43 / 88
41
Transformers + Substations Handbook: 2014
prevent hazardous sparking inside the building or structure. This
is achieved by means of equipotential bonding or a safety distance
between the components of the lightning protection system and
other conductive elements inside the building or structure.
Surge and lightning protection for electrical and
electronic systems
A lightning protection system, according to International Electro-
technical Commission (IEC) 62305-3, protects persons and mate-
rial assets of value in the buildings. It does not protect the elec-
trical and electronic systems, but it is precisely such systems – in
the form of building management, telecommunications, control
and security systems – that are rapidly becoming common in all
areas of residential and functional buildings. Whilst owners or
operators place high demands on the permanent availability and
reliability of these systems, few developers seem to appreciate
the fact that they are critically susceptible to externally and inter-
nally generated voltage transients and surges, especially those
produced by lightning.
Lightning up to a kilometre away can cause damage to sensitive
electrical and electronic equipment. At these distances, the in-
duced voltages can be as high as 200 V per metre of cable, which
is more than enough to cause damage to equipment. Even equip-
ment connected via cabling within a building can be damaged as
a result of the high electromagnetic induction that occurs under
lightning conditions.
Lightning damage falls into two main categories; primary and
secondary effects.
Primary effects are those resulting from direct lightning strikes,
which are a major cause of fire, instant destruction of property,
electrocution injury and death. Even though it is one of the most
common natural phenomena known to man, there has been no
practical method developed to prevent lightning strikes or to avoid
damage caused by a direct hit.
The most prevalent technology for dealing with lightning is to
divert the strike energy to a properly grounded lightning rod or
cabling system. The external lightning protection on a building is
only there to act as a preferential point of strike and offers a con-
trolled discharge path to earth, thus preventing structural damage
to the building. A common misconception is that if the building
has external lightning protection, or if there is a high mast in the
area, the equipment will not be damaged. It must be borne in mind
that a single earth-termination system for all the various electrical
To ensure uninterrupted supply,
substations and overhead line
networks must be maintained.