How do I calculate the life expectancy of a transient surge arrester?

The estimated life expectancy of transient surge arresters is determined by the formula:

Life expectancy = I_max/ (A_m × N_g)

Where:

A_m = area of lightning incidence on buildings

N_g = lightning density per km² per year

Let us take, for example, an isolated building in Cáceres for which we assume an area of lightning incidence on buildings (A_m) equal to 1 (see table below), and a lightning density per km² per year (N_g), obtained from the map below, equal to 1.5.

Incidence of lightning strikes on A_m

Close to other buildings or trees in the same height or higher	0,5
Surrounded by lower buildings	0,75
Isolated	1
Isolated on a hill or promontory	2

Source: Technical Building Code (CTE) – SU8 (Safety against lightning)

cuanto dura un protector de sobretensiones mapa2

Illustration: Map of impact density on terrain N
Source: Technical Building Code (CTE) SU8 (Lightning Safety)

Practical example of transient surge arrester lifetime calculation

If the Vigivolt V2T-15 equipment is installed, with an Imax of 15kA and adding the above data, we use all the variables to perform the following calculation.

Life expectancy =I_max / (A_m × N_g) = 15/(1 × 1.5) = 10 years

In other words, an Imax 15kA surge protector installed in a building of these characteristics in this area will be capable of receiving impacts for approximately 10 years.

Obviously this is an approximate calculation, since the density of lightning per km² per year is not fixed, but varies according to the year. We make the calculation with the map provided in the Technical Building Code (CTE) SU8.

If you need another type of transient surge protector, you can consult more equipment in OUR TRANSITORY SURGE PROTECTORS CATALOGUE.