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



Understanding LV Circuit Breaker Fault Ratings

I think this post is going to be helpful to several of our readers. While the IEC low voltage circuit breaker Standard [IEC 60947-2, Low voltage switchgear...

Calculating Cable Fault Ratings

When selecting a cable, the performance of the cable under fault conditions is an important consideration. It is important that calculations be carried...

Michael Faraday (the father of electrical engineering)

Famed English chemist and physicist Michael Faraday was born on September 22, 1791, in Newington Butts, a suburb of Surrey just south of the London Bridge...

Understanding Circuit Breaker Markings

IEC 60947 is the circuit breaker standard and covers the marking of breakers in detail. Any manufacturer following this standard should comply with the...

Are We Losing Professional Integrity

I have been thinking recently that there appears to be less professional integrity around than when I first started my career in electrical engineering...

How a Digital Substation Works

Traditionally substations have used circuit breakers, current transformers (CT), voltage transformers (VT) and protection relays all wired together using...

Photovoltaic (PV) Panel - Performance Modelling

In an earlier note on the site [Photovoltaic (PV) - Electrical Calculations], the theory of solar (PV) cell calculations was introduced.  In particular...

Useful Motor Technical Information

Sometimes it’s useful to be able to quickly lookup a piece of technical information.  This note is a collection of information related to motors, and in...

Robotics - Home Innovations

We have a sister note to this (Robots - Interesting Video), in which I have posted some videos of interesting robots developed by commercial corporations...

Difference Between Live and Dead Tank Circuit Breakers

A quick post in connection with an email question: Live Tank - the circuit breaker the switching unit is located in an insulator bushing which is live...

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