-3- 50863511.400-tos/hsm 09-5341 - noordzeewind · one of the tasks in this program is to gain...

© KEMA Nederland B.V., Arnhem, the Netherlands. All rights reserved. It is prohibited to change any and all versions of this document in any manner whatsoever, including but not limited todividing it into parts. In case of a conflict between the electronic version (e.g. PDF file) and the original paper versionprovided by KEMA, the latter will prevail. KEMA Nederland B.V. and/or its associated companies disclaim liability for any direct, indirect, consequential orincidental damages that may result from the use of the information or data, or from the inability to use the information ordata contained in this document. The contents of this report may only be transmitted to third parties in its entirety and provided with the copyright notice,prohibition to change, electronic versions’ validity notice and disclaimer.

-3- 50863511.400-TOS/HSM 09-5341 CONTENTS Page

SUMMARY...............................................................................................................................4

1 General ...................................................................................................................5

2 Location of the OWEZ ............................................................................................6

3 KNMI lightning data ................................................................................................8 3.1 General Information ................................................................................................8 3.2 Extraction of relevant data ....................................................................................11

4 Determination of potential strokes on turbines .....................................................14

5 Lightning data from OWEZ ...................................................................................28

6 Comparision of the OWEZ SCADA data with the KNMI data ...............................32 6.1 Comparison of the number of strokes...................................................................32 6.2 Taking the position-finding of the FLITS system in closer consideration..............32 6.3 Comparison between the FLITS and SCADA data on a daily time-scale.............33

7 Conclusion............................................................................................................36

REFERENCES.......................................................................................................................37

Appendix I Discharges and strokes in the wind farm and its vicinity ......................................38

-4- 50863511.400-TOS/HSM 09-5341 SUMMARY NoordzeeWind is a joint venture between utility company Nuon and oil company Shell and has been set up specifically for the development, construction and operation of the Off shore Wind farm Egmond aan Zee (OWEZ), which counts 36 wind turbines. As part of the OWEZ project NoordzeeWind has carried out an extensive measurement and evaluation program (NSW-MEP). One of the tasks in this program is to gain knowledge on the frequency of occurrence of lightning strokes on wind turbines offshore. In this report the results of an analysis are presented that KEMA has performed on lightning strike data during the years 2006 - 2009 from the FLITS system of the Royal Netherlands Meteorological Institute (KNMI) and the SCADA system of the off shore wind farm near Egmond aan Zee. The FLITS system is based on the measurements of radio frequency pulses which are emitted by lightning. The predicted amount of strokes in wind turbines using data from the FLITS system and the IEC 61024 method for determining the collection area of an isolated structure, are ten to hundred times lower than the amount of strokes detected by the SCADA system. Furthermore, there is a mismatch between the data of the FLITS and the SCADA system in both the position and the time of the strokes. In the same seconds or minutes the SCADA system detects strokes in wind turbines, the FLITS system hardly shows any corresponding strokes (this also applies to cloud-cloud discharges). Also on a daily time scale, there is no significant correlation between the number of strokes detected by the FLITS and the SCADA system. The reason for the mismatch between the data of the FLITS and the SCADA system is not clear. On the basis of 1) the comparison between the FLITS data and the SCADA data for the period September 2006 – December 2009 and 2) the comparison between detected number of strokes by the FLITS system in the OWEZ area and it’s vicinity and the numbers found in literature, the conclusion can be drawn that the FLITS system seems unsuitable for detecting strokes, nor for giving an indication of lightning stroke activity, in wind turbines at the location of the Off shore Wind farm Egmond aan Zee. Acknowledgement The Offshore wind Farm Egmond aan Zee has a subsidy of the Ministry of Economic Affairs under the CO2 Reduction Scheme of the Netherlands

-5- 50863511.400-TOS/HSM 09-5341 1 GENERAL NoordzeeWind is a joint venture between utility company Nuon and oil company Shell and has been set up specifically for the development, construction and operation of the Off shore Wind farm Egmond aan Zee (OWEZ). As part of the OWEZ project NoordzeeWind will carry out an extensive measurement and evaluation program (NSW-MEP). The contents of the NSW-MEP are about generating data and knowledge. The aim of task 1.1.3 - Design conditions lightning – of the NSW-MEP program is to gain knowledge on the frequency of occurrence of lightning strokes on wind turbines offshore. Lightning strokes hitting wind turbines or one of its components may cause failure of one or more systems and a stand still of the wind turbine. The consequences of a lightning stroke may differ to a considerable extent, from a temporarily outage of internal communication lines to a complete destruction of all rotor blades. On all wind turbines in the OWEZ offshore park there are lightning detection systems in the tree blades. This “native” lightning system reports lightning as alarms and warnings to the SCADA system. In this report the results of an analysis are presented that KEMA has performed on lightning strike data in the period September 2006 – December 2009 from the Royal Netherlands Meteorological Institute (KNMI) and the SCADA system of the off shore wind farm near Egmond aan Zee.

-6- 50863511.400-TOS/HSM 09-5341 2 LOCATION OF THE OWEZ The Off shore Wind farm Egmond aan Zee (OWEZ) is located 10-18 kilometres offshore from the Dutch coastal village Egmond aan Zee. Figure 1 shows the lay out of the wind farm (the boundaries of the concession area are shown as a solid line) [1]. Table 1 gives the coordinates of all individual wind turbines in the park, which are shown in figure 1 as triangles. The minimum distance between two wind turbines is 640 meters.

Figure 1 Boundary of the windpark and positions of the 36 wind turbines

-7- 50863511.400-TOS/HSM 09-5341 Table 1 Coordinates in WGS84 projection of the individual wind turbines of the park [1]

No NB OL NB (decimal) OL (decimal) 1 52º 34’ 43.6‘’ 4º 26’ 3.2’’ 52.57878 4.43422 2 52º 34’ 59.5’’ 4º 25’ 41.2’’ 52.58319 4.42811 3 52º 35’ 15.1’’ 4º 25’ 19.5’’ 52.58753 4.42208 4 52º 35’ 31.1’’ 4º 24’ 57.4’’ 52.59197 4.41594 5 52º 35’ 47.0’’ 4º 24’ 35.4’’ 52.59639 4.40983 6 52º 36’ 2.9’’ 4º 24’ 13.3’’ 52.60081 4.40369 7 52º 36’ 19.1’’ 4º 23’ 50.9’’ 52.60531 4.39747 8 52º 36’ 35.0’’ 4º 23’ 28.8’’ 52.60972 4.39133 9 52º 36’ 50.9’’ 4º 23’ 6.7’’ 52.61414 4.38519 10 52º 37’ 7.0’’ 4º 22’ 45.0’’ 52.61861 4.37917 11 52º 37’ 22.7’’ 4º 22’ 22.5’’ 52.62297 4.37292 12 52º 37’ 38.7’’ 4º 22’ 0.4’’ 52.62742 4.36678 13 52º 34’ 54.9’’ 4º 26’ 57.1’’ 52.58192 4.44919 14 52º 35’ 10.8’’ 4º 26’ 35.1’’ 52.58633 4.44308 15 52º 35’ 26.7’’ 4º 26’ 13.0’’ 52.59075 4.43694 16 52º 35’ 42.6’’ 4º 25’ 51.0’’ 52.59517 4.43083 17 52º 36’ 8.1 ’’ 4º 25’ 15.6’’ 52.60225 4.42100 18 52º 36’ 24.0’’ 4º 24’ 53.6’’ 52.60667 4.41489 19 52º 36’ 39.9’’ 4º 24’ 31.5’’ 52.61108 4.40875 20 52º 36’ 55.9’’ 4º 24’ 9.4’’ 52.61553 4.40261 21 52º 37’ 11.8’’ 4º 23’ 47.3’’ 52.61994 4.39647 22 52º 35’ 30.4’’ 4º 27’ 17.4’’ 52.59178 4.45483 23 52º 35’ 46.3’’ 4º 26’ 55.1’’ 52.59619 4.44864 24 52º 36’ 2.4’’ 4º 26’ 33.1’’ 52.60067 4.44253 25 52º 36’ 27.0’’ 4º 25’ 59.0’’ 52.60750 4.43306 26 52º 36’ 44.9’’ 4º 25’ 34.2’’ 52.61247 4.42617 27 52º 37’ 0.8’’ 4º 25’ 12.1’’ 52.61689 4.42003 28 52º 37’ 16.7’’ 4º 24’ 50.0’’ 52.62131 4.41389 29 52º 37’ 32.7’’ 4º 24’ 27.9’’ 52.62575 4.40775 30 52º 36’ 7.2’’ 4º 27’ 35.6’’ 52.60200 4.45989 31 52º 36’ 23.3’’ 4º 27’ 13.7’’ 52.60647 4.45381 32 52º 36’ 47.6’’ 4º 26’40.0’’ 52.61322 4.44444 33 52º 37’ 5.8’’ 4º 26’ 14.8’’ 52.61828 4.43744 34 52º 37’ 21.7’’ 4º 25’ 52.7’’ 52.62269 4.43131 35 52º 37’ 37.6’’ 4º 25’ 30.7’’ 52.62711 4.42519 36 52º 37’ 53.5’’ 4º 25’ 8.6’’ 52.63153 4.41906

-8- 50863511.400-TOS/HSM 09-5341 3 KNMI LIGHTNING DATA 3.1 General Information The registration of lightning by the KNMI (Royal Netherlands Meteorological Institute) is based on the measurements of radio frequency pulses which are emitted by lightning. KNMI uses the lightning detection system FLITS, which stands for Flash Localisation by Interferometry and Time of Arrival System [2]. The FLITS system uses two methods for determining the location of the discharge or stroke: • time of arrival (TAO): this method uses the time difference between detection of radio

waves in the Low Frequency (LF) area of the radio frequency (< 4 MHz) at several lightning detection stations

• detection finding: this method uses the angles of the received radio waves in the Very High Frequency (VHF) area of the radio frequency (about 110 MHz) at several lightning detection stations.

Figures 3 shows the location of the lightning detection stations in the Netherlands and Belgium. Every detection station consists of a pole of 17,5 meters high and is equipped with several sensors. The data from these stations is sent to a central unit at the KNMI where the data is processed. The data covers a large area, including the Netherlands, Belgium, parts of Germany and France and a large part of the North sea. The processed data from the FLITS system is stored in the Hierarchical Data Format (HDF). This is a general-purpose, machine-independent standard for storing scientific data in files. Table 2 gives an overview of the data columns in the KNMI lightning files.

-9- 50863511.400-TOS/HSM 09-5341 Table 2 The information stored in the KNMI lightning files [3] Time offset Time difference between the reference time (which can be found in the

metadata and filename of the lightning file) and the time of hit in seconds (hours : minutes : seconds) and milliseconds

Longitude Place of hit in decimal degrees Latitude Place of hit in decimal degrees Event type 0=isolated point, no lightning, e.g. communication intrusions

1=starting point of a cloud-cloud discharge 2=next point in a cloud-cloud discharge 3=end point of a cloud-cloud discharge 4=ground stroke 5=return stroke

Position error Error in position of the discharge in meters Rise time Rise time for a ground stroke in microseconds Decay time Decay time for a ground stroke in microseconds Current Calculated current in Ampere Lightning data for the period 01-07-2006 till 31-12-2009 are obtained from the KNMI and analysed in this report. For further analyses the KNMI lightning data has been split in four sets: 1 for the period 01-07-2006 till 31-12-2006 (Q3 and Q4 of 2006) 2 for the whole of 2007 3 for the whole of 2008 4 for the whole of 2009. The position error of the lightning data can be up to 7 kilometres, but at the location of the wind farm the position error is in general less than 1 kilometre (see figure 2 and 3), with a maximum of 4 kilometres (see figure 2). When analysing the KNMI lightning data one can see that in areas where the position error is more than 1 kilometre, the sensitivity of the FLITS lightning detection system decreases and less strokes are detected (see figure 4). OWEZ is located in an area where the FLITS lightning detection system should have sufficient sensitivity.

-10- 50863511.400-TOS/HSM 09-5341

0

500

1000

1500

2000

2500

3000

3500

4000

posi

tion

erro

r in

met

ers

detected strikes by FLITS

Figure 2 Ground and return strokes in the vicinity of the wind farm in the period September

2006 – September 2009 (336 in total), sorted by increasing position error

Figure 3 Locations of the FLITS detection stations. The stations are marked with a cross

and circle: De Kooy, Valkenburg, Deelen, Hoogeveen, Oelegem, Mourcourt and La Gileppe. The colour scale shows the position error [4]

-11- 50863511.400-TOS/HSM 09-5341

Figure 4 All cloud-to-cloud strokes (purple) and ground and return strokes (blue) in

Q3-2007. The little square is the OWEZ area 3.2 Extraction of relevant data For further analyses, all lightning events were extracted from the data files that took place within 7 kilometres of the outermost wind turbines of the OWEZ. The surface of the OWEZ including the buffer is 405 square kilometres. A buffer of 7 kilometres is chosen because this is the maximum possible location error of a stroke in the FLITS data. In practice, at the location of the wind farm the position error is less than 7 kilometres (see figure 2 and 3), but in order to be 100% sure all strokes that can theoretically occur in the wind farm are taken into account, a boundary of 7 kilometres is chosen. Analyses of the lightning data shows that the number of days that ground- and/or return strokes occur within 7 kilometres of the outermost wind turbines of the wind farm are limited. In Q3 and Q4 of 2006 there were 12 days with ground- and/or return strokes in the wind farm and its vicinity. In 2007, 2008 and 2009 there were respectively 9, 14 and 11 of such days, see table 3. The total amount of registered ground- and return strokes is 90 in Q3 and Q4 of 2006, 131 in 2007, 62 in 2008 and 80 in 2009 (table 3). That is 0.45, 0.32, 0.15 and 0.19 strokes/km2/year respectively. This is a considerable lower figure compared to figures found in literature for the Dutch coastal area. The KNMI gives an average of 1.3 strokes/km2/year [6] and the

-12- 50863511.400-TOS/HSM 09-5341 NEN1014 publication gives about 2.5 strokes/km2/year [5]. Both in time and space large fluctuations in the number of strokes exists (see figure 5). Table 3 Days with strokes occurring within 7 km of the outermost wind turbines of the wind

farm and the total number of ground- and return strokes in Q3 and Q4 of 2006, 2007, 2008 and 2009

datenumber

of strokes datenumber



of strokes20060705 3 20070121 3 20080301 2 20090526 220060722 4 20070608 42 20080331 1 20090717 220060802 3 20070627 2 20080531 1 20090730 4320060811 1 20070703 2 20080602 4 20090820 120060814 2 20070704 5 20080702 1 20090828 320060820 32 20070709 18 20080712 1 20090829 120060828 4 20070715 2 20080731 6 20091104 2020060929 2 20070716 43 20080801 1 20091106 320061001 34 20070722 14 20080807 17 20091123 120061002 2 20080813 2 20091128 220061118 1 20080823 19 20091204 220061129 2 20081027 3

20081028 320081204 1

total 90 total 131 total 62 total 80

July - Dec. 2006 2007 2008 2009

-13- 50863511.400-TOS/HSM 09-5341

Figure 5 Number of ground and return strokes per square kilometre per year according to

the KNMI for the period 1995-1998 [6] Most registered discharges are cloud tot cloud discharges. Only a small percentage of the discharges develops into a ground or return stroke. Appendix I gives an overview of all detected discharges and strokes by the FLITS system within 7 kilometres of the outermost wind turbines of the wind farm in the period September 2006 – December 2009.

-14- 50863511.400-TOS/HSM 09-5341 4 DETERMINATION OF POTENTIAL STROKES ON TURBINES By using the coordinates of the 36 wind turbines (see table 1), and the coordinates of the ground- and return strokes including their position error, all strokes can be determined that could theoretically have struck a wind turbine. A GIS (Geographical Information System) was used for carrying out this analysis. Figure 6, 7, 8 and 9 show the wind turbines (black dots), all the ground and return stokes (orange stars) and their position error (grey circles) in the vicinity of the wind farm in Q3 and Q4 of 2006, in 2007, in 2008 and in 2009. We can now select all strokes that contain a wind turbine within the range of the position error. These are all the ground and return strokes that could potentially have struck a wind turbine. In figure 10, 11, 12 and 13 all these strokes are highlighted in purple.

Figure 6 All ground and return strokes (orange stars) in Q3 and Q4 of 2006 in the vicinity of

the wind farm. The grey circles around the discharge events are the position error. The black dots are the wind turbines

-15- 50863511.400-TOS/HSM 09-5341

Figure 7 All ground and return strokes in 2007 in the vicinity of the wind farm


-16- 50863511.400-TOS/HSM 09-5341


Figure 10 The ground and return strokes in Q3 and Q4 of 2006 in the vicinity of the wind

farm which could potentially have struck one or more wind turbines

-17- 50863511.400-TOS/HSM 09-5341

Figure 11 The ground and return strokes in 2007 in the vicinity of the wind farm which could

potentially have struck one or more wind turbines


potentially have struck one or more wind turbines

-18- 50863511.400-TOS/HSM 09-5341


potentially have struck one or more wind turbines In Q3 and Q4 of 2006 there were 10 strokes that could potentially have struck a wind turbine in the wind farm. In 2007 this number was 15. In 2008 this number was only 3 and in 2009 this number was 8. Tables 4, 5, 6 and 7 show the details of all the potential strokes on wind turbines. The number of purple circles in figure 10, 11, 12 and 13 do not necessarily correspond with the number of potential wind turbine strokes in table 4, 5, 6 and 7. Some strokes have the same location and position error because one discharge channel can be used two times (or more) within a fraction of a second to produce ground or return strokes.

-19- 50863511.400-TOS/HSM 09-5341 Table 4 All ground and return strokes in and near the wind farm that could potentially have struck a wind turbine in Q3 and Q4 of 2006

4.458 52.601 20060802 84245 0.958 560 4 -25870 800 3100 304.461 52.601 20060802 84245 0.9677 560 5 -15020 288 2300 304.461 52.601 20060802 84245 0.98 560 5 -24530 387 3600 304.395 52.622 20060811 14045 0.6454 600 4 -12430 487 1800 214.406 52.599 20060820 74948 0.2271 1420 4 -13120 350 3000 4 5 6 7 17 18 194.397 52.609 20060820 74948 0.3708 1450 5 -12760 237 2200 6 7 8 9 18 19 20 214.401 52.625 20061001 231111 0.297 590 4 -8830 5.75 25 20 214.393 52.619 20061001 231111 0.316 590 5 -8550 2.62 20 8 94.422 52.614 20061001 231213 0.713 590 4 -26140 5.88 32 35 364.436 52.630 20061001 231214 0.21 580 4 -14710 3.38 29 34

LON LAT DATE TIME SUBSEC POSERR TYPE CURRENT

potentially struck windmills

RISETIME

DECAYTIME

-20- 50863511.400-TOS/HSM 09-5341 Table 5 All ground and return strokes in and near the wind farm that could potentially have struck a wind turbine in 2007

4.426 52.603 20070121 43646 0.0942 750 4 8790 3.87 49 17 254.437 52.598 20070608 3058 0.542 570 4 -21360 612 3600 16 244.385 52.621 20070608 3716 0.7172 600 5 -15090 500 2200 104.439 52.576 20070608 3829 0.515 560 4 -25750 650 4800 14.444 52.585 20070608 201924 0.6067 560 4 -19810 387 3500 13 144.444 52.591 20070608 202059 0.2117 670 4 -33740 725 2500 14 15 234.380 52.603 20070703 120026 0.4208 2050 4 -62140 1.62 23 6 7 8 9 104.422 52.621 20070709 85837 0.0006 720 4 -15310 3 17 27 28 34 354.369 52.625 20070716 170234 0.4672 2090 4 -34320 3.63 28 9 10 11 12 214.427 52.581 20070716 170715 0.57 740 4 -15170 4 30 1 24.357 52.626 20070716 171741 0.3553 800 4 -7710 3.5 21 124.424 52.580 20070716 172244 0.0797 690 4 -14550 4.25 23 24.399 52.643 20070716 173241 0.7816 2080 4 -52750 7.5 39 29 364.399 52.643 20070716 173241 0.8979 2080 5 -29790 2.88 25 29 364.448 52.615 20070722 63017 0.6627 730 4 -12420 4.25 40 32

SUBSEC POSERRLATLON DATE TIME TYPE CURRENT potentially struck windmills

RISETIME

DECAYTIME

Table 6 All ground and return strokes in and near the wind farm that could potentially have struck a wind turbine in 2008

4.423 52.632 20080813 210111 0.1321 720 4 -24280 350 2700 35 364.460 52.601 20080823 52440 0.9026 660 4 -16660 363 2000 304.426 52.584 20081027 180400 0.1791 690 4 7850 850 4900 2 3

SUBSEC POSERRLATLON DATE TIME TYPE CURRENT potentially struck windmills

RISETIME

DECAYTIME

-21- 50863511.400-TOS/HSM 09-5341 Table 7 All ground and return strokes in and near the wind farm that could potentially have struck a wind turbine in 2009

4.462 52.588 20090526 24447 0.0217 650 4 -8840 2.37 23 224.416 52.595 20090730 13425 0.4741 580 4 -28080 8.63 41 4 54.448 52.617 20090730 13601 0.9116 570 5 -17880 3.5 30 324.436 52.625 20090730 13656 0.0104 580 4 -10870 3.12 19 344.423 52.63 20090730 160016 0.851 760 4 5030 8 38 35 364.406 52.593 20090820 161246 0.0806 710 4 4080 4.87 50 4 54.449 52.596 20091104 223629 0.8345 560 4 -18490 8.38 34 234.395 52.616 20091123 164046 0.9948 590 4 -5910 10.75 21 20 21

RISETIME

DECAYTIME

potentially struck windmills

SUBSEC POSERR TYPE CURRENTLON LAT DATE TIME

-22- 50863511.400-TOS/HSM 09-5341 On a level surface, the place where lightning strikes can be considered as random. If there is a conductive object in the vicinity of the streak, the lightning will strike in this object. The striking distance (r) in which an object will attract the lightning is a function of the current (I). Different empirical formulas exist for calculating the striking distance. We will use here the formula of Armstrong and Whitehead [7, page 226], which gives a slightly larger striking distance then other formulas found in literature, and which should therefore be considered as a worst case formula. Armstrong and Whitehead’s formula: r=6,78*I0,8

According to this formula, and using the KNMI lightning data as input, the average striking distance of the strokes in the period July 2006 – December 2009 in the OWEZ area is 74 meter. The collection area (A) for the OWEZ wind turbines can then be calculated as a function of it’s striking distance and the height of the object, see figure 14. The collection area of a structure is defined as an area of ground surface which has the same annual frequency of direct lightning flashes as the structure. The height of the wind turbines in the OWEZ is 116 meters above Mean Sea Level [1] (tower plus blade). The wind turbines in OWEZ are designed according to the standard IEC 61024 (Protection of structures against lightning, 1993). According to IEC 61024 the collection area is not related to the current (I) of lightning strokes, but only to the height (h) of the wind turbine: “for isolated structures the equivalent collection area is the area enclosed with a border line obtained from the intersection between the ground surface and a straight line with a 1:3 slope which passes from the upper parts of the structure (touching it there) and rotating around it.” (IEC 61024: page 21). The same method is followed in IEC 61400-24 (2002). As a consequence: A = 9πh2. For the OWEZ wind turbines this means the striking distance is 348 meters and the collection area (A) is 380459 m2.

-23- 50863511.400-TOS/HSM 09-5341

r < h r > h

h

A = π·r2 A = π·h·(2r-h)

r

r r-h

h

r22 hhr −

Figure 14 Surface (A) in which the object will attract the lightning as a function of height (h)

and the striking distance(r) of the lightning stroke [7] Using the position error in the KNMI lightning files and the collection area (A), we can now give an indication of the chance the lightning struck a wind turbine. We assume that the chance of the stroke hitting the surface is the same everywhere within the radius of the position error. The results for Q3 and Q4 of 2006, 2007, 2008 and 2009 are shown in table 8, 9, 10 and 11. The collection area according to the IEC 61024 method as well as according to Armstrong & Whitehead’s formula are given in these tables.

-24- 50863511.400-TOS/HSM 09-5341 Table 8 All ground and return strokes in the OWEZ area in Q3 and Q4 of 2006 and their risk of hitting a wind turbine

Armstrong & Whitehead formula

4.458 52.601 20060802 84245 0.958 560 -25870 985204 90 25691 2.61% 38.62%4.461 52.601 20060802 84245 0.9677 560 -15020 985204 59 10764 1.09% 38.62%4.461 52.601 20060802 84245 0.98 560 -24530 985204 87 23595 2.39% 38.62%4.395 52.622 20060811 14045 0.6454 600 -12430 1130973 50 7952 0.70% 33.64%4.406 52.599 20060820 74948 0.2271 1420 -13120 6334708 53 8669 0.96% 42.04%4.397 52.609 20060820 74948 0.3708 1450 -12760 6605199 51 8292 1.00% 46.08%4.401 52.625 20061001 231111 0.297 590 -8830 1093589 38 4601 0.84% 69.58%4.393 52.619 20061001 231111 0.316 590 -8550 1093589 37 4370 0.80% 69.58%4.422 52.614 20061001 231213 0.713 590 -26140 1093589 91 26121 4.78% 69.58%4.436 52.630 20061001 231214 0.21 580 -14710 1056832 58 10411 0.99% 36.00%

CURRENT (ampère)

striking distance

(r)

chancemill is hit (%)

IEC 61024LON LAT DATE TIME surface

(A)

surfacePOSERR

(m2)

chancemill is hit (%)SUBSEC

POSERR(m)

-25- 50863511.400-TOS/HSM 09-5341 Table 9 All ground and return strokes in the OWEZ area in 2007 and their risk of hitting a wind turbine


4.426 52.603 20070121 43646 0.0942 750 8790 1767146 38 4568 0.52% 43.06%4.437 52.598 20070608 3058 0.542 570 -21360 1020704 78 18909 3.71% 74.55%4.385 52.621 20070608 3716 0.7172 600 -15090 1130973 59 10844 0.96% 33.64%4.439 52.576 20070608 3829 0.515 560 -25750 985204 90 25500 2.59% 38.62%4.444 52.585 20070608 201924 0.6067 560 -19810 985204 73 16762 3.40% 77.23%4.444 52.591 20070608 202059 0.2117 670 -33740 1410261 112 39294 8.36% 80.93%4.380 52.603 20070703 120026 0.4208 2050 -62140 13202545 182 90591 3.43% 14.41%4.422 52.621 20070709 85837 0.0006 720 -15310 1628602 59 11098 2.73% 93.44%4.369 52.625 20070716 170234 0.4672 2090 -34320 13722792 113 40381 1.47% 13.86%4.427 52.581 20070716 170715 0.57 740 -15170 1720336 59 10936 1.27% 44.23%4.357 52.626 20070716 171741 0.3553 800 -7710 2010620 34 3703 0.18% 18.92%4.424 52.580 20070716 172244 0.0797 690 -14550 1495712 57 10230 0.68% 25.44%4.399 52.643 20070716 173241 0.7816 2080 -52750 13591788 160 74271 1.09% 5.60%4.399 52.643 20070716 173241 0.8979 2080 -29790 13591788 101 32197 0.47% 5.60%4.448 52.615 20070722 63017 0.6627 730 -12420 1674155 50 7941 0.47% 22.73%

LON LAT DATE TIMEchance

mill is hit (%)IEC 61024

SUBSECPOSERR

(m)CURRENT (ampère)

striking distance

(r)

chancemill is hit (%)surface

(A)

surfacePOSERR

(m2)

Table 10 All ground and return strokes in the OWEZ area in 2008 and their risk of hitting a wind turbine


4.423 52.632 20080813 210111 0.1321 720 -24280 1628602 86 23211 2.85% 46.72%4.460 52.601 20080823 52440 0.9026 660 -16660 1368478 64 12705 0.93% 27.80%4.426 52.584 20081027 180400 0.1791 690 7850 1495712 35 3811 0.51% 50.87%

LON LAT DATE TIMEchance

mill is hit (%)IEC 61024

SUBSECPOSERR

(m)CURRENT (ampère)

striking distance

(r)

chancemill is hit (%)surface

(A)

surfacePOSERR

(m2)

-26- 50863511.400-TOS/HSM 09-5341 Table 11 All ground and return strokes in the OWEZ area in 2009 and their risk of hitting a wind turbine


4.462 52.588 20090526 24447 0.0217 650 -8840 1327323 38 4609 0.35% 28.66%4.416 52.595 20090730 13425 0.4741 580 -28080 1056832 97 29291 5.54% 72.00%4.448 52.617 20090730 13601 0.9116 570 -17880 1020704 67 14226 1.39% 37.27%4.436 52.625 20090730 13656 0.0104 580 -10870 1056832 45 6416 0.61% 36.00%4.423 52.63 20090730 160016 0.851 760 5030 1814584 24 1870 0.21% 41.93%4.406 52.593 20090820 161246 0.0806 710 4080 1583677 21 1338 0.17% 48.05%4.449 52.596 20091104 223629 0.8345 560 -18490 985204 69 15011 1.52% 38.62%4.395 52.616 20091123 164046 0.9948 590 -5910 1093589 28 2420 0.44% 69.58%

striking distance

(r)surface

(A)



IEC 61024SUBSEC

POSERR(m)

CURRENT (ampère)

surfacePOSERR

(m2)LON LAT DATE TIME

-27- 50863511.400-TOS/HSM 09-5341 The chance that a stroke hits a wind turbine is calculated by multiplying the surface (A) with the number of potentially hit wind turbines (see table 4, 5, 6 and 7) and divided by the surface area of the position error. By adding up all the chances in the table, one obtains the number of lightning strokes in wind turbines according to the theory of probability. Using Armstrong and Whitehead’s formula, this number is 0.16 strokes for Q3 and Q4 in 2006, 0.31 strokes for the year 2007, 0.04 strokes for the year 2008 and 0.10 strokes for 2009. Using the IEC 61024 approach, the amount of strokes is 4.82 for Q3 and Q4 in 2006, 5.92 strokes for the year 2007, 1.25 strokes for the year 2008 and 3.72 strokes for the year 2009. The IEC 61024 method for determining the collection area gives much greater values compared to the formula’s found in literature, which besides the height of the structure, also include the current of a lightning stroke. The number of potential strokes determined by the IEC 61024 method is still much smaller than the registered number of strokes by the SCADA system, as can be read in chapter 5. This means the IEC 61024 method for determining the collection area seems to be closer to reality than Armstrong & Whitehead’s or other comparative formula’s. Therefore, from this point on forwards, only the number of potential strokes according to the IEC 61024 method will be used. The position error is a factor which introduces a large uncertainty in the analyses carried out in this chapter. The meaning of the position error is unclear. The manufacturer does not provide information on this. According to the KNMI (oral communication) the position error of the lightning stroke could well be larger than the position error as given in the FLITS files.

-28- 50863511.400-TOS/HSM 09-5341 5 LIGHTNING DATA FROM OWEZ On all wind turbines in the OWEZ offshore park there are lightning detection systems in the three blades. The lightning system reports the maximum detected current peak of the stroke to the SCADA system. The registration of lightning strokes in wind turbines by the SCADA system in the OWEZ started in September 2006. Up to December 31st 2009, 290 strokes in wind turbines have been detected, see table 12. From these 290 strokes, 79 had a current of over 10 kAmpère.

-29- 50863511.400-TOS/HSM 09-5341 Table 12 Number of strokes in wind turbines per day detected by the SCADA system

-30- 50863511.400-TOS/HSM 09-5341 Figure 15 and 16 show the stroke current distribution and the number of strokes per wind turbine. As can be seen in table 12 and figure 15, most lightning strokes (73%) have a current between 6 kAmpère (the threshold value for the SCADA system) and 10 kAmpère. From the 290 strokes detected in the period September 2006 – December 2009 by the SCADA system, 13 had a current of over 50 kAmpère and were given the status ‘alarm’. The other 277 strokes were given the status ‘warning’. Table 13 shows the 13 strokes which had a current of over 50 kAmpère. The maximum current registered in the period September 2006 – December 2009 is 75 kAmpère.

0102030405060708090

100110120130140150160170180190200210220

6-10 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90Current [kA]

No

of S

trik

es

2009200820072006 Q3 Q4

Total Hits: 290Max. Current: 75 kA

Figure 15 Stroke current distribution at OWEZ in the period September 2006 – December

2009

-31- 50863511.400-TOS/HSM 09-5341

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

wind turbine

nr. o

f str

okes

Figure 16 Number of strokes per wind turbine in the period September 2006 – December

2009 Table 13 Strokes with a current > 50 kAmpère (September 2006 - December 2009) date time (UTC) turbine current (kAmpère) 21-1-2007 04:44:49 32 72 21-1-2007 05:35:40 20 63 21-1-2007 05:41:03 7 75 7-2-2007 08:46:19 24 52 19-3-2007 21:02:17 14 61 8-6-2007 00:40:23 36 64 8-6-2007 20:28:47 35 64 1-8-2008 00:48:34 15 60 28-10-2008 02:00:14 8 59 23-3-2009 20:14:00 27 52 25-5-2009 20:45:00 36 55 26-11-2009 11:55:16 33 61 28-11-2009 03:44:00 36 51

-32- 50863511.400-TOS/HSM 09-5341 6 COMPARISION OF THE OWEZ SCADA DATA WITH THE KNMI

DATA 6.1 Comparison of the number of strokes The number of strokes per square kilometre detected by the FLITS system is much lower than the number found in literature: 0.15 – 0.45 strokes/km2/year for the area within 7 kilometres of the outermost wind turbines of the wind farm (see chapter 3) versus 1.3 – 2.5 strokes/km2/year found in literature [5][6]. The numbers from the SCADA system are 2.2 – 5.0 strokes/km2/year in the area where the wind turbines are placed (about 20 km2). This figure is however not corrected for the limited number of strokes that can occur between the wind turbines. Therefore it can be concluded that the number of strokes per square kilometre detected by the SCADA system are about two times higher than found in literature. In 2007, 2008 and 2009, respectively 72, 100 and 96 strokes have been detected by the SCADA system. This contrasts sharply with the predicted 5.92 strokes in 2007, 1.25 strokes in 2008 and 3.72 strokes in 2009 using the data from the FLITS system from the KNMI (see chapter 4). According to NoordzeeWind there is no reason to cast doubt on the recordings of the SCADA system. The reason for the mismatch between the FLITS data and the SCADA data being the SCADA system detecting too many strokes is therefore not investigated. 6.2 Taking the position-finding of the FLITS system in closer

consideration Possible explanations for the huge difference between the number of detected strokes in wind turbines by the SCADA system and the number of predicted strokes by the FLITS system (72 versus 5.92 in 2007, 100 versus 1.25 in 2008 and 96 versus 3.72 in 2009) are: a Wind turbines have a much greater attraction on ground and return strokes as is

suggested by literature (IEC 61024, Armstrong and Whitehead’s formula and other formula’s [7])

b The position error in the FLITS data is larger in reality (but below 7 kilometres) c Not only ground and return strokes but also cloud-to-cloud discharges will strike wind

turbines when they are inside the range of it’s position error.

-33- 50863511.400-TOS/HSM 09-5341 In order to investigate the three possible reasons mentioned above, it’s being assumed that the time recordings of both the SCADA and the FLITS system are correct. The SCADA system registers lightning strokes with a precision of 1 second and the FLITS system with a precision of 1 millisecond. We determine if in the same second as the SCADA system has detected a lightning stroke, the FLITS system also detected a stroke within 7 kilometres of the outermost wind turbines of the wind farm. This is the case for only 1 out of 290 detected strokes by the SCADA system. This was at January 21st 2007, when the SCADA system detected a stroke in wind turbine 5 and the FLITS system detected a stroke between wind turbine 17 and 25. Now we use a time span of a minute instead of a second, so it is determined whether the two systems detect a stroke in the same minute. This is the case for only 3 out of the 290 strokes. If we also take into consideration cloud-to-cloud discharges (type 1 – 3, table 2) the score is 50 out of the 290 strokes. The average distance between the SCADA system location and the FLITS system location of these 50 strokes is however large, namely 9.4 kilometres, which is larger than the maximum position error. The above mentioned reasons a), b) and c) as possible reasons for the mismatch between the number of strokes detected by the SCADA and the FLITS system should on the basis of the this information be rejected. From the 290 strokes detected in the period September 2006 – December 2009 by the SCADA system, 13 had a current of over 50 kAmpère and were given the status ‘alarm’ (see table 13). In the same minute as the SCADA system detected these 13 ‘alarm’ strokes, the FLITS system never detected a ground or return stroke within 7 kilometres of the outermost wind turbines of the wind farm. By 4 out of these 13 ‘alarm’ strokes, cloud-to-cloud strokes were detected by the FLITS system in this area in the same minute. A clear illustration of the mismatch between the SCADA and the FLITS system is the lightning stroke detected by the SCADA system on March 19th 2007. This was an ‘alarm’ stroke with current of 61 kAmpère. On March 19th 2007 there was no lightning activity at all in the vicinity of the wind farm according to the FLITS system, not even a single cloud-to-cloud discharge. 6.3 Comparison between the FLITS and SCADA data on a daily time-scale Although in general on days of high lightning activity there are strokes detected by both the SCADA system and the FLITS system, the correlation between the two is very low. See figure 17. Here the number of detected strokes by the SCADA system is plotted on the x-axis and the number of strokes (ground- and return strokes) within 7 kilometres of the outermost wind turbines of the wind farm according to the FLITS system (see appendix I) is plotted on

-34- 50863511.400-TOS/HSM 09-5341 the y-axis. Every dot represents one day with lightning activity. The period taken into account is again September 2006 – December 2009. A comparable low correlation is found between strokes detected by the SCADA system and cloud-to-cloud discharges detected by the FLITS system (type 0 – 3, see table 2), as can be seen in figure 18. The blue points in figure 18 are isolated point discharges, these are not lightning discharges but events such as communication intrusions. The red squares are the starting points of cloud to cloud discharges and the green triangles the end of cloud to cloud discharges. Intermediate discharges during cloud to cloud discharges are also registered by the FLITS system and are represented in graph 18 as yellow dots. They are indicated as “next point cloud-cloud discharge”. There is hardly any correlation between amount of type 0 – 3 discharges from the FLITS system and the amount of detected strokes by the SCADA system. The highest correlation is R2 = 0.30 between the number of strokes detected by the SCADA system(x) and ‘next point of cloud-cloud‘ discharges (y): 64.23e0.2112x. The ‘next point of cloud-cloud’ discharges are apparently the best - but still insufficient - indicator for lightning stroke activity in the OWEZ area. Figure 18 doesn’t show the cases having zero strokes detected by the SCADA system, but one or more cloud-to-cloud discharges detected by the FLITS system. The number of days for which this applies are numerous.

R2 = 0.1

0

5

10

15

20

25

30

35

40

45

50

0 2 4 6 8 10 12 14 16 18

number of detected strikes by SCADA system

num

ber o

f stri

kes

in a

nd a

roun

d O

WEZ

by

FLIT

S da

ta

Figure 17 Number of strokes detected by the SCADA system and by the FLITS system in

and around OWEZ on a daily time scale

-35- 50863511.400-TOS/HSM 09-5341

y = 64.23e0.2112x

R2 = 0.3036

1

10

100

1000

10000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17number of detected strikes by SCADA system

num

ber o

f clo

ud-c

loud

dis

char

ges

in a

nd a

roun

d O

WEZ

by

FLIT

S da

ta isolated pointdischarge

start cloud-clouddischarge

next point cloud-clouddischarge

end cloud-clouddischarge

Figure 18 Number of strokes detected by the SCADA system and number of cloud-to-cloud

discharges by the FLITS system in and around OWEZ on a daily time scale

-36- 50863511.400-TOS/HSM 09-5341 7 CONCLUSION The number of strokes per square kilometre detected by the FLITS system in the OWEZ area and it’s vicinity is much lower (five to ten times) than the numbers found in literature. The amount of strokes per square kilometre detected by the SCADA system in the OWEZ area are about two times higher than the numbers stated in literature. The predicted amount of strokes in wind turbines using data from the FLITS system and the IEC 61024 method for determining the collection area of an isolated structure, are ten to hundred times lower than the amount of strokes detected by the SCADA system. From the information in chapter 4, 5 and 6 it can be concluded that there is a mismatch between the data of the FLITS and the SCADA system in both the location and time of the strokes. In the same seconds or minutes the SCADA system detects strokes in wind turbines, the FLITS system hardly shows any corresponding strokes (this also applies to cloud-cloud discharges). Also on a daily time scale, there is no significant correlation between the number of strokes detected by the FLITS and the SCADA system (see paragraph 6.3). On the basis of 1) the comparison between detected number of strokes by the FLITS system in the OWEZ area and it’s vicinity and the numbers found in literature and 2) the comparison between the FLITS data and the SCADA data for the period September 2006 – December 2009, the conclusion can be drawn that the FLITS system seems unsuitable for detecting strokes, nor for giving an indication of lightning stroke activity, in wind turbines at the location of the Off shore Wind farm Egmond aan Zee. The reason for the mismatch between the data of the FLITS and the SCADA system is not clear. A further research project, outside the OWEZ monitoring program, might shed light on this.

-37- 50863511.400-TOS/HSM 09-5341 REFERENCES [1] Near Shore Windpark Wbr/Wm vergunningaanvraag NSW, 2003. [2] Processing, validatie, en analyse van bliksemdata uit het SAFIR/FLITS systeem,

Saskia Noteboom. [3] Output format description of the FLITS HDF file converter program hdf2dis, version

2.1_20041028, KNMI. [4] Informatie over het bliksemdetectie systeem, Hans Beekhuis KNMI. [5] DOWEC CONCEPT STUDY TASK 7, Standards and criteria for offshore wind turbines,

ECN-CX--00-039, H.B. Hendriks, P.P. Soullié, 2000. [6] KNMI, Onweerswaarnemingen in Nederland, H.R.A. Wessels, 1999. Published in Zenit,

26, 1999, pages 260 – 264. [7] Insulation Coordination for power systems, Andrew Hileman, 1999.

-38- 50863511.400-TOS/HSM 09-5341 APPENDIX I DISCHARGES AND STROKES IN THE WIND FARM AND

ITS VICINITY Detected discharges and strokes by the FLITS system within 7 kilometres of the outermost wind turbines of the wind farm in Q3 and Q4 of 2006.

JUL AUG SEP OKT NOV DEC

type 0 6 type 0 4 type 0 4 type 0 48 type 1 4 type 1 1type 1 15 type 1 9 type 1 6 type 1 166 type 2 336 type 2 125type 2 254 type 2 100 type 2 68 type 2 2002 type 3 5 type 3 1type 3 13 type 3 7 type 3 10 type 3 171 type 4 1type 4 3 type 4 26 type 1 1

type 0 1 type 0 12 type 5 8 type 0 1 type 2 28

type 0 26 type 1 3 type 1 18 type 1 6 type 3 1type 1 47 type 2 22 type 2 444 type 0 5 type 2 72type 2 245 type 3 2 type 3 20 type 1 7 type 3 5 type 0 2type 3 48 type 4 1 type 4 2 type 2 124 type 4 2 type 1 5type 4 4 type 5 2 type 3 5 type 2 267

type 0 2 type 4 2 type 3 4

type 1 1 type 1 9type 3 1 type 2 121 type 1 2

type 3 8 type 2 28

type 4 1 type 3 2

type 0 6 type 0 1type 1 16type 2 561

type 3 15type 4 2

type 0 1

type 0 13 type 0=isolated point, no lightning, e.g. communication intrusionstype 1 46 type 1=start cloud-cloud dischargetype 2 984 type 2=next point in cloud-cloud dischargetype 3 44 type 3=end cloud-cloud dischargetype 4 24 type 4=ground stroke type 5 8 type 5=return stroke

type 1 5type 2 43type 3 8

type 0 1type 1 5

type 2 163type 3 4

type 4 4

type 0 1type 1 6type 2 93type 3 6

datum : 20060811

datum : 20060814

datum : 20060705

datum : 20060722

datum : 20060725

datum : 20060829

datum : 20060914

datum : 20060929

datum : 20060930

datum : 20060817

datum : 20060820

datum : 20060825

datum : 20060828

datum : 20060801

datum : 20060802

datum : 20061001

datum : 20061002

datum : 20061006

datum : 20061023

datum : 20061207

datum : 20061118

datum : 20061129

datum : 20061204

datum : 20061206

-39- 50863511.400-TOS/HSM 09-5341

Appendix I page 2 Detected discharges and strokes by the FLITS system within 7 kilometres of the outermost wind turbines of the wind farm in 2007.

JAN FEB MAA APR MEI JUN JUL AUG SEP OKT NOV DEC

type 1 4 type 1 1 type 1 1 type 1 2 type 2 1 type 0 1 type 1 1 type 1 2type 2 24 type 2 106 type 2 2 type 2 6 type 3 1 type 1 1 type 3 1 type 2 112type 3 5 type 3 1 type 3 1 type 3 1 type 4 2 type 2 22 type 3 2

type 2 36

type 0 1 type 1 1 type 0 636 type 0 3 type 3 1 type 1 1type 1 4 type 2 96 type 1 1186 type 1 19 type 2 7type 2 80 type 3 1 type 2 5167 type 2 286 type 1 1 type 3 1type 3 4 type 3 1199 type 3 18 type 3 5

type 4 33 type 4 4

type 1 1 type 5 9 type 5 1type 2 27type 3 1 type 0 2 type 0 31

type 1 13 type 1 95

type 0 1 type 2 157 type 2 1658type 2 116 type 3 12 type 3 90type 3 2 type 4 14

type 0 3 type 5 4

type 0 6 type 1 15type 1 26 type 2 363 type 0 33type 2 760 type 3 13 type 1 48type 3 25 type 4 1 type 2 216type 4 3 type 5 1 type 3 47

type 4 2

type 0 443type 1 592type 2 1754


type 0 3type 1 4type 2 59type 3 3


type 3 23

type 0=isolated point, no lightning, e.g. communication intrusions type 4 10

type 1=start cloud-cloud discharge type 5 4

type 2=next point in cloud-cloud dischargetype 3=end cloud-cloud discharge type 0 1

type 4=ground stroke type 5=return stroke type 0 1

datum : 20071201

datum : 20071207

datum : 20070723

datum : 20070730

datum : 20070822 datum : 20070917

datum : 20070715

datum : 20070716

datum : 20070720

datum : 20070722

datum : 20070918

datum : 20070925

datum : 20070627

datum : 20070703

datum : 20070704

datum : 20070709

datum : 20070507 datum : 20070607

datum : 20070608

datum : 20070620

datum : 20070118

datum : 20070121

datum : 20070207

datum : 20070228

datum : 20070101

datum : 20070110

datum : 20070111

-40- 50863511.400-TOS/HSM 09-5341


FEB

type 0 1 type 0 3 type 1 1 type 0 37 type 1 1 type 0 4 type 0 17 type 1 1 type 1 15 type 0 1 type 0 1

type 1 2 type 2 6 type 1 72 type 3 1 type 1 11 type 1 22 type 2 5 type 2 600 type 1 2

type 0 6 type 2 39 type 3 1 type 2 512 type 2 232 type 2 62 type 3 1 type 3 16 type 2 180 type 1 6

type 1 18 type 3 2 type 3 65 type 0 23 type 3 10 type 3 24 type 3 2 type 2 192type 2 261 type 0 2 type 4 1 type 1 45 type 4 1 type 4 1 type 2 3 type 0 1 type 3 6type 3 20 type 0 1 type 2 481 type 0 1 type 4 1type 4 2 type 3 42 type 0 1 type 0 31 type 1 5

type 0 1 type 4 4 type 1 1 type 1 53 type 2 165type 1 1 type 2 66 type 2 373 type 3 4

type 2 18 type 2 3 type 3 1 type 3 53 type 4 3type 4 1 type 4 8

type 0 1 type 5 9 type 0 6type 1 3 type 1 13type 2 38 type 1 1 type 2 302

type 3 3 type 3 2 type 3 14type 4 1 type 4 3

type 2 29type 1 1type 2 7 type 0 3type 3 1 type 1 17

type 2 246

type 0 1 type 3 13type 1 3 type 4 2type 3 3

type 0 1

type 0 8type 1 8 type 0 5

type 2 33 type 1 19type 3 6 type 2 281

type 0=isolated point, no lightning, e.g. communication intrusions type 3 18

type 1=start cloud-cloud discharge type 1 2 type 4 16

type 2=next point in cloud-cloud discharge type 2 9 type 5 3

type 3=end cloud-cloud discharge type 3 3

type 4=ground stroke type 4 5

type 5=return stroke type 5 1

NOV DECOKTMAA APR MEI JUN JUL AUG SEP20081122

20081123

20081201

20081204

20081003

20081017

20081027

20081028

20080814

20080823

20080904

20080911

20080807

20080808

20080812

20080813

20080726

20080728

20080731

2008080120080702

20080708

20080712

20080719

20080531 20080601

20080602

20080605

20080324

20080331

20080408

20080423

JAN2008032120080201

20080301

-41- 50863511.400-TOS/HSM 09-5341


JAN FEB

type 1 2 type 0 1 type 2 14 type 2 16 type 0 2 type 0 1 type 0 1 type 0 2 type 0 1 type 0 1

type 2 67 type 3 1 type 3 1 type 1 11 type 1 5 type 1 4 type 1 5

type 3 1 type 1 3 type 2 57 type 0 71 type 0 1 type 2 85 type 2 65 type 2 21

type 2 15 type 1 1 type 0 9 type 3 10 type 1 166 type 3 6 type 3 4 type 3 4type 3 5 type 2 2 type 1 1 type 4 2 type 2 775 type 0 1

type 3 1 type 3 1 type 3 163 type 0 1 type 0 1 type 0 3type 1 1 type 0 1 type 4 1 type 2 1 type 1 2type 2 5 type 0 1 type 2 4 type 0 1 type 2 79


type 2 30 type 1 24 type 1 101 type 4 1













type 3 10

type 4 3

type 0 1

type 0 1

type 0 5

type 1 8

type 2 49

type 3 8

type 4 1

type 0 3

type 1 15

type 2 324

type 3 15

type 0 3

type 1 5

type 2 185

type 3 5

type 0=isolated point, no lightning, e.g. communication intrusionstype 1=start cloud-cloud discharge type 0 2

type 2=next point in cloud-cloud discharge type 1 13

type 3=end cloud-cloud discharge type 2 183

type 4=ground stroke type 3 13

type 5=return stroke type 4 2

20091204

20091211

20091220

20091221

20091123

20091126

20091127

20091128

20091105

20091106

20091107

20091122

OKTMAA APR MEI JUN JUL AUG SEP20091203

NOV DEC20091102

20091103datum :

datum : 20091104

20090903

20090925

20090924

200910112009081920090717

20090721

20090820

20090514 20090616

20090618

20080410

20080415

20080427

20080323

20090829

20090831

20090516

20090517

20090525

20090526

20090724

20090730

20090828

-3- 50863511.400-tos/hsm 09-5341 - noordzeewind · one of the tasks in this program is to gain...

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