Sparks Electrical News September 2018

EARTHING & LIGHTNING

22

INNOVATIVE LIGHTNING PROTECTION FOR THATCH STRUCTURES

By Trevor Manas, Lightning Protection Concepts

T he installation of properly designed light- ning protection for thatch structures is es- sential, as these types of structures have a high risk of fire, which often results in the com- plete destruction of the structure. Traditionally, thatch roofed structures have been protected from lightning by means of freestanding masts, which are often unsightly and expensive. The main reason for the use of this method of protection is to ensure the separation distance between the thatching and the lightning protection system is large enough to prevent flashovers which could ignite the thatching. Besides being aesthetically unpleasing, freestanding masts pose a significant step-and- touch hazard especially when they are installed in public areas. In accordance with SANS standards, a minimum level 3 lightning protection system must be designed for thatch structures. The separation distance, angle of protection and rolling sphere methods of protection must therefore be applied to the lightning protection system. Until recently, the only method of effectively protecting thatch structures was by means of freestanding masts, but with the technological advances in lightning protection there are alternative protection methods available. HVRI (High Voltage Resistant Insulating) conductors have recently been included in the IEC 62305 and IEC 62561 Lightning Protection Standards. This means that lightning protection practitioners are now able to use HVRI conductors to provide protection for thatch structures that is aesthetically more pleasing and more cost effective than the older conventional methods of protection. HVRI protection of thatch structures The use of HVRI conductors enables the installa- tion of an ‘Isolated Lightning Protection System’ with an equivalent separation distance to that of freestanding masts. HVRI masts are installed di- rectly onto the roof structure. This means that the mast heights are vastly reduced resulting in an architecturally appealing and more cost effective lightning protection system. Lightning protection risk assessments The lightning protection system shall be designed and installed to meet the minimum requirements of a lightning protection level 3 system (SANS 10313:2012). The selected lightning protection level shall be confirmed via the mandatory light- ning protection risk assessments in accordance

with SANS/IEC 62305 Part 2. Each lightning protection level has its own characteristics for all of the lightning protection components that form the complete lightning protection system, e.g. Air Termination System, Down Conductor System, Earth Termination System, Equipotential Bonding System and Separation Distances. The lightning protection design and installation shall meet the normative requirements for buildings with thatched roofs in SANS/IEC 62305 Part 3. Air termination system When designing the air termination system, the rolling sphere method and/or the protection an- gle method is used to determine the zones of pro- tection over the thatch structure. According to the standards, a rolling sphere radius of 45 m must be used for level 3 protection systems. In the sketch in Figure 1, the height of the air terminal is 2,30 m; this height ensures that the dormer roof is located within the protected zone. HVRI masts and conductors The top of the HVRI mast is equipped with a 1 m stainless steel finial and the supporting tube is made of GRP (glass-fibre reinforced plastic), which houses the insulated HVI conductor. The lower end of the supporting tube is made of stain- less steel to ensure stability. Unwanted sparking may occur at this point as a result of the induction effects on adjacent parts. To avoid this, no earthed parts or electrical equipment may be located at a distance of less than 1 m around the stainless steel section of the supporting tube. The HVRI mast is fixed to the wooden rafters of the thatched roof by means of a specially designed bracket and the HVI conductors are then simply run inside or underneath the thatching. This is easily achieved during the construction phase of the structure. HVRI conductors are specifically designed to pre- vent creeping discharge and safe dissipation of a lightning current and therefore are suitable for the protection of thatch structures. Separation Distances The separation distances must be calculated in accordance with SANS/IEC 62305 Part 3 using the following parameters to carry out the sepa- ration distance calculations: lightning protection level, insulation materials (air or bricks), number of down conductors and length from the top of the air terminal to the ground. Once the required

separation distances have been calculated, the appropriate HVRI conductor can be selected. There are various types of HVRI conductors with different equivalent ion distances; care should be taken to select the correct HVRI conductor equiv- alent to the calculated separation distance. Equipotential Bonding It is imperative that the semi-conductive sheath of the HVI conductor is equipotentially bonded; this can be performed at the building main earth bar. All other equipotential bonding (electrical earthing system, water pipes, etc.) can also take place at the main earth bar. 3D Design The use of 3D modelling is a powerful tool in pro- viding accurate lightning protection designs. The 3D design process is effective in particular in the design of air-termination systems while taking into consideration the aesthetics of the structure. Due to the increasing requirements regarding the building architecture, 3D planning is a good so- lution for visually representing lightning protec- tion measures. The 3D designs also give clients a good idea of how to integrate the lightning protec- tion measures into the building architecture. Overview This article highlights an alternative lightning pro- tection method for the protection of thatch struc- tures. The recommendations included are in ac- cordance with the latest revisions of the relevant standards. The use of HVRI conductors offers an aesthetically pleasing and cost effective alterna- tive to the traditional lightning protection meth- ods for the protection of thatch structures. This method of lightning protection (HVRI conductors) represents the latest and most up to date light- ning protection technology available in the world

Figure 1

today. The article describes only one of the many applications where HVRI conductors can be used when the required separation distances (isolated LPS) are difficult to achieve. HVRI conductors can, for example, be used in zoned and explosive envi- ronments if required.

Enquiries: +27 (0)83 377 2844

EARTHING AND BONDING COURSE T he final earthing and bonding course for the year will be presented at the ECA’s Meadowdale offices on 29 and 30 November. The two-day course has been specifically designed for registered electrical contractors who want to deliv- er a more comprehensive service to clients and for electricians who would like to improve their knowledge and understanding of earthing and bonding. Topics to be covered include the regulations and standards for earthing and bonding; testing techniques and calculations; earthing of lightning masts; protection of PV installations, and earthing in specialised environments. Earthing – or grounding as it is sometimes called in other countries – is crucial to safety. From an Electrical Engineering perspective, earth is considered a zero-potential point, and provides a common reference point to measure other potential differences in systems, namely voltage. Earthing and bonding also protect valuable equipment from surges and lightning strikes and, ultimately, reduce company downtime. Insurance claims due to damage fromstray surges and strikes will be minimised and could reduce insurance premiums.

Enquiries: +27 (0)11 271 0686

SPARKS ELECTRICAL NEWS

SEPTEMBER 2018