHICKERELL
DUNGENESS
5%
0.92
10 %
0.85 SELLIN 0.88 DGE E de F (France)
Figure 6 Retained voltages at Norwich Main 400kV substation for faults in the GB network BEAULY
NORTH WEST-SSE
KEITH
1.00
PETERHEAD
KINTORE
FOYERS
1.00
CRUACHAN
ABERDEEN
1.00 NORTH SOUTH-SSE TEALING WINDYHILL BONNYBRIDGE
INVERKIP
1.00
400kV SSE & SP
LONGANNET
275kV
NEILSTON
0.99
Power flow boundary
COCKENZIE
0.99
HUNTERSTON
STRATHHAVEN
KILMARNOCK SOUTH
TORNESS
0.98
0.99
Voltage drop range
ECCLES
0.99 SP & NGC STELLA WEST
5%
0.99
HARKER
0.96
HAWTHORN PIT
NORTON
HUTTON
0.95
0.92
0.96
B1-NGC
10 %
THORNTON PENWORTHAM
DRAX
0.80
0.91
EGGBOROUGH
WYLFA
0.83
0.97 PENTIR
MACCLESFIELD
DEESIDE
0.92
0.95
LEAGCY TRAWSFYNYDD
CREYKE BECK 0.78 B2-NGC
KEADBY
30 %
0.78
COTTAM
0.89
0.76 CELLARHEA RATCLIFFE 0.88 D ON SOAR 0.85
WEST BURTON
0.67
B3-NGC
50
WALPOLE
DRAKELOW
0.92
0.95
0.87
NORWICH MAIN %
0.23
0.92
0.00
IRONBRIDGE
0.92
FECKENHAM
0.91
ENDERB 0.85 Y WYMONDL SUNDON EAST EY 0.61 CLAYDON 0.67
BRAMFORD
0.74
WALHAM
B9-NGC BRAINTREE
0.39
0.58
COWLEY
0.93
RAYLEIGH MAIN
0.77
0.59
CITY ROAD
0.81 SWANSEA
0.97 PEMBROKE
MELKSHAM
CILFYNYDD
0.94
0.99
LOVEDEAN
0.95 EXETER
0.98
LANDULPH
0.90
0.89
MANNINGTON
0.96 INDIAN QUEENS
CANTERBURY BOLNEY
0.95
ALVERDISCOTT
DUNGENESS
0.86 NINFIELD
FAWLEY NORTH
CHICKERELL
0.89
0.91
0.97
B7-NGC
0.99 10
30 %
0.71
0.82
HINKLEY POINT
0.97
KEMSLEY
LONDON AREA BRAMLEY
0.89
SIZEWELL
0.38
0.36
PELHAM
5%
10 %
0.79 SELLIN 0.83 DGE E de F (France)
4. Dynamic stability of large offshore wind farms 4.1 Dynamic performance of large offshore wind farms The dynamic performance of a 60 MW offshore wind farm connected to 400 kV substations at Deeside and Norwich Main was simulated. The results are shown in Figures 7 and 8. Figure 7 shows the dynamic performance of the wind farm at Deeside for a fault on the 400 kV busbar. The fault was applied at 2 second and cleared after 110 ms (the critical clearing time). During the fault, the 400 kV busbar voltage approaches zero. The terminal voltage of the wind turbines goes from 1p.u to 0.32 p.u. When the fault is cleared, the voltage and speed of the wind turbines return to their initial values in about 1.8 seconds. During this period, the wind farm absorbs a significant amount of reactive power from the network. Figure 8 shows a similar result for Norwich Main. The short-circuit levels on the 400 kV busbars at Penwortham and Walpole are almost the same as that at Deeside (see Table 1). Hence, the dynamic performance of a wind farm connected to Penwortham and Walpole will be similar to one connected to Deeside.
Figure 7 Dynamic performance of a 60 MW offshore wind farm connected to Deeside 400 kV busbar
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Figure 8 Dynamic performance of a 60 MW offshore wind farm connected to Norwich Main 400 kV busbar
4.2 Critical clearing times of large offshore wind farms Figures 9 and 10 show the variations of critical clearing time with voltage drops on the 400 kV busbars for 60 MW and 120 MW offshore wind farms at Deeside and Norwich Main. The voltage drop is defined as: voltage drop = [1 − retained voltage ( p.u.)]× 100% . The different voltage drops on the 400 kV busbar were obtained by changing the fault resistance.
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Figure 9 Variations of the critical clearing time with voltage drop at Deeside
Figure 10 Variations of the critical clearing time with voltage drop at Norwich Main
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From the “Technical and Operational Characteristics of the NGC Transmission System” [9], the normal clearance time for faults on the 400 kV transmission system is between 60-120 ms. Figure 9 shows the critical clearing times for the 60 MW and 120 MW offshore wind farms at Deeside. The critical clearing times are less than 120 ms when the voltage drops are larger than 90% for the 60 MW and 82% for the 120 MW. Hence for the 100% voltage drop, a fast clearing time (less than 100 ms) is required to maintain stable operation of a wind farm connected to Deeside. Figure 10 shows the critical clearing times of the offshore wind farm at Norwich Main. The critical clearing times are much lower than at Deeside due to the smaller short-circuit capacity at Norwich Main. The critical clearing times are less than 120 ms if the voltage drops are larger than 90% for the 60 MW wind farm and 75% for the 120 MW wind farm. So for a 100% voltage drop, a very fast clearing time (less than 90 ms) is required to prevent instability of the large offshore wind farm at Norwich Main.
5. Conclusions Simulations have been performed to investigate the impact of network faults on the stability of large offshore wind farms. Results are presented for balanced 3-phase faults applied on the GB 400 kV transmission system. This investigates a worst case scenario as the fraction of this type of fault occurring on the 400 kV transmission system is less than 5% of all faults [9]. The number of incidents of overhead-line faults, on the British system 132kV and above, is typically about 1 fault per 100km per year. The most common fault is the single line to earth fault which accounts for 75-85 % of all faults [9]. The impact of 1-phase faults upon the stability of fixed speed wind farms will be much less severe. The studies indicate that faults on the GB transmission system (close to the wind farm) may cause instability. The voltage drop investigations at Norwich Main (Figure 10) show that for a 100% voltage drop at the 400 kV connection point, a very fast clearance time (less than 90 ms) is required to maintain stable operation of a 120MW offshore wind farm. However, when the voltage drops are less than or equal to 60% on the 400 kV busbar at Norwich Main, the critical clearance times are longer than 140ms. The contours given in Figure 6 for the GB transmission system illustrate that for a 60% voltage drop the 3-phase fault would have to occur close to Norwich Main. Therefore the stability of the offshore wind farms may only be effected by relatively local faults. Possible remedial measures include the use of fast acting reactive power support as discussed in [10].
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6. References 1. The Crown Estate, Potential Offshore Wind Farm Sites Announced by the Crown Estate, 5 April 2001, http://www.crownestate.co.uk/news/pr20010405.shtml. 2. PIU, The Energy Review, 14 February 2002, http://www.piu.gov.uk 3. EA, Engineering Recommendation G.59/1, Recommendations for the Connection of Embedded Generating Plant to the Regional Electricity Companies’ Distribution Systems, 1991. 4. BWEA, Offshore Wind Farm Developers and Locations of Sites, http://www.offshorewindfarms.co.uk/sites.html. 5. Vestas, Generator data 2MW- 690V-50Hz. 6. Bungay E.W.G., McAllister D., Electric Cables Handbook (second edition), BSP Professional Books, 1990. 7. Weedy B.M., Electric Power System (book), John Wiley & Sons Ltd, 1992. 8. Alstom, Protective Relays Application Guide, GEC Alstom T&D, Protection & Control Limited. 9. NGC, Technical and Operational Characteristics of the Transmission System, April 2000. 10. Wu X. Arulampalam A., Zhan C. Jenkins N., Application of a Static Reactive Power Compensator (STATCOM) and a Dynamic Braking Resistor (DBR) to Stability Enhancement of a Large Wind Farm, Accepted for publication in Wind Engineering, Vol.27, Issue 2, 2003.
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The trans-disciplinary Tyndall Centre for Climate Change Research undertakes integrated research into the long-term consequences of climate change for society and into the development of sustainable responses that governments, business-leaders and decisionmakers can evaluate and implement. Achieving these objectives brings together UK climate scientists, social scientists, engineers and economists in a unique collaborative research effort. Research at the Tyndall Centre is organised into four research themes that collectively contribute to all aspects of the climate change issue: Integrating Frameworks; Decarbonising Modern Societies; Adapting to Climate Change; and Sustaining the Coastal Zone. All thematic fields address a clear problem posed to society by climate change, and will generate results to guide the strategic development of climate change mitigation and adaptation policies at local, national and global scales. The Tyndall Centre is named after the 19th century UK scientist John Tyndall, who was the first to prove the Earth’s natural greenhouse effect and suggested that slight changes in atmospheric composition could bring about climate variations. In addition, he was committed to improving the quality of science education and knowledge. The Tyndall Centre is a partnership of the following institutions: University of East Anglia UMIST Southampton Oceanography Centre University of Southampton University of Cambridge Centre for Ecology and Hydrology SPRU – Science and Technology Policy Research (University of Sussex) Institute for Transport Studies (University of Leeds) Complex Systems Management Centre (Cranfield University) Energy Research Unit (CLRC Rutherford Appleton Laboratory) The Centre is core funded by the following organisations: Natural Environmental Research Council (NERC) Economic and Social Research Council (ESRC) Engineering and Physical Sciences Research Council (EPSRC) UK Government Department of Trade and Industry (DTI) For more information, visit the Tyndall Centre Web site (www .tyndall.ac.uk) or contact: External Communications Manager Tyndall Centre for Climate Change Research University of East Anglia, Norwich NR4 7TJ, UK Phone: +44 (0) 1603 59 3906; Fax: +44 (0) 1603 59 3901 Email: [email protected]
Recent Working Papers Tyndall Working Papers are available online at http://www.tyndall.ac.uk/publications/working_papers/working_papers.shtml Mitchell, T. and Hulme, M. (2000). A Country-by-Country Analysis of Past and Future Warming Rates, Tyndall Centre Working Paper 1. Hulme, M. (2001). Integrated Assessment Models, Tyndall Centre Working Paper 2. Berkhout, F, Hertin, J. and Jordan, A. J. (2001). Socio-economic futures in climate change impact assessment: using scenarios as 'learning machines', Tyndall Centre Working Paper 3. Barker, T. and Ekins, P. (2001). How High are the Costs of Kyoto for the US Economy?, Tyndall Centre Working Paper 4. Barnett, J. (2001). The issue of 'Adverse Effects and the Impacts of Response Measures' in the UNFCCC, Tyndall Centre Working Paper 5. Goodess, C.M., Hulme, M. and Osborn, T. (2001). The identification and evaluation of suitable scenario development methods for the estimation of future probabilities of extreme weather events, Tyndall Centre Working Paper 6. Barnett, J. (2001). Security and Climate Change , Tyndall Centre Working Paper 7. Adger, W. N. (2001). Social Capital and Climate Change , Tyndall Centre Working Paper 8. Barnett, J. and Adger, W. N. (2001). Climate Dangers and Atoll Countries, Tyndall Centre Working Paper 9.
Gough, C., Taylor, I. and Shackley, S. (2001). Burying Carbon under the Sea: An Initial Exploration of Public Opinions, Tyndall Centre Working Paper 10. Barker, T. (2001). Representing the Integrated Assessment of Climate Change, Adaptation and Mitigation, Tyndall Centre Working Paper 11. Dessai, S., (2001). The climate regime from The Hague to Marrakech: Saving or sinking the Kyoto Protocol?, Tyndall Centre Working Paper 12. Dewick, P., Green K., Miozzo, M., (2002). Technological Change, Industry Structure and the Environment, Tyndall Centre Working Paper 13. Shackley, S. and Gough, C., (2002). The Use of Integrated Assessment: An Institutional Analysis Perspective , Tyndall Centre Working Paper 14. Köhler, J.H., (2002). Long run technical change in an energyenvironment-economy (E3) model for an IA system: A model of Kondratiev waves, Tyndall Centre Working Paper 15. Adger, W.N., Huq, S., Brown, K., Conway, D. and Hulme, M. (2002). Adaptation to climate change: Setting the Agenda for Development Policy and Research, Tyndall Centre Working Paper 16. Dutton, G., (2002). Hydrogen Energy Technology, Tyndall Centre Working Paper 17.
Watson, J. (2002). The development of large technical systems: implications for hydrogen, Tyndall Centre Working Paper 18. Pridmore, A. and Bristow, A., (2002). The role of hydrogen in powering road transport , Tyndall Centre Working Paper 19. Turnpenny, J. (2002). Reviewing organisational use of scenarios: Case study - evaluating UK energy policy options, Tyndall Centre Working Paper 20. Watson, W. J. (2002). Renewables and CHP Deployment in the UK to 2020, Tyndall Centre Working Paper 21. Watson, W.J., Hertin, J., Randall, T., Gough, C. (2002). Renewable Energy and Combined Heat and Power Resources in the UK, Tyndall Centre Working Paper 22. Paavola, J. and Adger, W.N. (2002). Justice and adaptation to climate change , Tyndall Centre Working Paper 23. Xueguang Wu, Jenkins, N. and Strbac, G. (2002). Impact of Integrating Renewables and CHP into the UK Transmission Network, Tyndall Centre Working Paper 24 Xueguang Wu, Mutale, J., Jenkins, N. and Strbac, G. (2003). An investigation of Network Splitting for Fault Level Reduction, Tyndall Centre Working Paper 25 Brooks, N. and Adger W.N. (2003). Country level risk measures of climate-related natural disasters and implications for adaptation to climate change , Tyndall Centre Working Paper 26
Tompkins, E.L. and Adger, W.N. (2003). Building resilience to climate change through adaptive management of natural resources, Tyndall Centre Working Paper 27 Dessai, S., Adger, W.N., Hulme, M., Köhler, J.H., Turnpenny, J. and Warren, R. (2003). Defining and experiencing dangerous climate change, Tyndall Centre Working Paper 28 Brown, K. and Corbera, E. (2003). A Multi-Criteria Assessment Framework for Carbon-Mitigation Projects: Putting “development” in the centre of decision-making, Tyndall Centre Working Paper 29 Hulme, M. (2003). Abrupt climate change: can society cope?, Tyndall Centre Working Paper 30 Turnpenny, J., Haxeltine A. and O’Riordan, T. A scoping study of UK user needs for managing climate futures. Part 1 of the pilot-phase interactive integrated assessment process (Aurion Project). Tyndall Centre Working Paper 31 Xueguang Wu, Jenkins, N. and Strbac, G. (2003). Integrating Renewables and CHP into the UK Electricity System: Investigation of the impact of network faults on the stability of large offshore wind farms, Tyndall Centre Working Paper 32
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