IEC 61400-24:2019+A1:2024 "Wind turbine generator systems - Part 24: Lightning protection" is a specialized standard by the International Electrotechnical Commission (IEC) regarding lightning protection for wind turbine generators, replacing the first edition from 2010. This revision involves major structural adjustments, concentrating normative requirements in the main text while moving extensive background information, calculation methods, and case studies to the annexes, making the standard clearer and easier to use. The standard clarifies lightning environment parameters and risk assessment methods, and proposes comprehensive protection requirements for blades, nacelles, towers, and electrical systems. Compared with the general lightning protection standards in the IEC 62305 series, this standard fully considers the tall structures, rotating components, and special operating environments of wind turbine generators, specifically introducing higher protection levels (LPL I) for large-scale offshore wind turbine generators.
Regarding technical evolution, the new standard adds guidance on lightning protection for carbon fiber reinforced polymer (CFRP) blades, introduces special considerations for winter lightning, and provides verification methods based on numerical simulations in the annexes. The 2024 revision further updates the lightning detection and monitoring system (Annex L), emphasizing the importance of intelligent monitoring in operation and maintenance.
The standard defines four lightning protection levels (LPL I～IV), corresponding to different maximum lightning current parameters. LPL I represents the most severe conditions and applies to wind farms with extremely high reliability requirements. The specific parameters are shown in the table below (based on IEC 62305-1):
| LPL Level | Peak Current I (kA) | Total Charge Q (C) | Specific Energy W/R (kJ/Ω) |
|---|---|---|---|
| I | 200 | 300 | 10 000 |
| II | 150 | 225 | 5 625 |
| III | 100 | 150 | 2 500 |
| IV | 50 | 100 | 625 |
Furthermore, the standard introduces the rolling sphere radius (R) corresponding to the LPL to determine the protection range of air termination systems: LPL I corresponds to 20 m, LPL II to 30 m, LPL III to 45 m, and LPL IV to 60 m. Wind turbine generator design must select the appropriate LPL based on the expected lightning exposure level.
Blades are the components of wind turbine generators most susceptible to lightning strikes, accounting for the majority of lightning-related failures. The standard requires blades to be equipped with an air termination system and internal down conductors, with reliable connections at the blade root to the hub. For large blades, air termination systems are typically arranged at the blade tip and trailing edge, using metal conductors or segmented current-carrying strips. For carbon fiber reinforced polymer (CFRP) blades, since carbon fiber has certain conductivity, special attention must be paid to the potential damage caused by current flowing through the structural layers. The standard recommends using the CFRP layer as part of the natural down conductor but requires verification of its current-carrying capacity and avoidance of local overheating.
Typical case: An offshore wind power project adopted LPL I protection, with a blade length of 70 m, three air termination devices installed at the blade tip, and copper braided straps used as internal down conductors connected to the hub's conductive slip rings. After years of operation, this design successfully withstood dozens of direct lightning strikes, effectively protecting the blade structure.
The grounding system is the foundation of lightning protection. The standard requires that the grounding resistance of wind turbine generators meet design requirements, with a typical target value of less than 10 Ω. For metal towers, they can be utilized as natural down conductors, provided electrical continuity is ensured between sections. For concrete towers or offshore foundations, artificial grounding electrodes (such as ring grounding bodies, vertical grounding rods, etc.) must be installed. The standard also emphasizes the importance of equipotential bonding: all metal pipes entering the nacelle, cable shielding layers, and equipment enclosures must be connected to the grounding system via equipotential bonding strips to prevent flashovers caused by potential differences.
At the wind farm level, it is recommended to interconnect the grounding systems of each unit via a grounding grid to form an overall equipotential plane, thereby reducing ground potential rise.
Based on the lightning protection zone (LPZ) concept, the standard requires the installation of surge protective devices (SPD) at the boundaries of different zones. For example, an I-class SPD should be installed at the power supply inlet in the nacelle (boundary between LPZ 0A and LPZ 1), and an II-class SPD should be installed in the control cabinet (boundary between LPZ 1 and LPZ 2). The discharge current capacity of the SPD must be calculated based on the expected lightning current distribution. For signal line SPDs, models matching the system operating voltage and transmission rate must be selected to avoid signal attenuation.
The standard also provides detailed guidance on SPD installation, including keeping connection wire lengths as short as possible (≤0.5 m) to avoid excessive induced voltage. It is recommended to adopt a "V"-shaped connection method, connecting the SPD grounding wire directly to the equipotential strip.
Chapter 7 and Annex B of the standard provide a complete lightning risk assessment process. The core involves calculating the expected annual number of lightning strikes (N) and comparing it with the acceptable risk level. For a single unit, its equivalent collection area (A_d) is calculated based on the unit height and rolling sphere radius. The assessment must consider risk components for four scenarios: lightning strike to the unit (S1), lightning strike nearby (S2), lightning strike to connecting lines (S3, S4). Parameters such as the probability factor P_B (probability of physical damage) can be obtained from standard tables. When the risk exceeds allowable values, the protection level must be increased or additional protective measures added.
Implementation recommendations: During the design phase, it is recommended to use local lightning location system (LLS) data, combined with unit height and terrain factors, to correct the number of lightning strikes. For areas prone to upward lightning, such as mountainous regions or coastlines, the probability of upward lightning should be additionally considered.
Annex D (normative) of the standard provides testing methods for blade air termination systems, including initial leader attachment tests, subsequent return stroke attachment tests, and high-current physical damage tests. The test current parameters correspond to LPL I (peak 200 kA, charge 300 C). Additionally, Annex P proposes testing requirements for lightning current paths in rotating components (such as bearings), requiring verification that they do not sustain damage under simulated lightning currents.
In conclusion, IEC 61400-24:2019+A1:2024 provides a systematic and international technical framework for lightning protection of wind turbine generators. Adhering to this standard can significantly enhance unit safety and reliability while reducing lightning strike losses.
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Update:
Mon, 13 Jul 2026 17:33:16 +0000