Electricity + Control January 2017

EARTHING + LIGHTNING PROTECTION

Surge and Fire Protection Arresters with SCI Technology for dc Circuits

Kirk Risch, DEHN Africa

W ind, water, biomass and the sun are viable alternatives to the dwindling reserves of fossil fuels and complex gas production. Photovoltaics (PVs), in particular, offer huge growth potential for the production of electricity. The increasing popu- larity of this type of system, both roof- and ground-mounted, is set to continue into the longer term. Each PV systemmust be maintained to ensure continuous yield and also requires special lightning, fire and surge protection, especially on the direct current (dc) side, in order to prevent failure and ensure a longer lifespan. Electrical arcing that may occur over high-voltage dc lines is the main cause of solar PV fires. This can occur any time if there is a compromise of the wiring or connection of the electrical system. As a result, the risk of arcs increases over time. And while this can be attributed to the normal ‘wear and tear’ that a solar PV system is subjected to, it places a significant emphasis on the importance of systemmaintenance. In line with this sentiment, the EN 50539-11 [1] test standard requires the short-circuit current rating I SCPV on the surge protective devices that are used in PV systems to be regularly tested, in order to ensure that the maximum dc short-circuit current of the PV system does not exceed the typical I SCPV value of the arrester. DEHN is the only company worldwide to provide surge arresters that include innovative Short-Circuit Interruption (SCI) technology. This patented technology provides maximum safety and is key to fire prevention. The specifically dimensioned fuse integrated into the short-circuit path ensures the safe disconnection of short-circuit With energy needs on a global scale steadily increasing, the future belongs to renewable energy sources.

currents in case of an overload at any time. Moreover, the interaction of the SCI technology and the Y circuit ensures reliable surge protec- tion for maximum operational reliability and fail-safe performance. Surge arresters with SCI technology can also: save extra back-up fuses up to the I SCPV value; fulfil customer needs and international standards for surge protective devices; provide excellent surge and fire protection; and offer permanent active protection. Requirements on arresters used in PV systems de- pending on the time The main function of the fuses present within PV systems with central inverters is to protect against return currents. The maximum avail- able current depends on the actual radiation - depending on the time of day and the operation state, these fuses only

trip after some minutes. Furthermore, SPDs positioned in generator junction boxes should be dimensioned for the possible total current (operating current and return current) and must be independently discon- nected in case of an overload without arc formation.

The selection of surge arresters for PV systems Roof-mounted and ground-mounted PV systems are equipped with string or central inverters. When correctly dimen- sioned, surge protective devices provide the combination of surge-, personal- and fire protection all within a single device. When selecting dc arresters, it is essential to consider the fol- lowing criteria: • Place of installation and distance from terminal equipment • Surge Protection Devices (SPDs) class: type 1 or type 2

Electricity+Control January ‘17

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