Electricity + Control January 2017

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

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

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

Surge and Fire Protection

Arresters with SCI Technology for dc Circuits

With energy needs on a global scale steadily increasing, the future

belongs to renewable energy sources.

Kirk Risch, DEHN Africa

EARTHING + LIGHTNING PROTECTION

Electricity+Control

January ‘17