Mining conveyors are prone to being struck by lightning, owing to the vast area they cover and the varying heights of the conveyor structure, says earthing systems, lightning, surge and over voltage protection specialist Advanced Lightning Protection (ALP).
ALP MD Bertie van Zyl explains that a lightning bolt is “basically a large conductor with a massive electromagnetic field around it that can extend for up to 1km from the actual strike”, and that all electronic and electrical equipment will be exposed to the magnetic field during the strike, as well as to a second, collapsing magnetic field once the strike is over.
He adds that, if lightning were to strike within 100 m of equipment, for example, the induced voltages could be up to 2 000 V/m, which is why equipment could suffer damage during a lightning storm, even though it might not have been struck directly.
The installation of a lightning protection system should be preceded by a risk analysis, conducted in accordance with South African National Standards (SANS) specifications.
“This will determine whether lightning protection is required and what level of lightning protection must be used in the design to limit the risk of damage accordingly.”
Should the risk analysis support the installation of a lightning protection system, which includes soil resistivity surveys, the protection level can then be calculated.
The design of earthing and lightning protection systems must be performed in accordance with SANS 62305, 10313 and 10199 specifications.
The design of a conveyor’s lightning protection generally comprises a structural lightning protection system, an earthing system, an electrical earthing system, a surge protection system and the equipotential bonding of all protection systems.
“The electrical earthing system must be designed to allow for the safety devices to operate correctly and for the dissipation of any fault currents that might occur. Its purpose is to save equipment from damage and to protect personnel from injury,” Van Zyl stresses.
For additional protection of electronic equipment, it is essential that the power supply, telecommunications and data lines are equipped with adequate surge protection devices. Further, it is vital that the entire electronics system is at the same potential to ensure that the lightning protection is effective.
SANS 62305 states that it is necessary for lightning protection system installations to be inspected and tested regularly, to ensure any damage is repaired.
Therefore, strict quality-control measures need to be adhered to when installing such systems and all the material used needs to comply with SANS standards.