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

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Status
Not Published
Current Stage
PPUB - Publication issued
Start Date
14-Dec-2006

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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.

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SIST-TS IEC/TS 62257-7-1:2008
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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: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch

PRICE CODE
Commission Electrotechnique Internationale
International Electrotechnical Commission
For price, see current catalogue
МеждународнаяЭлектротехническаяКомиссия
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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

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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

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

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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.
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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.
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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.).

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.
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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
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.
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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
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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;

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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
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
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
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SIST-TS IEC/TS 62257-7-1:2008
TS 62257-7-1© IEC:2006(E) – 11 –
3.15
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
3.16
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
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
...

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