Electricity + Control April 2015

ELECTRICAL PROTECTION + SAFETY

Maximum HVI conductor length Based upon the separation distance calculations SANS / IEC 62305 Part 3 [1], the maximum conductor length of the HVI conductors was calculated as follows:

• Prevention of creeping discharge • Have sufficient current carrying capability via sufficient cross sectional area of the inner conductor

Connection to Air terminal

Sealing end range

· S

k

Injection of lightning Impulse current

m

=

L

max

· k

k

Connection to the Equipotential bonding System

i

c

Inner conductor

Where: k m

Semiconductive Sheath

= Insulation material - air = 1 = Separation distance = 0,88 m

High-voltage Resistant insulation

S k k

= Selected Lightning Protection Level (LPL 1) = 0,08

Components of an HVI conductor.

i

= Number of down conductors = 1

c

The specifically designed HVI conductors allow for the prevention of creeping discharge and the safe dissipation of the lightning current into the ground. HVI conductors via their semi-conductive sheath prevent creep- ing discharge of the lightning current by specifically influencing the electric field within the ‘sealing end’ range. Therefore the lightning current is trapped into the special cable and is safely dissipated while maintaining the required separation distance. It is of vital importance that the electric field within the ‘sealing end’ range not be interfered with.

Therefore: L max = 11 m

The maximumHVI conductor length of 11mwould not be sufficient to meet the requirements on the site due to the fact that the length to the zero potential point (concrete steel reinforcing) was 18 m. Therefore a lightning protection system using two HVI down conductors from the air terminals had to be designed! Isolated air termination system The air termination system was designed to intercept the lightning strike and prevent penetration into the protected space (i.e. LED screens and frames). The air termination system was designed in accordance with SANS / IEC 62305 Part 3 [1] using two methods of protection: Angle of protection The angle of protection was calculated using a lightning protection level 1 system at a height of 18 m. The calculated angle of protection = 27 °, which gives a zone of protection of 9,17 m from the top of the air terminal. This zone of protection covers the structural steelwork of the LED frames.

The basic principle of HVI conductors is that the lightning current carrying conductor is covered with insulating material to main- tain the required separation distance from other conductive parts of the structure.

Types of HVI conductor Since 2003, three different types of HVI conductor have been de- veloped to meet the growing requirements of different installation environments: • HVI light conductor [separation distance = 45 cm (air), 90 cm (solid material) - suitable for LPL 3, 4] • HVI long conductor [separation distance = 75 cm (air), 150 cm (solid material) - suitable for LPL 2 ,3, 4] • HVI power conductor [separation distance = 90 cm (air), 180 cm (solid material) - suitable for LPL 1, 2, 3, 4]

Angle of protection LPL1 @ 18m high

27°

Angle of Protection

a

h= Height of the air termination rod

Route of HVI power Conductor

3m HVI Mast & Bracket

Distance of Protection Zone

The HVI power conductor was found to be suitable for the Project Lumen installation.

Electricity+Control April ‘15

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