LIGHTNING AND OVERVOLTAGE
During the development of the NORDEX N54, the outmost attention in creating an efficient
and safe Lightning- and Overvoltage protection system was undertaken.
This has resulted in the most reliable protection of all components within the wind
turbine, from the blade tip to the turbine foundation.
The protection system is designed according to the most strict protection class under
IEC-10274-1/2.
Turbine network:
The 690 V turbine network is a TN-C network. The turbine controller and auxiliary is
supplied from a 690/400 V, 3 phase transformer. The 400 V network is a TNT-C-S network.
The most vital parts of the components are supplied from an aux-transformer in an IT
network.
Overvoltage Protection:
The 690 V network in the main switchboard is protected by spark gap (coarse protection).
The 690 V network in the nacelle switchboard and the 400 V network in the main switchboard
are protected by varistors (medium protection). All the electronic components for the
controller- and telecommunication modules, as well as for the power supply module for the
wind measuring instruments are protected by special varistors (fine protection). The
function of the varistors are supervised by the controller.
All signal wiring from outside are connected to terminals with integrated overvoltage
protection.
Blades:
The blades are from the manufacturer LM Glasfiber equipped with lightning receptors at the
blade tip. When a lightning strikes the blade tip, it will be led from the receptor to the
hub and the main rotor shaft via a steel wire inside the blade. From the rotor shaft the
lightning will be led to the mainframe of the nacelle by 2 brush commutators.
Anemometer/Windvane:
The anemometer and windvane is equipped with lightning receptor, which is connected to
earth. The signals from the instruments are transmitted via optic fibre cables and are
therefore galvanic isolated from the turbine controller. The power supply to the
instruments is equipped with an overvoltage protection located in the switchboard in the
nacelle.
Generator:
The generator is equipped with an overvoltage protection located near to the generator
terminals.
Switchboard in Nacelle:
All the electronic components in the switchboard are equipped with an overvoltage
protection. The controller housing is connected to earth for potential
equalisation. The data transmission to the main switchboard/controller in the bottom of
the tower, is transmitted via an optic fibre cable.
Nacelle:
A lightning receptor is mounted on the nacelle top and connected to the main frame by a
120 mm2 wire. All the component-structures in the nacelle such
as main bearings, generator, gearbox, hydraulic station etc. are connected to the nacelle
main frame for potential equalisation.
The nacelle main frame is by 2 x 120 mm2 earthing wires connected to the turbine tower and
all tower sections are interconnected by 240 mm2 earthing
wires. A lightning stroke will therefore cause no harm to the azimuth gear.
Tower:
The turbine tower is connected to the foundation earthing rings, by 4 earth wires which
are welded to the tower base frame.
Foundation:
The turbine earthing system consists of 4 earthing rings arranged in an equal distance
around the foundation and connected to the tower base frame. One earthing ring is placed
around the transformer and connected to the turbine earthing system and the turbine
foundation armouring. The earthing system is made according to DIN 18014.
The complete earthing system ensures that a lightning stroke is led into the ground,
without damaging any of the turbine components!
Main Switchboard:
The turbine is connected to the grid by a circuit breaker. The power supply to the turbine
controller, outputs and all devices connected to the UPS are protected by a
FI-protection-relay. The signal transmission, between the main switchboard controller and
the controller in the nacelle, are via optic fibres.
The switchboard frame is a closed metal box which is connected to the earth.
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