Wind turbine construction usually consists of three large metal constructions: the hub,
nacelle bed plate and tower. Some nacelle constructions have solid metal plate nacelle
cover, and others have a glass fibre cover mounted on a steel frame construction. These
large ‘natural’ metal components should be used as much as possible for shielding,
earthing and equipotential bonding purposes, thereby providing the best possible
backbone for an effective lightning protection system at close to no extra cost. This
is also in accordance with the lightning protection standard IEC 62305, which recommends
the use of natural metallic components for shielding, earthing and equipotential
bonding purposes, and with electrical codes corresponding to IEC 60364/
Cenelec HD 384, part 6, and Cenelec HD 637 S1, part 2, which allow the use of
large metal components as part of the earthing system and that require equipotential
bonding of large metallic components to an earthing system. Hence, the main earthing
connection of the wind turbine should be via the hub, nacelle construction and the
tower (i.e. these large metal constructions should be used both as Faraday cages
and as earthing connections through which the lightning current is conducted to
earth). All major metal objects should be equipotential bonded to this earthing connection
system (e.g. ladders, hoist cables, platforms, etc.) with equipotential bonding connections
or preferably via the means mounting the objects to the tower (clamps,
brackets, bolts etc.). Dedicated earthing terminals should be provided at each assembly
and at each major component of the generator circuit and high-voltage (HV) system.
Earthing terminals should be without paint, and should be designed to ensure direct
and permanent metal-to-metal contact to equipotential bonding and earthing connections
with sufficient contact area. For earthing of cable shields earthing terminals
should be positioned close to where the cables enter the wind turbine.