Electricity + Control October 2019

EARTHING + LIGHTNING PROTECTION

Separation distance(s) In terms of SANS 62305-3, a certain separation distance(s) must be maintained between a lightning protection system and a PV system. The separation distance is the minimum distance required to avoid uncontrolled flashovers to adjacent conductive elements as a result of a direct lightning strike to the lightning protection system. In a worst case, the uncontrolled flashover can cause a fire and the separation distance(s) should therefore be implemented wherever possible. The separation distances required between the PV panels together with their conductive elements and the structural LPS should be calculated in accordance with SANS 62305-3 and must be maintained. The use of HVI conductors is an acceptable method of ensuring separation distances in cases where physical separation is not possible. Core shadows on PV panels The distance between the PV panels and the external lightning protection system is essential to prevent excessive shading. Diffuse shadows cast by, for example, overhead lines, do not significantly affect the PV panels or their yield. Core shadows that cast a dark, clearly defined shadow will negatively affect the PV panels in such a way that they influence the current flowing through the panels. For this reason, lightning protection air termination masts should be installed as far as possible to thesouthsideof thePVpanels (southern hemisphere) and the distance of the north side air termination masts should be calculated and maintained so as not to affect the performance of the PV system negatively. For example, for a 10 mm diameter air termination mast, the minimum distance away from a PV panel should be 1.08 m so that only a diffuse shadow is cast onto the panel.

Whether the structure and PV system require a structural lightning protection system or not, the installation of a coordinated surge protection system for the PV installation is imperative. The type and placement of the coordinated surge protection system is dependent on whether or not the structure has an existing lightning protection system. According to Supplement 5 of IEC 62305-3, even if a building is not equipped with a structural lightning protection system, surge protection devices must be installed to rooftop PV systems. Cable routing of PV systems Cables must be routed in such a way that large conductor loops are avoided. This precaution must be observed when combining dc circuits to form a string and when interconnecting several strings. Care should also be taken with the routing of data and sensor lines, and the same precaution must be observed when connecting the inverters to the electrical grid. In order to prevent the creation of large conductor loops, all power cables (ac and dc) and data lines must be routed together with the equipotential bonding conductors along their entire route. PV modules are typically mounted on metallic mounting systems. The earthing or equipotential bonding of the metal frames into the lightning protection system, or the electrical earthing system (in the case of a structure without a LPS), will ensure the correct bonding and earthing of the PV modules. The way in which the equipotential bonding is implemented is dependent on whether or not the structure has an existing lightning protection system and whether or not the required separation distances can be maintained. Earthing and equipotential bonding of PV systems

Figure 1.1 Functional earthing of the PV mounting system.

Figure 1.2 Equipotential bonding of the PV mounting system.

Figure 2. Separation distances must be maintained between the LPS and the PV panels.

Electricity + Control

OCTOBER 2019

27