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Due to their exposed location and height, wind turbines are and depend on the manufacturer and type. The IEC 61400-24
vulnerable to the effects of direct lightning strikes. Several (EN 61400-24) standard provides important information in this
studies have shown that at least 10 direct lightning strikes to respect.
wind turbines in the multimegawatt range have to be expected
every year. The feed-in compensation must amortise the high Lightning protection zone concept
investment costs within a few years, meaning that downtime The lightning protection zone concept is a structuring measure
caused by lightning and surge damage and the resulting repair for creating a defined EMC environment in an object. This de-
costs must be avoided. For this reason, comprehensive light- fined EMC environment depends on the immunity of the elec-
ning and surge protection measures are required. When plan- trical equipment used. The lightning protection zone concept
ning lightning protection measures, not only cloud-to-earth allows to reduce conducted and field-bound interference at
flashes, but also earth-to-cloud flashes, so-called upward lead- the boundaries to defined values. For this reason, the object to
ers, must be considered for objects at exposed locations with be protected is subdivided into protection zones.
a height of more than 60 m. The high electric charge of these The rolling sphere method is used to determine LPZ 0 A , namely
upward leaders must be particularly observed for the protec- the parts of a wind turbine which may be subjected to direct
tion of the rotor blades and for the design of the lightning lightning strikes, and LPZ 0 B , namely the parts of a wind tur-
current arresters. bine which are protected from direct lightning strikes by ex-
ternal air-termination systems or air-termination systems in-
Standardisation tegrated in parts of a wind turbine (for example in the rotor
The IEC 61400-24 (EN 61400-24) standard, the IEC 62305 blade). According to the IEC 61400-24 (EN 61400-24) stand-
(EN 62305) standard series and the guidelines by Germanischer ard, the rolling sphere method must not be used for the rotor
Lloyd (e.g. GL 2010 IV – Part 1: Guideline for the certification blade itself. For this reason, the design of the air-termination
of wind turbines) form the basis for the protection concept. system should be tested according to subsection 8.2.3 of the
IEC 61400-24 (EN 61400-24) standard. Figure 9.16.1 shows
Protection measures a typical application of the rolling sphere method, Figure
The IEC 61400-24 (EN 61400-24) standard and GL 2010 guid- 9.16.4 the possible division of a wind turbine into different
line recommend to protect all sub-components of the lightning lightning protection zones. In this context, the division of a
protection system of a wind turbine according to lightning pro- wind turbine into lightning protection zones depends on the
tection level (LPL) I unless a risk analysis demonstrates that a design of the wind turbine. Therefore, the structure of the wind
lower LPL is sufficient. A risk analysis may also reveal that dif- turbine should be observed. However, it is decisive that the
ferent sub-components have different LPLs. The IEC 61400-24 lightning parameters which are injected into LPZ 0 A from the
(EN 61400-24) standard recommends a comprehensive light- outside are reduced by suitable shielding measures and surge
ning protection concept. protective devices at all zone boundaries so that the electrical
Lightning protection (LP) for a wind turbine consists of an exter- and electronic devices and systems inside a wind turbine are
nal lightning protection system (LPS) and surge protection meas- not interfered with.
ures (SPMs) for protecting electrical and electronic equipment.
In order to plan protection measures, it is advisable to subdivide Shielding measures
the wind turbine into lightning protection zones (LPZs). The nacelle should be designed as a closed metal shield. Thus,
The lightning protection system of a wind turbine protects a volume with an electromagnetic field that is considerably
two sub-systems which can only be found in wind turbines, lower than the field outside the wind turbine is generated in
namely the rotor blades and the mechanical drive train. The the nacelle. In accordance with IEC 61400-24 (EN 61400-24), a
IEC 61400-24 (EN 61400-24) standard describes in detail how tubular steel tower, which is frequently used for large wind tur-
to protect these special parts of a wind turbine and how to bines, can be regarded as an almost perfect Faraday cage for
prove the effectiveness of the lightning protection measures. electromagnetic shielding. In case of concrete hybrid towers,
The standard recommends to verify the lightning current with- the function of the galvanic cage must be ensured by reinforc-
stand capability of these systems in high-current tests with ing steel as well as earthing and electrical connection of the
the first stroke and the long stroke, if possible, in a common individual components. The switchgear and control cabinets in
discharge. the nacelle and, if any, in the operations building should also
In the following, it will be described how to implement be made of metal. The connecting cables should feature an
lightning and surge protection measures for electrical and external shield that is capable of carrying lightning currents.
electronic devices / systems of a wind turbine. The complex Shielded cables are only resistant to EMC interference if the
problems concerning the protection of the rotor blades and shields are connected to the equipotential bonding system on
rotably mounted parts / bearings must be examined in detail both ends. The shields must be contacted by means of fully

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