Description

The key factors and parameters taken into account in the calculations include:

A. Protection level according to the “risk profile” of the structure (decided mainly by its height) or chosen by the customer (see table below).

B. Downward leader charge distribution model and dynamic electric field of the downward leader as it approaches the structure.

C. Striking distance computations using a leader propagation model that takes structure height into account and utilizes capture volumes.

D. Electric field enhancement of the ambient electric field by the structure and its geometric features.

E. Allowance for lightning approaching at an angle.

F. Computation of striking distance surfaces for the structure and air terminals.

G. The speed of the downward and upward leaders (the so-called “race condition”).

H. Selection of the correct CAT terminal for the particular installation, e.g., CAT II is used at a greater height above the structure and/or on taller structures due to its larger geometry and greater ability to minimize pre-corona.

I. Additional allowance for the corona-minimizing characteristics of the air terminal.

J. Determination of protection coverage, i.e., whether coverage is achieved based on the relative distances between the surfaces and
typical leader velocities. Based on lightning statistics from AS 1768 and IEC 62305, the following “protection levels” and their associated
physical parameters are used for each of the CAT terminals in protection calculations.