Placement Methodology (Software) - Lightning Protection International GUARDIAN PLUS Installation Manual

Placement Methodology (Software)

The placement of the G+ air terminal range on structures and within facilities is achieved
via the Standards-compliant "leader inception theory" published in IEEE Std. 998 and other
international codes. In brief, the steps required to obtain capture areas and volumes according
to this method involve the computation of:
(a) Geometric factor R (induced voltage component due to the physical geometry of the
problem being solved);
(b) Leader inception proximity factor (which quantifies the "suppressing influence" of the
structure on which a protective air termination is installed);
(c) Space potential proximity factor (ratio of space potential at the air terminal tip position to
that which would have existed in the absence of the structure); and
(d) Critical ambient electric field required to initiate and sustain the continuous upward leader.
LPI's in-house software (LITCALC) has been developed using a world-first three-stage approach
to identifying areas around the structure or facility where the strike probability exceeds a
minimum level and treating those areas appropriately. The computational stages implemented
are:
(a) Identification of likely strike points on a structure using the rolling sphere method per IEC
62305-3 for a range of stroke currents per lightning statistics as published in IEC 62305-1;
(b) Computation of the capture areas and volumes of those likely strike points on a structure
in accordance with the leader inception theory published in IEEE Std. 998; and
(c) Placement of air terminals on the structure at those locations and computations of the
capture areas and volumes of the air terminals in accordance with the leader inception
theory published in IEEE Std. 998.
(Refer to diagrams on Page 4.)
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