Electricity + Control January 2017

EARTHING + LIGHTNING PROTECTION

installation of PV systems must be distinguished between an instal-

lation on a building without lightning protection and buildings or

structures that are or have to be equipped with a permanently effec-

tive lightning protection system.

The installation of PVmodules on buildings does not increase the

risk of a lightning strike. The necessity for lightning protection cannot

be derived directly from the mere existence of a PV system. There

may however be an increased danger for the electric facilities of the

building in the event of a lightning strike. This is based on the fact

that, due to the wiring of the PV lines inside the building in existing

risers and cable runs, strong conducted and radiated interferences

may result from lightning currents. Therefore, it is necessary, to es-

timate the risk by lightning strikes according to SANS/ IEC 62305-2

[1], and to take the results from this into account for the LPS design.

Measures to protect the sensitive electronic system components

from failure due to lightning flashes and surges are therefore abso-

lutely necessary. The system concept of competent installers of PV

Systems should include and take into account the expenditures for

lightning and surge protection from the start.

Surge protection for PV systems

Causes for surges in PV systems are inductive or capacitive voltages

deriving from lightning discharges and switching operations in the

upstream ac system. Lightning surges in the PV system can damage

PVmodules and inverters. This can have serious consequences for the

operation of these systems, high repair costs, for example, those of

the inverter, have a negative effect, and, secondly, the system failure

can result in considerable power cuts for the operator of the structure.

Lightning Protection

for Rooftop PV Plants

Based upon the fact that self-generated electricity is cheaper and

provides a high degree of independence from the electrical grid,

PV systems are fast becoming an integral part of many electrical

installations. Many of these systems are located and installed in

exposed places such as roof tops, these PV systems will therefore be

subjected to all weather conditions (including lightning) for decades.

Trevor Manas, Pontins

he cables of PV systems frequently enter the building and

extend over long distances until they reach the electrical con-

nection point. Lightning discharges cause field-based and

conducted electrical interference and this effect increases in relation

to cable lengths or conductor loops. Surges do not only cause damage

to PV systems but can also cause damage to the other internal devices

inside the building. Most importantly, production facilities can easily

be damaged causing production to come to a halt.

Need for rooftop lightning protection

The energy released by a lightning discharge is one of the most

frequent causes of fire, therefore the protection of personal and the

prevention of fire is of paramount importance in the case of a direct

lightning strike to the building.

At the design stage of a PV system, the building should be as-

sessed to determine whether or not a lightning protection system

is installed to the building or for new structures whether lightning

protection is required. The necessity of lightning protection for the

Electricity+Control

January ‘17