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  • Distribution of protected area into the lightning protection zones

    The standard IEC 13 12-1 and IEC 62 305 defines the lightning protection zones LPZ from the respect of the direct even indirect lightning effect. These zones are characteristic thanks to fundamental breaks of the electromagnetic conditions in their limited zones.

    LPZ 0A :
    Zone where items are subject to direct lightning strokes, and therefore may have to carry up to the full lightning current; the unattenuated electromagnetic field occurs here.
    LPZ 0B :
    Zone where items are not subject to direct lightning strokes, but the unattenuated electromagnetic field occurs.
    LPZ 1 :
    Zone where items are not subject to direct lightning strokes and where currents on all conductive parts within this zone are further reduced compared with zones 0B. In this zone the electromagnetic field may also be attenuated depending on the screening measures.

    LPZ

    The subsequent zones (LPZ 2 and so on):
    If a further reduction of conducted currents and/or electromagnetic field is required, subsequent zones shall be introduced. The requirement for those zones shall be selected according to the required environmental zones of the system to be protected. In general, the higher the number of the zones, the lower the electromagnetic environment parameters. At the boundary of the individual zones, bonding of all metal penetrations shall be provided and screening measures might by installed. Note: Bonding at the boundary between LPZ 0A, LPZ 0B and LPZ 1 is defined in IEC 13 12-1 and IEC 62 305. The electromagnetic fields inside a structure are influenced by opening windows, by currents on metal conductors ( e.g. bonding bars, cable shields and tubes), and by cable routing.

    The following figure shows an example for dividing a structure into several zones. There all electric power and signal lines enter the protected volume (LPZ 1) at one point, and are bonded to bonding bar 1 at the boundary of LPZ 0A, LPZ 0B and LPZ 1. In addition, the lines are bonded to the internal bonding bar 2 at the boundary of LPZ 1 and LPZ 2. Furthermore, the outer shield 1 of the structure is bonded to bonding bar 1 and the inner shield 2 to bonding bar 2. Where cables pass from one LPZ to another, the bonding must be executed at each boundary. LPZ 2 is constructed in such a way that partial lightning currents are not transferred into this volume and cannot pass through it.

    The above described segmentation of the protected object into protection zones gives possibilities of active protection of the LV power system thanks to insertion of the protective SPDs (usually at the zone boundary LPZ 0→1 and LPZ 1→2) and other protective SPDs at the zone boundary LPZ 2→3.

    Standardly it is recommended to insert so-called 1st stage protection – surge arrester class I tested by lightning current Iimp(10/350) at the zone boundary LPZ 0→1. It is recommended to insert 2nd stage protection – surge arrester class II tested by testing impulse Imax (8/20) at the boundary zone LPZ 1→2. At the boundary of LPZ 2→3 and subsequently along the consequential circuit there is also recommended to shoulder after every cca 10m by socalled 3rd stage protection class III also tested by testing impulse Imax (8/20) or UOC.

    For extra important protected equipment it is recommended to secure it by a quality continuous surge protection class III with high-frequency filter at the boundary of LPZ 2→3. If there are adjacent structures between which power and communication cables pass, the earthing system shall be interconnected, and it is beneficial to have many parallel paths to reduce current in the cables. A meshed earthing system fulfills this requirement. The lightning currents are further reduced, e.g. by enclosing all the cables in metal conduits or gridlike reinforced concrete ducts, which must be integrated into the meshed earthing system.

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