Lightning Risk Assessment (IEC 62305) 

By on

IEC 62305 'Protection against lightning' requires a risk assessment be carried out to determine the characteristics of any lightning protection system to be installed. There is a lot of hype about about this being a complicated process, however in reality it is very simple.

Risk Assessment

The procedure requires assigning a tolerable level of risk. A lightning protection level is then chosen to ensure that the calculated risk level is lower than the assigned tolerable level.  This is carried out for each of the following risk types:

  • Loss of Human Life
  • Loss of Public Services
  • Loss of Cultural Heritage
  • Economic Loss

Each country defines it's own tolerable risk values (for example the UK assigns the tolerable risk for loss of cultural heritage as 10-4).  General representative values listed in the standard are:

Type of Loss

Tolerable Risk

Loss of human life or permanent injuries

10-5

Loss of service to the public

10-3

Loss of cultural heritage

10-3

Economic loss

10-3

 

Note: surge protective devices (SPD) when installed, can lower the calculated risks obtained during any assessment exercise.

Lightning Protection Level (LPL)

Four protection levels (I, II, III and IV) are defined by considering the peak current, charge, specific energy, duration of various lightning strokes and the probability of these being exceeded.  Lighting Protection Level I is the most severe, with level IV being the least.

Once a lightning protection level has been selected, this fixes many of the parameters for the design and installation of the system.  For example, the size of the rolling sphere for calculating protection zones is 20 m for a protection level of I, and increases to 60 m for level IV.

Calculation

After reading the standard, calculating the risk level may seem like a complicated process. Help is at hand however. In purchasing the standard the 'IEC Risk Assessment Calculator' software is provided free of charge. This is a very straightforward piece of software to use requiring the structure dimensions to be entered and various parameters selected from drop down lists. The entire process can be completed in only a few minutes and assessment reports generated.

The attached images show the input screen for the software and an example of the assessment report generated. Click on the images to view a bigger picture. this being a complicated process, however in reality it is very simple.

Related Links

The standard can be purchased at:

IEC Risk Assessment Calculator

 

Lightning Assessment Report 1.2

 

Lightning Assessment Report 2.2

 



Steven McFadyen's avatar Steven McFadyen

Steven has over twenty five years experience working on some of the largest construction projects. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. About the author

myElectrical Engineering

comments powered by Disqus



Variable Frequency Drive

Variable frequency drives are widely used to control the speed of ac motors.  This note looks at the mechanisms which enable drive units to control the...

Battery Cars A to Z

Battery powered cars are a hot topic and widely debated. The pros, cons, issues and time frames can be talked about endlessly. An article by the Telegraph...

Lithium Ion Battery

Over recent years the Lithium Ion battery has become popular in applications requiring high power densities with small weight and footprint.  Today Lithium...

Introduction to Cathodic Protection

If two dissimilar metals are touching and an external conducting path exists, corrosion of one the metals can take place.  Moisture or other materials...

How to Write an Electrical Note

Electrical notes are a collaborative collection of electrical engineering information and educational material. Any registered user can add content. ...

Voltage Levels – Confused?

I was having a conversation the other day about voltage levels.  While everyone was in agreement that low voltage was 1000 V and less, there was more confusion...

Electrical Engineering

Electrical engineering is a field that covers a wide variety of sub-fields, including electricity and electronics. It is a field that goes back to the...

Control Theory

Control theory looks at how systems work and are controlled from a mathematical view.  This note gives a brief introduction to some of the concepts – more...

Thermoplastic and Thermosetting Insulation

While there are a vast array of cable insulation materials, these are often divided into two general types; Thermoplastic or Thermosetting. For example...

Generator Sizing & Operation Limits

When selecting a generator, there are inherent limits on the active and reactive power which can be delivered. Generators are normally sized for a certain...

Have some knowledge to share

If you have some expert knowledge or experience, why not consider sharing this with our community.  

By writing an electrical note, you will be educating our users and at the same time promoting your expertise within the engineering community.

To get started and understand our policy, you can read our How to Write an Electrical Note