Electricity + Control April 2015

CABLES + ACCESSORIES ELECTRICAL PROTE TION + SAFETY

Rolling sphere method In accordance with a lightning protection level 1 system a sphere with a radius of 20 m was used to determine the height and positioning of the air terminals.

r = 20m

3m Air Terminal

S= 1,67m

Top of Steelwork

16m

Installation of HVI Down conductors.

There are two applicable distances between the air terminals; namely 12 m apart and 16 m apart. The sag of the sphere (20 m radius - LPL1) is calculated using the following formula:

Earthing and equipotential bonding The correct earthing and equipotential bonding of the Lumen light- ning protection system is imperative for the effective protection of the LED screens. To this end the following measures were employed: • The HVI conductors were positively bonded to the concrete steel reinforcing of the structure at a level below the LED frames • The concrete steel reinforcing was tested in numerous positions and found to be electrically continuous with various parallel paths to earth • The use of the concrete steel reinforcing vastly increases the cur- rent division capabilities of the entire lightning protection system

P = r - [r² - (d/2)²]

Where: P

= Penetration depth (sag) = Radius of sphere (20 m)

r

d

= Distance between air terminals

The calculated sag between the air terminals is therefore:

- 12 m distance = 0,92 m - 16 m distance = 1,67 m

HVI Power Conductor

Clamped Connection To Reinforcing

PVC Insulated Copper Conductor

The area between the air terminals is therefore covered via the rolling sphere method of protection.

Mini Earth Bar

Concrete Steel Reinforcing

Isolated air termination system Air termination masts and brackets

Earthing of HVI power conductors.

In order to comply with the design requirements, i.e. two 3 m masts to be installed to the top of the steel LED frames, specialised mast brackets had to be designed and manufactured to house the 3 m long HVI power masts. Down conductor system Each mast location is equipped with two HVI power down conductors that run from the mast connection point to the zero potential con- nection point (concrete steel reinforcing). The HVI down conductors are fixed to the structural steelwork (I-Beams) by means of stainless steel clamps and brackets.

Equipotential bonding The semi-conductive sheath of the HVI power conductors were equi- potentially bonded to the electrical earthing system at a level below the LED frames. In turn the electrical earthing system was bonded to the concrete steel reinforcing at ground floor level. The LED screens and frames are equipotentially bonded to the electrical earthing system via the electrical reticulation. In order for the HVI system to work properly it is imperative that this equipotential bonding be performed.

Electricity+Control April ‘15

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