SIST-TS IEC/TS 62257-7-1:2008

Recommendations for small renewable energy and hybrid systems for rural electrification - Part 7-1: Generators - Photovoltaic arrays

Specifies the general requirements for erection and operation of PV arrays in decentralized rural electrification systems. Provides safety and fire protection requirements for ELV and LV PV arrays intended to uninformed persons, including owners and users of the premises where photovoltaic arrays are installed; informed workers (e.g. electricians) working on these systems; and emergency workers (for example fire fighters).

Priporočila za sisteme malih obnovljivih virov energije in hibridne sisteme za elektrifikacijo podeželja - 7-1. del: Generatorji - Fotonapetostni nizi

General Information

• Status: Published
• Public Enquiry End Date: 30-Sep-2008
• Publication Date: 01-Oct-2008
• ICS: 27.160 - Solar energy engineering
• ICS: 27.190 - Biological sources and alternative sources of energy
• ICS: 29.160.20 - Generators
• Technical Committee: PVS - Solar photovoltaic energy systems
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 24-Sep-2008
• Due Date: 29-Nov-2008
• Completion Date: 02-Oct-2008
• Ref Project: IEC/TS 62257-7-1 - Recommendations for small renewable energy and hybrid systems for rural electrification - Part 7-1: Generators - Photovoltaic arrays

Standards Content (Sample)

SLOVENSKI STANDARD
SIST-TS IEC/TS 62257-7-1:2008
01-november-2008
3ULSRURþLOD]DVLVWHPHPDOLKREQRYOMLYLKYLURYHQHUJLMHLQKLEULGQHVLVWHPH]D
HOHNWULILNDFLMRSRGHåHOMDGHO*HQHUDWRUML)RWRQDSHWRVWQLQL]L
Recommendations for small renewable energy and hybrid systems for rural electrification
- Part 7-1: Generators - Photovoltaic arrays
Ta slovenski standard je istoveten z: IEC/TS 62257-7-1
ICS:
27.160 6RQþQDHQHUJLMD Solar energy engineering
27.190 Biološki viri in drugi Biological sources and
alternativni viri energije alternative sources of energy
29.160.20 Generatorji Generators
SIST-TS IEC/TS 62257-7-1:2008 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------

SIST-TS IEC/TS 62257-7-1:2008

---------------------- Page: 2 ----------------------

SIST-TS IEC/TS 62257-7-1:2008


TECHNICAL IEC


SPECIFICATION TS 62257-7-1





First edition
2006-12


Recommendations for small renewable energy
and hybrid systems for rural electrification –
Part 7-1:
Generators – Photovoltaic arrays
© IEC 2006 ⎯ Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: [phone] Telefax: [phone] E-mail: [e-mail] Web: www.iec.ch
PRICE CODE
XC
Commission Electrotechnique Internationale

International Electrotechnical Commission
For price, see current catalogue
МеждународнаяЭлектротехническаяКомиссия

---------------------- Page: 3 ----------------------

SIST-TS IEC/TS 62257-7-1:2008
– 2 – TS 62257-7-1© IEC:2006(E)
CONTENTS
FOREWORD.4
INTRODUCTION.6

1 Scope.7
2 Normative references .8
3 Terms and definitions .9
4 Design.15
4.1 Electrical design.15
4.2 Mechanical design.27
5 Safety issues.28
5.1 General .28
5.2 Protection against electric shock and fire .28
5.3 Protection against overcurrent.28
5.4 Protection against effects of lightning and over-voltage .31
6 Selection and erection of electrical equipment.32
6.1 Component requirements .32
6.2 Location and installation requirements .36
7 Acceptance .43
7.1 General .43
7.2 Conformance with system general specification.43
7.3 Wiring and installation integrity.43
7.4 Open circuit voltage .43
7.5 Open circuit voltage measurements for large PV arrays .44
7.6 Short circuit current measurements .45
7.7 Commissioning records .46
8 Operation/maintenance .47
8.1 General .47
8.2 Safety .47
8.3 Operation and maintenance procedures .47
9 Replacement .47
10 Marking and documentation.48
10.1 Equipment marking.48
10.2 Requirements for signs.48
10.3 Labelling of PV array and PV sub-array junction boxes.48
10.4 Labelling of disconnection devices .48
10.5 Fire emergency information signs.48
10.6 Documentation .49

Annex A (informative) Examples of commissioning records.50
Annex B (informative) Example of maintenance schedule .53
Annex C (informative) Replacement.55
Annex D (informative) Examples of signs.56
Annex E (informative) Case studies .57
Annex F (informative) Double switching in PV array.72

---------------------- Page: 4 ----------------------

SIST-TS IEC/TS 62257-7-1:2008
TS 62257-7-1© IEC:2006(E) – 3 –

Figure 1 – General functional configuration of a PV powered system .15
Figure 2a – Unearthed PV array and unearthed d.c. load application circuit.17
Figure 2b – Unearthed PV array and earthed d.c. load application circuit.17
Figure 2c – Unearthed PV array connected to a.c. loads via an isolated PCU
application circuit.18
Figure 2d – Unearthed PV array connected to a.c. loads via a non-isolated PCU
application circuit.18
Figure 2e – Earthed PV array and unearthed d.c. load application circuit.18
Figure 2f – Earthed PV array and earthed d.c. load application circuit.19
Figure 2g – Earthed PV array connected to a.c. loads via an isolated PCU application
circuit.19
Figure 2h – Centre-tapped earthed PV array connected to a.c. loads via an isolated
PCU application circuit.19
Figure 2i – Earthed PV array connected to a.c. loads via a non-isolated PCU
application circuit.19
Figure 2 – PV system earthing configurations .19
Figure 3 – PV array exposed-conductive parts earthing decision tree .20
Figure 4 – Unearthed PV array and d.c. loads configuration.21
Figure 5 – PV array diagram – single string case .22
Figure 6 – PV array diagram – multi-string case.23
Figure 7 – PV array diagram – multi-string case with array divided into sub-arrays .24
Figure 8 – Blocking diode implementation (example) .36
Figure 9 – PV string wiring with minimum loop area .41
Figure D.1 – Example of sign required on PV array junction box (10.3) .56
Figure D.2 – Example of sign required adjacent to PV array main switch (10.4.2.) .56
Figure D.3 – Example of fire emergency information sign required in main building
switchboard (10.5.1) .56
Figure F.1 – Floating PV array operating at maximum power point.73
Figure F.2 – Floating PV array with single earth fault .74
Figure F.3 – Floating PV array with double earth fault.75
Figure F.4 – Floating PV array with double earth fault.76

Table 1 – Voltage domains for PV arrays .7
Table 2 – PV system earthing configurations .16
Table 3 – Number of parallel strings without overcurrent protection, n .29
P
Table 4 – Requirements for location of overcurrent protective devices according to the
earth configuration.30
Table 5 – Current rating of PV array circuits .34
Table 6 – Disconnecting means requirements in PV array installations .37
Table 7 – Location of disconnection devices according to system configuration, where
required .37
Table E.1 – Case studies overview list.57

---------------------- Page: 5 ----------------------

SIST-TS IEC/TS 62257-7-1:2008
– 4 – TS 62257-7-1© IEC:2006(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

RECOMMENDATIONS FOR SMALL RENEWABLE ENERGY AND
HYBRID SYSTEMS FOR RURAL ELECTRIFICATION –

Part 7-1: Generators – Photovoltaic arrays


FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
– the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
– the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC 62257-7-1, which is a technical specification, has been prepared by IEC technical
committee 82: Solar photovoltaic energy systems.
This first edition of IEC 62257-7-1 is based on IEC/PAS 62111 (1999); it cancels and replaces
the relevant parts of IEC/PAS 62111.

---------------------- Page: 6 ----------------------

SIST-TS IEC/TS 62257-7-1:2008
TS 62257-7-1© IEC:2006(E) – 5 –
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
82/406A/DTS 82/446/RVC

Full information on the voting for the approval of this technical specification can be found in
the report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 62257 series, published under the general title, Recommendations
for small renewable energy and hybrid systems for rural electrification can be found on the
IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual edition of this document may be issued at a later date.

---------------------- Page: 7 ----------------------

SIST-TS IEC/TS 62257-7-1:2008
– 6 – TS 62257-7-1© IEC:2006(E)
INTRODUCTION
The IEC 62257 series of publications intends to provide to different players involved in rural
electrification projects (such as project implementers, project contractors, project supervisors,
installers, etc.) documents for the setting-up of renewable energy and hybrid systems with
a.c. voltage below 500 V, d.c. voltage below 750 V and power below 100 kVA.
These publications provide recommendations for
– choosing the right system for the right place;
– designing the system;
– operating and maintaining the system.
These publications are focused only on rural electrification concentrated in, but not specific
to, developing countries. They must not be considered as all-inclusive of rural electrification.
The publications try to promote the use of renewable energies in rural electrification. They do
not deal with clean mechanism developments at this time (CO emission, carbon credit, etc.).
2
Further developments in this field could be introduced in future steps.
This consistent set of publications is best considered as a whole, with different parts
corresponding to items for the safety and sustainability of systems at the lowest possible life-
cycle cost. One of the main objectives of the series is to provide the minimum sufficient
requirements relevant to the field of application, i.e. for small renewable energy and hybrid
off-grid systems.
The purpose of this part of IEC 62257 is to propose a framework for project development and
management and it includes recommended information that must be taken into consideration
during all the steps of the electrification project.

---------------------- Page: 8 ----------------------

SIST-TS IEC/TS 62257-7-1:2008
TS 62257-7-1© IEC:2006(E) – 7 –
RECOMMENDATIONS FOR SMALL RENEWABLE ENERGY AND
HYBRID SYSTEMS FOR RURAL ELECTRIFICATION –

Part 7-1: Generators – Photovoltaic arrays



1 Scope
This part of IEC 62257 specifies the general requirements for erection and operation of PV
arrays in decentralized rural electrification systems.
This technical specification contains requirements for ELV and LV PV arrays (see Table 1).
Particular attention must be paid to voltage level, as this is important for safety reasons and
has an influence on protective measures and on the skill and ability level of people operating
the systems.
Table 1 – Voltage domains for PV arrays
Voltage domain Voltage (volts)
Alternating current Smoothed direct current
ELV
U ≤ 50 V U ≤ 120 V
n oc
LV
50 V < U ≤ 1 000 V 120 V < U ≤ 1 500 V
n oc
Note ELV limits are provided by IEC 61201.

For the sake of completeness, this technical specification gives requirements for d.c. voltages
below and above 120 V. However for rural electrification projects it is strongly recommended
to choose a voltage in the range of extra low voltage, taking into account the assumed skills
of the operators, installers and users. Nevertheless, designers must be aware that decreasing
the voltage means increasing the current and thus transferring voltage hazards to current
risks (risk of fire, etc.).
The following PV array configurations are considered (see Figure 5 to Figure 7):
a) single string of modules;
b) multi-string PV array;
c) PV array divided into several sub-arrays.
Direct current systems, and photovoltaic systems in particular, pose various hazards in
addition to those derived from conventional a.c. power systems, for example the ability to
produce and sustain electrical arcs with currents that are not much greater than normal
operating currents. This technical specification addresses those safety requirements arising
from the particular characteristics of photovoltaic systems.
The aim is to provide safety and fire protection requirements for:
− uninformed persons, including owner(s)/occupier(s) and users of the premises where
photovoltaic arrays are installed;
− informed workers (e.g. electricians) working on these systems; and
− emergency workers (for example fire fighters).
For installation of PV arrays see IEC 60364-7-712.

---------------------- Page: 9 ----------------------

SIST-TS IEC/TS 62257-7-1:2008
– 8 – TS 62257-7-1© IEC:2006(E)
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60050-811:1991, International Electrotechnical Vocabulary – Chapter 811: Electric
traction
IEC 60287 (all parts), Electric cables – Calculation of the current rating
IEC 60364 (all parts), Low-voltage electrical installations
IEC 60364-4-41, Low-voltage electrical installations – Part 4-41: Protection for safety –
Protection against electric shock
IEC 60364-5-54, Electrical installations of buildings – Part 5-54: Selection and erection of
electrical equipment – Earthing arrangements, protective conductors and protective bonding
conductors
IEC 60449, Voltage bands for electrical installations of buiildings
IEC 60529, Degrees of protection provided by enclosures (IP Code)
IEC 61140, Protection against electric shock – Common aspects for installation and
equipment
IEC 61173, Over-voltage protection for photovoltaic (PV) power generating systems – Guide
IEC 61201, Extra-low voltage (ELV) – Limit values
IEC 61215, Crystalline silicon terrestrial photovoltaic (PV) modules − Design qualification and
type approval
IEC 61643-12, Low voltage surge protective devices − Part 12: Surge protective devices
connected to low voltage power distribution systems − Selection and application principles
IEC 61646, Thin−film terrestrial photovoltaic (PV) modules − Design qualification and type
approval
IEC 62257-5, Recommendations for small renewable energy and hybrid systems for rural
electrification – Part 5: Protection against electrical hazards
IEC 62257-6, Recommendations for small renewable energy and hybrid systems for rural
electrification – Part 6: Acceptance, operation, maintenance and replacement
IEC 62305-2, Protection against lightning – Part 2: Risk management
IEC 62305-3, Protection against lightning – Part 3: Physical damage to structures and life
hazard

---------------------- Page: 10 ----------------------

SIST-TS IEC/TS 62257-7-1:2008
TS 62257-7-1© IEC:2006(E) – 9 –
3 Terms and definitions
3.1
available, readily
capable of being reached for inspection, maintenance or repairs without necessitating the
dismantling of structural parts, cupboards, benches or the like
3.2
blocking diode
diode connected in series to module(s), panel(s), sub-arrays and array(s) to block reverse
current into such module(s), panel(s), sub-array(s) and array(s)
3.3
bypass diode
diode connected across one or more cells in the forward current direction to allow the module
current to bypass shaded or broken cells to prevent hot spot or hot cell damage resulting from
the reverse voltage biasing from the other cells in that module
3.4
cable
assembly of one or more conductors and/or optical fibres, with a protective covering and
possibly filling, insulating and protective material
[IEV 151-12-38]
3.5
cable core
the conductor with its insulation but not including any mechanical protective covering
3.6
shield (of a cable)
a surrounding earthed metallic layer to confine the electric field within the cable and/or to
protect the cable from external electrical influence
Note Metallic sheaths, armour and earthed concentric conductors may also serve as shields.
[IEV 461-03-04]
3.7
class I equipment
equipment in which protection against electric shock does not rely on basic insulation only,
but which includes an additional safety precaution in that accessible conductive parts are
connected to the protective earthing conductor in the fixed wiring of the electrical installation
in such a way that accessible parts cannot become live in the event of a failure of the basic
insulation
NOTE 1 Class I equipment may have parts with double insulation or parts operating at SELV.
NOTE 2 For equipment intended for use with a flexible cord or cable, this provision includes a protective earthing
conductor as part of the flexible cord or cable.
3.8
class II equipment
equipment in which protection against electric shock does not rely on basic insulation only,
but in which additional safety precautions such as double insulation or reinforced insulation
are provided, there being no provision for protective earthing or reliance upon installation
conditions. Such equipment may be one of the following types:
− equipment having durable and substantially continuous enclosures of insulating material
which envelops all metal parts, with the exception of small parts, such as nameplates,
screws and rivets, which are isolated from live parts by insulation at least equivalent to
reinforced insulation. Such equipment is called insulation-encased Class II equipment;

---------------------- Page: 11 ----------------------

SIST-TS IEC/TS 62257-7-1:2008
– 10 – TS 62257-7-1© IEC:2006(E)
− equipment having a substantially continuous metal enclosure, in which double insulation is
used throughout, except for those parts where reinforced insulation is used, because the
application of double insulation is manifestly impracticable. Such equipment is called
metal-encased Class II equipment;
− equipment that is a combination of the types described in Items (a) and (b)

NOTE 1 The enclosure of insulation-encased Class II equipment may form part of the whole of the supplementary
insulation or of the reinforced insulation.
NOTE 2 If the equipment with double insulation or reinforced insulation throughout has an earthing terminal or
earthing contact, it is considered to be of Class I construction.
NOTE 3 Class II equipment may be provided with means for maintaining the continuity of protective circuits,
insulated from accessible conductive parts by double insulation or reinforced insulation.
NOTE 4 Class II equipment may have parts operating at SELV.
3.9
class III equipment
equipment in which protection against electric shock relies on supply at SELV and in which
voltages higher than those of SELV are not generated
NOTE Equipment intended to be operated at SELV and which have internal circuits that operate at a voltage other
than SELV are not included in the classification and are subject to additional requirements.
3.10
double insulation
insulation comprising both basic insulation and supplementary insulation
[IEV 195-06-08]
3.11
earthing
a protection against electric shocks
3.12
extra-low voltage
ELV
voltage not exceeding the relevant voltage limit of band I specified in IEC 60449
[IEV 826-12-30]
NOTE 1 See also IEC 61201.
NOTE 2 Voltage not exceeding 50 V a.c. and 120 V d.c. ripple free are considered to be ELV.
3.13
I
MOD_REVERSE
the current a module can withstand in the reverse direction to normal without damage to the
module. This rating is obtained from the manufacturer at expected operating conditions
NOTE 1 This current rating does not relate to bypass diode rating. The module reverse current is the current
flowing through the PV cells in the reverse direction to normal current.
NOTE 2 A typical figure for crystalline silicon modules is between 2 and 2,6 times the normal short circuit current
rating ISC MOD.
3.14
I
SC MOD
the short circuit current of a PV module or PV string at Standard Test Conditions (STC), as
specified by the manufacturer in the product specification plate
NOTE As PV strings are a group of PV modules connected in series, the short circuit current of a string is equal
to I .
SC MOD

---------------------- Page: 12 ----------------------

SIST-TS IEC/TS 62257-7-1:2008
TS 62257-7-1© IEC:2006(E) – 11 –
3.15
I
SC S-ARRAY
the short circuit current of a PV sub-array at Standard Test Conditions (STC), and equal to:
I = I × S
SC S-ARRAY SC STC MOD SA
where S is the number of parallel-connected PV strings in the PV sub-array
SA
3.16
I
SC ARRAY
the short circuit current of the PV array at Standard Test Conditions, and is equal to:
I = I × S
SC ARRAY SC STC MOD A
where S is the total number of parallel-connected PV strings in the PV array
A
3.17
junction box
closed or protected connecting device allowing making of one or several junctions
[IEV 442-08-03]
3.18
live part
conductor or conductive part intended to be energized in normal operation, including a neutral
conductor, but by convention not a PEN conductor or PEM conductor or PEL conductor
NOTE This conc
...