Richard Evert, National Director of the Earthing and Lightning Protection Association (ELPA) has provided Sparks Electrical News with a comprehensive series on lightning issue. The series will cover Risk Management; Lightning Protection Design; Lightning Protection System (LPS) Installations; Surge Protection Measures; Earthing and Resistance; and more. Be sure to catch all the articles over the next six months.
Lightning protection must address not only the behaviour of lightning but also the consequential over-voltages created by that lightning behaviour.
Lightning behaviour
The primary principle behind lightning protection design is to divert lightning away from the asset and property that is of interest to the vested property stakeholder.
- Therefore, the lightning protection designer will identify the following key factors to the design:
- Qualities of the lightning as the source of that risk.
- The use of the property, to qualify the extent of the potential losses.
- The desired or considered tolerance level that the vested property stakeholder can withstand.
The designer is responsible for:
- Consulting with all parties.
- Understanding the tolerances of installed electrical and electronic equipment.
- Understanding the electrical wiring within the structures, into and out of the structures.
- Understanding the civil works and construction of the structure including the steelwork reinforcing in columns, foundations and platforms.
- Appropriate earth electrode schemes in accordance with the prevailing soil resistivity conditions.
- Assigning the correct lightning protection level (LPL) risk in the best interests of the vested property stakeholder.
- Submitting suitable mitigation recommendations of LPS and SPM as applicable, to the vested property stakeholder for adoption.
Lightning current
The most dangerous point during a lightning discharge to ground, is the point of contact to ground. At this point, the full electrical charge being transferred from cloud to ground, will pass through this point into the earth.
The designer will utilise all data to determine the probability that lightning will terminate on the structure of interest. The higher the probability, the more likely the designer will recommend a Lightning Protection System (LPS).
The designer is responsible for ensuring that the bulk of lightning at or near the structure will terminate on the LPS and not on some portion of the structure.
The designer is responsible for ensuring that the path created by the LPS is adequately separated from all other conductive surfaces such that lightning current will be concentrated in and limited to the primary electrical path offered by the LPS.
The designer is responsible for ensuring that the lightning current will be entirely absorbed into the ground at the designated earth electrodes designed for this purpose. Useful information on the process for an LPS is carefully laid out in SANS 62305-3.
Subsequent over-voltageLightning current, whether concentrated through an LPS or in an uncontrolled discharge at one of many possible termination points, will cause a 'ground potential rise'.
- Any electrical current.
- Flowing through a path of resistance and/or impedance.
- Produces a voltage.
The designer is responsible for controlling the ground potential rise at the base of the LPS, if an LPS is installed or forms part of the designer's recommendations. Appropriate equipotential bonding and surge protection will form part of the LPS design. Where the designer deems that an LPS is not required, the existing structure will have adequate means by which lightning current will not pose a risk to the assets of the vested property stakeholder.
Indirect lightning events can produce a voltage rise at the structure of interest. The designer is therefore responsible for controlling all possible sources of voltage rise due to lightning both at the structure and in the vicinity of the structure.
It is for this reason that the designer takes responsibility for controlling over-voltages on all electrical and electronic wiring into and out of the structure. The designer will utilise all data to determine the probability that dangerous voltages may appear at the structure of interest.
The higher the probability, the more likely the designer will recommend appropriate Surge Protection Measures (SPM) over and above the surge protection included in the LPS design.
In the next issue, we will explore Lightning Protection System installations.
Enquiries: www.elpasa.org.za
Read the first article in the series: Risk management: https://www.crown.co.za/sparks-electrical-news/contractors-corner/24412-lightning-series-part-1-risk-management
