Content uploaded by Francisco Jurado
Author content
All content in this area was uploaded by Francisco Jurado on Sep 02, 2013
Content may be subject to copyright.
IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 23, NO. 4, OCTOBER 2008 1961
Lightning and Surge Protection in
Photovoltaic Installations
Jesús C. Hernández, Pedro G. Vidal, and Francisco Jurado, Senior Member, IEEE
Abstract—The aim of this paper is to give scientific background
and essential assumptions to be introduced into the design of light-
ning and surge protection in photovoltaic installations (PVIs), with
particular emphasis on the aspects of standardization to be cov-
ered. For this purpose, the relevant protective measures given in
the standards for conventional low-voltage power distribution sys-
tems (CLVPDSs) are adapted in part. This revision is required be-
cause the peculiar characteristics of PVIs are different from those
of CLVPDSs. The resulting protection approach that determines
the advisable protective measures by a risk management has been
applied to an actual grid-connected PVI (GCPVI), Univer Project.
The extra cost of this protection in this PVI (approximately 3.6% of
the system cost) is of secondary importance because of the increase
of safety and availability. Furthermore, in order to fulfill with this
protection, the surge withstand capability (SWC) of PV modules
has been investigated as well.
Index Terms—Lightning, photovoltaic power system, safety,
standards, surge.
I. INTRODUCTION
PHOTOVOLTAIC installations (PVIs), due to their in-
herently exposed locations on roofs and the facades of
buildings or as free-standing installations in unsheltered and
extended areas, are more vulnerable to both direct lightning
flashes and surges than conventional low-voltage power distri-
bution systems (CLVPDSs).
Lightning and surge protection of PVIs is a subject actu-
ally not widely investigated. In the past, only primary lightning
protection was considered and thereby achieved by the use of
grounded vertical rods and/or overhead earth wires [1], [2]. In
the 1990s, focus was drawn to the importance of induced voltage
associated to magnetic fields (MFs) of lightning flashes in any
PV loops that could endanger the whole PVI [3]–[5]. Reference
[6] focused on typical stresses created by lightning and surges
in PVIs. Historical protection approach, based on IEC 61024
series [7] and IEC 61312 series [8], was presented in [9], [10].
Lastly, an approach closer to the present one is given in [11]. In
general, field experience is limited and applied protective mea-
sures do not follow a general rule.
At this time, the dedicated standard (IEC 61173 [12]) in this
scope for PVIs is too generic. Hence, the use of the standards
of CLVPDSs in this matter and their later adaptation in part is
Manuscript received August 22, 2007. First published March 3, 2008; current
version published September 24, 2008. Paper no. TPWRD-00522-2007.
The authors are with the Department of Electrical Engineering, Uni-
versity of Jaén, Polytechnic School (Jaén), Spain (e-mail: jcasa@ujaen.es;
pgvidal@ujaen.es; fjurado@ujaen.es).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TPWRD.2008.917886
required due to the particular characteristics of PVIs different
from CLVPDSs ones such as: electrical and geometric charac-
teristics, expositions and locations.
Lightning and surge protection is the main matter of the stan-
dard IEC 62305 (parts 1 to 4). Part 1 [13] lists terms, damages
due lightning, protection needs and measures, lightning current
parameters, and basic criteria for protection of structures and
services. Part 2 [15] provides the risk management method to
select optimal combination of protection measures. Part 3 [16]
concerns the lightning protection system (LPS). Part 4 [14] con-
siders the protection against lightning electromagnetic impulse
(LEMP) for the electrical/electronic systems. On the other hand,
standard IEC 61643-12 [17] describes the selection and appli-
cation principles of surge protective devices (SPDs) connected
to CLVPDSs.
All the above-mentioned standards are taken into consider-
ation for the approach of the modern concept of lightning and
surge protection in PVIs described later on. This concept inte-
grates the determination of the need for protection with the se-
lection of adequate protective measures to reduce the risk to a
tolerable level by means of risk management.
The knowledge of both typical stresses created in the PVI and
SWC of the PV equipment is necessary to the application of
this protection. These matters are described firstly in this paper.
Secondly, we explain the potential protective measures adapted
for PVIs. Lastly, we present the risk management method that
determines the advisable protection system and its application in
an actual PVI, Univer Project [18]: a 200-kW GCPVI located
at the parking of the Jaén University Campus.
II. SURGES AND RESULTING DAMAGES IN A PVI
The damage of the electrical and/or electronic equipment
of a PVI due to surges is originated by LEMP as well as by
switching electromagnetic impulse (SEMP). In most cases,
LEMP stress is the main role in PVIs. SEMP surges are impor-
tant in high-voltage (HV) and extra HV power systems but not
in CLVPDSs [17]. Temporary overvoltages caused by faults
between HV systems and earth (section 442 of [19]) are only
concern in CLVPDSs [17].
Lightning affecting a PVI not only can cause failure of its
electrical/electronic systems (type of damage D3 [13]), but also
can injure its occupants (D1) as well as cause physical damage
(D2). The above damages may produce the following conse-
quential losses [13]: loss of human life (L1); loss of service to
the public (L2); loss of cultural heritage (L3); loss of economical
value (L4). As regards it origin, the damage due to lightning can
be classified as follows (Fig. 1): flashes to the PVI (S1); flashes
0885-8977/$25.00 © 2008 IEEE
1962 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 23, NO. 4, OCTOBER 2008
Fig. 1. Sources of surges and potential LPZs in a large PVI.
near the PVI (S2); flashes to the services connected to the PVI
(S3); flashes to nearby services connected to the PVI (S4).
Protection against LEMP, as shown later, is based on the light-
ning protection zone (LPZ) concept [13]: a hierarchy of zones of
protection where the severity of threatening parameters caused
by LEMP is reduced in steps. Depending on the number, type
and SWC of electrical and electronic PV equipment, suitable
inner LPZs are defined (Fig. 1), from small local zones up to
large integral zones.
Lightning surges originating the D3 damage type together
with temporary overvoltages are explained below in detail.
A. Surges on the dc Side of the PVI
Temporary overvoltages due to various system faults are neg-
ligible with regard to lightning surges. All faults on the dc side
of PVIs—TT/TN systems—must be quickly removed for per-
sonnel safety [20]. Only earth faults—IT system—create this
overvoltage but lower than nominal voltage.
When analyzing lightning surges, depending on the tripping
influencing variable, the main coupling modes are:
Galvanic Coupling: Direct lightning flashes at grounded ex-
posed-conductive-parts (ECPs) of the PVI (Fig. 1: S1-a) may
create the breakdown of insulation of the PV equipment.
Resistive Coupling: Direct lightning flashes at the external
LPS (Fig. 1: S1-b) or into the immediate surroundings of the
PVI (Fig. 1: S2-a) originate an earth potential rise.
Inductive Coupling: The lightning discharge creates a vari-
able MF around both the flash channel of the discharge and the
conductors of the external LPS (if available). This field change
induces surges in all wiring loops of the PVI. Not only direct
flashes at PVIs but also nearby flashes (within clouds or to
nearby objects) induce this surge (Fig. 1). There are two types
Fig. 2. Potential loops in PVIs.
of induction loops in PVIs (Fig. 2): a loop induced by active
drivers and by active wires and a protective bonding conductor.
The internal loop of single PV modules must also be taken into
account.
Capacitive Coupling: The electric field of a thunderstorm
cloud originates a charge separation in the ECPs and semicon-
ductors of the PVI [9]. At the moment of lightning discharge
occurs, the electric field collapses and a new charge transfer ap-
pears once again. The charge flows through all conductors con-
nected to the earth as transient surge.
B. Surges on the ac Side of the PVI
In GCPVIs, all the services which enter the PVI from out-
side—e.g., ac LV/HV mains, telecommunication lines —are
potentially facilitating the way for external conducted surges
HERNÁNDEZ et al.: LIGHTNING AND SURGE PROTECTION IN PVIS 1963
(Fig. 1: T1, T2, S3-a/b, S4-a/b). International standard IEC
61643-12 [17] gives types and their main characteristics.
III. LIGHTNING DATA AND EVALUATION OF SURGES
DUE TO INDUCTION AND CONDUCTED EFFECTS
FOR PROTECTION PURPOSES
PV equipment located in outer zones (LPZ ) can be at
risk due to the non-attenuated MF and surges up to a full
lightning current of a direct lightning flash (Fig. 1). However,
when it is located in inner zones , it can be at risk
due to the surges induced in internal loop and/or conducted from
outside by incoming services .
A. Expected Surges Due to Flashes to the PVI
The lightning protection concept is based on actual lightning
data measured over years. For engineering purposes, four light-
ning protection levels (LPLs) are defined [13]: I–IV. For each
LPL a set of minimum and maximum lightning current param-
eters is fixed. The minimum values define the interception effi-
ciency of LPS. The maximum values define the lightning threat
(lightning current and its associated MF , Fig. 1) for the
components of LPS and the equipment to be protected.
The lightning current consists of one or more different
strokes: short strokes and long strokes. Mechanical effects
of lightning current depend on its specific energy and
current peak value . Thermal ones are related to
and charge . Lastly, induced surges are related to the average
steepness di/dt.
The lightning current to be considered consists of a first stroke
(typically with a s waveshape ) and a negative
subsequent stroke (with a 0.25/100 s waveshape ).
The parameters of the above waveshapes are selected according
to relevant standard [13] for LPL from I to IV. Hence, for the
waveshape , the and ranges in the in-
tervals 200–100 kA, 100–50 C, and 10–2.5 MJ/ , respectively.
The maximum value of di/dt is determined by , where
di/dt and its ranges in the intervals 200–100 kA/ s and
50–25 kA respectively.
The quantitative knowledge of the factors influencing the
sharing of the lightning current [13], [15], [17] within the
external LPS, if available, and/or among several services (e.g.,
water and gas pipes, power and signal lines ), earth-termina-
tion system and external conductive parts at particular points of
the PVI is essential for effective selection and dimensioning of
conductors, SPDs Determining of this current distribution
may be accomplished either by a computer simulation using
network analyzing software [22], or by approximation as given
in [13], [17]. Current sharing not only concerns its peak value,
but also to its specific energy, charge, and steepness.
B. Expected Surges Due to Conduced and Induction Effects
In GCPVIs, the waveshape and amplitude of conduced surges
due to flashes to/near the incoming services—similar to those
ones of CLVPDSs—depends on several factors as mentioned in
[13]. The waveshape (10–5 kA for LPLs from I to IV)
and the (10–5 kA/ s and 2.5–1.25 kA) usually simu-
late direct flashes. The 8/20 s current impulse (5–2.5 kA)
simulates indirect one. Lastly, conduced surges due to switching
event in CLVPDSs always are expected to be at less than 6 kV
[17].
Surges due to induction effects from MFs, generated either
from direct lightning flashes to the PVI/LPS (S1) or from
nearby lightning flash (S2), have an typical waveshape
[13]. These impulse currents, are shown in
Fig. 1. Care should be taken that peak values of expected surges
in PVIs will be greater than proposed ones for CLVPDSs [13]
due to larger loops and lesser attenuation of MF.
Annex A of IEC 62305-4 [16] presents a theoretical method,
approved with experiments [21], to evaluate the maximum value
of the induced voltage and current as a function of different pa-
rameters for the cases of lightning flashes to/near the protected
structure. Its analysis and calculation requires the use of elabo-
rate models. The complexity of these models calls for an imple-
mentation into computer codes because they require a numerical
integration or the relevant equations [22].
Specific researches have been carried out about induced volt-
ages in single PV modules and strings [3], [5] both theoretical
and experimental ones. They highlight that induced voltage is
essentially determined by the orientation of internal wiring loop
and the presence of both the metal frame (reduction factor (RF)
by 3–5) and aluminum foil at the backside (RF by 7–10). Volt-
ages up to one kV have been measured for a typical single PV
module located to 0.07 m of the full lightning current.
IV. CHARACTERISTICS OF THE PV EQUIPMENT
TO BEPROTECTED
A. General PV Equipment
The SWC of the LV general electrical equipment is defined in
their product specifications (applicable standard) or, if not avail-
able, should be tested according to international standard IEC
61000-4-5 [23]. The relevant U.S. standard is IEEE C62.45 [24].
Working groups of IEC and IEEE Standards have developed
different standard surge waves for testing SWC. Thus, interna-
tional standard applies an current surge and a s
voltage surge in the tests of SWC of current and voltage,
respectively.
The rated SWC of the equipment, according to [23], depends
largely on the installation conditions: class 1 to 4. This classifi-
cation is very similar like that of LPZs (4–1). For these classes,
the rated impulse withstand voltage and impulse withstand
current ranges in the intervals 0.5–4 kV and 0.25–2 kA, respec-
tively. Besides, as electrical equipment is usually energized di-
rectly from the LV mains, its SWC must also meet IEC 60664-1
[25] to achieve the insulation coordination. Similar rated levels
of , but not the same to the previous ones, are defined ac-
cording to nominal voltage of mains and the equipment over-
voltage category (I–IV) [25]. Overvoltage category classifica-
tion (I–IV) may be considered equivalent to that of LPZs
.
The choice of for the whole ac/dc PV equipment will be
carried out according to [25] and the aforesaid relationship be-
tween LPZs/overvoltage categories, except for dc PV equipment
1964 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 23, NO. 4, OCTOBER 2008
Fig. 3. View of the high impulse-voltage generator with a foil-type PV module
of 106
W
.
located in outer zones (e.g., PV modules). In LPZ , this re-
lationship must be reviewed. Thus, although the PV equipment
is located at the origin of the installation, due to reliability and
availability requirements, it is advisable to include it into over-
voltage category III [26]. PV equipment overvoltage category
located potentially in LPZ cannot be extrapolated because in
IEC 60664-1 [25] effects of direct lightning are not considered.
Even so, it is suggested to use the PV equipment of overvoltage
category III as well.
PVIs use electrical equipment widespread standardized ex-
cept for PV modules and inverters. Hence, most of the standard
PV components have generally assigned its by specific stan-
dards allowing realizing the insulation coordination. SWC of
PV modules and inverter is analyzed below in detail.
B. PV Modules
SWC of PV modules is set in IEC 61730-2 [26] by means an
impulse voltage test (IVT) with a rated value ( 8 kV)
dependent upon the maximum system voltage and potential PV
application type: A, B, or C in relation to its potential hazards
associated. However, in literature, no information is available
yet about PV module behavior against voltage surge. In order
to give the PV engineer useful information extended IVTs over
different single PV modules have been performed in our HV
laboratory at the Jaén University. For theses tests, a high im-
pulse-voltage generator ( up to 200 kV) is used.
Common PV-modules (foil type modules) consist of a front
soda lime glass (superstrate), in EVA embedded solar cell
strings and a protective back sheet material (substrate), which
mostly is made as a laminated film composite (polymers).
Some manufacturers use another glass at the reverse side using
resin fill-in as alternative to EVA (glass type modules).
Foil and glass type modules that range in size 55–106
have been tested (IVT) according to [26] (Fig. 3). Requirements
of IVT have been met in all accomplished tests. However, it is
found that results depend considerably on the design and layout
of the module: clearance and creepage distances, module type
(foil or glass) and composition of laminated film materials.
Dielectric breakdown of the foil type framed modules by sur-
face tracking has usually been observed. Nonetheless dielectric
Fig. 4. Classification of lightning and surge protection measures.
breakdown at the backside has also happened when creepage
distance (between internal current-carrying parts and edge of
glass) is large ( mm). Therefore, to meet with this
creepage distance [27] is as important as to have sufficient back-
side solid insulation properties as stated in [27]. Depending on
the considered specimen, 16–28 kV values have been reached
in these IVTs before dielectric breakdown or surface tracking
of the module.
Surface tracking has always been observed in glass type
modules due to the high SWC of the solid insulation (glass) of
module. Values in the interval 19–35 kV have been obtained
for modules of similar dimension and peak power to those of
foil type.
C. PV Inverters
No particular international standard exits yet to assess the
SWC of PV inverters. The potential standard that will treat
this subject, IEC 62109 [28], is under development. Hence,
its SWC may be tested in accordance with the USA standard
UL 1741 [29] and IEEE 1547 [30]. Consistent new versions
of both standards are under development. Nonetheless, for
CE certification, inverters must meet electromagnetic com-
patibility standards (IEC 61000 series), in particular part 4–5
[23] that establishes the SWC. When applying this SWC, it is
recommended to include inverters as equipment of overvoltage
category I due to their sensitive electronic components. Since a
PV inverter is a utility-interactive PV equipment must also meet
relevant interconnections standards [31], [32]. In this standard
set, SWC is not still a subject analyzed in the grid-interfacing
requirements except for [30].
V. LIGHTNING AND SURGE PROTECTION SYSTEM
First ensuring personnel safety and lastly avoiding physical
damages and/or failures in a PVI due to lightning requires a
good coordination of the lightning and surge protection concept.
The comprehensive protection system that achieves both objec-
tives includes a full set of design rules that may be classified into
three groups (Fig. 4): LPS, LEMP protection measures system
(LPMS) and protection measures against injury to living beings.
The need for protection and the selection of adequate pro-
tection measures should be determined in the terms of risk
HERNÁNDEZ et al.: LIGHTNING AND SURGE PROTECTION IN PVIS 1965
management [13] by means the reported method in [14]. This
method provides a procedure for the evaluation of the total risk
. The selection from among different protection measures,
to reduce the risk to or below the tolerable risk , takes into
account their efficiency as well as the cost of their provision
(cost-effectiveness).
The risk [14] is defined as the probability of having an an-
nual loss in the structure or its content. Four types of risks are
considered associated to the four types of aforemen-
tioned losses . In turn, each risk is the
sum of different components or
, i.e., injury to living beings by touch and step voltages, phys-
ical damage by dangerous sparking and thermal effects, failure
of electrical/electronic systems by LEMP, etc.). Each risk com-
ponent depends on the point of strike and on the annual
number of dangerous events attached to X, the related prob-
ability of damage (damage to the structure) and the conse-
quent annual loss due to a single lightning flash (related to
the total amount of persons or goods) so that
(1)
Sometimes it is interesting to divide the PVI into zones al-
lowing the designer to consider the peculiar characteristics of
each part in the evaluation of risk components and to select
the most suitable protection measures tailored zone by zone, re-
ducing the overall cost of protection.
A. Lightning Protection System
A LPS is intended to prevent or to minimize the physical
damage due to lightning flashes to the protected PVI. It con-
sists of both external and internal LPS.
External LPS (Fig. 1) intercepts the lightning flash to the PVI
(with an air-termination system—e.g., vertical air-termination
rods/mast, horizontal wire or mesh air-termination system),
conducts the lightning current safely toward earth (using a
down-conductor system—concealed or exposed), and disperses
the lightning current into the earth (using an earth-termination
system—e.g., buried conducting loops or foundation earth
electrode).
IEC 63305-3 [15] offers a guideline for physical design
and construction, maintenance and inspection of an external
LPS. Items of design analyzed are: class of LPS, need to
isolate external LPS from protected structure, potential use of
natural components, positioning, materials and sizing. Volume
protected by the external LPS is obtained using one of the
following methods: protection angle or rolling sphere or mesh
method. The second one is preferred in all cases [33]. However,
this method should still be improved in complex structures [34].
In PVIs, external LPS must be designed so that all PV com-
ponents shall be inside the protected volume: LPZ or higher
as shown in Fig. 1. PV generator (PVG)—dc side of the PVI—is
usually located in LPZ without an external LPS. PVG com-
prises PV modules, dc wiring and PV array/generator junction
boxes. Proper design of external LPS should also avoid shad-
owing of neighboring modules [4] and increase the distance be-
tween lightning current path and potential PV loops to decrease
damage due to induced voltages [5].
Internal LPS shall prevent dangerous sparking within the
protected PVI by equipotential bonding and safety separation.
Equipotentialization is reached by interconnecting the external
LPS with the following parts: structural metal parts, external
conductive parts, internal metal installations and systems and
incoming services. Bonding external LPS at the further point
from reference bonding point (Fig. 1) is necessary when it is
not possible to maintain an adequate separation [15] between
the external LPS an all the above conductive parts.
B. LEMP Protection Measures System (LPMS)
The aim of LPMS is to avoid failure of electrical and elec-
tronic equipment of a PVI due to LEMP caused by conducted
and induced surges via connecting wiring. This system works
by avoiding the formation of surges and equalizing all different
potentials to a common potential at the instant of surge. A LPMS
divides the protected space into successive zones—volumes or
LPZ. For each one, LPMS attempts that the LEMP severity must
be compatible with the SWC of the internal systems enclosed.
The system comprises the following basic measures analyzed
in detail hereafter.
1) Grounding: Dc PV equipment grounding refers to the
bonding to earth of all ECPs and frames [35] of the PVG
including any structural metalwork. These ECPs need not
be earthed if protection against electric shock is achieved
by: use of class II insulation—safety class II—or extra-LV
(ELV)—safety class III—in accordance with [27]. However,
dc PV equipment grounding is mandatory when protection by
automatic disconnection of supply is applied—safety class I.
PVG system grounding is not always required [36], [37].
From the personnel and fire safety viewpoint, floating configu-
rations are safer than grounded configurations [20], [38]. The
opposite case occurs when considering the lightning protection
viewpoint. Thus, both viewpoints shall be weighted by engi-
neers for the best choice of PVG system grounding.
When it is necessary an grounding electrode for dc/ac PV
equipment grounding as well as lightning purposes, it is ad-
visable to have a single integrated structure earth-termination
system (Figs. 1 and 5). If a separate grounding electrode is pro-
vided for dc PV equipment grounding shall be bonded to the
installation earth. Design recommendations of the earth-termi-
nation system are given in [15] with type B grounding arrange-
ment as recommended.
2) Equipotential Bonding: A bonding network (BN) mini-
mizes potential differences and may reduce MF. BN can be ar-
ranged (Fig. 1) by integrating magnetic shields of the LPZ at the
periphery (three-dimensional meshed structure), or conductive
parts of the systems inside of the LPZ, and by bonding metal
parts or conductive services at the boundary of each LPZ di-
rectly or by using reliable SPDs.
BN connected to the earth-termination system constitutes
the complete grounding system. Bonding bars (BBs) (e.g.,
ring BBs, several BBs at different points) shall be installed
for bonding of (Figs. 1 and 5): a) structural metal parts;
b) external conductive parts; c) magnetic shields that constitute
the boundary of each LPZ; d) internal metal installations;
e) metal components of internal systems by means protective
conductor (i.e., ECPs of the systems inside of a LPZ); f) all
metal parts and conductive services entering a LPZ (directly or
by using reliable SPDs); g) internal systems (via SPDs).
1966 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 23, NO. 4, OCTOBER 2008
Fig. 5. General schema of a large PVI with some of the potential hardware of the LPMS.
Where possible, incoming services should enter the LPZ at
the same location and be connected to the same BB (Fig. 1). In
other cases, bonding to a ring BB is recommended.
Design, material and dimensions of BN are explained in detail
in [15] and [19, Sect. 443].
3) Magnetic Shielding: Magnetic shielding is intended to re-
duce the MF inside a LPZ arising from lightning flashes to/near
the PVI. Thus, the non-attenuated MF is reduced to a suffi-
ciently low value of (Fig. 1).
Spatial shields are used to create single protected volumes as
follows (Fig. 1): a) the whole inverter-control building—LPZ
1; b) a single room containing sensitive PV equipment (e.g.,
PV inverter—LPZ 1 or 2); c) volume restricted to the sensitive
PV equipment by means of its shielded enclosure (e.g., PV
monitoring equipment—LPZ 2 or 3). Steel reinforcement (in
concrete) and metal facades are generally used to enclose build-
ings/rooms (mesh width below 5 m). Meanwhile, shielding of
lines (cable screening) is restricted to cabling (power and/or
telecommunication) by means metallic shield of cables or
closed metallic cable ducts.
Design, material and dimensions of magnetic shields for
both spatial shields and line shielding in PVIs may be derived
from IEC62305-4 [16]. This standard also outlines a theoretical
method, approved in [21], to evaluate the MF attenuation.
In PVIs, shielding of the single PV modules using metallic
frames and aluminum foil at the backside is very important as
aforementioned. Besides, metallic support structure of PV ar-
rays may be part of the BN helping strongly to shield PVG
(Figs. 1 and 5).
Reference [37] requires line shielding of PVG when its
ECPs are bonded to the external LPS. Nevertheless, in outer
zones, line shielding is always advisable for dc long cables
(m) In inner zones, line shielding is desirable
when feed sensitive PV equipment.
4) Line Routing: Suitable line routing minimizes induction
loop area thereby reducing induced internal overvoltages. The
loop area must be minimized by routing the cables as close as
possible to protective bounding conductors [37] (or inside nat-
ural components of BN—U-shaped conduits or metal trunking
[39]) and/or by routing electrical and signal lines together. Line
routing of PVG must meet: cables must be installed to provide
as short runs as possible; the PV string, PV array, and PV dc
main cables (+ and -) must be bundled together. The layout of
the PVG wiring is also important: enclosed wiring areas should
be kept as small as possible [6], [10], [37]. Examples of good
line routing techniques, which may be extrapolated to PVIs, are
given in [15], [39] and [19].
Line routing and shielding are important measures in outer
zones as well as in LPZ 1 if the effectiveness of its spatial
shielding is negligible.
Reference [22] highlights that routing precautions and line
shielding appear to be more effective measures to limit LEMP
coupling than the spatial shield.
5) Isolating Interfaces: Isolating interfaces may be used to
avoid induced overvoltages through the sensitive PV equipment
and its connected signal lines due to large loops or bad BN. Class
II equipment or isolation transformers meet the requirements.
6) Application of SPDs: SPDs are the most convenient de-
vices to achieve lightning and surge equipotential bonding for
live conductors of incoming lines in a LPZ and its connected
internal live circuits both power and signal. The basic approach
to the coordination of SPDs is the same in both circuit types,
but its differences lead to specific rules for the selection and in-
stallation: IEC 61643-12 [17] and IEC 61643-22 [40] for power
and signal lines, respectively.
HERNÁNDEZ et al.: LIGHTNING AND SURGE PROTECTION IN PVIS 1967
TABLE I
INSTALLATION OF SPDSACCORDING TO PVG SYSTEM GROUNDING
Fig. 6. Flowchart to apply SPDs in a PVG.
Power lines of PVIs will be the focus from now on. Require-
ments to apply SPDs on the ac side of PVIs are well known [17],
[41]. However, an adaptation of these requirements is necessary
on the dc side (i.e., PVG) due to its exclusive characteristics,
so that the following scheme in six steps should be addressed
(Fig. 6).
a) Step 1: Location of SPDs: The location of SPDs must
follow a general rule where it is established that SPDs shall be
installed at the entry of any LPZ (Figs. 1 and 5), as close as
possible to the boundary. Nonetheless, the effective protection
of the PV equipment inside the whole LPZ has to be ensured
against oscillation and induction phenomena as well. Additional
location of SPDs, inside a LPZ, will be necessary if the protec-
tion distance of the SPD [17] does not cover the protected equip-
ment. Thus, oscillation and induction phenomena could cause a
PV equipment failure in spite of the presence of a SPD when a
safety acceptable distance is not met.
The oscillation protection distance can be evaluated by
using [16]
(2)
with being equal to 25 V/m and the resulting effective
protective level, i.e., limited voltage between the SPD terminals
during the operating state.
The induction protection distance , for direct flashes (worst
case), can be estimated as [16]
(3)
being the factor of the shielding effectiveness at
boundary LPZ the corresponding one at boundary
LPZ or higher and the factor of routing precaution on
wiring.
More detailed information on formulas (2) and (3) and values
of different factors are given in [16].
As can be deduced from above formulas, oscillation and in-
duction protection distance depends on several parameters, as
shown in [16], [17], and [22]: SPD protection level, of
equipment and its input surge impedance, characteristics of both
lightning current at a particular point and connecting conduc-
tors, and lastly, protection measures to limit LEMP coupling.
Good design practices [17] advise that connecting conductors
of SPDs shall be as short as possible, without wiring loops.
SPDs shall withstand the discharge current expected at their
installation points in accordance with previous Section III
(Figs. 1 and 5). Class I tested SPD [42] realizes the transition
from LPZ to LPZ 1. Its discharge capacity, impulse
current current surge—ranges 25–100 kA. Its
voltage protection level is below 4 kV . At the
boundary from LPZ 1 to LPZ 2, Class II tested SPD [42] is used.
Its maximum (nominal) discharge current
current surges—ranges 10–65 kA (5–20 kA). Its is below
2 kV. Downstream at the boundary from LPZ 2 to 3, Class III
tested SPD [42] is recommended. Its maximum nominal values
of the combination wave generator are
20 kV/10 kA with a below 1 kV.
In order to protect PV modules and dc wiring the best location
of Class I tested SPDs is the PV array junction boxes (Figs. 1 and
5). Large PV array and PV dc main cables ( 15–20 m [37]) may
lead to the need of additional protection with SPDs at the outer
PV generator junction box (if available), when the requirements
for the protection distances and are not fulfilled. In the
same way, the distance of PV string cable between SPD and PV
modules should not exceed protection distances. In the dc main
distribution board, Class I tested SPDs shall ensure that par-
tial lightning current will mainly be diverted into the grounding
system. Lastly, to protect the inverter, Class II tested SPDs shall
be fitted at the inverter end of the dc cabling (dc secondary dis-
tribution board), as close as possible to the inverter. PV moni-
toring equipment and sensitive PV equipment may need addi-
tional Class III tested SPDs.
The mode of protection depends on the PVG system
grounding (Table I). Nevertheless, in TT (grounded line -)
and IT systems, two SPDs may solely protect in common and
differential mode if one of them fulfils requirements of [41].
b) Step 2: Selection of Electrical Characteristics: The pre-
ferred type of SPD for PVG circuits is voltage limiting type SPD
[42] (e.g., metal-oxide varistors). Voltage switching type SPD
[42] (e.g., spark gap devices) is not suitable.
PVG open-circuit voltage, under standard test conditions
(STC), , with a margin of 25% [27], [37], sets
the maximum continuous operating voltage of SPDs in
any PVG system grounding (TT, TN, IT). The choice of the
SPD energy withstand and depending
on Class of SPD) shall be based on the current surge to be
expected at the installation point dependent upon the chosen
LPL (Section 3).
PVGs are current-limiting installations therefore, short-cir-
cuit protection in the SPD is not necessary. On the other hand,
the protective device (PD) to achieve personnel safety on the
dc side—dc residual current monitor (grounded systems) or in-
sulation monitoring device (floating systems) [43]—may also
work with a disconnector function of thermal protection. Thus,
1968 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 23, NO. 4, OCTOBER 2008
a disconnector inside or outside the SPD to get thermal and per-
sonnel safety protection is not required if the PD of personnel
safety is already present in the PVG.
c) Step 3: Failure Modes: It is safer to select a SPD which
fails open rather than to select an SPD which fails short. In the
first case service priority is overriding, the SPD is isolated and
the equipment is no longer protected. In the second one, the
PVG is disabled by means of the performance of the PD of per-
sonnel safety.
d) Step 4: Relation of the SPD With Other Devices: In both
normal and fault conditions SPDs shall not cause disturbance to
the PD of personnel safety. When coordinating SPDs and the
PD, it is recommended that, at the nominal discharge current
this last device shall not operate, but at higher currents it is not
obligatory.
e) Step 5: Choice of :For each LPZ, the of the PV
equipment shall be greater than or equal to of their SPDs
with at least 20% [17] of safety level [16], [17]).
f) Step 6: SPD Coordination: PVGs usually may require
the use of two (or more) SPDs in cascade in order to reduce the
electrical stress over the protected PV equipment to an accept-
able value. To get an acceptable sharing of the stress between
the SPDs, according to their energy withstand, coordination is
needed [16], [17]. The coordination principle requires knowl-
edge of the characteristics of both SPDs and protected PV equip-
ment as well as the threat (waveform) at the point of the PVG:
partial lightning current or induced/conduced current
(or ). An additional test current, having a minimum
steepness of 0.1 kA/ s , is also necessary [16] for coor-
dination purposes. Coordination must be assured with relevant
waveshapes.
Keeping in mind that only voltage limiting type SPDs may be
used on PVGs, there are two coordination variants: the residual
voltage of all SPDs is the same or it rises stepwise from the outer
SPD to the inner SPD.
The coordination may be proved by the application of coordi-
nated SPD families of any manufacturer or by calculation [16]
that may require computer simulation with complex PVIs.
C. Protection Measures Against Injury to Living Beings
While LPS has been designed according to [15], there is a
risk of injury to living beings due to touch and step voltages.
In case of general measures [15] does not prevent this risk it is
recommended: to design extended meshed grounding systems,
use of insulation for the exposed down-conductors, use of high
resistivity for the surface layer of the soil and warning notices.
VI. ASSESSMENT AND MANAGEMENT OF RISK DUE TO
LIGHTNING AND SURGES IN AN ACTUAL PVI: UNIVER PROJECT
The Univer Project [18] consists of four PVGs, completely
integrated at Jaén University Campus with different architec-
tural solutions and configurations (PVGs and inverters). In
Fig. 7, a general arrangement describing the Univer Project
PVI and their components is illustrated.
In Univer Project, the very detailed risk assessment of light-
ning and surges has been possible by using the reported method
in [14]. In this assessment, a wide range of parameters has been
considered as follows [17]: environmental, incomes services
Fig. 7. Arrangement of Univer Project.
layout, personnel safety, economics (the cost of repair or re-
placement of PV equipment) and the expense of protection (cost
of materials, design and installation).
Firstly, for this assessed PVI, the parameters influencing and
their values have to be selected. Secondly, based on that, risk
components may be identified and calculated, then they
are summed to obtain the risks to . Results of each risk
have to be compared with the tolerable value (defined by
a designer). If lightning protection is not
necessary, otherwise protection measures shall be adopted. Fur-
thermore, the knowledge of allows the designer to evaluate
the economic benefits of installing protection measures. When
lightning protection is necessary, the installation of an adequate
type of LPS is only compulsory if . The installation
of an adequate LPMS helps to decrease the risk until
whether LPS is not necessary or LPS is already
planned.
Critical parameters, according to the share of each risk com-
ponent in the total risk , have to be identified to determinate
the most efficient measures to reduce the risk . However, in
Univer Project, lightning and surge protection was performed
in its design and assembly phase, before the development of
the risk management method presented in [14]. Therefore, this
method is now used in order to assess the actual risk with the
already existing protection measures.
Two main zones are defined and evaluated individually in
Univer Project: inside the inverter-control building and the four
PVGs. The relevant types of selected losses are: loss of human
life (D1) and loss of economic value (D4).
Due to space limitations, the description in detail of this risk
assessment is not possible in this paper, therefore, only a short
overview of results (Table II) and the main adopted measures
could be given. The SIRAC software tool [14] has assisted us in
the calculation of the risk components.
The protection measures for the four PVGs are as follows.
•Class IV LPS: nine air-termination rods bonded to the
single earth-termination system. Exposed down-conduc-
tors are equipped with a PVC-isolation.
•Equipment grounding of PVGs is a single ring earth
electrode bonded to the foundation earth electrode of the
HERNÁNDEZ et al.: LIGHTNING AND SURGE PROTECTION IN PVIS 1969
TABLE II
LOSSES AND RISK VALUES FOR UNIVER PROJECT
Fig. 8. Ring earth electrode of PVGs 1 and 2.
inverter-control building (Fig. 8). The electrode depth is
greater than 0.5 m. 10 m are kept as maximum distance
between different ring conductors.
•Construction of BNs (2-D meshed structures) formed
by metalwork of support structure of PV modules [see
Fig. 9(a)–(c)]. Several BBs are located in each indepen-
dent support structure for bonding of: ECPs of dc side, PV
dc and signal cables via SPDs.
•Shielding by means of framed PV modules. In PVGs 1
and 2, dc cable trenches are covered along their full length
with a buried bare guard wire. Besides, their large PV
string cables are shielded using closed metallic cable ducts
[Fig. 9(a)]. PVGs 3 and 4 also use the same practice of
line shielding for PV array and PV dc main cables [see
Figs. 9(b) and (c)].
•Suitable line routing: PV dc cables are bundled together
as close as possible to protective bounding conductors
(Fig. 9).
•Class I tested SPDs to protect PV modules and dc wiring
are located at both the PV array junction boxes [Fig. 10(a)]
and outer PV generator junction box.
•Use of tar layer (high resistivity) as soil surface (Fig. 8).
Protection measures for the inverter-control building are as
follows.
•Class IV LPS: on the roof edge and parapet air-termination
wires bonded to the single earth-termination system via six
down-conductors.
•Single-foundation earth electrode of the inverter-control
building bonded to: external LPS, external metal installa-
tion, structural metal parts, and BN.
Fig. 9. BNs of: (a) PVG 1 or 2; (b) PVG 3; (c) PVG 4.
•Construction of a spatial shielding (three-dimensional
meshed structure) for the whole inverter-control building
volume (LPZ 1). The PV inverters are located inside LPZ
2 by means their enclosures only (Fig. 11). Line shielding
is used for signal lines. Four BBs are located inside this
building for bonding of: internal metal installation, ECPs
of the PVI (ac and dc side), PV dc/ac power lines and
signal cables via SPDs (both incoming and inner lines).
•Suitable line routing: PV dc main and ac PV supply ca-
bles are bundled together as close as possible to protective
bounding conductors.
•Class I tested SPDs are installed at ac and dc main dis-
tribution board [see Fig. 10(b) and (c)]. Class II tested
1970 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 23, NO. 4, OCTOBER 2008
Fig. 10. For the PVIs 1 and 2, available SPDs at: (a) PV array junction boxes;
(b) and (c) ac and dc main distribution board; (d) ac secondary distribution
board.
Fig. 11. Spatial shielding of PV inverter (middle) of PVG 1. Main and sec-
ondary distribution boards (dc—right and ac—left).
SPDs are located at ac and dc secondary distribution board
[Fig. 10(d)]. Class III tested SPDs are used for signal lines.
The hardware cost for the lightning and surge protection rep-
resented the 3.60% of the system cost. Cost was divided about
70% for LPS (mainly due to earth-termination system) and 30%
for LPMS (0.30% due to SPDs). It is important to remark that
some above hardware, such as grounds, realizes additionally
functions such as personnel and fire safety.
VII. CONCLUSION
Lightning and surge protection in PVIs is feasible both tech-
nically and economically. On the one hand, the particular char-
acteristics of PVIs, together with a lack of specific standard for
them in this scope, obligate the adaptation of the general stan-
dards of CLVPDSs to know the potential protective measures.
A comprehensive set of design rules is provided in this paper as
basic guidance. On the other hand, a later risk assessment (by
means of technical/economical balance) in each PVI will deter-
mine the tailored specific set of advisable protective measures.
In Univer Project, the extra cost of this protection (3.60% of the
system cost) is of secondary importance given the increase of
safety and availability.
REFERENCES
[1] C. B. Rogers, “The protection of photovoltaic power systems from
lightning,”in Proc. 15th IEEE Photovoltaic Specialists Conf., May
1981, pp. 761–766.
[2] D. C. Carmichael and G. T. Noel, “Development of low-cost modular
designs for photovoltaic array fields,”IEEE Trans. Power App. Syst.,
vol. PAS-104, no. 5, pp. 1005–1011, May 1985.
[3] H.-J. Stern and H. C. Karner, “Lightning induced EMC phenomena
in photovoltaic modules,”in Proc. IEEE Int. Symp. Electromagnetic
Compatibility, Aug. 1993, pp. 442–446.
[4] H. Häberlin and R. Minkner, “A simple method for lightning protection
of PV-systems,”in Proc. 12th EPSEC, Apr. 1994, pp. 1885–1888.
[5] H. Häberlin, “Interference voltages induced by magnetic fields of sim-
ulated lightning currents in PV modules and arrays,”in Proc. 17th
EPSEC, Oct. 2001, pp. 2343–2346.
[6] H. Becker, TÜV Rheinland Apr. 2000, Lightning and overvoltage pro-
tection in photovoltaic and solar thermal systems.
[7] Protection of Structures against Lightning, IEC Std. 61024 ser., 1994.
[8] Protection against Lightning Electromagnetic Impulse, IEC Std. 61312
ser., 1998.
[9] H. Becker, W. Vaaßen, and F. Vaßen, “Lightning and overvoltage pro-
tection in PV and solar thermal systems,”in Proc. 16th EPSEC, May
2000, pp. 2257–2260.
[10] Common Practices for Protection Against the Effects of Lightning on
Stand-Alone Photovoltaic Systems Tech. Rep. IEA-PVPS T3-14, Oct.
2003, International Energy Agency.
[11] A. Kern and F. Krichel, “Considerations about the lightning protection
system of mains independent renewable energy hybrid-systems. Prac-
tical experiences,”J. Electrostatics, vol. 60, pp. 257–263, Mar. 2004.
[12] Overvoltage Protection for PV Power Generating Systems—Guide,
IEC Std. 61173,, 1992.
[13] Protection Against Lightning—Part 1: General Principles, IEC Std.
62305-1, 2006.
[14] Protection against Lightning—Part 2: Risk Management, IEC Std.
62305-2, 2006.
[15] Protection against Lightning—Part 3: Physical Damage to Structures
and Life Hazard, IEC Std. 62305-3, 2006.
[16] Protection against Lightning—Part 4: Electrical and Electronic Sys-
tems within Structures, IEC Std. 62305-4, 2006.
[17] LV Surge Protective Devices—Part 12: Surge Protective Devices Con-
nected to LV Power Distribution Systems—Selection and Application
Principles, IEC Std. 61643-12, 2002.
[18] M. Drif, P. J. Pérez, J. Aguilera, G. Almonacid, P. Gomez, J. de la Casa,
and J. D. Aguilar, “Univer project. A grid connected PV system of
at jaén university. Overview and performance analysis,”Solar Energy
Materials and Solar Cells, vol. 91, pp. 670–683, May 2007.
[19] Electrical Installations of Buildings—Part 4–44: Protection for Safety-
Protection against Voltage Disturbances and Electromagnetic Distur-
bances, IEC Std. 60634-4-44, 2006.
[20] J. C. Hernandez, P. G. Vidal, and F. Jurado, “Guidelines to require-
ments for protection against electric shock in PV generators,”in Proc.
IEEE Power Eng,. Soc. General Meeting, Jun. 2005, pp. 17–22.
[21] A. Kern, F. Heidler, M. Seevers, and W. Zischank, “Magnetic fields
and induced voltages in case of a direct strike. Comparison of results
obtained from measurements at a scaled building to those of IEC
62305-4,”J. Electrostat., vol. 65, pp. 379–385, May 2007.
[22] F. Fiamingo, M. Marzinotto, C. Mazzetti, Z. Flisowski, G. B. Piparo,
and G. L. Amicucci, “Evaluation of SPD protection distance in low-
voltage systems,”J. Electrostat., vol. 65, pp. 363–370, May 2007.
[23] Electromagnetic Compatibility—Part 4–5: Testing and Measurement
Techniques—Surge Immunity Test, IEC Std. 61000-4-5, 2005.
[24] Recommended Practice on Surge Testing for Equipment Connected to
LV (1000 V and less) AC Power Circuits, IEEE Std. C62.45, 2002.
[25] Insulation Coordination for Equipment within LV Systems—Part 1:
Principles, Requirements and Tests, IEC Std. 60664-1, 2007.
[26] PV Module Safety Qualification—Part 2: Requirements for Testing,
IEC Std. 61730-2,, 2004.
[27] PV Module Safety Qualification—Part 1: Requirements for Construc-
tion, IEC Std. 61730-1, 2004.
[28] Safety of Power Converters for Use in PV Power Systems, IEC Std.
62109, to be published.
HERNÁNDEZ et al.: LIGHTNING AND SURGE PROTECTION IN PVIS 1971
[29] Inverters, Converters, Controllers and Interconnection System Equip-
ment for Use With Distributed Energy Resources, UL Std. 1741, 1999.
[30] Standard for Interconnecting Distributed Resources with Electric
Power Systems, IEEE Std. 1547, 2003.
[31] PV Systems-Characteristics of the Utility Interface, IEC Std. 61727,
2004.
[32] Recommended Practice for Utility Interface of PV Systems, IEEE Std.
929, 2000.
[33] C. Bouquegneau, “A critical view on the lightning protection interna-
tional standard,”J. Electrostat., vol. 65, pp. 395–399, May 2007.
[34] M. Becerra, V. Cooray, and Z. A. Hartono, “Identification of lightning
vulnerability points on complex grounded structures,”J. Electrostat.,
vol. 65, pp. 562–570, Aug. 2007.
[35] Electrical Installations of Buildings—Part 7: Requirements for Special
Installations or Locations—Section 712: Solar PV Power Supply Sys-
tems, IEC Std. 60364-7-712, 2002.
[36] LV Electrical Installations—Part 1: Fundamental Principles, Assess-
ment of General Characteristics, Definitions, IEC Std. 60364-1, 2005.
[37] Installation and Safety Requirements for PV Generators, PNW 82-481
(Ed. 1.0), IEC Std., to be published.
[38] W. I. Bower and J. C. Wiles, “Analysis of grounded and ungrounded
photovoltaic systems,”Proc. 1st WCPEC, pp. 809–812, Dec. 1994.
[39] Electromagnetic Compatibility—Part 5–2: Installation and Mitigation
Guidelines—Earthing and Cabling, IEC/TR Std. 61000-5-2, 1997.
[40] LV Surge Protective Devices—Part 22: Surge Protective Devices Con-
nected to Telecommunications and Signalling Networks—Selection
and Application Principles, IEC Std. 61643-22, 2004.
[41] Electrical Installations of Buildings—Part 5–53: Selection and Erec-
tion of Electrical Equipment-Isolation, Switching and Control, IEC
Std. 60364-5-53, 2002.
[42] LV Surge Protective Devices—Part 1: Surge Protective Devices Con-
nected to LV Power Distribution Systems—Requirements and Tests,
IEC Std. 61643-1, 2005.
[43] P. G. Vidal, G. Almonacid, P. J. Pérez, and J. Aguilera, “Measures
used to protect people exposed to a PV generator: ‘Univer project’,”
Progress in Photovoltaics: Research and Applications, vol. 9, pp.
57–67, Feb. 2001.
Jesús C. Hernández was born in Jaén, Spain. He received the M.Sc. and Ph.D.
degrees from the University of Jaén, Jaén, Spain, in 1994 and 2003, respectively.
Since 1995, he has been an Associate Professor in the Department of Elec-
trical Engineering, University of Jaén. His research interests are in the area of
renewable energy.
Pedro G. Vidal was born in Jaén, Spain. He received the M.Sc. and Ph.D. de-
grees from the University of Jaén, Jaén, Spain, in 1982 and 2001, respectively.
Since 1984, he has been an Associate Professor (with tenure) at the Depart-
ment of Electrical Engineering University of Jaén, Spain. His scientific interests
are in renewable energy.
Francisco Jurado (M’00–SM’06) was born in Linares, Spain. He received the
M.Sc. and Ph.D. degrees from the UNED, Madrid, Spain, in 1995 and 1999,
respectively.
Since 1986, he has been a Professor in the Department of Electrical Engi-
neering, University of Jaén, Jaén, Spain. His research activities have focused on
the topics of power systems and renewable energy.
