IEC TR 61400-24:2002

TECHNICAL IEC
REPORT
TR 61400-24
First edition
2002-07
Wind turbine generator systems –
Part 24:
Lightning protection
Reference number
IEC/TR 61400-24:2002(E)
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TECHNICAL IEC
REPORT
TR 61400-24
First edition
2002-07
Wind turbine generator systems –
Part 24:
Lightning protection
 IEC 2002  Copyright - all rights reserved
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– 2 – TR 61400-24  IEC:2002(E)

CONTENTS
FOREWORD . 5

INTRODUCTION .7

1 Scope . 8

2 Definitions . 8

3 Lightning and wind turbines .12

3.1 The properties of lightning .12
3.2 Lightning discharge formation and electrical parameters.12
3.3 Cloud-to-ground flashes.13
3.4 Upward initiated flashes.17
3.5 Lightning protection of wind turbines – the generic problem .19
3.6 Existing IEC standards and technical reports dealing with lightning protection .20
4 Damage statistics .21
4.1 Data on wind turbine lightning damage .21
4.2 Damage statistics .21
4.3 Database merits and weaknesses.27
4.4 Conclusions and recommendations.28
5 Evaluation of the risk of lightning damage to a wind turbine .29
5.1 Introduction .29
5.2 Assessing the lightning flash frequency to a wind turbine.29
5.3 Use of IEC 61024-1-1 .30
5.4 Use of IEC 61662 .32
5.5 Analysis of blade lightning protection system costs.34
5.6 Analysis of lightning protection costs for wind turbine control systems .35
6 Lightning protection of wind turbine blades .36
6.1 Blade structure .36
6.2 Blade damage mechanism .38
6.3 Lightning protection for wind turbine blades .38
6.4 Interception efficiency.40
6.5 Sizing of materials .41
6.6 Blade to hub connection .43

6.7 Carbon reinforced plastic (CRP) .43
6.8 Wiring inside blades .43
7 Protection of bearings and gearbox.44
7.1 Damage to bearings due to AC and DC currents.44
7.2 Damage to bearings due to lightning currents .44
7.3 Laboratory investigations.44
7.4 Lightning damage to gearbox.45
7.5 Lightning protection of bearings and gearbox elements.45
8 Protection of electrical and control system .46
8.1 Introduction .46
8.2 Configuration of electrical equipment.46
8.3 Lightning protection zones .50
8.4 Surge coupling mechanisms .52
8.5 Bonding and shielding .53

TR 61400-24  IEC:2002(E) – 3 –

8.6 Surge protection .56

8.7 Summary .58

9 Earthing.58

9.1 Lightning protection system earth termination for a single wind turbine.58

9.2 Lightning protection system earth terminations in a wind farm .60

10 Personnel safety.61

10.1 General .61

11 Conclusions and recommendations for further work .62

Annex A Typical lightning damage questionnaire.64
Bibliography.66
Figure 1 – Processes involved in the formation of a cloud-to-ground flash [4].14
Figure 2 – Typical profile of a negative cloud-to-ground flash (not to scale) .15
Figure 3 – Typical profiles of negative cloud-to-ground flashes (not to scale) .16
Figure 4 – Typical profile of a positive cloud-to-ground flash .17
Figure 5 – Typical profile of a negative upward-initiated flash.17
Figure 6 – Different profiles of negative upward initiated flashes (not to scale).18
Figure 7 – Faults by component (Germany).23
Figure 8 – Faults by component (Denmark).23
Figure 9 – Faults by component (Germany).24
Figure 10 – Faults by component (Denmark) .24
Figure 11 – Repair costs by component and size (Germany) .25
Figure 12 – Average down time by component and size (Germany).25
Figure 13 – Annual variation in lightning activity and damage (Denmark) .26
Figure 14 – Faults caused by lightning (Denmark 1990-1998) .26
Figure 15 – Lightning damage events (Germany 1991-1998).27
Figure 16 – Equivalent collection area of the wind turbine .30
Figure 17 – Types of wind turbine blades .37
Figure 18 – Lightning protection for large modern wind turbine blades .39

Figure 19 – Alternative current path to reduce lightning current.46
Figure 20 – Principle configuration of electrical equipment in a grid-connected wind
turbine .47
Figure 21 – Principle control system configuration.49
Figure 22 – Rolling sphere model.50
Figure 23 – Example of the division of the interior of a wind turbine into protection zones.51
Figure 24 – Differential and common mode coupling .53
Figure 25 – Two control cabinets located on different metallic planes inside a nacelle .54
Figure 26 – Magnetic coupling mechanism .55
Figure 27 – Example design of a combination type SPD.57
Figure 28 – Typical wind turbine earthing arrangement .59

– 4 – TR 61400-24  IEC:2002(E)

Table 1 – Cloud-to-ground lightning current parameters .15

Table 2 – Upward initiated lightning current parameters .18

Table 3 – Standards and technical reports issued by IEC (Mid 2001) .20

Table 4 – IEC TC 81 work in progress (Mid 2001) .21

Table 5 – Lightning damage frequency.22

Table 6 – Regional effect on lightning damage (Germany) .22

Table 7 – Lightning fault summary (Sweden).23

Table 8 – Energy and availability loss compared to other faults.26
Table 9 – Lightning protection system levels .31
Table 10 – Maximum values of lightning parameters corresponding to protection levels .32
Table 11 – Minimum dimensions of lightning protection system materials.41
Table 12 – Proposed minimum dimensions for lightning protection system materials.41
Table 13 – Physical characteristics of typical materials used in lightning protection
systems .42
Table 14 – Temperature rise [K] for different conductors as a function of W/R .42
Table 15 – Lightning protection zones .50
Table 16 – Examples of component requirements in given zones .52
Table 17 – Effect of various protection measures on screen transient voltages .56
Table 18 – Suitability of electrode types .60
...