Sparks Electrical News April 2015

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sparks
ELECTRICAL NEWS april 2015
IN May of 2013, Absa, a member of Barclays,
switched on Project Lumen, the world’s largest
Light Emitting Diode (LED) display – four giant LED
screens (38 m by 17 m) atop the 29-storey Absa Tow-
ers building – which utilise energy-saving technol-
ogy and consume the least power in their class.
At the time, the huge LED displays were a world
first and have since become an instantly recognis-
able landmark in the city of Johannesburg.
However, there was a problem: the tall building
is situated in an area that experiences very high
lightning density – about 12 strikes per square
kilometre per year – and since being switched on,
the Project Lumen LED screens have been damaged
by numerous lightning strikes. This called for
a specially designed protection system.
Lightning protection systems (LPS) provid-
er, Pontins’ engineers together with German
partners, DEHN, designed and developed an
insulated, high-voltage resistant HVI conduc-
tor to solve the problem.
Trevor Manas, MD at Pontin, says that the
previous ‘cross bonded’ system had failed
on Project Lumen because the conventional
technology “did not maintain a separation
distance between the lightning protection
conductors and the LED panels or the electri-
cal/data supply cables of the panels”.
Before installing the HVI conductor to
SANS/IEC 62305 standards, Pontins under-
took risk assessments and calculated the
required separation distance. The risk assess-
ments determined that the highest lightning
protection level (LPL) – level one – was
required for Project Lumen.
Separation distance – determined utilising
DEHN Toolbox software – is the minimum
distance between the protection device and
electrically conductive materials to prevent
flashover and sparking, and to ensure that
the lightning currents are reliably conducted
to the earth-termination system.
The ABSA Towers building was constructed
using steel-reinforced concrete. Electric con-
tinuity tests performed on the concrete steel
reinforcing at strategically exposed points es-
tablished that the interconnected reinforcing
should be used as natural down conductors,
and natural earth electrodes, to enhance the
division (splitting) of the lightning’s current
in the event of a direct strike.
“Basically, a conductor must have sufficient
current-carrying capacity, be insulated to
the sufficient electrical strength and prevent
creeping discharge or flashover and the
particular HVI conductor that we installed fits
the bill perfectly,” says Manas.
“The HVI conductor is unique. This coaxial
conductor has an inner copper core wrapped
in thick-walled high-voltage-resistant
insulation that is encased within a special semi-con-
ductive weather-resistant sheath,”Manas explains.
For this installation, two three-metre masts were
installed, with two HVI power conductors (LPL 1)
carrying the current down from each mast to the
rebar.
“Once we’d established the requirements, we de-
signed the isolated air terminal system to intercept
and prevent penetration of strikes, calculated the
height and positioning of these terminals and the
angle of protection to cover the LED’s steelwork
frames,”Manas explains.
“We also designed the earthing, equipotential
bonding, current-division, layout and specialised
mast brackets, which we specifically manufactured,
in order to attach the masts to the I-beams,” he says.
Additional surge-protection devices completed the
LPS.
Since this showcase project was completed in
December 2014, no damage of the LED system has
been reported. Pontins is able to monitor the LPS
through ABSA’s CCTV system and Manas says that
Pontins will share footage of lightning striking the
HVI LPS when it becomes available.
In the meantime, a video of the installation can be
viewed at:
Enquiries: +27 11 792 1300
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Protection system for huge LED display atop Jo’burg city building
The Universal Technic current probe model SC 2000 has a
capability of measuring ac/dc current up to 2 000 A and
the frequency range is from dc to 10 kHz with an accuracy
on dc of ± 1% and ac accuracy at 50Hz of ±0.5%. The
model in the above photograph has a 52 mm jaw and a
co-axial cable terminated with a BNC connector. Other
jaw sizes and current ratings up to 7 500 A are available
from Denver Technical Products.
Enquiries: +27 11 626 2023
High accuracy
current probes
motor control centres and motor protection