## Lightning Protection Calculators

This page is dedicated to spreadsheet type calculators that can be used to assist all surge protection stakeholders in their effort to improve the reliablity of power systems. These calclators are for your education on the subject. Arresterworks is not responsible for how the data is applied. Enjoy....... Jonathan Woodworth

## Distribution Arrester Value Calculator

The following calculator can be used to derermine the real worth of a distribution arrester installed on your system. The basic concept is that the value of the arrester is equal to the value of the equipment it saves from damage due to lightning over the life of the arrester.
The number of saves in a life time are calculated using internationally accepted formulea from IEEE Standard 1410 "Application Guide on Improving the Lightning Performance of Distribution Lines". Also, for details about this calculator see "ArresterFacts 038 "How to Calculate the Value of a Distribution Arrester" which outlines the rationale of this calculator and evaluation method.

Ground Flash Density Map of World (Click image to zoom)

More Detailed Ground Flash Density Map of US (click image to zoom)

Definition of Terms
1. Conductor Height: The height of the lines above the ground.

2. Distribution System Width: For a horizontal cross arm configuration, this is the width of system.

3. Ground Flash Density (GFD): This is a measure of the incidence of lightning in the area where the value is being calculated. It is measured in flashes/km2/year .

4. Installed Transformer Cost: This can be in any currency, as long as the final value is in the same currency. It is quite difficult to determine the installed value, so if that is not available, just use the purchase cost.

5. Length of Span: This is the distance between the distribution poles. It is used to calculate the collection area for the calculator.

6. Collection Area: This is the length of line that can be struck by lighting and the surge amplitude remains high enough to exceed the protected equipment BIL (generally less than 800km)

7. Evaluation Period: This is a nebulous value that is even difficult to get from manufacturers. 20 years is a life span that is generally agreed upon as an arrester life. It certainly can be longer or shorter.

8. Flash Collection Rate N: This value is calculated using equation 1 in this document. It is presented in IEEE 1410 and is accepted world wide as a reasonable prediction of the collection rate a lines for lightning studies.

9. Strike Rate per Span: This is simply the 100km/year collection rate (N) divided by the number of spans in the system.

10. Collection Area Strike Rate: This is the single span strike rate times the number of spans in the collection area.

11. Years between strikes to the Collection Area: This is the inverse of the Area Collection Rate.

12. Number of Saves over the Life of the Arrester: This is the life of the arrester divided by the years between strikes to the collection area. It is also assumed here that if there was no arrester installed, that each strike would result in transformer failure.

13. Value of a Distribution Arrester: This is equal to the replacement cost of the failed transformers over the life of the arrester assuming the arrester was not installed.