With increasing global supply of photovoltaic (PV) modules into free field as well as building added applications, product safety aspects have received increased attention. To address the latter Working Group 2 (WG2) of the Technical Committee for Solar Photovoltaic Energy Systems (TC 82) of the International Electrotechnical Commission (IEC) invested a considerable effort in updating the governing PV module safety standards – IEC 61730 series. Part 1 of IEC 61730 addresses the minimum requirements for module design while Part 2 covers the required test protocols and test sequences. In particular, PV system voltages of up to 1.500 V d.c. impose requirements on component materials and module construction that deserve a more detailed explanation rooted in international horizontal standards. A key underlying concept relevant to electrical safety is Insulation Coordination in accordance to IEC 60664 taking into consideration the service environment of the PV module as well as the system voltage (Pollution Degree and Overvoltage Category). Resulting from the latter are material properties (Material Groups) and construction requirements (spacing) governing protection against electric shock – e.g., type of insulation (basic, double, functional, reinforced, solid), minimum clearances (cl) and creepage distances (cr) as well as distance through insulation (dti) for cemented joints. This paper explains how the governing horizontal standard of Insulation Coordination (IEC 60664) relates to specific material and construction requirements of PV modules as a function of their intended use and application (system voltage, deployment environment) and the resulting requirements laid down in the new IEC 61730 series. A generic example will be given at the end to ease understanding.
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SAFETY OF PHOTOVOLTAIC MODULES – FOCUS ON INSULATION COORDINATION
Bengt Jaeckel1 , Guido Volberg2a , Joerg Althaus2b, Gerhard Kleiss3, Peter Seidel4, Markus Beck5 and Arnd Roth6
1 UL International GmbH, Admiral-Rosendahl- Strasse 9, 63263 Neu-Isenburg (Zeppelinheim), Germany
2a TÜV Rheinland LGA Products GmbH, Am Grauen Stein, 51105 Köln, Germany
2b TÜV Rheinland Energie und Umwelt GmbH, Am Grauen Stein, 51105 Köln, Germany
3 SolarWorld AG, Martin-Luther-King-Straße 24, 53175 Bonn, Germany
4 First Solar GmbH, Rheinstraße 4, 55116 Mainz, Germany
5 Siva Power, 2387 Bering Drive, San Jose, CA 95131, United States
6 VDE Prüf- und Zertifizierungsinstitut GmbH, Merianstraße 28, 63069 Offenbach, Germany
ABSTRACT:
With increasing global supply of photovoltaic (PV) modules into free field as well as building added applications,
product safety aspects have received increased attention. To address the latter Working Group 2 (WG2) of the
Technical Committee for Solar Photovoltaic Energy Systems (TC 82) of the International Electrotechnical
Commission (IEC) invested a considerable effort in updating the governing PV module safety standards – IEC 61730
series. Part 1 of IEC 61730 addresses the minimum requirements for module design while Part 2 covers the required
test protocols and test sequences.
In particular, PV system voltages of up to 1.500 V d.c. impose requirements on component materials and module
construction that deserve a more detailed explanation rooted in international horizontal standards. A key underlying
concept relevant to electrical safety is Insulation Coordination in accordance to IEC 60664 taking into consideration
the service environment of the PV module as well as the system voltage (Pollution Degree and Overvoltage
Category). Resulting from the latter are material properties (Material Groups) and construction requirements
(spacing) governing protection against electric shock – e.g., type of insulation (basic, double, functional, reinforced,
solid), minimum clearances (cl) and creepage distances (cr) as well as distance through insulation (dti) for cemented
joints.
This paper explains how the governing horizontal standard of Insulation Coordination (IEC 60664) relates to specific
material and construction requirements of PV modules as a function of their intended use and application (system
voltage, deployment environment) and the resulting requirements laid down in the new IEC 61730 series. A generic
example will be given at the end to ease understanding.
Keywords: IEC, IEC 60664, IEC 61730, safety, insulation coordination, protection against electric shock
protection class, pollution degree, cemented joint
1. INTRODUCTION
In 2014 the globally installed photovoltaic (PV) capacity
reached 178 GWp and at the time of writing the
200 GWp milestone has most likely already been
reached. While distributed generation (DG) of small (≈1
kWp - 20 kWp) roof top PV systems still constitutes a
significant market share, the trend in today's PV systems
is to medium (≈ 100 kW p - 1 MWp ) and increasingly
large-scale (> 1 MWp ) installations where , in particular,
the demand for higher system voltages arises . With
average PV module sales prices decreasing to the
≈$US0.70/Wp level balance of system (BOS) costs
constitute a far larger portion than in the past. In
particular, labor and cabling dominate BOS costs driving
system designs to increasingly higher system voltages –
in the 1.000 V - 1.500 V range. Higher voltages further
reduce electrical system losses, but such high d.c.
voltages constitute new challenges for PV system
component designs and materials that need to be
addressed in the relevant standards. As such,
maintenance of the pertinent standards needs to assure
compliance with state-of-the- art knowledge and best
practices for d.c. voltages of up to 1.500 V.
2. MOTIVATION
Over the past several years TC 82 WG 2 directed
significant efforts towards upda ting the IEC 61730 series.
One key objective was to align the main PV safety
standard to IEC horizontal standards, mainly to
IEC 60664 [4],[5],[6] and therefor implement the concept
of Insulation Coordination for PV modules. To
understand this concept is crucial for applying it to PV
modules. This paper, therefore, will review the key
aspects in IEC 60664 and highlight s the following four
points:
• Overvoltage Category
• Classes
• Pollution degree (PD)
• Material Groups (MG)
However, this paper or IEC 61730 are not intended to
obsolete the obligation to study IEC 60664 in detail.
3. TERMS AND DEFINITIONS
Standard series IEC 61730 [7] requires numerous key
definitions and a detailed understanding of electro
technical horizontal standards. Several terms where
highlighted in [1] like distance through insulation (dti),
clearance (cl) and creepage (cr). Additional terms and
definitions are provided in the standard [7] as well as in
IEC 60050 [8].
For the purpose of this paper the terms and definitions of
solid insulation, clearance, and creepage are important. In
addition the following terms need to be comprehended:
• Insulation Coordination
• Overvoltage Category
• Classes
• Pollution Degree (PD)
• Material Group (MG)
4. INSULATION COORDINATION
In a more historical approach Insulation Coordination
was described in the following way by D. V. RAZEVIG
in the The Great Soviet Encyclopedia published in 1979:
"measures taken to coordinate the level of insulation in
electrical equipment with the magnitudes of the
overvoltages acting on it and the characteristics of the
protection devices (protective gaps). The choice of an
insulation level is a technical-economic problem: for
each rated voltage of the electrical equipment there exists
a technically achievable and economically most
advantageous insulation level.
Before the advent of reliable arresters, insulation
coordination was a method of grading insulation in
which insulation breakdown 'for example, in the
equipment of an electric power substation' would be most
probable at a place where the consequences of the
breakdown are the least serious for service. Thus, the
insulation of a power line is reduced as it approaches a
substation, regarding the line as a unique arrester, and
the strength of the internal insulation was made
substantially greater than that of the external insulation:
breakdowns of external insulation usually do not cause
permanent damage. As methods of protection against
overvoltages developed, the insulation level in electrical
equipment came closer to the "natural level," which for
aerial power lines is defined as the breakdown voltage of
the insulation under load and, for electrical machines
and apparatus, as the rated service life of the insulation.
Insulation chosen according to natural level must have a
reliable system for protection from or limiting of
overvoltages. Statistical methods, which were necessary
because of the probabilistic nature of overvoltages, the
process of aging of insulation, and other factors, came
into general use in the 1960's for solving the problems of
the choice of insulation levels and the coordination of
insulation."
As part of IEC 60664 a far short er and more readily
comprehensible definition was established:
"insulation coordination: mutual correlation of
insulation characteristics of electrical equipment taking
into account the expected micro-environment and other
influencing stresses"
Insulation coordination is also defined in IEC 60050
[IEV 604-03 -08] as: "The selection of the electric
strength of equipment in relation to the voltages which
can appear on the system for which the equipment is
intended, and taking into account the service
environment and the characteristics of the available
protective devices."
While slightly different and with a different emphasize
the brief description s in IEC 60664 [4] , [5], [6] an d
IEC 60050 [8] are well suited to describe the use in
photovoltaics. I.e. the correlation of live parts in a micro -
climate where the micro-climate must be assessed and
can be very different depending on position of the live
part in the PV module and its purpose.
The concept of Insulation Coordination was first
introduced in power system to arrange the electrical
insulation levels of different components in the electrical
power system in such a manner that the failure of
insulators, when occurring, is confined to the place where
it would result in the least damage of the system and is
easy to repair and replace. This leads to a probability of
failure study of all insulating parts to find the weakest
insulation point nearest to the power source. I.e . the aim
of insulation coordination is to reduce the risk of failure
to an economically and operationally acceptable level of
cost and disturbance of normal operation caused by
insulation failure.
Based on the definition and the scope for electronic
devices the following aspects are essential:
• What are the voltages that can occur?
! Overvoltages, system voltage and
working voltage.
• The intended use of the equipment – here the
PV module.
• Environment and serviceability of the
equipment.
a. Overvoltage C ategory
The Overvoltage Category is defined in IEC 60664-1 [4] .
The concept of Overvoltage Categories is used for
equipment energized directly from the low voltage mains.
The Overvoltage Categories have a probabilistic
implication rather than the meaning of physical
attenuation of the transient overvoltage downstream in
the installation.
An Overvoltage Category is a measure which defines a
condition concerning the transient overvoltage.
Categories I, II, III, and IV are applied for equipment
used in low voltage systems and PV installations must
comply with these requirements. A detailed description
of each category is given in IEC 60664- 1.
As per the definitions from IEC 60664 and with
agreement of TC 109 (Insulation coordination for low-
voltage equipment) PV modules are defaulted to
Overvoltage Category III equipment.
b. Concept of Classes:
Protection against electrical shock is achieved by a
combination of the constructional arrangements for the
equipment and device, together with the method of
installation.
Four classes are defined per IEC 61140 [9] and used in
the concept of Insulation Coordination for determination
of spacing requirements. Most PV modules were and
will be constructed following Class II requirements and
are therefore allowed to be installed in non-restricted
access areas.
Class II equipment must be marked with the graphical
symbol no. 5172 of IEC 60417 (double square) [10] .
c. Pollution Degree (PD )
Pollution Degree is a very important parameter and most
likely will vary between parts in a PV module. The
micro-environment determines the effect of pollution on
the insulation. The macro-environment, however, has to
be taken into account when considering the micro-
environment. It is important to differentiate between the
marco-climate and the local micro- climates of each live
part. Different construction means may reduce impact of
pollution at the insulation under consideration by
effective use of enclosures, encapsulation or hermetic
sealing. Such means to reduce pollution may not be
effective when the equipment is subject to condensation.
Small clearances can be bridged completely by pollutants
such as solid particles, dust and water and therefore
minimum clearances are specified where pollution may
be present in the micro-environment. Creepage distances
are similarly affected by pollutants. In g eneral , pollution
will become conductive in the presence of humidity or
water. Pollution caused by contaminated water, soot,
metal or carbon dust is inherently conductive.
IEC 60664 -1 [4] states four degrees of pollution: PD 1 to
PD 4. Here PD 1 represents a micro-climate with n o
pollution or only dry, non-conductive pollution. The
pollution has no influence on Insulation. The w orst- case
is represented by PD 4 where a continuous conductivity
occurs due to conductive dust, rain or other wet
conditions. For a PV module PD 4 may exist on the outer
surfaces, but those are typically not part of clearances or
creepages distances. For all other parts within the
module or better with in the laminate PD 1 to PD 3 apply.
For most PV module designs and their components the
default Pollution Degree is PD=2 while under test
defined in IEC 61730- 2. Special design can be
implemented and tested to verify compliance with PD 1.
This is an important aspect to understand because the
Pollution Degree has a great impact of required clearance
and creepages distances. More details can be found in
IEC 61730 [7] and [1].
The pollution will impact clearance and c reepage, but the
mirco-climate has further environmental stressors
impacting spacing. Relative humidity, condensation of
moisture and rain are obvious, but temperature and air
pressure will have an impact as well. This is why
materials must have certain temperature stability and why
de-rating of system voltage applies for high altitude
applications.
d. Material Group
IEC 60664-1 [4] defines four Material G roups as follows:
• Material Group I: 600 ≤ CTI; PLC=0
• Material Group II: 400 ≤ CTI < 600; PLC=1
• Material Group IIIa: 175 ≤ CTI < 400;
• Material Group IIIb: 100 ≤ CTI < 175. PLC=4
For simplicity of requirements in IEC 61730 MG IIIa and
IIIb are combined into MG=3.
CTI (comparative tracking index) is determined in
accordance to IEC 60112 [11] using solution A. The CTI
compares the performance of various insulating materials
under test conditions to form conductive tracks or show
tracking induced by high voltages. CTI provides a
qualitative comparison and in the case of insulating
materials having a tendency to form tracks, it also gives a
quantitative comparison. UL 746A [12] uses a PLC
classification of 0 to 5. For glass, ceramics or other
inorganic insulating materials which do not track,
creepage distances need not be greater than their
associated clearance for the purpose of insulation
coordination. Most materials used today in photovoltaic
modules typically fall within material groups I and II.
5. EXAMPLE
While the new standard indeed appears more complex it
draws on the established horizontal standards, complies
with IEC regulations, enables innovative new ways to
apply advanced materials and construction methods, and
can lead to lower costs via reduced spacing.
The following example provides a comparison between
Edition 1 and 2 on a mock-module that was formally an
application class A module and is now a Class II module.
All details, especially the spacing are summarized in
Table 1.
Details within this example: All materials to be used for
insulation have a CTI rating of >600 and therefor fall
under the Material Group I (MG=I). Based on the
installation site and the required Class (e.g. by national
electric code – for this example Class II) it is assumed
that the insulation system must be treated as Pollution
Degree II (PD=II). Table 3 of IEC 61730-1 Ed . 2
provides all spacing requirements. The resulting module
will have a live part – outer surface (touchable) – spacing
of 10mm which is slightly larger than today. But if it can
be proven that the encapsulation system of live parts
reduced the pollution degree to PD=1 the spacing could
be reduced to 6.4mm, lower than today.
However, if the module design allows for the use of the
concept of a Cemented J oint the spacing requirements are
even lower (2mm), but the requirements for testing and
verification are more stringent.
What does this mean? Adhesive joints within PV
modules can be considered Cemented Joints and are
acceptable as equivalent to reinforced insulation under
consideration of distances through C emented Joints per
Tables 3 and 4 of IEC 61730 Edition 2. Table 3 of
IEC 61730- 1 allows to reduce the spacing to only 2.0mm
in this 1.000 V system voltage example if a Cemented
Joint can be demonstrated under test.
Table 1: Comparison of a module designed for a
system voltage of 1.000 V and the impact of
Edition 2 vs E dition 1 on spacing. (PD=Pollution
Degree, MG=Material Group)
Application Class /
Class
Requirements of
polymeric materials
serving as support
for live parts
Based on
UL 746A
Section 5.3
CTI>250
(Usys<600V)
Thickness of
Backsheet/Frontsheet
Not defined,
results from
partial
discharge
test
8.4mm
(Table 4 in
edition 1)
Not defined
and
differently
interpreted
6.4mm for
PD=1
10.0mm for
PD=2 and
MG=I
Spacing live part to
outer surface
6.4mm
(PD=1)
or
10.0mm
(PD=2)
6. SUMMARY
A significant amount of work has been invested in
developing Edition 2 of IEC 61730. The project is
expected to come to a successful end soon and
publication of the new standard is expected in 2016.
The fast paced price reduction of PV modules not only
raised concerns about their quality but also about their
safety. To better define safety relevant parameters and to
comply with IEC regulation to use horizontal standards
the current draft was developed employing the concepts
of Insulation Coordination, Classes, P ollution Degree and
Material Groups. The respective background s of th ese
concepts were highlighted in this paper. As evident from
the example provided in section 5, some designs will
require larger spacing. However, innovative module
design enables improve d total area efficiency of PV
modules due to reduced component spacing. This, in
turn, will result in further cost reduction and make clean
PV energy even more competitive.
7. REFERENCES
[1] Jaeckel, B., et al, "Safety of Photovoltaic Modules –
an Overview of the Significant Changes Resulting
from Maintenance of IEC 61730 Series", 29th
European Photovoltaic Solar Energy Conference –
Amsterdam (2014)
[2] Jaeckel, B., et al, "Combined standard for PV module
design qualification and type approval: New IEC
61215 – series", 29th European Photovoltaic Solar
Energy Conference – Amsterdam (2014)
[3] IEC Guide 108 "Guidelines for ensuring the
coherency of IEC publications – Application of
horizontal standards."
[4] IEC 60664-1: Insulation coordination for equipment
within low-voltage systems – Part 1: Principles,
requirements and tests
[5] IEC/TR 60664-2- 1: Insulation coordination for
equipment within low-voltage systems – Part 1:
Principles, requirements and tests
[6] IEC 60664-3: Insulation coordination for equipment
within low-voltage systems – Part 3: Use of coating,
potting or molding for protection against pollution
[7] IEC 82/923/ CDV and 82/924/CDV 61730- series,
Photovoltaic (PV) Module Safety Qualification
[8] IEC 60050- series, International Electrotechnical
Vocabulary
[9] IEC 61140:2001, Protection against electric shock –
Common aspects for installation and Equipment with
Amendment 1 (2004)
[10] IEC 60417: Graphical symbols for use on equipment
–Symbol originals
[11] IEC 60112:2003, Method for the determination of the
proof and the comparative tracking indices of solid
insulating materials
[12] UL 746C: Polymeric Material- Use in Electrical
Equipment Evaluations
ResearchGate has not been able to resolve any citations for this publication.
Since release of Edition 1 of IEC 61730 series the photovoltaic industry has experienced rapid growth and undergone a large number of changes. As a result, during the past two years Working Group 2 (WG2) of the technical committee for Solar Photovoltaic Energy Systems (TC82) of the International Electrotechnical Commission (IEC) invested a considerable effort in updating the governing PV module safety standards to respond to PV industry needs as well as reflect technological changes and advances. In particular, with the revision of IEC 61730 a need to reflect the current understanding of low voltage DC (up to 1,500V d.c.) components and materials used in the construction of PV modules arouse. This includes permitting new materials and new designs while at the same time complying with international horizontal standards that need to be met in order to comply with governing national electric codes. Part 1 of IEC 61730 addresses the minimum requirements for module design while Part 2 deals with the required tests protocols and test sequences. New tests have been added to Part 2 of Edition 2 as the material requirements necessitate the confirmation of their properties during PV module operation. This paper explains the most crucial changes to Edition 1 of IEC 61730 series and shows that most PV modules on the market today already fulfill the requirements of the second edition. In this context it is important to understand the concepts of component approvals, insulation coordination, protection against electric shock, overvoltage category, protection class, material group and pollution degree as well as the resulting voltage limitation conjunction to minimum clearances (cl) and creepage distances (cr) and distance through insulation (dti) for cemented joints.
The commercial success of photovoltaics (PV) is largely based on the long-term reliability of the PV modules. Current PV modules tend to carry a performance warranty of 25 years. These modules are typically qualified to IEC 61215 or IEC 61646 – design qualification and type approval for terrestrial crystalline Si (c-Si) or thin-film (TF) technologies, respectively. These qualification tests have shown to adequately identify design, material, and process flaws that could lead to premature field failures. Consequently, PV module customers have come to appreciate the criticality of the tests set forth in IEC standards 61215 and 61646. The PV market has come to trust these IEC standards, and as such they represent an essential component of the success of the rapid growth of the PV market. Since the last revisions of the standards the knowledge of PV failure modes increased dramatically. To retain market trust in the IEC standards, maintenance of the pertinent standards needs to assure compliance with state-of-the-art knowledge and best practices. To be prepared for the upcoming technology developments this new structure allows fast changes to keep the standards up-to date. Over the past two years Working Group 2 (WG2) of the technical committee for Solar Photovoltaic Energy Systems (TC82) within the International Electrotechnical Commission (IEC) invested a considerable effort to update and merge the terrestrial PV module design qualification and type approval standards into a single IEC 61215 series. Part 1 addresses the minimum requirements for testing with subparts 1-1 through 1-4 addressing PV technology specific deviations – e.g. stabilization – while Part 2 deals with the required tests protocols and test sequences. In the current committee draft of edition 3 the power output verification has been completely overhauled, new tests have been added, and pass/fail criteria revised. This paper explains the most crucial changes to edition 3 of IEC 61215 and provides the rationale for the applied changes. There are multiple reasons for the changes, but one significant justification is that the new standard series allows more flexibility and faster responses to changes in any given PV technology.
Protection against electric shock -Common aspects for installation and Equipment with Amendment
IEC 61140:2001, Protection against electric shock -Common aspects for installation and Equipment with Amendment 1 (2004)
60664-2-1: Insulation coordination for equipment within low-voltage systems – Part 1: Principles, requirements and tests
- Iec Tr
IEC/TR 60664-2-1: Insulation coordination for equipment within low-voltage systems – Part 1: Principles, requirements and tests
Guidelines for ensuring the coherency of IEC publications – Application of horizontal standards
- Iec Guide
IEC Guide 108 " Guidelines for ensuring the coherency of IEC publications – Application of horizontal standards. "
Method for the determination of the proof and the comparative tracking indices of solid insulating materials
IEC 60112:2003, Method for the determination of the proof and the comparative tracking indices of solid insulating materials
Combined standard for PV module design qualification and type approval: New IEC 61215 -series
- B Jaeckel
Jaeckel, B., et al, "Combined standard for PV module design qualification and type approval: New IEC 61215 -series", 29th European Photovoltaic Solar Energy Conference -Amsterdam (2014)
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