Electricity + Control January 2017

EARTHING + LIGHTNING PROTECTION

Lightning Protection for Rooftop PV Plants

Trevor Manas, Pontins

Based upon the fact that self-generated electricity is cheaper and provides a high degree of independence from the electrical grid, PV systems are fast becoming an integral part of many electrical installations. Many of these systems are located and installed in exposed places such as roof tops, these PV systems will therefore be subjected to all weather conditions (including lightning) for decades. T he cables of PV systems frequently enter the building and extend over long distances until they reach the electrical con- nection point. Lightning discharges cause field-based and conducted electrical interference and this effect increases in relation to cable lengths or conductor loops. Surges do not only cause damage to PV systems but can also cause damage to the other internal devices inside the building. Most importantly, production facilities can easily be damaged causing production to come to a halt. Need for rooftop lightning protection The energy released by a lightning discharge is one of the most frequent causes of fire, therefore the protection of personal and the prevention of fire is of paramount importance in the case of a direct lightning strike to the building. At the design stage of a PV system, the building should be as- sessed to determine whether or not a lightning protection system is installed to the building or for new structures whether lightning protection is required. The necessity of lightning protection for the

installation of PV systems must be distinguished between an instal- lation on a building without lightning protection and buildings or structures that are or have to be equipped with a permanently effec- tive lightning protection system. The installation of PVmodules on buildings does not increase the risk of a lightning strike. The necessity for lightning protection cannot be derived directly from the mere existence of a PV system. There may however be an increased danger for the electric facilities of the building in the event of a lightning strike. This is based on the fact that, due to the wiring of the PV lines inside the building in existing risers and cable runs, strong conducted and radiated interferences may result from lightning currents. Therefore, it is necessary, to es- timate the risk by lightning strikes according to SANS/ IEC 62305-2 [1], and to take the results from this into account for the LPS design. Measures to protect the sensitive electronic system components from failure due to lightning flashes and surges are therefore abso- lutely necessary. The system concept of competent installers of PV Systems should include and take into account the expenditures for lightning and surge protection from the start. Surge protection for PV systems Causes for surges in PV systems are inductive or capacitive voltages deriving from lightning discharges and switching operations in the upstream ac system. Lightning surges in the PV system can damage PVmodules and inverters. This can have serious consequences for the operation of these systems, high repair costs, for example, those of the inverter, have a negative effect, and, secondly, the system failure can result in considerable power cuts for the operator of the structure.

Electricity+Control January ‘17

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