Electricity + Control August 2016

ELECTRICAL PROTECTION + SAFETY

String Inverter In case of string inverters, the power supply cables act as equipotential bonding conductors between the ‘local’ earth termination of the PV array which was directly hit by lightning and the ‘remote’ equipotential surface of the infeed transformer. Partial lightning currents flow on the ac lines, therefore the installation of Type 1 SPDs on the ac side of the string inverters and on the low-voltage side of the infeed transformer is necessary. Type 2 SPDs, which mainly limit induced interference impulses, are sufficient on the dc side of the string inverters.

Conclusion In South Africa, the high lightning flash indexes, coupled with the large size and vulnerability of Free Field PV Power Plants, makes the correct design and installation of the lightning and surge protection systems imperative. Proper lightning and surge protection for all systems gives enhanced performance of these power plants. The service and maintenance time as well as the repair and spare part

costs are also reduced. The use of DEHN lightning arresters and surge arresters with their SCI (patented) disconnect technology is recommended for PV Power Plants.

References [1] SANS/IEC 62305-1, 2, 3: Lightning Protection Standard.

Part 1: General principles. Part 2: Risk management. Part 3: Protection of the structure. Part 4: Electronic systems protection.

[2] SANS 10313. 2012. Protection against lightning - Physical damage to structures and life hazard. [3] DEHN & Sohne - Lightning Protection Guide (3 rd edition) . Note IEC 62305 (part 3) Supplement 5. Lightning and Overvoltage Protection for Photovoltaic Power Supply Systems (this has not yet been adopted by the SABS standards committee but the writer believes that it can be considered as good practice and would recommend the use of this supplement).

Figure 10: PV System with central inverter.

Figure 11: PV System with string inverters.

Trevor Manas started his lightning protection career at Pontins in 1991 as an installation technician, learning the ropes by working on various sites and doing physical installations. Within two years, he was promoted to sales engineer, where he was involved in site assessments, soil resistivity surveys and compiling quotations. In 1996, Tre-

Protection of data systems The ability to obtain reliable data from remote maintenance equip- ment via data cables is essential in the effective operation of the PV Plant. It is therefore important to provide adequate surge protection to these data systems to prevent damage to the data system. The string and inverter monitoring system, weather data acquisition unit, anti-theft protection and external communication system, are based on different physical interfaces. Surge protection devices specifically suited to each type of interface must be selected.

vor was promoted to the position of director and was in charge of ensuring the company`s compliance with the earthing and lightning protection codes of practice. In 1999, Trevor became the managing director of Pontins. In 2013, Pontins formed a partnership with DEHN Africa which gave Pontins access to world class cutting edge lightning protection technologies. Enquiries: Email trevor@pontins.co.za

Electricity+Control August ‘16

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