Reliability of supply can be classified in terms of AS/NZS 3000 definitions. This Wiring Rules standard states compliance to reliability of supply requires the installation to be designed by dividing the installation into appropriate circuits and selecting protective devices with appropriate discrimination.
Reliability can be so much more. Various standards refer to continuity of supply and continuity of service which could be seen as reliability. The term continuity of supply means there is a continuous availability of supply to essential parts of the installation even though a fault may interrupt one element. Continuity of service differs from this as there may be a momentary interruption of the supply caused by a fault condition, however the supply automatically returns after the fault condition passes.
Lightning and surge protection can assist with ensuring continuity of supply and service for the installation it is protecting. The significant impact of a lightning induced impulse current or a lower-level surge current from grid switching, motor starting or load variations, has the potential to damage electrical infrastructure and/or cause protective devices to operate and disconnect otherwise healthy circuits.
To provide system reliability, including continuity of supply and service, appropriate measures need to be considered for protection against lightning and surges.
The Australian Lightning Protection Standard AS 1768:2021 details a risk assessment process that can be applied to structures. The assessment calculations in this standard are based on the risk assessment process of the International Lightning Protection standard IEC 62395-2. The assessment is designed to compare a calculated risk of a structure against a tolerable risk based on statistical data. The aim is to recommend some minimum protective measures that can be undertaken to reduce the risk to a tolerable level.
The standard provides examples of tolerable risk as:
| Loss of human life |
1 in 100,000 |
| Loss of service to the public |
1 in 1,000 |
| Loss of cultural heritage |
1 in 10,000 |
| Loss of economic value |
1 in 1,000 |
The risk assessment process calculates risk factors based on the construction, usage and exposure to lightning strikes. Once the initial data is entered into the risk assessment, mitigation measures can be applied to reduce the risk below the tolerable limits.
An important comment is made in AS 1768:2021 clause 2.2 relating to the spreadsheet that is included with the standard:
“The decision to provide lightning protection requires judgement on the part of the user. The spreadsheet provides guidance to support this process. Factors such as the risk to people or the value of the site and its operation may determine that there needs to be minimal avoidable risk. Therefore, protection measures may be justified regardless of the outcome of any risk assessment”.
The risk assessment is designed to cover various threats:
a) Death or injury from step and touch voltages
b) Death from fire, explosion, mechanical and chemical effects caused by lightning strikes
c) Mechanical damage to structures and contents
d) Damage and failure of equipment
e) Fire damage from a lightning strike
Safety of people is a major concern for lightning protection. Ensuring the electrical infrastructure is well protected against the devasting effects of lightning is also important to ensure reliability of the supply network.
After considering lightning risk, the installation of surge protection devices to the electrical infrastructure also contributes to the reliability of the supply. Surge protection can be sized according to the possible risk of lightning impulse damage, as well as non-lightning related low value surges and transients that commonly exist in all networks. These lower-level surges can cause damage over time as they can gradually degrade the insulation barriers protecting electrical and electronic equipment, which can ultimately result is failure and loss of reliability.
Lightning and surge protection solutions are readily available, simple to implement, and cost-effective relative to the value of the equipment they safeguard. The insurance offered by the installation of appropriate lightning and surge protection measures can ensure reliability of supply and provide security against the loss of valuable infrastructure.
IPD offers a comprehensive range of solutions from leading manufacturers Dehn and Novaris, coupled with expert application assistance to ensure optimal site protection and reliability.
For more information, contact IPD at 1300 556 601 or visit our website. |