Earthing and Lightning Protection System for Renewable Energy Solution

Earthing and Lightning Protection System for Renewable
Energy Solution
Hybrid Renewable Energy Systems
By
.............................................
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Abstract: The Earthing and lightning protection of renewable energy solution in the villages of
Kwazulu-Natal is paramount importance to the residents of this part of the larger South Africa.
This is because this part of the world depends solely on renewable sources of energy to provide
them with energy needs. They depend on three types of renewable energy sources namely; PV
installations, wind turbines and fuel energy. This three sources are connected to form a hybrid
energy solution which ensures that there is always power and constant supply to various homes
regardless of changes in weather and fluctuations in supply from individual power sources. And
since this hybrid system works off-grid there is great need to have a proper Earthing and
lightening system to protect the hybrid connections and installations from breakdowns and
damages that can be caused by power overvoltages and lightning and thunderstorms. The
realisation of the need of the Earthing and lightening protection and to work out the risk
management measures are among initial steps in setting up of a viable Earthing and lightning
system. This research article summarises various basic lightning protection techniques,
grounding systems and selection of the properties of the equipment to be used. In addition, risk
management measures are discussed.
Keywords: Photovoltaic. Overvoltages. Grounding. Lightning. Underground. Plant. Renewable
energy solution. Hybrid power plant. Induced current.
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Table of Content
Abstract.......................................................................................2
Introduction..................................................................................4
Lightning
Lightning current............................................................................5
Description of the hybrid renewable energy
system....................................6
Installation of a lightning protection system............................................7
Thunderstorms Mitigation..................................................................10
Tests of connection components.........................................................11
Tests of earth electrodes, conductors and accessories...............................13
Overvoltages in PV installation.........................................................13
Earthing
Description..................................................................................14
Evaluation of Soil Resistivity Measurements...........................................15
Grounding System Design ................................................................19
Installation of a grounding system.......................................................21
Risk Management for the Hybrid System..............................................23
Risks and risk components in a PV system.............................................24
Conclusion...................................................................................25
Appendix
Figure 1....................................................................................7
Figure 2....................................................................................8
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Figure 3....................................................................................9
Figure 4....................................................................................9
Figure 5....................................................................................10
Figure 6....................................................................................16
Figure 7....................................................................................21
Figure 8....................................................................................22
Figure 9....................................................................................22
Figure 10...................................................................................24
Figure 11...................................................................................25
Table 1......................................................................................18
References....................................................................................27
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1. Introduction
All Renewable Energy Systems use various of energy including wind, hydrogen, solar and
others. In the recent past ever-increasing prices of oil, depletion of fossil fuel reserves in
countries such as middle eastern region and political instabilities being experienced in oil-rich
nations and permanent damages caused by fossil fuels to the environment and whole earth
generally have led to accelerated need to explore renewable sources of energy. This is one the
reasons why rural areas such as Kwazulu-Natal in South Africa have developed reliable sources
of energy which is off-grid [1]. This is because it is very costly to install power in many rural
areas in South Africa due to high cost of producing HEP power and lower economic activities to
guarantee returns to power production companies if power is supplied to rural areas [2].
Normally in high voltage substations built locally to cater for locally produced energy from
renewable sources, electronic devices are present. In the case of wind turbines, those located at
high altitude sites are most at risk of being hit by lightning and thunderstorms. But small wind
turbines and located at low altitude areas are not that much endangered. As for the case of
photovoltaic systems, when the systems are being installed, protection is normally done
internally without considering direct strikes from lightning. These systems have protection
against possible overvoltages and surge protective components are used which may not over any
protective against powerful lightning strikes [3]. The surge protective components usually
installed in the internal system of photovoltaic plant include return current diodes, bypass diodes
and resistors. In addition, the internal protection system that has been installed in the plant can be
weakened or completely destroyed by repeated lightning strikes. This will eventually lead to
weakening of electrical strength of the photovoltaic module separation which can potentially
cause extremely high heat development which can be disastrous by even, for instance leading to
fires which can destroy both the plant and environment.
Therefore, in this study we are dealing with design and installation of a proper Earthing and
lightning protection system in the photovoltaic, wind and fuel cell hybrid energy system [4] at
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the rural area of Kwazulu-Natal in South Africa. This hybrid power supply is serving homes and
small scale economic activities in the villages which are not connected to the national grid.
2. Lightning
2.1. Lightning current
In the simplest case, this relationship can be described using Ohm ́s Law [5].
The steepness of lightning current Δi/Δt, which is effective during the interval Δt, determines the
height of the electromagnetically induced voltages. The square wave voltage U induced in a
conductor loop during the interval Δt is;
According to Ewald Fuchs [5] if an active electric current, that does not depend on load, flows
through conductive components, the amplitude of the current, and the impedance of the
conductive component the current flows through, help to regulate the potential drop across the
component flown through by the current. This relationship is better described by Ohm’s Law.
U = M*Δi/Δt. (1)
where M denotes mutual inductance of the loop and Δi/Δt denotes steepness of lightning current .
The charge of the lightning current (Q) determines the energy deposited at the precise striking
point, [6] and at all points where the [7] lightning current continues in the shape of an electric
arc along an insulated path;
Q= ∫idt. (2)
The energy W deposited at the base of the electric arc is given by the product of the charge Q and
the anode- /cathode voltage [8] drop with values in the micrometre range U A, K. The average
value of UA,K is a few 10 V and depends on influences such as the height and shape of the
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current;
W= Q*UA,K , (3)
where Q denotes charge of lightning current and U A, K denotes anode/cathode voltage drop [8].
The specific energy W/R of an impulse current is the energy deposited by the impulse current [9]
in a resistance of 1 Ω. This energy deposition is the integral of the square of the impulse current
over the time for the duration of the impulse current;
W / R= ∫i2dt. (4)
The specific energy is therefore often called the current square impulse [10]. It is relevant for
the temperature rise in conductors through which a lightning impulse current is flowing, as well
as for the force exerted between conductors flown through by a lightning impulse current.
For the energy W deposited in a conductor with resistance R we have
W=R. ∫i2dt=R*W / R, (5)
where R denotes (temperature dependent) d.c. resistance [11] of the conductor and W/R denotes
specific energy.
2.2. The Hybrid Energy System
This system comprises of photovoltaic plant and those installed in various houses in the village,
wind turbines and fuel cells connected to form one energy supply, just like the national grid
works. The system works in such way to provide sufficient and constant supply of energy to
homes and work stations of residents of the Kwazulu-Natal region. For instance, below is a
picture showing how photovoltaic plant is installed. Figure 1.
As shown in figure 1, the hybrid system is designed in a such way that the installations are able
to optimally tap the sun and wind energies using PV cells and wind turbines. This, in addition,
puts in mind to avoid using any fossil-based energy sources [13] with the aim of protecting the
environment. As shown in figure 1 above, the photovoltaic panels are installed in a tilting angle
for maximum sunlight exposure. In addition, this fixed and tilted photovoltaic modules are put
on the roof of the building and in roofs of houses of the villagers of the Kwazulu-Natal area.
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Then to go concurrently with photovoltaic panels, sun trackers are put. It is estimated that in
every ten photovoltaic panels installed on the roof there is one sun tracker [14]. This means that
each sun tracker serves up to 1.25 KW of power [15].
2.3. Setting up of a lightning protection system.
Installation of a lightning protection system involves various processes. Firstly, connections are
established to link the grounding conductors put in the ground and the air termination rods. This
rods are installed in building housing the installations and devices of the hybrid renewable
energy [38]. The air termination rod is put on the roof of the building, the grounding rod is
buried in the soil and the conductor is connected from the air termination rod and the grounding
rod through a check clamp. The soil resistance of the area is taken into calculated and taken into
consideration before laying of the rods and cables is done. This is to make sure that the potential
created between the grounding rod and the air termination rods is of the required range to avoid
lightning strikes and surge voltages (Note that soil resistivity and calculation are dealt with as
you go down this article).
The conductors and air termination rods at the hybrid energy plant roof are set up and positioned
in such way that they protect the whole building against lightning strikes and power overvoltages
as shown in figure 3 and figure 4. In addition, to offer protection to sun tackers, the air
termination rods are mounted as shown in figure 3 which offer protection against direct lightning
strikes. Also, air termination rods are put in wind turbines to protect them against lightning
strikes as shown in figure 4 [8].
In wind turbines, air termination rods of height 3.2 metres each and conductors fitted with
special specifications to withstand high voltage surges called excessive voltage insulation, HVI
are mounted [39]. This type of high voltage insulation protects the digital system installed in the
wind turbines against electromagnetic waves which can be caused by lightning strikes.
To prevent lightning strikes and surge overvoltages from hitting the installation of the hybrid
renewable system, grounding rods are also connected to the surge arrestors surrounding the
hybrid energy system. This is to protect the system against mainly surge that may arise from the
atmosphere as shown in figure 7 [7].
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