LIGHTNING AND OVERVOLTAGE

During the development of the NORDEX N43, 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 the IEC-10274-1/2 specifications.

Turbine network:
The 690 V turbine network is a TN-C network. The turbine controller and auxiliary are 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 switchboard in the tower bottom is protected by spark gap (coarse protection). The 690 V network in the nacelle and the 400 V network in the 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 cables for signals transmition coming from outside are connected to terminals with integrated overvoltage protection.

Foundation:
The turbine earthing system consists of one earthing ring arranged 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!

Tower:
The turbine tower is connected to the foundation earthing ring by means of 3 earthing wires which are welded to the tower base frame.

Nacelle:
The lower half of the nacelle and the main frame is made of steel. All the components in the nacelle such as main bearings, generator, gearbox, hydraulic station etc. are connected to the nacelle main frame for potential equalisation by means of well dimensioned earthing bands.
The nacelle is connected to the turbine tower and to the foundation by means of one 150 mm2 earthing wire. Additionally there is a connection between the nacelle and the yaw brake disc through earthing wires. A lightning stroke will therefore cause no harm to the azimuth gear.

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 carbon brushes.

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 cables for the power supply to the instruments and the cables for signal transmition to the controller are equipped with overvoltage conductors.

Generator:
The generator is equipped with an overvoltage protection located near to the generator terminals.

Switchboard in the tower bottom :
The turbine is connected to the grid by a circuit breaker. The power supply to the controller of the wind turbine is protected by a FI-protection-relay.
The switchboard frame is a closed metal box which is connected to the earth for potential equalization.