Page 348 - 35_DS702_E_2014_Lightning_Protection_Guide

¨ Cable routing and cable shielding to determine the immunity level. The specific immunity level of
¨ Installation of coordinated surge protective devices components in an LPZ directly defines the voltage protection
level required at the LPZ boundaries. The immunity of a system
Protection of the lines at the transition from LPZ 0 A must be proven, where applicable, with all SPDs installed and
to LPZ 1 and higher the equipment they are supposed to protect.
To ensure safe operation of electrical and electronic devices,
the boundaries of the lightning protection zones (LPZs) must Protection of power supply systems
be shielded against field-based interference and must be The transformer of a wind turbine may be housed at different
protected against conducted interference (Figures 9.16.4 locations (in a separate distribution station, in the tower base,
and 9.16.5). To this end, surge protective devices that are in the tower, in the nacelle). In case of large wind turbines,
capable of discharging high partial lightning currents without for example, the unshielded 20 kV cable in the tower base is
destruction must be installed at the transition from LPZ 0 A to routed to the medium-voltage switchgear installation consist-
LPZ 1 (also referred to as lightning equipotential bonding). ing of a vacuum circuit breaker, mechanically locked selector
These surge protective devices are referred to as type 1 light- switch disconnector, outgoing earthing switch and protective
ning current arresters and are tested by means of impulse cur- relay. The medium-voltage cables are routed from the medium-
rents of 10/350 μs waveform. At the transition from LPZ 0 B voltage switchgear installation in the tower of the wind tur-
to LPZ 1 and higher only low-energy impulse currents caused bine to the transformer which may be situated in the tower
by voltages induced on the system or surges generated in the base or in the nacelle (Figure 9.16.4). The transformer feeds
system must be coped with. These surge protective devices are the control cabinet in the tower base, the switchgear cabinet in
referred to as type 2 surge arresters and are tested by means the nacelle and the pitch system in the hub by means of a TN-C
of impulse currents of 8/20 μs waveform. system (L1, L2, L3, PEN conductor). The switchgear cabinet in
According to the lightning protection zone concept, all incom- the nacelle supplies the electrical equipment in the nacelle
ing cables and lines must be integrated in the lightning equipo- with an a.c. voltage of 230/400 V.
tential bonding system by means of type 1 lightning current ar- According to IEC 60364-4-44, all pieces of electrical equip-
resters at the boundary from LPZ 0 A to LPZ 1 or from LPZ 0 A to ment installed in a wind turbine must have a specific rated
LPZ 2. This affects both power supply and communication lines. impulse withstand voltage according to the nominal voltage
An additional local equipotential bonding system where all ca- of the wind turbine (see IEC 60664-1 (EN 60664-1): Table 1,
bles and lines entering this boundary are integrated must be insulation coordination). This means that the surge arresters
established for every further zone boundary within the volume to be installed must have at least the specified voltage pro-
to be protected. Type 2 surge arresters must be installed at tection level according to the nominal voltage of the wind
the transition from LPZ 0 B to LPZ 1 and from LPZ 1 to LPZ 2, turbine. Surge arresters used to protect the 400/690 V supply
whereas type 3 surge arresters must be provided at the transi- must have a minimum voltage protection level U p ≤ 2.5 kV,
tion from LPZ 2 to LPZ 3. The function of type 2 and type 3 whereas surge arresters used to protect the 230/400 V supply
surge arresters is to further reduce the residual interference of must have a voltage protection level U p ≤ 1.5 kV to ensure pro-
the upstream protection stages and to limit the surges induced tection of sensitive electrical / electronic equipment (Figures
on the wind turbine or generated in the wind turbine. 9.16.6 and 9.16.7).
Surge protective devices shall be capable of discharging light-
Selection of SPDs based on the voltage protection ning currents of 10/350 μs waveform without destruction and
level (U p ) and the immunity of the equipment shall have a voltage protection level of U p ≤ 2.5 kV (Figure
To describe the required voltage protection level U p in an LPZ, 9.16.8).
the immunity levels of the equipment located in an LPZ must
be defined, e.g. for power lines and connections of equipment Protection of the transformer infeed
according to lEC 61000-4-5 (EN 61000-4-5) and lEC 60664-1 The medium-voltage transformer infeed is protected by
(EN 60664-1), for telecommunication lines and connections DEHNmid medium-voltage arresters which must be adapted
of equipment according to lEC 61000-4-5 (EN 61000-4-5), to the system configuration and voltage of the medium-volt-
ITU-T K.20 and ITU-T K.21 and for other lines and connections age system (Figure 9.16.9).
of equipment according to the manufacturer’s instructions.
Manufacturers of electrical and electronic components or de- 230/400 V supply
vices should be able to provide the required information on the Type 2 surge arresters, for example DEHNguard M TNC 275 CI FM,
immunity level according to the EMC standards. If this is not should be used to protect the voltage supply of the control
the case, the wind turbine manufacturer should perform tests cabinet in the tower base, the switchgear cabinet in the na-

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