January 24, 2023 | Author: Anonymous | Category: N/A
IEC/TS 62257-7-1 ®
Edition 2.0 2010-09
TECHNICAL SPECIFICATION
Recommendations for small renewable energy and hybrid systems for rural electrification – Part 7-1: Generators – Photovoltaic generators
) E ( 0 1 0 2 : 1 7 7 5 2 2 6 S T / C E I w
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IEC/TS 62257-7-1 ®
Edition 2.0 2010-09
TECHNICAL SPECIFICATION
Recommendations for small renewable energy and hybrid systems for rural electrification – Part 7-1: Generators – Photovoltaic generators
INTERNATIONAL ELECTROTECHNICAL COMMISSION
PRICE CODE
ICS 27.160
XC
ISBN 978-2-88912-177-9
® Registered trademark of the International Electrotechnical Comm ission w
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–2–
TS 62257-7-1
© IEC:2010(E)
CONTENTS FOREWORD................................................ FOREWORD.............................. ................................... ................................... .................................... ................................... ...................... .....6 6 INTRODUCTION........................................ INTRODUCTION....................... ................................... ................................... .................................. .................................. ......................... ........8 8 1
Scope ................................ ................................................. .................................. .................................. .................................. ................................. ........................... ...........9 9
2
Normative references ................................. .................................................. .................................. ................................. ................................. .................... ...9 9
3 4
Terms and definitions ................................. .................................................. .................................. ................................... .................................. ................11 11 Design............................................. Design............................ .................................. ................................... ................................... .................................. ........................... ..........17 17 4.1 4. 1
Electrical design ................................ ................................................. ................................. ................................. ................................. .................. .. 17 4.1.1
General ................................. ................................................... ................................... .................................. ................................. ................17 17
4.1.3
Extra low voltage segmentation ................................ ................................................. ................................. ................20 20
4.1.2
4.1.4
Earthing system of a IES or a CES including a PV array............................ 18
Earthing system......................................... system.......................................................... .................................. ............................... ..............20 20
4.1.5 Ar Arch chit itect ect ures ur es ... ..... ..... ... ... ... ..... ..... ... ... ... ..... ..... ... ... ..... ... ..... ... ... ..... ... ..... ... ... ..... ... ..... ... ... ..... ... ..... ... ... ..... ... ..... ... ... ..... ... .. 28 4.1.6
Series-parallel configuration ................................. .................................................. ................................. .................... .... 32
4.1.8
Considerations due to prospective fault conditions within a PV array ......... .........32 32
4.1.7
4.1.9
Batteries in s ystems .................................. .................................................. ................................. ................................ ...............32 32
Considerations due to operating temperature ................................ ............................................ ............32 32
4.1.10 Component voltage ratings ................................ ................................................ ................................. ........................ ....... 33
4.2 4. 2
4.1.11 Performance issues ................................ ................................................. ................................. ................................. ................... 33
Mechanical design......................................... design......................................................... ................................. .................................. ....................... ...... 34 4.2.1
General ................................. ................................................... ................................... .................................. ................................. ................34 34
4.2.3
Mechanical loads on PV structures .................................. ................................................... .......................... .........34 34
4.2.2
4.2.4
4.2.5
5
4.2.6
Wind............................................... Wind.............................. .................................. .................................. ................................... ......................... .......34 34
Material accumulation on PV array ................................. .................................................. ........................... ..........34 34
Corrosion ............... ................................. ................................... .................................. .................................. ............................... ..............34 34
Safety issues ................................ .................................................. ................................... .................................. .................................. .............................. .............35 35 5.1 5. 1
General .................................. .................................................... ................................... .................................. .................................. ........................... ..........35 35
5.3 5. 3
Protection against overcurrent ................................. .................................................. ................................. ............................. .............35 35
5.2 5. 2
Protection against electric shock and fire ............... ................................ ................................. .............................. ..............35 35
5.4 5. 4
5.3.1 5.3.2
General ................................. ................................................... ................................... .................................. ................................. ................35 35 Overcurrent protection requirements for PV strings ............. ............................. ...................... ...... 35
5.3.4
Overcurrent protection sizing ............... ................................ .................................. .................................. .................... ... 36
5.3.3
5.3.5
Discrimination...................................... Discrimination...................... ................................. ................................. ................................. ..................... .... 36
Overcurrent protection location .............................. .............................................. ................................. .................... ... 37
Protection against effects of lightning and over-voltage ............................... ......................................... .......... 38 5.4.1
General ................................. ................................................... ................................... .................................. ................................. ................38 38
5.4.3
Protection against over-voltage ................................. ................................................. ................................ ................39 39
5.4.2
6
Thermal aspects ............................... ................................................ ................................. ................................. ........................ ....... 34
Protection against direct stroke from lightning ............................... ........................................... ............38 38
Selection and erection of electric al equipment ............................... ................................................ ................................. ................40 40 6.1 6. 1
Component requirements ............................... ................................................ ................................. ................................. ...................... ..... 40 6.1.1
PV modules ................................ .................................................. ................................... .................................. ............................ ...........40 40
6.1.3 6.1.4
Switching devices ................................ ................................................ ................................. ................................. ..................... ..... 40 Cables................................................. Cables................................ .................................. ................................... ................................... ................... .. 41
6.1.6
Plugs, sockets and couplers ................................. .................................................. ................................... .................... .. 44
6.1.2
6.1.5
PV array a nd PV su b-array junction boxes............................................ boxes................................................. ..... 40
Protection devices and cables sizing process ................................ ............................................ ............43 43
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TS 62257-7-1
© IEC:2010(E)
6.1.7
Fuses ................................. .................................................. .................................. .................................. ................................... .................... .. 44
6.1.9
Blocking diodes ................................ ................................................. ................................... ................................... ...................... ..... 45
6.1.8
6.2 6. 2
–3–
By-pass diodes .................................. .................................................. ................................. .................................. ....................... ...... 44
Location and installation requirements ............................... ................................................ ................................. .................. .. 45 6.2.1
6.2.2
Disconnecting m eans ............................... ................................................ .................................. ................................ ...............45 45
PV array pr oduction optimization .................................. ................................................... ............................. ............47 47
6.2.3 Ar Arra ra y v olta ol tage ge .. ..... ... ... ... ..... ..... ... ... ... ..... ..... ... ... ... ..... ..... ... ... ..... ... ..... ... ... ..... ... ..... ... ... ..... ... ..... ... ... ..... ... ..... ... ... ..... ... ..... ... 48 6.2.4
Wiring system ................................. .................................................. .................................. .................................. ......................... ........48 48
6.2.6
Earthing arrangement, protective conductors ............... ............................... .............................. ..............51 51
6.2.5
Surge protective devices ................ ................................ ................................. ................................. .......................... ..........51 51
7 Ac Acce cept ptan ance ce .. ..... ... ... ... ... ..... ..... ... ... ... ... ... ..... ..... ... ... ... ... ..... ..... ... ... ... ..... ... ..... ... ... ... ..... ... ..... ... ... ... ... ..... ... ..... ... ... ... ..... ... ..... ... ... ... . 51 7.1 7. 1
General .................................. .................................................... ................................... .................................. .................................. ........................... ..........51 51
7.3 7. 3
Wiring and installation integrity........................................... integrity............................................................ ................................. .................. .. 51
7.2 7. 2
7.4 7. 4
Conformance with system general specification ................................ ................................................ ..................... ..... 51
7.3.1
7.3.2
7.4.1
8
7.7 7. 7
General ................................. ................................................... ................................... .................................. ................................. ................51 51
Procedure......................................... Procedure........................ .................................. .................................. .................................. ....................... ...... 52
Open voltage measurements for PV arrays with a large number of .............52 stringscircuit ................................. ................ .................................. .................................. ................................... ................................... .............................. 52 7.5.1
General ................................. ................................................... ................................... .................................. ................................. ................52 52
7.5.3
PV arrays and sub-arr ays measurement ................................. ................................................. ................... ... 52
7.5.2
7.6 7. 6
Compliance with this sta ndard ................................ ................................................. .................................. ................... 51
Open c ircuit volta ge ................................ ................................................. .................................. ................................. ............................ ............51 51 7.4.2
7.5 7. 5
Compliance with wiring s tandards............................................... tandards.............................................................. ...............51 51
Procedure......................................... Procedure........................ .................................. .................................. .................................. ....................... ...... 52
Short circuit current m easurements .................................. .................................................. ................................. ..................... .... 53 7.6.1
7.6.2
General ................................. ................................................... ................................... .................................. ................................. ................53 53
Procedure......................................... Procedure........................ .................................. .................................. .................................. ....................... ...... 53
Commissioning records ................................... .................................................... .................................. .................................. .................... ... 54
Operation/maintenance ................................. ................................................. ................................. ................................. ................................ ................55 55
8.1 8. 1
General .................................. .................................................... ................................... .................................. .................................. ........................... ..........55 55
8.3 8. 3
Operation and maintenance procedures .............................. ............................................... ................................. .................. 55
8.2 8. 2
Safety ................................. .................................................. ................................... ................................... .................................. .............................. .............55 55
9 .................................................. ................................... .................................. .................................. .............................. .............56 56 Replacement ................................ 10 Marking and documentation ................................ ................................................. ................................. ................................. ........................... ..........56 56 10.1 Equipment marking........................................ marking......................................................... .................................. .................................. ...................... ..... 56
10.2 Requirements for signs...................................... signs....................................................... ................................. ................................. ................... .. 56
10.3 Labelling of PV array and PV sub- array junction boxes.............................. boxes.......................................... ............56 56 10.4 Labelling of disconnection d evices ................................... .................................................... .................................. .................... ... 56
10.4.1 General ................................. ................................................... ................................... .................................. ................................. ................56 56
10.4.2 PV array disconnecting device.............................................. device.............................................................. ..................... ..... 56
10.5 Fire emergency information signs ................................. .................................................. .................................. ........................ ....... 56
10.5.1 General ................................. ................................................... ................................... .................................. ................................. ................56 56
10.6 Documentation ................................ ................................................ ................................. .................................. .................................. .................... ... 57
Anne An nex x A (i (inf nfor orma mati tive) ve) Ex ample am ple s of comm co mm iss io ioni ning ng re reco cords rds ... ..... ... ..... ... ... ..... ... ..... ... ... ..... ... ..... ... ... ..... ... ..... ... ... ... 58 Anne An nex x B (i (inf nfor orma mati tive) ve) Ex ample am ple of maint ma int en enan ance ce sche sc hedu dule le ..... .. ..... ..... ... ... ... ... ... ... ..... ... ..... ... ... ... ... ... ..... ... .... .. 61 Anne An nex x C ( in info form rm at ativ ive) e) Rep la lace ceme ment nt .. ..... ... ... ... ... ..... ..... ... ... ... ..... ... ..... ... ... ... ..... ... ..... ... ... ... ..... ... ..... ... ... ... ..... ... ..... ... ... ... ... . 63
Anne An nex x D ( in info form rm at ativ ive) e) Ex Exam ampl ples es of sign si gns s .. ..... ... ... ... ... ... ..... ..... ... ... ... ..... ... ..... ... ... ... ..... ... ..... ... ... ... ..... ... ..... ... ... ... ..... ... .... .. 64 Anne An nex x E (i (inf nfor orma mati tive) ve) Case Ca se st stud udies ies .. ..... ..... ..... ... ... ... ... ... ..... ..... ... ... ... ..... ... ..... ... ... ... ..... ... ..... ... ... ... ..... ... ..... ... ... ... ..... ... ..... ... .. 65
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TS 62257-7-1
© IEC:2010(E)
Anne An nex x F ( in info form rmat ativ ive) e) Doub Do uble le swit sw itch chin ing g in PV arra ar ra y .. ..... ..... ..... ... ... ... ... ... ..... ... ..... ... ... ... ... ... ... ..... ... ..... ... ... ... .. 75 Bibliography........................................... Bibliography.......................... .................................. .................................. ................................... ................................... ........................... ..........81 81 Figure 1 – General functional configuration of a P V system ............................... ............................................... ................... ... 18 Figure 2 – Configuration A – PV alone IES P
< 500
W – without inverter – d
< 15
m ..... .......... ........ ...24 24
Figure 3 – Configuration G – PV alone IES P
< 500
W – without inverter – d
> 15
m............. 24
Figure 4 – Configuration B – PV alone IES P
< 500
W – with inverter – d
< 15
m .................. .................. 25
Figure 5 – Configuration H – PV alone IES P
< 500
W – with inverter – d
> 15
m.................. 25
Figure 6 – Configuration C and E – PV alone IES or CES – P < 500 W – with inverter – d < 15 m .................................. ................................................... .................................. ................................... ................................... .................................. ........................ .......26 26 Figure 7 – Configuration I and K – PV alone IES or CES – P < 500 W – with inverter – d > 15 m .................................. ................................................... .................................. ................................... ................................... .................................. ........................ .......26 26 Figure 8 – Configuration D and F – Hybrid IES or CES – PV generator + inverter and other generator – d < 15 m................................... m.................................................... .................................. ................................... ............................... .............27 27 Figure 9 – Configuration J and L – Hybrid IES or CES – PV generator + inverter and other generator – d > 15 m................................... m.................................................... .................................. ................................... ............................... .............28 28 Figure 10 – PV array diagram – s ingle string case .................................. .................................................... .............................. ............29 29 Figure 11 – PV array d iagram – multi-string case................................................ case................................................................. ................... 30 Figure 12 – PV array diagram – multi-string case with array divided into into sub-arrays .............31 ............. 31
Figure 13 – Needs for overcurrent protection in PV strings ............................... ............................................... .................... .... 36 Figure 14 – Blocking diode implementation (example)......................................... (example).......................................................... ................... 45
Figure 15 – PV string wiring with minimum loop area ................................. .................................................. ........................... ..........49 49 Figure D.1 – Example of sign required on PV array junction box (10.3) ................. ................................. ................64 64 Figure D.2 – Example of sign required adjacent to PV array main switch (10.4.2) ................. ................. 64 Figure D.3 – Example of fire emergency information sign required in main building switchboard (10.5.1) ................................. .................................................. .................................. .................................. ................................... ......................... .......64 64 Figure F.1 – Floating PV array operatin g at maximum power point........................................ point........................................76 76 Figure F.2 – Floating PV array with single earth fault ................................. ................................................... ........................... .........77 77 Figure F.3 – Float ing PV arra y with double earth fault ................................. .................................................. .......................... .........78 78 Figure F.4 – Float ing PV arra y with double earth fault ................................. .................................................. .......................... .........79 79 Table 1 – Voltage domains f or PV arrays ................................. .................................................. .................................. .............................. .............9 9 Table 2 – Functions fulfilled by the technical room ................................ ................................................. ................................ ...............18 18 Table 3 – PV system earthing configurations – distance “d”
<
15 m....................................... m.......................................22 22
Table 4 – PV system earthing configurations – distance “d”
>
15 m....................................... m.......................................23 23
Table 5 – Requirements for location of overcurrent protective devices according to the earth configuration ................................. .................................................. ................................... ................................... .................................. ........................... ..........38 38 Table 6 – Current rating of PV arr ay circuits ................................. ................................................. ................................. ........................ ....... 42 Table 7 – Disconnecting means requirements in PV array installations ............... .............................. .................. ... 46 Table 8 – Location Location of disconnection devices according to system configuration, where required ................................... .................................................... .................................. .................................. ................................... ................................. ........................ .........46 46 Table A.1 – Verification of PV array general ratings and technical technical specifications ............... .................. ... 58 Table A.2 – Verification of compliance with the requirements of IEC 62257-7-1 ............... .................... ..... 59 Case 1: ELV PV array with number of parallel strings
< 3
– No battery ................................. .................................65 65
Case 2: ELV PV array with number of parallel strings
< 3
– With battery............................... 67
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TS 62257-7-1
© IEC:2010(E)
–5–
Case 3: ELV array with number of parallel strings
> 3
– No batter y ................................... ....................................... .... 69
Case 4: ELV array with number of parallel strings
≥ 3
– With battery ................................ .................................... .... 71
Case 5: ELV array with number of parallel strings
≥ 3
– 2 sub arrays – With battery ..... .......... ........ ... 73
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TS 62257-7-1
© IEC:2010(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION _ __ ___________ RECOMMENDATIONS FOR SMALL RENEWABLE ENERGY AND HYBRID SYSTEMS FOR RURAL ELECTRIFICATION – Part 7-1: Generators – Photovoltaic generators
FOREWORD 1) The International Electrotechnical Electrotechnical Commissi Commission on (IEC) is a worldwi worldwide de organization for standardization standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation 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)”). 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 nongovernmental 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 t wo organizations. 2) The formal decisions decisions or agreements of IEC on technical matters express, express, as nearly as possibl possible, e, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees. 3) IEC Publications Publications have the form of recommendations for international use and are accepted 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 misinterpre tation 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 itself does not provide any attestation of conformity. conformity. Independent certification bodies prov provide ide conformity assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any services carried out by independent certification bodies. 6) All users should should ensure that they have the latest ed edition ition of this publica publication. tion. 7) No liability shall attach to IEC or its directors, directors, employees, serv servants ants or agents including indiv individual idual 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 references cited in this publication. Use of the referenced referenced publications is indispensable for the correct application of this publication. 9) Attention is drawn to the possibility possibility that some of the elements of this IEC Publi Publication cation 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 –
th the e re qu quir ired ed supp su ppor ortt ca cann nnot ot be ob obta tain ined ed fo forr th the e pu publ blica ica tio n of an Inter In ter na nati tion onal al Stan St anda dard rd,, despite repeated efforts, or
–
th the e su subj bj ect is st stililll un unde derr te tech chni nica call de deve velo lopm pmen entt or whe re re,, for fo r an any y othe ot herr re reas as on on,, ther th ere e is the th e 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 specificat ion, has been prepared b y IEC technical committee 82: Solar photovoltaic energy systems.
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TS 62257-7-1
© IEC:2010(E)
–7–
This second edition cancels and replaces the first edition issued in 2006 and constitutes a technical revision. The main technical changes with regard to the previous edition are the following: – –
Th This is ne new w versi ver si on is fo focus cus ed on sm all PV ge gener ner at ator ors s up to 10 100 0 kW p. Cas e stud st udie ies s are ar e prov pr ovid ided ed..
The text of this technical specification is based on the following documents: Enquiry draft
Report on voting
82/583/DTS
82/604/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 lis t of all al l pa part rts s of th the e IE IEC C 62 6225 257 7 seri se ri es es,, pu publ blis ishe hed d un under der the th e ge gene nera rall ti tle , 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 stability 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 be •
transformed into an International standard,
•
reconfirmed,
•
withdrawn,
•
replaced by a revised edition, or
•
amended.
A bi lin gu gual al ed edit itio ion n of th this is doc um umen entt ma y be b e iss ue ued d at a lat er da date te..
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates that it contains colours which are considered to be useful for the correct understanding of its contents. Users should therefore print this document using a colour printer.
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© IEC:2010(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 –
choo ch oosi sing ng th the e r ig ight ht sy syst st em fo forr th the e r ig ight ht pl ace ;
–
des ig igni ning ng th the e sys te tem; m;
–
op oper erat atin ing g an and d ma maint int aini ai ning ng th the e syst sy stem em..
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 2 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 lifecycle 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 IEC 62257-7-1 is to pr opose a technical specification f or the design and building of small PV generators (e.g. up to 100 kW p) used in rural electrification. Numerous experts of TC 82 have expressed the opinion that the first edition of IEC/TS 622577-1 is far more general than just the PV array for rural electrification but can also be used for big PV arrays in big PV power stations. Therefore it is now necessary to develop a second edition more dedicated and more specific to rural electrification. It is the purpose of this second edition to specify the general requirements for the design and the safety of PV generator used in decentralized rural electrification systems.
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TS 62257-7-1
© IEC:2010(E)
–9–
RECOMMENDATIONS FOR SMALL RENEWABLE ENERGY AND HYBRID SYSTEMS FOR RURAL ELECTRIFICATION – Part 7-1: Generators – Photovoltaic generators
1
Scope
This part of IEC 62257 specifies the g eneral requirements for the design and safety of generators used in decentralized rural electrification systems. The earthing systems of the exposed conductive parts and neutral earthing systems which are considered in this technical specification are those specified in IEC 62257 series for IES (see IEC 62257-9-3 and IEC 62257-9-4) and CES (IEC 62257-9-2). 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 V Alternating current
Smoothed direct current
U n ≤ 50 V
U oc ≤ 120 V
ELV LV
50 V
< U n ≤ 1
000 V
120 V
< U oc ≤ 1
500 V
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. 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.
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 (IEV) – Chapter 811: Electric traction
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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 60364-7-712:2002, Electrical installations of buildings – Part 7-712: Requirements for special installations or locations – Solar photovoltaic (PV) power supply systems IEC 60529, Degrees of protection provided by enclosures (IP Code) IEC 61140, Protection against electric shock – Common aspects for installation and equipment IEC 61215, Crystalline silicon terrestrial photovoltaic (PV) modules − Design 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 Selection and application principles IEC 61646, Thin − film f ilm terrestrial photovoltaic (PV) modules − Design qualification and type approval IEC 61730 (all parts), Photovoltaic (PV) module safety qualification IEC 62257-1, Recommendations for small renewable energy and hybrid systems for rural electrification – Part 1: General introduction to rural electrification IEC 62257-5, Recommendations for small renewable energy and hybrid systems for rural electrification – Part 5: Protection against electrical hazards
IEC 62257-6, –Recommendations foroperation, small renewable energy hybrid systems for rural electrification Part 6: Acceptance, maintenance and and replacement IEC 62257-9-1, 62257-9-1, Recommendations for small renewable energy and hybrid systems for rural electrification – Part 9-1: Micropower systems IEC 62257-9-2, Recommendations for small renewable energy and hybrid systems for rural electrification – Part 9-2: Microgrids IEC 62257-9-3, Recommendations for small renewable energy and hybrid systems for rural electrification – Part 9-3: Integrated system – User interface IEC 62257-9-4, Recommendations for small renewable energy and hybrid systems for rural electrification – Part 9-4: Integrated system – User installation 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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Terms and definitions
For the purposes of this document, the following terms and definitions apply. 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 3.5 cable core the conductor with its insulation but not including any mechanical protective covering 3.6 CES Collective electrification system 3.7 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, sheaths, armour and earthed earthed concentric conductors conductors may al also so serve as shi shields. elds.
[IEC 60050-461:1984, 461-03-04] 3.8 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 equipment may have par parts ts with double ins insulation ulation or parts o operating perating at SELV.
NOTE 2 For equipment intende intended d for use with a flexible cord or c cable, able, this provision provision includes a protective earthing earthing conductor as part of the flexible cord or cable.
3.9 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
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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;
−
equipment having a substantially continuous metal enclosure, in which double in insulation sulation 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 (b))
NOTE 1 The enclosure of of insulation-enca insulation-encased sed Class II equipmen equipmentt may form part of the whole whole of the supplementary supplementary insulation or of the reinforced insulation. NOTE 2 If the equipment with double insula insulation tion or reinforced insu insulation lation throughout has an earthing terminal 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 maintaining the continuity of protective circuits, circuits, insulated from accessible conductive parts by double insulation or reinforced insulation. NOTE 4 Class II equipment equipment may have parts operating operating at SEL SELV. V.
3.10 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 intended to be operated at SELV and and which have inter internal nal circuits that operate operate at a voltage other than SELV are not included in the classification and are subject to additional requirements.
3.11 double insulation insulation comprising both basic insulation and supplementary insulation [IEC 60050-195:1998, 195-06-08] 3.12 earthing a protection against electric shocks 3.13 extra-low voltage ELV voltage not exceeding the relevant voltage limit of band I specified in IEC 60449 [IEC 60050-826:2004, 826-12-30] NOTE 1
See also IEC 61201.
NOTE 2
Voltage not exceeding exceeding 50 V a.c. and 120 V d d.c. .c. ripple fre free e are considered tto o be ELV.
3.14 HMPS hybrid micropower technologies
system:
micropower
system
including
3.15 IES Individual electrification system
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3.16 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 typ ica l fig ur e fo forr cry sta lli ne sil ico n mo modul dul es is bet wee n 2 and 2, 6 tim es the nor ma mall sho rt cir cui t cu curre rre nt rating ISC MOD.
3.17 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 group of PV modules connec connected ted in series, the short short circuit current of a str string ing is equal to I SC MOD .
3.18 I SC S-ARRAY
the short circuit current of a PV sub-array at Standard Test Conditions (STC), and equal to: I SC S-ARRAY = I SC STC MOD × S SA where S SA is the number of parallel-connected PV strings in the PV sub-array 3.19 I SC ARRAY
the short circuit current of the PV array at Standard Test Conditions, and is equal to: I SC ARRAY = I SC STC MOD × S A where S A is the total number of parallel-connected PV strings in the PV array 3.20 ju junc ncti tion on box bo x closed or protected connecting device allowing making of one or several junctions [IEC 60050-442:1998, 442-08-03] 3.21 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 concept does not necessarily imply a risk of electric shock.
[IEC 60050-195:1998, 195-02-19] 3.22 PEL conductor conductor combining the functions of both a protective earthing conductor and a line conductor [IEC 60050-195:1998, 195-02-14]
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3.23 protected extra-low voltage PELV an extra-low voltage system which is not electrically separated from earth, but which otherwise satisfies all the requirements for SELV 3.24 PEM conductor conductor combining the functions of both a protective earthing conductor and a midpoint conductor [IEC 60050-195:1998, 195-02-13] 3.25 PEN conductor conductor combining the functions of both a protective earthing conductor and a neutral conductor [IEC 60050-195:1998, 195-02-12] 3.26 power conditioning unit PCU a system that converts the electrical power delivered by the PV array into the appropriate frequency and/or voltage values to be delivered to the load, or stored in a battery or injected into the electricity grid 3.27 power conditioning unit, isolated a power conditioning unit where there is electrical separation between the input and output circuits (e.g. by means of an isolation transformer) 3.28 power conditioning unit, non-isolated a power conditioning unit where there is no electrical separation between the input and output circuits 3.29 PV array a) a mechanically integrated assembly of modules or panels and support structure that forms a d.c. electricity-producing unit. An array does not include foundation, tracking apparatus, thermal control, and other such components [IEC 61836:2007, 3.3.45 a) ] b) a mechanically and electrically integrated assembly of of PV modules, and other necessary components, to form a d.c. power supply unit [IEC 60364-7-712:2002, 712.3.4] NOTE A PV array may consist of a single PV module, module, a single PV string, or several several parallel-conn parallel-connected ected strings, or several parallel-connected PV sub-arrays and their associated electrical components. For the purposes of this standard the boundary of a PV array is the output side of the PV array disconnecting device. Two or more PV arrays, which are not interconnected in parallel on the generation side of the power conditioning unit, shall be considered as independent PV arrays.
3.30 PV array cable the output cable of a PV array that connects the PV array junction box to the PV array disconnecting device
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3.31 PV array, earthed a PV array where one of the poles of the d.c. output circuit is electrically bonded to earth 3.32 PV array, unearthed a PV array where none of the poles of the d.c. output circuit is electrically bonded to earth 3.33 PV array, floating a PV array where none of the po les of the d.c. output circuit is electrically bonded to earth and connected to an application circuit which is either unearthed or double isolated 3.34 PV array, isolated a PV array where there is at least a simple electrical separation between the PV array output circuit (d.c. side) and the a.c. system NOTE
A simple electrical separation of power circuits is usually achieved by means of a power transformer.
3.35 PV array junction box a junction box where all strings of any array are connected [IEC 60364-7-712:2002, 712.3.5, modified] 3.36 PV array voltage the PV array voltage is considered to be equal to V OC ARRAY under worst case conditions NOTE
The open circuit vo voltage ltage is depende dependent nt on the ce cell ll temperature and technology.
3.37 PV cell a) the basic unit of photovoltaic conversion, a semiconductor device that can convert light directly into electrical energy; b) the basic photovoltaic device [see IEC 60904-3] NOTE The preferred term is "solar photovoltaic cell" or "photovoltaic cell", colloquially referred to as a "solar cell".
3.38 PV module the smallest complete environmentally protected assembly of interconnected cells [IEC 60904-3] NOTE Colloquially referred to as a "solar module".
3.39 PV module junction box an enclosure affixed to a PV module, where the electrical connections to the PV module are made 3.40 PV string a circuit of series-connected modules
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3.41 PV string cable a cable connecting the modules in a PV string, or connecting the string to a junction box or to the d.c. terminals of the power conditioning unit 3.42 PV sub-array the portion of an array that can be considered as a unit 3.43 PV sub-array cable the output cable of a PV sub-array that carries only the output current of its associated subarray in normal operation, and that connects the PV sub-array with the other PV sub-arrays that constitute the PV array NOTE PV sub-array cables cables are only relevant for PV arrays that are divided into subsub-arrays arrays (see Figure 7 for clarification).
3.44 PV sub-array junction box an enclosure where all the PV strings of a PV sub-array are electrically connected in parallel and where protection devices may be located if necessary (see Figure 7) NOTE
PV sub-array junction boxes are only relevant for PV arrays that are divided into sub-arrays.
3.45 reinforced insulation insulation of hazardous-live-parts which provides a degree of protection against electric shock equivalent to double insulation NOTE Reinforced insulation insulation may comprise sever several al layers which cannot be tested singly as bas basic ic insulation or supplementary insulation.
[IEC 60050-195:1998, 195-06-09] 3.46 supplementary insulation independent insulation applied in addition to basic insulation, for fault protection [IEC 60050-195:1998, 195-06-07] 3.47 simple separation separation between electric circuits or between an electric on a local earth by means of basic insulation [IEC 60050-826:2004, 826-12-28] 3.48 ripple-free d.c. for sinusoidal ripple voltage, a ripple content not exceeding 10 % r.m.s. NOTE
Therefore the maximum peak value value does not exceed 120 120 V for a nominal 108 V ripple-free d.c. system.
3.49 SELV safety extra-low voltage an extra-low voltage system which is electrically separated from earth and from other systems in such a way that a single fault cannot give rise to the risk of electric shock
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3.50 STC standard test conditions a standard set of reference conditions used for the testing and rating of photovoltaic cells and modules. The standard test conditions are: a)
PV cell temperature of 25 ºC;
b)
irradiance in the plane of the PV cell or module of 1 000 W/m 2 ;
c)
light spectrum corre corresponding sponding to an atmospheric air mass of 1,5
3.51 V OC MOD
the open circuit voltage of a PV module at the coldest expected operating condition 3.52 technical room / cabinet room or cabinet where are located devices and apparatus dedicated to inter-connection of the different generators, protection of the different circuits, monitoring and control of the micropowersystem and interfacing with the application 3.53 trip current current which activates the protection device 3.54 V OC ARRAY
the open circuit voltage at Standard Test Conditions of a PV array, and is equal to: V OC ARRAY = V OC MOD × M where M is the number of series-connected PV modules in any PV string of the PV array. NOTE This technical specification specification assumes tha thatt all strings withi within n a PV array are connected in para parallel; llel; hence the open circuit voltage of PV sub-arrays and PV strings is equal to V OC ARRAY.
3.55 voltage differences of potential normally existing between conductors and between conductors and earth as follows: a) extra-low voltage: not exceeding 50 V a.c. or 120 V ripple-free d.c.; b) low voltage: exceeding extra-low voltage, but not exceeding 1 000 V a.c. or 1 500 V d.c. c) high voltage: exceeding low voltage. NOTE In consideration of ELV status, V OC ARRAY must be used.
4
Design
4.1 4.1.1
Electrical design General
The cases of use of PV arrays which are considered in this document are the following: PV array alone
For IES application circuit (IEC 62257-9-3 and IEC 62257-9-4)
PV array coupled to another generator (see IEC 62257-9-1)
and CES application circuit (IEC 62257-9-2)
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Figure 1 illustrates the general functional configuration of a PV powered system with the localization of the functions described in Table 2.
A PV generator
B
D
C
E Application circuit
Technical room/cabinet
Loads
F
F
F IEC
2079/10
Figure 1 – General functional configuration of a PV system Table 2 – Functions fulfilled by the technical room Function
Description
A
Interface: connection connection between PV generator a and nd technical room
B
Interface: isolation of the technical room from the PV generator
C
Other functions of the technical room + energy conversion, energy management, storage, if any
D
Interface: isolation of the application circuit from the technical room
E
Interface: connection between technical room and the application circuit
F
Earthing of exposed conductive part if required
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.). 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. Except where the array is less than 200 W and the array voltage is ELV, all current-carrying conductors from the array shall be capable of being interrupted using a load-breaking switch. NOTE
In unearthed systems this this is a ge general neral requirement requirement of IEC 60364.
In earthed systems (where the application circuit is earthed), the switch is required to interrupt current caused by an earth fault within the array. Because the array is current limited, overcurrent protection cannot provide interruption of this fault situation.
4.1.2 4.1.2.1
Earthing system of a IES or a CES including a PV array General
To consider the PV array earthing it is necessary to consider the complete system earthing configuration. Two separate issues are addressed: w
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ea eart rthi hi ng of the po powe werr cabl ca bles es (f (fun unct ctio iona nall e art hi ng) whe re re requ quire ire d for fo r op oper erat atio iona nall o r des ig ign n reasons;
–
ea eart rthi hi ng of ex expo pose sed d co cond nduc ucti ti ve par ts fo forr liligh ghtn tning ing pr prot otect ect io ion n an and/ d/or or eq equi ui pot en enti ti al bo bond ndin ing g (protective earthing).
NOTE
To realize earthing on the field, see IEC 62305-3.
An ea eart rth h co cond nduc ucto torr may ma y pe perf rfor orm m one or more mo re of thes th ese e func fu nc tio ns in an ins tall ta llat ation ion . Th The e dimensions and location of the conductor are very dependent on its function. Exposed conductive parts of the PV array need not be earthed only: –
if th the e li ght ni ng ri risk sk is ass es esse sed d to be lo low, w, an and d
–
if th the e PV arr ay in inst stal al lat io ion n co comp mplilies es wit h an y of o f th the e f ol lo lowin win g pr prov ovis isio ions ns (a (a,, b or c): c) : a) double insulation (applies only if the PV array complies with all 1), 1), 2) and 3): 1) general. PV modules complying with class A in accordance with IEC 61730; 2) wiring outside junction boxes. Where cables may co come me into contact with accessible PV array conductive parts, the cables shall be of a type affording double insulation; 3) wiring inside junction boxes. Conductors within junction boxes having double insulation shall be protected, secured or insulated so that, if any one conductor becomes detached from its termination, neither the conductor nor its functional insulation can come into contact with accessible metal. The attachment of one conductor to another by tying, lacing, clipping or the like, in such a manner as to prevent either conductor coming into contact with accessible conductive parts if it becomes detached from its termination, shall be deemed to comply with this requirement; b) protection by electrical separation in accordance with IEC 60364-4-41; c) protection by SELV or PELV in accordance with IEC 60364-4-41.
4.1.2.2
Earthing system of the power cables
DC power cables of the PV array shall be earthed when there is a risk of high frequency overvoltages due to lightning (see Figures 3, 5, 7). In this case the one pole of the PV array shall be earthed. NOTE
It is preferable preferable to earth the positive positive pole of the PV array array to avoid possible possible corrosion problems. problems.
If there is an equipotential bonding the earthing of the cables shall be made through the equipotential bonding system (see Figure 9). 4.1.2.3
Earthing of the technical room
The earthing of the exposed conductive parts of the technical room shall follow the requirements indicated in 4.1.2.4. 4.1.2.4 . The earthing of the electrical components included in the technical room, like the power conditioner, shall follow the recommendations of the manufacturers. 4.1.2.4
Earthing system of exposed conductive parts
There are two possible reasons for earthing exposed conductive parts of a PV array: a) to provide a path for fault currents to flow; b) to provide a path for high frequency currents due to lighting overvoltages to flow. To determine if a protection against lightning is necessary s ee IEC 62257-9-1, 6.1.2.2.
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Protection against lightning overvoltage is always required when the linear distance between the PV array and the technical room is more than 15 m. The surge arresters should be placed as close as possible to the PV array and to the technical room. 4.1.2.5
Equipotential bonding
Equipotential bonding is required as soon as PV array is coupled to another a.c. generator. Equipotential bonding is used to avoid uneven potentials due to overvoltages (including lightning overvoltages), across the system. The cable of the equipotential bonding between the generators and the technical room shall be run as physically close as possible to the live conductors in order to avoid any wiring loops able to induce perturbations in the circuits. The connections to earth shall be realized as close as possible to the equipment to be earthed. 4.1.2.6
Earthing conductor sizing
The sizing of the earthing cable shall b e made according to IEC 60364-5-54. In case of protection against lightning, the cross-section of this cable shall be at least 16 mm². In all cases, the cross-section of this cable shall withstand at least the 1,25 × I SSC C ARR AY continuously. The conductor shall comply with the provisions for earthing conductors specified in national wiring standards or in absence of such standards, with the provisions set out in IEC 60364-554 with respect to material and type, insulation, identification, installation, connections and aluminium conductors. 4.1.2.7
Recommended PV system earthing configurations
The following Table 3 and Table 4 show the recommended PV system earthing configurations for the different cases of use of PV array considered in this Technical Specification. To define the earthing configuration of a PV array, it is necessary to consider both the earthing status of the cables and the earthing status of the exposed conductive parts.
4.1.3 Extra low voltage segmentation In low voltage PV arrays, means should be provided to sectionalise each PV string into segments whose open circuit voltage at STC is within ELV. 4.1.4 4.1.4.1
Earthing system Earthing electrode
If a separate earthing electrode is provided for the PV array, this electrode shall be bonded to the installation earth. See recommendations on the design of electrodes for lightning protection in 62257-5, 9.6. 4.1.4.2
Earthing conductors
Al l PV arra ar ra yand e artconnection hin g co cond nduc uc to tors rs shal sh alll comp co mp ly wit h in th the eIEC mate ma60364-5-54. teri ri al, type ty pe,, ins ulat ul atio ion, n, id iden enti tific fic atio at ion, n, installation requirements specified
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Earthing terminal of PV system
When the PV array is earthed, the connection to earth shall be made at a single point and this point shall be bonded to the installation earth. In systems without batteries, this connection point shall be between the PV array disconnection device and the power conditioning unit and as close as possible to the powerconditioning system. In systems containing batteries, this connection point shall be between the charge controller and the battery protection device. NOTE 1 This is to allow for interruption interruption of any earth earth fault cur current. rent. NOTE 2 The earthing statu status s of the various sections sections of the installation is de determined termined at the design stag stage. e. Tables 1 and 2 are simply a guide to location of a suitable example wiring diagram for a variety of design options.
How to use Table 3 or 4: •
check the distance “d” between the PV array and the technical room and select the right table;
•
identify the type of system you want to install in the left column;
•
go through the table from the left left to the right and find an example of earthing.
4.1.4.2.2
PV system earthing conductor
If the PV array is earthed, the PV system earthing conductor shall be sized to carry 1,25 × I SC ARR ARR AY continuously, and comply with the provisions for earthing conductors specified in national wiring standards or in absence of such standards, with the provisions set out in IEC 60364-5-54 with respect to material and type, insulation, identification, installation, connections and aluminium conductors. The 15 m limit designates the linear distance “d” between the output of the photovoltaic array and the input of the technical room. The cable length may be longer than 15 m. The Engineering consultant in charge of the system design shall try to reduce the cable length for two reasons: •
Reduce the cost
•
Reduce the risk of of overvoltages due to to undesiderable loops (see IEC 62257-9-1)
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Table 3 – PV system earthing configurations – distance “d” PV generator Type of micropower system and configuration
PV alone IES P
earthed
a.c. only
earthed + surge arrester if any (see 62257-9-1 and 62257-9-4)
unearthed
indoor installation
Hybrid IES
J
all PV generator generators + inverter earthed and other generators (ex: genset)
PV alone CES
K
PV generator +inverter + microgrid
pv array
Hybrid CES
L
PV generator + inverter + microgrid
all generators
earthed
earthed + surge arrester (see 62257-9-1 and 62257-9-4)-
a.c. only
earthed
earthed
Figure 9
earthed
earthed + surge arrester (see 62257-96225 7-9-1 1 and 62257-9-4)-
a.c. only
earthed
earthed
Figure 7
earthed
earthed + surge arrester (see 62257-96225 7-9-1 1 and 62257-9-4)-
a.c. only
earthed
earthed
Figure 9
unearthed
earthed
micro grid
For ELV array supplying LV application circuit the inverter shall provide electrical separation between the PV array (and / or battery) and the application circuit. Annex G provides a test to determine if any inverter provides this separation. The lightning stroke risk shall be assessed according to IEC 62257-1, Annex B and the results used to decide on the need for surge protection. The only floating PV system is the one described in Figure 2. The following Figures 2 to 9 illustrate the different system earthing arrangements.
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Technical room/cabinet Application circuit
PV generator
+
DC loads
−
IEC
Exposed conductive part if any
NOTE
2080/10
Some components of such small pho photovoltaic tovoltaic IES may not have any exposed conductive part.
Figure 2 – Configuration A – PV alone IES P
500 W – without inverter – d
15 m
Technical room/cabinet Application
PV generator
circuit
d > 15 m +
DC loads
−
IEC
Figure 3 – Configuration G – PV alone IES P
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15 m
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Technical room/cabinet Application circuit
PV generator d 15 m
+
DC
DC loads
−
AC
AC loads
PE
IEC
Figure 5 – Configuration H – PV alone IES P
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500 W – with inverter – d > 15 m
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Technical Techn ical room room
Application circuit
PV generator d 15 m
+
AC
−
AC loads
PE for IES systems (see IEC 62257-9-3) PEN for CES systems (see IEC 62257-9-2) IEC
Figure 7 – Configuration I and K – PV alone IES or CES – P 500 W – with inverter – d > 15 m
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Technical room/cabinet Application circuit
PV generator + _
AC
AC loads
PE
AC generator
IEC
Figure 8 – Configuration D and F – Hybrid IES or CES – PV generator + inverter and other generator – d 15 m
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TS 62257-7-1
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Technical room/cabinet Application circuit
PV generator +
d > 15 m
_
d > 15 m AC
AC loads
PE See details below
AC generator
Equivalent to
IEC
2087/10
Figure 9 – Configuration J and L – Hybrid IES or CES – PV generator + inverter and other generator – d > 15 m 4.1.4.3
Particular case of a.c. application circuits
For all PV systems including a.c. application circuits, it is required that all a.c. application circuits be earthed. For small portable PV IES producing a.c. power through an inverter and for which it is impossible to earth the poles of the a.c. circuit, the inverter shall be double insulated. 4.1.5
Architectures
The diagrams in Figure 10 10 to Figure 12 12 show the basic electrical configurations of singlestring, multi-string and multi-sub-array PV respectively. The voltages to be used in rural electrification systems shall be chosen according to the skill of the local operators (see IEC 62257-9-1, Clause 9). The architecture of the PV array shall be chosen in order to comply with economic and operation constraints in order to provide the right power at the right voltage level.
The of ELV canpower be made only for small systems the value of increase the current low. use As soon as the of the s ystem increases it iswhere necessary to also theremains voltage in order to reduce both the current and the cross section of the power cables.
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PV array
Techical room PV module
−
Bypass diode
−
PV array main switch
PV array cable
NOTE 1
IEC
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If the array is designed designed with mor more e than 2 modules, ar array ray voltage could be over ELV limits. limits.
NOTE 2 Unless a battery is present a load-breaking load-breaking isolator is s sufficient ufficient as the PV a array rray main switch. switch. If a battery is present, overcurrent protection is required.
Figure 10 – PV array diagram – single string case
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e c i v e t d n n y e r o r i a t r c r u c e a r t e V v o r P o p
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0 1 / 9 8 0 2 C E I
m o o r l a c i h c e T +
n o i t c e n n o c s i d g n i r e t c s i V v e P d
e c i v e t d n n g e o r i n r t i r u c t c e s r t V e v o r P o p
TS 62257-7-1
h c t y i w a r r s n a i V a P m
−
e l b a c y a r r a V P
s e s a c l l a m e n t i s d y e s r i b u u q s e r r t o o n m e e t r s a y t s a f h o t s e r y r t a n u s d e o n m l c u e n o l E E B
x x o o b b y n y a n a r r o o r i i r t t a a c c n V n V o P j j u P
y a r r a V P
g n i r t e s l V b a P c +
y e K
−
g n i r t s V P
+
+
−
−
Figure 11 – PV array diagram – multi-string case
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PV array PV sub-array
PV sub-array unction box
PV sub-array cable PV string cable
PV string disconnection device
PV sub-array disconnection devices PV string overcurre overcurrent nt protection device
PV array overcurrent protection device
Technical room
PV array cable PV array main switch PV array unction box PV sub-array overcurrent protection devices
PV sub-array cable from nth PV array
Key
Elements that are not required in all cases Enclosure Boundary of system or sub-system
IEC
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Figure 12 – PV array diagram – multi-string case with array divided into sub-arrays NOTE In Figures 10 to 12, 12, components drawn in d dotted otted format are not requi required red in all cases. The fi figures gures indicate the location in the circuit when they are required. See text for requirements (Tables 5, 6 and 7, and subclauses 6.1.7 and 6.1.8 are examples).
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4.1.6
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Series-parallel configuration
To reduce mismatch and improve PV array yield, all PV strings within a PV array should be of the same technology, have the same number of series connected PV modules. In addition, all PV modules within the PV array should have similar rated electrical characteristics including short circuit current, open circuit voltage, maximum power current, maximum power voltage and rated power (all at STC). NOTE This is a design issue w which hich needs to be considered by the project implement er, particularly when replacing modules or modifying an existing system.
4.1.7
Batteries in systems
Batteries in PV systems can be a source of high prospective fault currents. The location of fault current protection related to battery systems is generally between the battery and charge controller and as close as practical to the battery. This protection can be used to provide overcurrent protection for PV array cables (see 5.3.4.3) provided the PV array cable is rated to withstand the same current as the battery overcurrent protection device. NOTE The current rating of of string cables must be much highe higherr in battery systems if no indi individual vidual o/c protection iis s provided (see Table 6). In this case, the nearest downstream o/c protection may be the battery fuse.
4.1.8
Considerations due to prospective fault conditions within a PV array
In any installation, the source of prospective fault currents needs to be identified. Systems containing batteries may have high prospective fault currents due to the battery characteristic (see 4.1.5). In a PV system without batteries, as the PV cells (and consequently PV arrays) behave like current sources under low impedance faults, much greater than normal full load currents will not always flow even under short circuit conditions. The fault current depends on the number of strings, the fault location and the irradiance level. This makes short circuit detection within a PV array very difficult. Electric arcs can be formed in a PV array with fault currents that would not trip an overcurrent device. The implications for PV array design that arise from these PV array characteristics are as follows. a) The possibility of line-to-line line-to-line faults, earth faults and inadvertent wire disconnections in the PV array need to be minimized more than for conventional electrical installations. (Note that in conventional electrical installations the large inherent fault current capability of the system will generally blow a fuse, trip a circuit breaker or other protection system in the case where a fault occurs.) b) Earth fault detection and disable could be required as part the system protection functions, depending on the array size and location, to eliminate the risk of fire. 4.1.9
Considerations due to operating temperature
PV modules ratings are stated at standard temperature conditions (25 °C). Under normal operating conditions, 25 °C is a comm on steady state tem perature rise with respect to the ambient temperature for crystalline silicon PV modules operating at the maximum power point under 1 000 W/m 2 solar irradiance and with adequate ventilation. This temperature rise can go to upa tofully 35 charged °C when battery). modules The are temperature open circuited (i.e. the array has been disconnected due rise can bePV even higher when irradiance levels are greater than 1 000 W/m 2 and when modules have poor ventilation.
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The following two main requirements on the PV array design derive from this operating characteristic of PV modules. a)
For some PV technologies, the efficiency reduces as the operating temperature increases (for crystalline silicon solar cells the maximum power decreases between 0,4 and 0,5 % per each °C rise in operating temperature). Therefore adequate ventilation of the PV array should be a design goal, in order to ensure optimum performance for both modules and associated components.
b)
All the components and e equipment quipment that may be in direct contact or near the PV array (conductors, inverters, connectors, etc.) need to be capable of withstanding the expected maximum operating temperature of the PV array.
c)
Under cold conditions, for crystalline silicon technology based cells, increases (see 4.1.8 for further considerations).
4.1.10
the voltage
Component voltage ratings
Open circuit voltage is one of the normal operating conditions of any PV array. Open circuit voltage can be as large as twice the nominal d.c. bus voltage. PV array components shall be rated for at least the open circuit voltage for a module temperature equal to the lowest ambient temperature of the site. 4.1.11
Performance issues
A PV arra ar ra y’s pe perf rfor orma manc nc e m ay be af affe fect cted ed by ma ny fact fa ct ors , suc h as: as : – shad sh adin ing; g; –
tem pe pera ratur tur e ris e;
–
volta vo lta ge drop dr op in cabl ca bles es;;
–
po pollllut utio ion n of th the e surf su rfac ace e of th the e arra ar ray. y.
Care shall be taken in selecting a site for the PV array. Nearby trees and buildings may cause shadows to fall on the PV array during some part of the day. It is important that any shadowing be almost eliminated or at least reduced to a very small time period as even the smallest shadow on the array can severely limit its performance. Issues of performance degradation due to temperature rise and the need for good ventilation 4.2.2.. Care should be taken to keep modules as cool as practicable. are described in 4.2.2 In the design process the sizing of cables within the array and in cable connections from the array to the application circuit affect the voltage drop in those cables under load. This can be particularly significant in systems with low output voltage and high output current. It is recommended that under maximum load conditions the voltage drop from the most remote module in the array to the terminals of the application circuit should not exceed 5 % of the nominal system voltage. Pollution of the surface of PV modules caused by dust, dirt, bird droppings, snow, etc. can significantly reduce the output of the array. Arrangements should be made to clean the modules regularly in situations where significant pollution may be a problem. Suitable devices shall be fitted to the photovoltaic array in order to limit dirt building up as the result of bird droppings. Devices such as spikes or tubing-covered wires mounted on the apex of the array can be useful deterrents for birds. Where such effects as sand winds or land animals may be present, the photovoltaic array shall be installed at suitable height above ground (typically 1,5 m to 2 m).
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NOTE For cold climates, climates, consider the max maximum imum voltage rating o off components for the maximum maximum voltage expected increase at the lowest expected temperature of the PV modules.
4.2 4.2.1
Mechanical design General
Support structures and module mounting arr angements should comply with applicable building codes (including earthquake requirements where relevant), regulations and standards. 4.2.2
Thermal aspects
Provisions should be taken in the mounting arrangement of PV modules to allow for the maximum expansion/contraction of the modules under expected operating temperatures, according to the manufacturer’s recommendations. NOTE Some types of PV modules degrade significantly significantly in perfor performance mance when inadequate ventilation ventilation allows the modules to operate at high temperature.
4.2.3
Mechanical loads on PV structures
The PV array support structures should comply with national standards and regulations with respect to loading characteristics. Particular attention should be given to wind loads on PV arrays. NOTE
4.2.4
Support structures structures are not usually a problem for small PV sy systems. stems.
Wind
The indications provided under this heading are for quality guidance. Under no circumstances shall these instructions be used as a replacement for a case-by-case, detailed calculation. Wind force applied to the PV array will generate a significant load for building structures. This extra load should be accounted for in assessing the capability of the building to withstand the resulting forces. On assessing this component, the maximum wind speed observed (or known) on site shall be used, with due consideration for punctual wind events such as cyclones, tornadoes, hurricanes, etc. The PV array structure shall be secured in an appropriate manner or in accordance with local building standards. 4.2.5
Material accumulation on PV array
Snow, ice, or other material may build up on the photovoltaic generator and should be accounted for when calculating the supporting structure for the modules and likewise, when calculating the building capability to support the generator. 4.2.6
Corrosion
When possible all structures shall be made of corrosion resistant materials e.g . aluminium, galvanized steel, treated wood poles or structures, etc. If the structure is metallic, aluminum or hot dipped galvanized steel are well suited to this type of use. If the array is installed in a marine or other highly corrosive environment, aluminum shall be anodized. Care should be taken to ensure that different metals are not in direct contact as this will encourage corrosion particularly in a salt environment. The same applies to all bolts, nuts and fasteners.
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Safety issues
5.1
General
Refer to the IEC 62257-5 technical specification. 5.2
Protection against electric shock and fire
For protection against electric shock the requirements of IEC 61140 shall apply. Referring to the 62257-5 technical specification the following requirements shall be applied: Protection by extra-low voltage systems (SELV and PELV systems) systems shall be classified as Class III or better. For all other systems, protection by double or reinforced insulation between any live conductor and any earthed or exposed conductive part (i.e.Class II modules and double or reinforced insulation for the whole PV array) is required. Earthing of one of the live conductors of the d.c. side is permitted, if there is at least simple separation between the d.c. side and the a.c. side. 5.3 5.3.1
Protection against overcurrent General
Fault currents due to short circuits in modules, in junction boxes or in module wiring or earth faults in array wiring can result in overcurrent in a PV array. PV modules are current limited sources but because they can be connected in parallel and also connected to external sources (e.g. batteries), they can be subjected to overcurrents caused by either multiple parallel adjacent strings or from external sources or both. 5.3.2
Overcurrent protection requirements for PV strings
Situations where overcurrent protection is required in PV strings are introduced in Figure 13 13..
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Yes
No Number of strings > 3?
No
Yes PV techno = cSi?
Yes
No
Refer to PV manufacturer
Yes
No
Battery?
Battery?
Protection
No Protection
Protection
Protection
IEC
NOTE 1
For systems systems including including batteri batteries, es, see 5.3.4.3.
NOTE 2
For cable ratings, see 6.1.4.
NOTE 3
cSi refers to crystalline silicon, (either mono-cryst alline or multi-cryst alline).
2091/10
Figure 13 – Needs for overcurrent protection in PV strings 5.3.3
Discrimination
Overcurrent protection within the PV array shall be graded in such a way that lower level protection trips first in the event of fault currents flowing from higher current sections to lower current sections of the PV array. NOTE When circuit breakers breakers with overcurrent overcurrent protection elements are used, they also also provide the disconnecting means required in clause 6.2.1 6.2.1..
5.3.4 5.3.4.1
Overcurrent protection sizing PV string overcurrent protection
If there are more than two strings in parallel then the maximum fault current which can flow in any one string is equal to the (number of strings –1) times the short circuit rating of one of the strings. Therefore if there are three or more parallel strings, the PV modules could be subjected to reverse currents of two or more times their nominal short circuit current. It is for this reason that the number of strings able to be connected in parallel without overcurrent protection in each string is linked to the reverse current rating of a module. Fault current protection is irrelevant when there are only one to two strings in parallel, and there is no battery storage system, provided the PV modules are capable of withstanding a reverse current equal to their short circuit current. For crystalline silicon modules, the number of strings in parallel without fusing shall not exceed 3.
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For other technologies, refer to manufacturer’s instructions if any. If no instructions are available, fuses shall be installed on every string. The rated tripping current (I ( I TRIP ) of overcurrent protection devices for PV strings shall be as specified by the PV module manufacturer. If the manufacturer does not give any recommendation, I TRIP shall be determined with the following formula: 1,45
× I
SC MOD NOTE 1
≤ I TRIP STRING
≤ 2
× I
.
SC MOD
The trippin g current is the current which activates the protection device.
NOTE 2 In some PV module technologies I SC S C MOD is higher than the nominal rated value during the first weeks or months of operation. This should be taken into account when establishing overcurrent protection and cable ratings.
5.3.4.2
PV sub-array overcurrent protection
The rated trip current (I ( I TRIP ) of overcurrent protection devices for PV sub-arrays shall be determined with the following formula: 1,45
× I SC S-ARRAY ≤ I TRIP S-ARRAY ≤ 2 × I SC S-ARRAY .
NOTE 1 PV sub array pro protection tection is not compulsory compulsory but if it is not used then the size of of the conductor for the su sub b array cable may be excessively large. Refer to Table 3. If PV sub array cables are used and protection provided then the protection and the cable size is related to I TRIP S-ARRAY. NOTE 2
It is thus better to compare compare two solutions th the e first one withou withoutt fuse in the sub array cable and the second
one with fuse. The physical size of the cables and the cost may be rather different from one solution to the other. It is the responsibility of the engineering consultant to choose the best techo-economic compromise. The greater the number of sub arrays, the higher the probability that fuses are usefull. See formula of sub array cables in Table 4 (sizing of PV array circuits).
5.3.4.3
PV array overcurrent protection
PV array cable overcurrent protection is only required for systems connected to batteries or where other sources of current may feed into the PV array under fault conditions. The trip current (I ( I TRIP ) of PV array overcurrent protection devices shall be rated as follows: 1,45
× I SC ARRAY ≤ I TRIP ARRAY ≤ 2 × I SC ARRAY
NOTE 1 The PV array overcurrent overcurrent protection dev devices ices are commonly insta installed lled between the battery and the char charge ge controller as close as possible to the battery. If these devices are appropriately rated, they provide protection to both, the charge controller and the PV array cable. In such c ases, no further PV array cable overcurrent protection between the PV array and the charge controller is required. NOTE 2 The current rati must be much higher higher battery sys systems tems if nobattery individual protection is provided (see Table rating 6). ng In of thisstring case,cables the nearest downstream o/c in protection may be the fuse.o/c protection
5.3.5
Overcurrent protection location
Overcurrent protection devices where required by the above clauses for PV array, PV subarray, and PV strings shall be placed electrically at the load end of those cables. NOTE The location location of the overcurrent overcurrent protection devic devices es at the load end of the w wiring iring is to pr protect otect the system and and wiring from fault currents flowing from other sections of the PV array or from other sources such as batteries.
Overcurrent protective devices location requirements are introduced in Table 5.
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Table 5 – Requirements for location of overcurrent protective devices according to the earth configuration
String cables and sub-array cables
Is the PV array floating? a
PV array cables in systems with batteries (5.3.4.3)
No
Yes
Is the PV array installation double insulated? b
No
Yes Protection on
Protection on
ONE
ALL ALL
live conductor
live conductors c
a
Floating PV array: which which is not directly connected to e earth arth and conne connected cted to an application application circuit circuit which is either unearthed or isolated.
b
If the PV array installation installation is dou double ble insulated w with ith respect to earth, th the e risk of an earth earth fault is greatly reduced. It is only under conditions of a double earth fault on a floating PV array that overcurrent protection would be required in both live conductors. A single overcurrent protection will clear faults which develop within junction boxes and short circuits between live conductors. Reducing the number of overcurrent protection devices, reduces the number of joints in the wiring system thus reducing the risk of fire due to bad joints and also reduces cost and installation time.
c
In an earthe earthed d PV array it is consi considered dered that th there ere is only one live cond conductor uctor (it is the one w which hich is not connected to earth).
5.4 5.4.1
Protection against effects of lightning and over-voltage General
For protection against over-voltages refer to IEC 61173 , IEC 62305-2 and IEC 62305-3. 5.4.2
Protection against direct stroke from lightning
A liligh ghtn tnin ing g prot pr otec ec ti tion on sy st stem em ha has s th the e ta task sk of preve pr eve ntin nt ing g sever se ver e da dama mage ge caus ca used ed by fi re or mechanical destruction in case of a direct lightning strike in a building or structure. (For the assessment of the lightning stroke risk, see Annex B of IEC 62257-9-1.) Lightning protection systems consist of three essential components: a) an air termination system, consisting of metallic masts or rods of sufficient height to divert lightning currents through their structure; b) a down conductor of sufficient sufficient cross-sectional area to conduct llightning ightning currents to earth; and c) an earth termination system. The installation of a PV array on a building has a negligible effect on the probability of direct lightning strikes; therefore it does not necessarily imply that a lightning protection system should be installed if none is already present. However, if the physical characteristics or prominence of the building do change significantly due to the installation of the PV array, it is
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recommended that the need for a lightning protection system be assessed in accordance with IEC 62305-2 and, if required, it should be installed in compliance with IEC 62305-3. For practical assessment of lightning risk in the field see also IEC 62257-9-1 Annex B. If a lightning protection system is already installed on the building, it should be verified that the PV array and associated equipment are within the protection zone of the system. If the PV array is not within the protection zone of the existing lightning protection system, additional air termination(s) in accordance with IEC 62305-3 should be provided. When a PV array is protected by a lightning protection system, the metal structure of the PV array should be bonded to the lightning protection system, unless the minimum safety clearances as specified in IEC 62305-3 can be achieved. 5.4.3 5.4.3.1
Protection against over-voltage Equipotential bonding
Damage caused by over-voltage is ultimately due to the failure of insulation between live parts or between live parts and earth. The intention of over-voltage protection is to equalize all exposed metallic sections of an installation to a common potential during the event of an over-voltage, to prevent insulation flashover. Equipotential bonding is therefore a most important over-voltage protection measure and shall be done in accordance with national standards or IEC 60364-5-54 (see also IEC 62257-5, IEC 61173). To avoid the formation of wiring loops between earthed conductors and d.c. cabling, equipotential bonding conductors should run parallel and as close as possible to the d.c. cabling. It is also recommended to branch the bonding conductor to run parallel with all the d.c. cabling branches (see 6.2.4.3.). 5.4.3.2 5.4.3.2.1
Surge arresters General guide
Surge arresters are a very common method of protecting electrical systems and equipment against over-voltages. When these devices are used the recommendations of IEC 61643-12 should be observed. Over-voltage protection with surge arresters should be provided when the PV power system meets any of the following criteria: a)
the risk of overvoltages due to lightning lightning has been assessed as as high (see Annex B IEC 62257-9-1),
b)
the system supplies critical loads (e.g. ttelecommunication elecommunication repeater stations), or
c)
the PV array has a rated capacity greater than 500 W, or
d)
the PV array is protected with with a lightning protection system.
Many commercial PV inverters and charge controllers are fitted with surge arresters on the PV input terminals, therefore this should be considered when specifying the over-voltage protection of the PV array. 5.4.3.2.2
Recommended specifications
The recommended specifications for surge arresters to protect PV arrays from over-voltages caused by indirect lightning strikes are as follows (refer to list of parameters for surge arrester selection in IEC 61643-12): a)
maximum continuous operating voltage ( U C ): U C > 1,3
b)
maximum discharge current ( I ma x): I ma x ≥ 5 kA;
× V OC STC GEN;
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c)
voltage protection level ( U p ): U C < U p < 1,1 kV.
6
Selection and erection of electrical equipment
6.1
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Component requirements
6.1.1 6.1.1.1
PV modules Operational conditions and external influences
Crystalline silicon PV modules shall com ply with IEC 61215. Thin film PV m odules shall comply with IEC 61646. 6.1.1.2
Equipment Class
PV modules should be Class II. 6.1.2 6.1.2.1
PV array and PV sub-array junction boxes Environmental effects
PV Array and PV Sub-array junction boxes exposed to the environment shall be at least IP 54 compliant in accordance with IEC 60529, and shall be UV resistant. 6.1.2.2
Location of PV array and PV sub-array junction boxes
PV array and PV sub-array junction boxes, where installed, shall be readily available. 6.1.3 6.1.3.1
Switching devices General
Al l s witc wi tchi hing ng de devi vices ces , s ha hallll comp co mply ly wit h th the e fo follo llo wing wi ng re requ quire ire ment me nts: s: −
be rated for d.c. use (especially when voltage is over 30 V due to the risk of arcs);
−
have a voltage rating equal to or greater than V OC ARRAY ;
−
not have exposed live metal parts in connected or or disconnected state;
−
interrupt all poles poles,, except in the case of a pole connected either to earth or to a protective conductor.
6.1.3.2
Disconnectors
In addition to the requirements of 6.1.3.1, 6.1.3.1 , disconnectors (see IEC 60050-811:1991, 811-2917) shall have a current rating equal to or greater than the associated overcurrent protection device, or in the absence of such device, have a current rating equal to or greater than the required current carrying capacity of the circuit to which they are fitted (refer to Table 6). In addition, circuit breakers and any other load breaking disconnection devices used for protection and/or disconnecting means shall comply with the following requirem ents: −
not be polarity sensitive (fault currents in a PV array may flow in the opposite direction of normal operating currents);
−
be rated to interrupt full load and prospective fault currents from the PV array and any other connected power sources such as batteries, generators and the grid if present;
−
when overcurrent protection is incorporated, the trip current shall be rated according to 5.3.4.. 5.3.4
Plug connections for interruption under load may also be used if equivalent level of safety can be assured.
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NOTE Only specially constructed constructed plugs and sockets are capa capable ble of interrupting load safely. All sy systems stems with an open circuit voltage greater than 30 V can experience d.c. arcs. Plugs and sockets which are not specially constructed for load interruption if disconnected under load represent a safety risk and generally incur damage to the connection which will compromise the quality of the electrical connection and could lead to overheating of the connection.
6.1.4 6.1.4.1 6.1.4.1.1
Cables Sizing General
Cable sizes for PV string cables, PV sub-array cables and PV array cable shall be determined with regard to both, the minimum current capacity and the maximum voltage drop requirements. The larger cable size obtained from these two criteria shall be applied. 6.1.4.1.2
Current carrying capacity (CCC)
The minimum cable sizes for PV array wiring, based on CCC, shall be based upon a current rating calculated from Table 6, and the current carrying capacity of cables as specified in IEC 60287 series. NOTE In some some PV module technologies technologies I SC S C MOD is higher than the nominal rated value during the first weeks or months of operation. This should be taken into account when establishing cable ratings.
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TS 62257-7-1
© IEC:2010(E)
Table 6 – Current rating of PV array circuits Minimum current upon which cable cross sectional area should be chosen a, b
Type of cable
I
STRING CABLE
c protection n device + device + 1,45 × = Trip current of the nearest downstream overcurrent protectio
I SC MOD × ( (S S PO – 1) 1) Where: S PO is the number of parallel connected strings protected by the nearest overcurrent protection device. device. The nearest downstream overcurrent protection is the sub-array overcurrent protection.
PV string cable cable
I STRING CABLE = I
PV string overcurrent protection not provided
TRIP S-ARRAY
+ 1,45
× I
SC MOD
× (S ( S P0 – 1)
with : 1,45 × I
SC S-ARRAY
≤ I
TRIP S-ARRAY
≤ 2
× I
SC S-ARRAY
.
NOTE When no sub array array overcurren overcurrentt protection is used S PO is the total number of parallel connected strings in the PV array; and the trip current of the nearest overcurrent protection device is replaced by zero. The nearest downstream overcurrent protection is the string overcurrent protection. PV string overcurrent protection provided
I STRING CABLE = I TRIP STRING with : 1,45 × I
I 2 × I SC MOD . SC MOD ≤ TRIP STRING ≤
I
S-ARRAY CABLE
I SC
MOD
=Trip current c of the nearest downstream overcurr overcurrent ent protection device + 1,45
×
× ( S PO – 1) 1)
Where: S PO is the number of parallel connected strings protected by the nearest overcurrent protection protection device. device. The nearest downstream overcurrent protection is the array overcurrent protection. PV sub-array cable
a)
The greater of the following: Trip current c of the PV array overcurrent protection device + 1,45 of short circuit current of all ot her sub-arrays
b)
1,45
I PV sub-array overcurrent protection not provided
S-ARRAY CABLE =
× I SC S-ARRAY (of
× Sum
relevant array)
NOTE When PV array overcurrent overcurrent pr protection otection is not used, used, the corresponding corresponding parameter is replaced by zero in equation (a). PV sub-array overcurrent protection provided
PV array cable
I
S-ARRAY CABLE =
Trip current c of the PV sub-array overcurrent protection
device
PV array overcurrent protection not provided
I ARR AY
CA BL E =
PV array overcurrent protection provided
I ARR AY
CA BL E =
1,45 × I
SC ARRAY
Trip current c of the PV array overcurrent protection device
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a
The oper operating ating tempera temperature ture of PV PV module modules s and con consequently sequently the their ir associated associated wiring wiring can be significa significantly ntly higher than the ambient temperature. A minimum operating temperature of maximum expected ambient temperature + 40 °C should be considered for cables installed near or in contact with PV modules.
b
The loc location ation and method of installation (i.e. enclosed, enclosed, clipped, bu buried ried etc) of cables also needs to be considered considered in establishing a cable rating. Cable manufacturers recommendations need to be taken into account in establishing the rating according to installation method.
c
Trip cur current rent is the the nominal current current at whi which ch the over overcurrent current prote protection ction device is calibrated calibrated to operate. operate. The current current at which the device trips will generally be greater than the nominal rated current.
6.1.4.2
Insulation
The insulation of cables used within the PV array shall: −
have a voltage rating of at least V OC ARRAY,
NOTE 1 The use of single core core insulated and sheathed cab cable le is recommended for w wiring iring of LV PV arrays, arrays, to minimise the risk of faults within the wiring. −
have a temperature rating according to the application,
NOTE 2 PV modules freque frequently ntly operate at tempera temperatures tures of the order of 40 °C above ambient temperature. temperature. Cable insulation of wiring installed in contact or near PV modules need to be rated accordingly. −
if exposed to the environment, environment, be UV-resistant, or be protected protected from UV light by appropriate protection, or the cables be installed in UV-resistant conduit;
−
be fire resistant.
6.1.5
Protection devices and cables sizing process
Step 1: sizing of the overcurrent protection of the strings: see 5.3.4.1 5.3.4.1;; location of the protection devices: see Table 5. Step 2: sizing of the overcurrent protection devices of the sub-arrays: see 5.3.4.2 5.3.4.2;; location of the protection devices: see Table 5. 5. Step 3: sizing of the overcurrent protection devices of the arrays: see 5.3.4.3; location of the protection devices: see Table 5 5.. Step 4: sizing of the cables of the arrays based on the rating of the overcurrent protection of the arrays in systems with batteries otherwise sizing based on 1,45 × current rating of the array. Step 5: sizing of the cables of the sub-arrays based on the rating of the overcurrent protection of the sub-arrays. Step 6: sizing of the cables of the strings based on the rating of the overcurrent protection of the strings. Some case studies relevant with small PV power systems for rural electrification are proposed in Annex E to illustrate the sizing process: Case 1: ELV PV array with number of parallel strings
< 3,
no battery
Case 2: ELV PV array with number of parallel strings
< 3,
with battery
Case 3: ELV PV array with number of parallel strings
> 3,
no battery
Case 4: ELV PV array with number of parallel strings
≥ 3,
with battery
Case 5: ELV PV array with number of parallel strings
≥ 3,
2 sub-arrays with battery
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6.1.6
TS 62257-7-1
© IEC:2010(E)
Plugs, sockets and couplers
Plugs, sockets and couplers shall comply with the following requirements: –
be ra rate ted d fo forr d.c. d. c. use ;
– –
ha have ve a vo volt ltag age e ra rati ting ng eq equa uall or grea gr eate terr th than an V OC ARRAY ; be pr prot otec ecte ted d fr from om cont co ntact act wit with h li ve pa part rts s in conn co nnec ecte ted d an and d di disc sc on onne nect cted ed stat st ate e (e (e.g .g..
–
shrouded); ha have ve a curr cu rren entt ra rati ti ng eq equa uall to or grea gr eater ter th than an th the e c ab able le to whic wh ich h they th ey ar are e fitt fi tted ed;;
–
re requ quir ire e a de delib lib erat er ate e f orce or ce to disc di scon onnec nec t;
–
ha have ve a te temp mper erat atur ure e r at atin ing g suit su itab able le for fo r th their eir in inst stal al la lati tion on loc atio at ion; n;
–
if mult mu ltip ipol olar ar,, be po pola lari rise sed; d;
–
com ply pl y w it ith h Cl ass II;
–
if ex po pose sed d to th the e env ir iron onme ment, nt, be ra rate ted d fo forr ou outd tdoo oorr us use, e, be UV-r UV -res esis ista tant nt an and d be at le leas astt IP 54 compliant;
–
plugs pl ugs an and d so sock ck et ou outl tlet ets s nor ma ll y us used ed fo forr th the e co nn nnec ecti tion on of ho hous useh ehol ol d eq equi ui pmen pm entt to lo low w voltage a.c. power shall not be used in PV arrays.
NOTE
The purpose of this requirement requirement is to prevent confusion confusion between a.c. and d.c. circuits within within an installation.
6.1.7 6.1.7.1
Fuses General
Fuses used in PV arrays shall comply with the following requirements: –
be ra rate ted d fo forr d.c. d. c. use ;
–
ha have ve a vo volt ltag age e ra rati ting ng eq equa uall or grea gr eate terr th than an V OC ARRAY ; be ra rate ted d to in inter ter ru rupt pt fu fullll lo load ad an and d pros pr ospec pec ti tive ve fa fault ult curr cu rr en ents ts fr from om the th e PV ar arra ra y an and d an any y other connected power sources such as batteries, generators and the grid, if present;
– –
be of an ov erc ur urre rent nt an and d sh shor ortt curr cu rren entt pr prot otect ect iv ive e typ e suit su itab able le for fo r PV – e.g. e. g. DC ra rate ted d typ e gR fuse.
NOTE When fuses are provided for overcurrent protection, the use of fused switch-disconn switch-disconnectors ectors (fusecombination units) is recommended.
6.1.7.2
Fuse holders
Fuse holders shall comply with the following requirements: – –
ha have ve a vo volt ltag age e ra rati ting ng eq equa uall or grea gr eate terr th than an V OC ARRAY ; ha have ve a curr cu rren entt ra rati ti ng eq equa uall or great gr eat er th than an th the e corr co rresp esp on ondin din g f us e;
–
prov pr ovid ide e a de degr gree ee of pro te tect ctio ion n no nott le less ss th than an IP 2X 2X..
6.1.8
By-pass diodes
By-pass diodes may be used to prevent PV modules from being reverse biased and consequent hot spot heating. If by-pass diodes are used, and they are not embedded in the PV module encapsulation, they shall comply with the following requirements: –
ha have ve a vo volt ltag age e ra rati ting ng at le leas astt 2 × V OC MOD of the protected module;
–
ha have ve a curr cu rren entt ra rati ting ng of at le leas astt 1, 1,45 45
–
be ins ta talllled ed acc ordi or ding ng to modu mo dule le manu ma nufa fact ctur urer er’s ’s re reco comm mm end ation at ion s;
–
be ins ta talllled ed so no lilive ve pa part rts s are ar e ex expos pos ed ed;;
–
be pro tec te ted d fr from om de degr grad adat ation ion du due e to en envir vir on onme ment ntal al fact fa ctor ors. s.
× I SC MOD ;
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– 45 –
Blocking diodes
Blocking diodes may be used but they are not a substitute for overcurrent protection. In systems containing batteries it is recommended that some device will be implemented to avoid reverse current leakage from the batteries into the array at night. A number of solutions exist to achieve this including blocking diodes. If used, blocking diodes shall comply with the following requirements: – –
ha have ve a vo volta lta ge ra rati ting ng at le leas astt 2 × V OC ARRAY ; ha have ve a cu curr rren entt ra rati ting ng of at le least ast 1, 1,45 45 tim es th the e shor sh ortt circ ci rc uit curr cu rren entt at ST STC C of the th e circ ci rc uit that they are intended to protect; that is: •
1,45
× I SC MOD for
PV strings;
•
1,45
× I SC S-ARRAY for
•
1,45
× I SC ARRAY for
PV sub-arrays;
PV arrays;
–
be ins ta talllled ed so no lilive ve pa part rts s are ar e exp os osed ed;;
–
be pro tec te ted d fr from om de degr grad adat ation ion du due e to en envir vir on onme ment ntal al fact fa ctor ors. s.
If there is a special recommendation from the manufacturer or from local regulation to use blocking diodes in PV strings of the PV array, these diodes shall be installed as shown in the following Figure 14. 14 .
Blocking diodes
−
−
−
−
−
−
−
− −
IEC
2092/10
Figure 14 – Blocking diode implementation (example) 6.2
Location and installation requirements
6.2.1 6.2.1.1
Disconnecting means General
Disconnecting means shall be provided in PV arrays according to Table 7 and Table 8 to isolate the PV array from the power conditioner and vice versa and to allow for maintenance and inspection tasks to be carried out safely.
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NOTE
TS 62257-7-1
© IEC:2010(E)
This subclause subclause does not apply to module inverters inverters where the inve inverter rter is an integral integral part of the PV module. module.
6.2.1.2
Installation
Suitably rated circuit-breakers used for overcurrent protection may also provide load breaking disconnecting facilities. Other disconnection and isolation devices having the characteristics described in 6.1.3.2 may be used as a disconnection means. Fuse systems used for overcurrent protection are acceptable non-load breaking disconnecting means if they have removable fusing elements, preferably with a disconnection mechanism (fuse-combination unit). For a reference to the location of disconnection devices see Table 8 which indicates with respect to the system configuration where the disconnecting mean should be installed (on one or both live conductors of the cable) and which type is this connecting mean. Table 7 – Disconnecting means requirements in PV array installations PV array Voltage
ELV
LV
Circuit or subcircuit
Type of disconnecti on device
Requirement
String cable
Disconnection device
Recommended
Sub-array cable
Readily available disconnecti on device
Required
Arr ay cab le
Readily available load-breaki load-breaking ng disconnection device
Required
String cable
Readily available disconnection device
Required
Sub-array cable
Readily available load-breaki load-breaking ng disconnection device
Required
Arr ay cab le
Readily available lockable a load-breaking disconnection disconnectio n device
Required b
a
“Lockable” disconnection disconnection device is a switch or circuit brea breaker ker that has provi provision sion for insertion of a mechanical device to prevent the switch being closed b y an unauthorized person. A m echanical device in this context could constitute sealing with plastic cord, a pin, a wire or other device that prevents operation of the switch.
b
A lockable disconnection disconnection device device is not requir required ed if the whole cir circuit cuit is visib visible le from the location of of the switch.
Table 8 – Location of disconnection devices according to system configuration, where required Location of disconnecting devices System configuration
Unearthed PV array
PV string cables
PV sub-array cables
On all live conductors a
Earthed PV array
PV array cable On all live conducto rs On all current carrying conductors b, c
a
Live conductors are those not directly connected to e earth. arth.
b
The di disconnection sconnection d device evice is required iin n this situation situation to interrupt th the e earth conductor conductor so that earth fault currents may be interrupted.
c
In earthed arrays the earthed earthed conducto conductorr is a cur current rent carrying carrying conductor and and needs to be be able to be disconnected to allow for interruption of any earth fault condition.
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© IEC:2010(E)
– 47 –
PV array production optimization
To optimize the PV array production it is necessary to fulfil the following requirements: 6.2.2.1
Orientation, tilt angle and flatness
In so far as possible, the orientation and tilt angle of the modules shall optimize the production of energy in relation to the needs. The north or south orientation of the modules is hemisphere dependent. However, the building may not necessarily allow ideal orientation of these two parameters (roof not orientated south or north, vertical front, etc.) and therefore they shall be clearly accounted for in the production calculation at the sizing design phase. Whatever the array latitude, it is generally recommended that the slope keeps to a minimum value of ten degrees (10°) in relation to the horizontal, thus preventing stagnation and allowing rain water to carry away dust deposits. Moreover, periodical cleaning actions shall be performed, however, as need be. The surface for fitting photovoltaic modules to structures shall be perfectly flat in order not to induce mechanical stresses on securing the modules in order to avoid risks of module rupture. 6.2.2.2 6.2.2.2.1
Location: accounting for shadow Environmental
Shadowing of the PV array should be minimized or preferably eliminated over the whole day with consideration given to all seasons of the year. A sh shad adow ow blank bl ank in ing g of offf a ph phot otov ovol olta taic ic cell ce ll ma y caus ca use e lo loss ss of alm ost the th e who le pr prod oduct uct ion of this module, significantly reducing the performance of a string of modules. 6.2.2.2.2
One line of photovoltaic modules over the other
On flat roofs, photovoltaic modules are arranged in rows. The first row is fully exposed to sunshine and therefore, the shadow thus generated may affect the next row and so on. As a ba basi sic c ru rule le,, no sh shad adow ow sh shou ould ld be ge gene nera rate ted d fr from om on one e ro row w to an anot othe her. r. It may occur that the available space will not allow the ready application of this rule: an energy production studyhence versus theorvarious structure configurations should be conducted (e.g., more or less high, more less spaced structures, acceptance of shadow early in the morning and end of the afternoon, change of orientation and/or of slope, etc.). A co comp mpro romi mise se sh ou ould ld be re reta ta ine d al lo lowin win g to be best st fulf fu lfill ill me ment nt of the th e site si te re requ quire ire me nts for fo r energy yield. NOTE Where more than one row row of adjacent mod modules ules are on a mountin mounting g rack and the low lower er row of modules modules may be subject to some form of shading then the wiring configuration should be arranged if possible to put all the shaded modules in the same string so that if shading occurs then only one string is affected. This will make it possible for upper modules to continue producing energy even though lower modules are in the shadow.
6.2.2.3
Location: other recommendations
Prior to implementing a solar generator, it is important to know the behavior and habits of the users and neighborhood. Some locations shall be avoided, especially those exposed to damage that could occur to modules. Due consideration for environmental risks provides for system durability and is directly linked to the project designers’ knowledge of the local social canvas.
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6.2.2.4
TS 62257-7-1
© IEC:2010(E)
Maintaining the integrity of the covering
The attachment of structures to the building shall keep to the sealing efficiency of the covering and mechanical integrity of the building. Special care shall be exercised with terrace fitted units where the quality of the covering and related structure is often very poor. It is advisable to have structures laid onto the building instead of attached to it. it. 6.2.2.5
Theft prevention devices
Where building maintenance does not oblige to remove the modules and if the latter are accessible, theft prevention bolt and nuts shall be adopted. In the opposite case, standard bolting will be used. Where small structures (a few modules per structure) are used, a theft prevention device shall also be used for securing structures to the building. 6.2.3
Array voltage
6.2.3.1
General
V OC ARRAY shall not exceed the maximum allowed operating voltage of the PV modules (as specified by the manufacturer). 6.2.4
Wiring system
6.2.4.1
General
Wiring of PV arrays shall be laid in such a way that the possibility of line to line and line to earth faults occurring is minimised. Al l conn co nnec ecti tions ons shal sh alll be ver if ifie ied d fo forr ti gh ghtn tness ess an and d po pola lari rity ty du duri ring ng ins talla ta lla tio n to re redu duce ce the th e ri risk sk of faults and possible arcs during commissioning and operation. 6.2.4.2
Compliance with wiring standards
The PV array wiring shall comply with the wiring requirements mandated by local standards and regulations. In absence of national standards and or regulations, wiring systems used in PV arrays shall comply with the IEC 60364 series. NOTE
Particular attention should be given given to the protection of wiring sy systems stems against external external influences.
6.2.4.3
Wiring loops
To reduce the magnitude of lightning-induced over-voltages, the PV array wiring should be laid in such a way that the area of conductive loops is minimum, e.g. by laying cables in parallel as shown in Figure 15.
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− +
PV module
− +
− +
PV module junction box
Return conductor
+ −
+ −
+ −
IEC
2093/10
Figure 15 – PV string wiring with minimum loop area 6.2.4.4
String wiring
Wiring of PV strings between modules may be done without laying cables in conduit, provided that the following requirements are met: −
insulated and sheathed cables are used, and
−
cables are protected from mechanical damage, and
−
the cable is clamped to relieve tension in order to prevent the conductor from coming free from the connection.
6.2.4.5
Wiring installation in junction boxes
The following provisions apply to the installation of wiring systems in junction boxes: Where conductors enter a junction box without conduit, a tension relief system shall be used to avoid cable disconnections inside the junction box (for example by using a gland connector). Al l c ab able le en entr trie ies s when wh en in inst stal alle led d shal sh al l m ai aint ntai ain n th the e IP ra tin g of the th e en encl clos osur ure. e. NOTE Water condensation condensation inside junction boxes may be a problem in some locati locations; ons; provisi provision on may need to be provided to drain water build-up.
For LV PV arrays, where any return conductor is routed through module junction boxes, such return conductor(s) shall be a single-core double-insulated cable, and the cable and its insulation shall maintain double insulation status over its entire length, particularly through junc ju nctio tio n bo boxe xes s (i (i.e .e.. th thes es e prov pr ov is ision ion s also al so ap appl pl y t o an any y j oint oi nts) s)..
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TS 62257-7-1
© IEC:2010(E)
Wiring identification
Ap prop Appr opri riat ate e ide nt ntif ifica ica tio n shal sh al l be prov pr ov ide d for PV ar arra ray y cabl ca bl ing wh wher ere e it can ca n be conf co nfus used ed wi with th other wiring systems. 6.2.4.7 6.2.4.7.1 6.2.4.7.1.1
Over-voltage protection Surge arresters Selection
The preferred type of surge arresters for over-voltage protection of PV arrays is metal-oxide varistors (MOVs). These devices are voltage dependent resistors that have a high resistance at normal circuit operating voltage, but their resistance reduces continuously with increased surge voltage and current. Spark gap devices are not suitable for use in d.c. circuits as once conducting, they will not stop conducting until the voltage across their terminals is typically less than 30 V. Because the performance of MOVs deteriorates with repeated operation (their resistance decreases), it is usual to allow a high safety margin in the selection of the device rating in lightning prone areas. Alternatively, facilities should be provided to give an indication of device failure. The use of thermally monitored MOVs is recommended to avoid excessive system losses and troubleshooting time caused by device failure. 6.2.4.7.1.2
Usage and installation
The following recommendations should be observed for the utilization and connection of surge arresters to protect PV arrays: A surg su rge e arres ar res ter sh shou ould ld be conn co nnec ecte ted d be betw twee een n ea each ch po pole le of the th e PV ar arra ray y cable ca ble an and d ear th. th . Differential mode protection is not required unless the voltage protection level (VP) of the surge arresters is greater than 1 100 V. In sub-divided PV arrays, the provision of surge arresters in both poles of each PV sub-array cable is recommended. The cable distance between the surge arresters and the PV modules should not exceed 15 m. When the PV array cable exceeds 20 m, surge arresters should be connected at each end of the cable, one set next to the PV array, and the other one next to the power conditioning device. For this purpose, it should be verified if the power conditioning equipment is already fitted with surge arresters. Junction boxes are a good place to install the surge arresters. Care should be taken to connect them on the PV module side of any disconnecting devices. The common terminal of surge arresters should be connected to both, conductive PV array frames and structures, and to the equipotential bonding system. Cables for connecting surge arresters should be as short as possible and have a crosssectional area not less than 6 mm 2. 6.2.4.7.2
Shielding
When the PV array frame is bonded to a lightning protection system, the PV array cable should be shielded by one of the following methods, and the shielding conductor should be connected to earth at both ends:
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–
wit h a meta me tallllic ic cabl ca ble e armo ar mour ur or shie sh ield ld wit h an equ ivale iv ale nt cr oss sect se ctio iona nall ar area ea of 6 mm 2 Cu; or
–
wit h a m et etal allic lic cond co nduit uit suit su itab able le as a bo bond nding ing co nd nduct uct or or;; or
–
wit h an eq equi uipo pote tenti nti al bo bond ndin ing g c on ondu duct ctor or with wi th a cros cr osss-se sect ctio iona nall a re rea a of 6 mm 2.
6.2.4.8
Automatic disconnection devices
Earth fault detection installed on the d.c. side shall cause disconnection of the PV array from the application circuit. The disconnecting device shall be located between the PV array and the earthing point of the PV array as shown in Figures 5 and 7. 6.2.5
Surge protective devices
Refer to 5.4.3.2 5.4.3.2.. 6.2.6
Earthing arrangement, protective conductors
Refer to 4.1.2.
7
Acceptance
7.1
General
PV array acceptance procedure will refer to the IEC 62257-6 technical specification. Commissioning tests are specified in 7.3 to 7. 7.4 4 to ensure that the PV array complies with the requirements of this standard. The tests specified in 7.5 to 7.6 7. 6 are additional recommended tests for commissioning of PV arrays larger than 10 kW. 7.2
Conformance with system general specification
The PV array shall be inspected for conformity with the general ratings and technical specifications stated in the contract. 7.3 7.3.1
Wiring and installation integrity Compliance with wiring standards
The PV array wiring shall be inspected for compliance with wiring standards and regulations in accordance with 6.2.4 6.2.4.. 7.3.2
Compliance with this standard
The PV array installation shall be inspected for compliance with the requirements set out in this standard and corrected if necessary. 7.4
Open circuit voltage
This subclause discusses open circuit voltage for a) systems with with less than 20 strings; 7.5 5). b) systems with more (see 7. 7.4.1
General
This test is intended to ensure that wiring polarity and continuity of the PV array are correct.
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TS 62257-7-1
© IEC:2010(E)
Procedure
The open circuit voltage of every string shall be measured before connecting to other strings. Al l PV stri st ring ng op open en circ ci rcui ui t volt vo ltag ages es shal sh al l be with wi thin in 5 % vari va riat atio ion; n; othe ot herw rwis is e the th e conn co nnec ecti tion ons s shall be verified for polarity, continuity and possible faults and repaired. Once the verification is complete and satisfactory, the PV strings can be connected in parallel.
The sameand procedure carried out to verifyconnecting PV sub-array open circuittovoltages (if relevant) PV arrayshall openbecircuit voltage before to the PV array the power conditioning unit. NOTE All meas measurements urements should be made whe when n practic practicable able under stable irradiance irradiance conditions. Conditions close to solar noon are p referable.
7.5 7.5.1
Open circuit voltage measurements for PV arrays with a large number of strings General
This procedure is a guide on open circuit voltage measurements for PV arrays with a large number of PV strings (20 or more) where the environmental conditions and PV array operating conditions are likely to change significantly during the measurements due to the time required for each measurement. 7.5.2
Procedure
Before closing any switches and installing fuses, the open circuit voltage of each PV string shall be measured. The measured values shall be compared with the expected value. Temperature corrections shall be applied where required according to manufacturers’ specification. Module temperature shall be measured in the back of one of the central modules of each string. Voltage measurements should b e made with an accur acy of 2 %; temperature measurements shall have an accuracy of 1 ºC. NOTE 1 Voltages less than the expected value may indicate one or more modules connected with the wrong polarity, or a partial line-to-line or line-to-ground fault due to insulation damage and/or water accumulation inside conduits. NOTE 2
High voltage readings are usually the result of wiring errors.
The measured open circuit voltage of each PV string shall be within 3 % of the expected value. If there are larger differences, the PV string should be verified for any of the conditions in Note 1 above and the wiring corrected. Once every string has been verified and if necessary corrected, they should be parallel connected via switching devices and/or by installing fuse elements. 7.5.3
PV arrays and sub-arrays measurement
Once the PV strings have been verified and connected in parallel, the open circuit voltage of each PV sub array (if relevant) and of the PV array shall be measured using the same procedure as with PV strings. The measured values shall be within 3 % of the expected value; otherwise the wiring shall be verified and corrected if necessary. In addition to wrong polarity and insulation faults, defective surge protection devices could be the cause of lower than expected voltage readings in the case of PV arrays and sub-arrays. NOTE Line-to-ground voltages voltages in bipolar arr arrays ays should be relatively ba balanced lanced around zero with one li line ne above zero (positive) and one line below zero (negative).
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Short circuit current measurements
7.6.1
General
PV array short circuit measurements shall be included in the acceptance of large PV arrays to further verify that there are no faults within the PV array wiring and that the PV modules and other components are in good condition. It is very difficult to obtain accurate results under variable irradiance conditions. It is recommended to use this method only under stable irradiance conditions. Under these stable conditions, it is possible to compare current measurements in different strings to check for major wiring faults. It can be dangerous to interrupt short circuit currents in PV arrays. The recommended procedure should be carried out in order to prevent injuries. 7.6.2
Procedure
Procedure 1: 1: Current measurement under normal application circuit load using clipon ampere meter
The first recommended procedure is to connect the array to the application circuit and use a clip-on ampere meter to compare current measurements in each string.
Procedure 2: Short circuit current measurement using clip-on ampere meter
a) If there is any current source (e.g. batteries) in the a application pplication circuit, these sources should be isolated and any precaution taken to prevent any switch-on of theses sources (the same person shall switch off the sources and switch them on again after measurement). b) Ensure PV array load-breaking disconnecting device or load-breaking switch is open. c) Connect a short circuit between positive and negative terminals on the application side o off the disconnecting device. d) Ensure the conductor used for this short circuit iis s rated equal to or greater than the the current rating of the PV array cable and that it is securely connected (e.g. screwed connections). e) Close all arrays di disconnection sconnection devices. f)
Close the load-breaking disconnecting device or switch.
g) Use a clip-on ampere meter to compare current measurements in each string. h) After measurement completed, open the load breaking disconnection switch. i)
Remove short circuit.
Procedure 3: Short circuit current measurement when a clip on ampere meter is not available
a)
If there is any current source (e.g. batteries) in the application circuit these sources should be isolated and any precaution taken to prevent any switch on of these sources. (the same person shall switch off the sources and switch them on again after measurement).
b)
Ensure PV array load breaking disconnecting device or load breaking switch is open.
c)
Connect an ampere meter between positive and negative terminals on the application
d)
side of the disconnecting device. Ensure the conductor and the ampere meter is is rated equal to or greater than the current rating of the PV array cable and that it is securely connected (e.g. screwed connections).
e)
Open all arrays disconnection devices.
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f)
Switch on one string.
g)
Close the load-breaking disconnecting device or switch.
h)
Measure the short circuit current.
i)
Open the load-breaking disconnecting device.
j)
Switc Sw itc h off of f th the e s tr trin ing. g.
k) l)
Repeat steps f) to j) for each string. After measurement completed, open the load breaking disconnection switch.
m) Remove ampere meter. Where large discrepancies are found between string currents under stable irradiance conditions, the strings with low measured current should be investigated for faults. It is very difficult to carry out these procedures for very large arrays due to the main difficulty to have stable irradiance conditions over the period of measurement. For larger arrays a possible procedure is to use procedure 1 and compare the current supplied to the application circuit with N times times the current in a single string. Where a significant discrepancy is observed, the currents have to be compared at the subarray level and so on. NOTE 1 The expected shor shortt circuit current of an arr array ay may be estimated more accurately accurately if a measure measurement ment of in plane irradiance is available, e.g. using a pyrometer or reference cell.
Use the formula below to estimate the short circuit current: I SC EXPECTED = n × I SC MOD × GI × 0,95 where: I SC EXPECTED = expected short circuit current of the segment under test (A); n
= number of parallel connected strings in the segment under test;
G I
= plane of array irradiance (kW/m 2);
0,95
= factor to account for mismatch.
NOTE 2 I SC of the PV array or array segment should be measured with the array not shaded under clear sky, and as close as possible to noontime conditions. NOTE 3 The short circuit current current of crystalline silicon-ba silicon-based sed PV devices is relatively insensitive insensitive to variations in ambient t emperatur e over a wide operati ng range (–10 °C to 40 °C), increas ing slig htly with i ncreasing temperature. NOTE 4 Other PV cell technologies technologies may be more sen sensitive sitive to temperatur temperature e or to other conditions such such as spectral content. Additional constraints may have to be observed or modifications made to the above equation. NOTE 5 Some PV module technologies have a settling time per period iod when the output electrical parameters parameters are significantly higher than the nominal values. This fact should be taken into account to modify the above equation accordingly. NOTE 6 Low I SC measurements can indicate the presence of circulating ground fault currents in the array due to multiple ground faults or shading. Higher than expected measurements can indicate an array configuration other than expected or increased irradiance on the array not being sensed by the pyranometer.
7.7 Commissioning records The inspecting personnel shall prepare a commissioning report that includes the applicable records from the list of items a) to e) below:
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a) a report that states whether the PV array complies wi with th the general ratings and technical specifications established in the contract; b) a certificate stating if the work done on the installation meets the requirements of this standard and either th ose of local wiring codes or the IEC 60364 series according to 6.2.4.2;; 6.2.4.2 c) a table with the final open circuit voltage measurements for each string, sub array and array; and a statement with the condition of the PV array wiring after the test, including any repairs and corrections carried out as a result of the inspections. When temperature measurements were carried out, these values should also be tabulated along with the actual voltage readings and the expected voltage values; d) when relevant, a report with the measured trip values of current and/or resistance of the earth fault protection system before and after any adjustments to the calibration; e) when short circuit current measurements are made as part of the acceptance process, a report that includes the test procedures used and the current measurements, stating the condition of the PV array wiring after the test, including any repairs and corrections carried out as a result of the inspections; 1) this report shall be given to the owner, and if necessary to the relevant authorities. Examples of commissioning records are given in Annex A.
8 8.1
Operation/maintenance General
This clause gives general guidance for the preparation of operation and maintenance procedures for PV arrays. Examples of such procedures are given in Annex C. 8.2
Safety
At Atte tent ntio ion n sh shou ould ld be gi give ven n in th the e op oper erat atio ion n an and d main ma inte tena nanc nce e pr proc oced edur ures es to the th e foll fo llowi owi ng safe sa fety ty requirements: a) emergency shutdown procedure; b) obey all warning signs; c) shut system down and interrupt PV array currents according to the manual shutdown procedure; d) split strings into extra low voltage sections (if relevant); e) warn of the live parts that cannot be de-energised during daylight. 8.3
Operation and maintenance procedures
PV arrays do not generally require control actions in normal operation. The most important operation procedures for PV arrays are those related to switching and shutdown for emergency and maintenance purposes. Operation and maintenance procedures should include the following: a) a short description description of the function and operation of of all installed installed equipment. More detailed information should be available from the manufacturer’s documentation (see item d); b) emergency and maintenance shutdown procedures; c) periodic maintenance requirements including procedures and schedule. Annex B gives an example of a maintenance schedule; d) equipment manufacturer’s documentation (data sheets, handbooks, etc.) for all equipment supplied.
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Replacement
For each project the project implementer will have to list the replacement criteria. Some guidance for criteria can be found in the maintenance schedule (see Annex B). Particular attention is drawn to the measurement of short circuit current of the array, which may give an indication of deterioration in performance for which replacement criteria thresholds could be specified, provided measurements of irradiance are available.
10 Marking and documentation 10.1
Equipment marking
Al l elec el ectr tric ical al eq equip uip me nt sh shal alll be ma mark rk ed ac acco cord rding ing to the th e re requ quire ire ment me nts s for fo r ma mark rk ing in IEC IE C or to local standards and regulations when applicable. Markings should be in the local language or use appropriate local warning symbols. English examples of sign texts are included here. 10.2
Requirements for signs
Al l s ig igns ns re requ quir ired ed in th this is claus cl aus e shall sh all : a) comply with IEC; b) be indelible; c) be legible from at least 0,8 m unle unless ss otherwise specified in tthe he relevant clauses (or see examples of signs in Annex D); d) be constructed and affixed to remain legible for the li life fe of the equipment it is attached or related to; e) be understandable by the operators. Examples of signs are given in Annex D. 10.3
Labelling of PV array and PV sub-array junction boxes
A si gn co cont ntai aini ning ng th the e te text xt ‘S ‘SOL OLAR AR d. d.c. c.’’ sh shal al l be atta at tach ched ed to PV ar arra ray y an and d PV subsu b-ar arra ra y junc ju nctio tio n bo boxe xes s as well we ll as lab els in indic dic at atin ing g “l iv e du duri ring ng da yli gh ght” t” to d.c .j unc tio n bo boxe xes s an and d switches. 10.4 10.4.1
Labelling of disconnection devices General
Disconnection devices shall be marked with an identification name or number according to the PV array wiring diagram. Al l s witc wi tches hes shal sh al l h ave th the e O N an and d OFF OF F po posi si tio ns cl ear ly in indi dica cate ted. d. 10.4.2
PV array disconnecting device
The PV array main switch shall be provided with a sign affixed in a prominent location with the following text: ‘PV ARRAY MAIN SWITCH’. 10.5 10.5.1
Fire emergency information signs General
For PV arrays installed on buildings that have a PV array voltage greater than 120 V, a sign shall be displayed next to the main building switchboard. This sign shall state ‘Warning:
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Electric Solar Array’ and give an indication of its location. This sign shall be legible from at least 1,5 m. The sign shall also include the following PV array information: a) open circuit voltage; b) short circuit current. NOTE In small installations installations the indication of location location may be simple, e.g e.g.. “On Roof”. In larger larger installation installations s more detail should be provided.
10.6
Documentation
The PV system designer shall prepare the following documents and a copy shall be handed to the PV system owner: a) A basic circuit diagram that that includes the electrical ratings of the PV array, in including cluding the information required by 10.5. 10.5 . b) PV system or parts certification as required by relevant authorities and provided by manufacturer. c) A copy of the emergency shutdown procedure procedure including the location of relevant switching devices. d) A copy of the operation and maintenance procedures in accordance with Clause Clause 8 .
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Annex A (informative) Examples of commissioning records
Table A.1 – Verification of PV array general ratings and technical specifications Characteristi c
Reference value
Nominal power Technology Quantity Manufacturer Model Standards PV modules
IEC 61215 / IEC 61646
Equipment class Reverse current withstand
2,6 × I SC
Cell appearance
No defects
Sealing
No defects
Frames
No corrosion or defects
STC MOD
By-pass diodes Total rated power Nominal voltage Nominal current V OC ARRAY PV array
I SC
ARRAY
No. of series modules No. of parallel strings Inclination Azi muth mu th Total area
7.4 and 7.5
Conform Yes /No
Remarks
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Table A.2 – Verification of compliance with the requirements of IEC 62257-7-1 Characteristi c Protection against electric shock and fire
Insulation system
Strings Sub arrays Protection against overcurrent
5.2
5.3.2 and 5.3.4 5.3.2 and 5.3.4 (if relevant)
Arr ay
5. 3.2 and an d 5 .3. 4
Discrimination
5.3.3
Location
5.3.5
Lightning protection
Lightning and over-voltage protection
Reference value
Equipotential bonding
IEC 62305-2 and IEC 62305-3 recommended 4.1.2 and 5.4.3.1
Wiring loops
5.4.3.1 and 6.2.6.3 recommended
Surge arresters
5.4.3.2 and 6.2.6.7.1 recommended
Shielding
6.2.6.7.2 recommended
Components requirements PV modules
6.1.1
Junction boxes
6.1.2 (if relevant)
Switching devices
6.1.3 (if relevant)
Plugs, sockets and couplers
6.1.5 (if relevant)
Fuses
6.1.6 (if relevant)
By-pass diodes
6.1.7 (if relevant)
Blocking diodes
6.1.8 (if relevant)
Wiring installation Selection and erection of equipment
String wiring
6.2.6.4
Junction boxes wiring
6.2.6.5
Junction boxes location
6.1.2.2
Wiring identification
6.2.6.6
Cable selection Cable size
6.1.4.1
Insulation
6.1.4.2
Disconnecting Disconnecti ng means
6.1.3.2 and 6.2.1.2
ELV segmentation
6.2.2 (if relevant)
Earthing
Operation and maintenance
Electrode
6.2.3.1
Equipment earthing
6.2.3.2
System earthing
6.2.3.3
Safety and procedures
8.2 recommended
Conform Yes /No
Remarks
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Characteristi c
Reference Value
Marking
Marking and documentation
Mechanical
Equipment
10.1
Signs requirements
10.2
Junction boxes
10.3
Disconnection Disconnecti on devices
10.4
PV array main switch
10.4.2
Fire emergency information
10.5
Documentation
10.6
Ventilation
Recommended
Wind loading
Recommended
TS 62257-7-1
Conform Yes /No
© IEC:2010(E)
Remarks
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Annex B (informative) (informative) Example of maintenance schedule
Sub-system or component
Maintenance action
Freq.
Arr ay fi eld
Verify cleanliness (accumulation of dust or other shading materials)
Quarterly
Check for visual defects •
Fractures
•
Browning
•
Moisture penetration
•
Seal integrity
Remarks The array field should be cleaned if necessary Modules with visual defects should be further inspected for performance and safety to determine the need for replacement
1 year
• Frame corrosion
PV modules
Any def ect ive sea ls, cla mps and bypass diodes should be replaced
Inspect junction boxes •
Tightness of connections
•
Water accumulation/buildup accumulation/buildup
•
Integrity of lid seals
•
Integrity of cable entrance and/or conduit sealing
•
Integrity of clamping devices
1 year
• Verify by-pass diodes
5 years
Any damaged conduit should be replaced
Insulation integrity of cables installed without conduit
5 years
Any damaged cable should be replaced
Junction boxes
1 year
Any defective seals, clamps blocking diodes and surge arresters should be replaced
Mechanical integrity of conduits
Wiring installation
•
Tightness of connections
•
Water accumulation/buildup accumulation/buildup
•
Integrity of lid seals
•
Integrity of cable entrance and/or conduit sealing
•
Integrity of clamping devices
•
Verify blocking diodes
• Verify surge arresters for
degradation
Earthing connections •
1 year
Tightness of connections
• Corrosion
Electrical characteristics
Measurement of open circuit voltages
1 year
According to 7.4 and 7.7
Measurement of short circuit currents
1 year
According to 7.6
1 year
If the recorded values of insulation resistance drop significantly (20 % to 30 % or m ore), special attention shall be paid to the variation of the
Measurement of insulation resistance in dry and wet conditions
values. If the value of the resistance continues to decrease, check the wiring and installation. Measurement of earth resistance
1 year
Measurement of I-V characteristics characteristics
5 years
Refer to IEC 61829
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Protective devices
Mounting structures
Maintenance action
TS 62257-7-1
Freq.
Verification of fuses
1 year
Verificatio n of CBs and RCDs
1 year
Verification of earth fault protection system
1 year
Verify tightness anddevices integrity of bolts and other fastening
5 years
Verify if there is significant corrosion
5 years
© IEC:2010(E)
Remarks
According to 7.7
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Annex C (informative) (informative) Replacement
PV module(s) and structures should be replaced if considered unsafe. This may occur due to extreme climatic conditions or through age and corrosion of structural materials. PV modules should be considered for replacement when they are no longer capable of supplying useful service. This can occur: −
after normal expected lifespan,
−
deterioration of a module(s) under warrantee, or
−
deterioration of a module(s) due to fault conditions within within the array.
PV field junction boxes may be prone to failure due to corrosion and should be replaced as needed. When replacing a module(s) or the whole array it is important that: − −
the array be shut down according to proper procedure; any LV s strings trings within the array be sectionalized into ELV sections;
−
the replacement be be carried out by suitably qualified personnel;
−
the module(s) or the whole array should be replaced by mechanically and electrically compatible parts.
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Annex D (informative) (informative) Examples of signs
This annex provides examples (see Figures D.1 to D.3) of appropriate signs as specified in Clause 10 10..
SOLAR DC IEC
2094/10
Figure D.1 – Example of sign required on PV array junction box ( ( 1 0.3) 0.3)
PV ARRAY MAIN SWITCH IEC
2095/10
Figure D.2 – Example of sign required adjacent to PV array main switch ( ( 1 0.4.2) 0.4.2)
WARNING
ELECTRIC ARRAY ONSOLAR ROOF
220 V
30 A IEC
2096/10
Figure D.3 – Example of fire emergency information sign required in main building switchboard ( ( 1 0.5.1 0.5.1))
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f n o o i e t l p a c i m l a p x p E a
y r e t t a b o N – 3
s g n i r t
) e v E i t x a e m n r o n f A i n (
s e i d u t s e s a C
l s e l l a r a p f o r e b m u n h t i w y a r r a V P V L E : 1 e s a C
n o i t a r u g i f n o c g n i h t r a e m e t s y S
n o i i t t a u c c i r l i p c p A
m o o r l a c i n h c e T r o t a r e n e g V P
C D d s e d n h t o r a o i t a l p e i n r c U s e d l a c i d n e h h c t e r a T e n U
Y A R R A P
V 4 W 4 = 5 8 Y A = R
y r e t t a B
o N
f ) o s 2 r g e n = b i 2 0 r P t m S s ( N u
a t a d y a r r A
D O M P
R A C O V
V 2 2 =
A 0 1 =
D O M C O V
A 5 = D O M C S I
) * ( A 8 e l b a C
W 0 4 3 =
p
e g l a a t n l i c o m o v V o y L n V E 4 a r V 4 r a 4 2 V P
d e h t r a e n U
p
m e t s y s g n i p m u p
A 6 1 e l b a C
Y A R R A C S I
A N = Y A R R A S C S I
n o i t a c t i i l u p c r p i A c s y d r e a t t o l a b C o D n
0 1 / 7 9 0 2 C E I
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) * ( e u l a v l a n i F
g n i t a r
g s e i n l z b i a S c d n a s e c i v e d n o i t c e t o r P
p e t s s s e c o r p g n i z i S
A N
A N
n o i t c e t o r p t n e r r u c r e v o o n
A N
A N
n o i t c e t o r p t n e r r u c r e v o A N
n o i t c e t o r p y a r r 2 . a 4 . b 3 u . s 5 2 p e t S
n o i t c e t o r p 3 . y 4 . a r . r 3 a 5 3 p e t S
) * ( A 8
. f e r F e x s e u l a n C A
) 1 – 0 P S (
×
D O M C A S 5 I 2 ,
e c i e u o l h a c V e c i × v A e R 5 R × d A n S 5 o 4 i , t P I 1 c R T + e n I 0 n = = o c E E s L L i B B D A A
7 = 5 4 , ) 1 1 2 + ( Y ×
o n
) 3 3 1 ≤ e l r e i u l l S g a r c i F a P p : e e n y s i ( g s l o g o y n n o r i n : r e t h y t t s c r a f t e t e b o t b V a A o n P B N N
n o i t c e t o r p 1 . g 4 . n i r 3 . t s 5 1 p e t S
) * ( A 6 1
TS 62 6225 2577-77-1 1
Y A R R A C S I ×
A 5 , 4 1 = 0 1 ×
5 5 4 4 , , 1 1 = = E E L L B B A A C C Y Y A A R R R R A A I I
6 e l b a T e – l b 2 a . c 1 . y 4 . a r . r 1 a 6 4 p e t S
A N
6 e e l b l b a a T c – y 2 a . r r 1 . a 4 . b 1 u . s 6 5 p e t S
C C G G N I I N R R T T S S I I
6 e l b a T e l b – a 2 . c 1 . g 4 . n i r 1 . t s 6 6 p e t S
F x e n n A e e s ? g i h n c t i w s e l o p e l b u o d e v a h o t y r a s s e c e n
f e R t n ) e ( 1 m m o C
. t e k r a m e h t n o l e b a l i a v a s e u l a v d r a d n a t s e h t o t g n i d r o c c a e u l a f v o d e d n u o R )
© IEC:2010(E)
* (
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p
f n o o i e t l p a c i m l a p x p E a
y r e t t a b h t i W – 3
s g n i r t s l e l l a r a p f o r e b m u n h t i w y a r r a V P V L E : 2 e s a C
n o i t a r u g i f n o c g n i h t r a e m e t s y S
n o i i t t a u c r c i l i p c p A
C D d s e h d t r a o a l e n U
m o o r l a c i n h c e T r o t a r e n e g V P
d e h t r a e n U
S E I l l a m S
W 0 4 3 = Y A R R A P
V 4 W 4 = 5 8 Y A = R p
y r e t t a B
s n e o y i t p i r a t c a s d e d y l a a r r c i f A n h o 2 r s c e g e b n 2 = i 0 T r P t m S s N u
e g l a a t n l i c o o v V m V y L o E n 4 a r V 4 r a 4 2 V P
d e h t r a e n U
D O M P
R A C O V
V 2 2 =
A 0 1 =
D O M C O V
A 5 = D O M C S I
Y A R R A C S I
A N = Y A R R A S C S I
) * ( A 8 s e l b a C
A 8 s e s u F
A 6 1 e l b a C
A 6 1 e s u F
n o i t a t c i i l u p c r p i A c s d y r a h e o t i t l t w a C b D
0 1 / 8 9 0 2 C E I
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) * ( e u l a v l a n i F
) * ( A 8
G N I R T S P I R T I
g n i t ≤ a r g D s e i n l z b i a S c d n a s e c i v e d n o i t c e t o r P
p e t s s s e c o r p g n i z i S
. f e r F e s x u e a n l n C A
×
2 ≤
5 ×
2 ≤
G 0 N 1 I R T S P I R
≤
×
≤
5 5 5 4 , 2 , , 4 1 1 7 ) 3 3 1 ≤ e r l u e i l g l S i a r c F a P e p : e s n y ( i g s s l e g o y o n i n y t r h s c : r f t e t e o t b V a n P B
n o i t c e t o r p 1 . g 4 . n i 3 . t s r 5 1 p e t S
0
Y 1 A × R R 2 A ≤ P I Y 0 R A 2 T R I R ≤ ≤ A Y A Y P R A I R R T R A R A I P ≤ I C 0 R S 1 I T I
G N I R T S T O I M P I C ≤ R T S 5 I I ×
A N
) * ( A 8
© IEC:2010(E)
Y A R R A C S I
×
≤
A 6 1
A N
D O M C S I
2
) * ( A 6 1
TS 62 6225 2577-77-1 1
×
×
) 1 – 0 P S (
×
D
O M C A S 5 I 2
, 7 5 = 4 , ) 1 1 2 + (
≤
×
5 5 5 , A 4 , 4 , 4 N 1 1 1 Y A R R A C S I ×
A 5 , 4 1 = 0 1
Y × A 5 R R × A - 5 S 4 , P I 1 R + T I 0
×
5 5 4 4 , , 1 1 = =
A N
n o i t c e t o r p y a r r 2 . a 4 . b 3 u s 5 . 2 p e t S
y r e t t a B
n o i t c e t o r p 3 . y 4 . a r 3 r a 5 . 3 p e t S
= =
E E L L B B A A C C Y Y A A R R R R A A I I
A N
E E L L B B A A C C G G N I N I R R T T S S I I
6 e l b a T e – l b 2 a . c 1 . y 4 . a r 1 . a r 6 4 p e t S
6 e l e b l b a a T c – y 2 a . r r 1 . a 4 . b 1 u s 6 . 5 p e t S
6 e l b a T e – l b 2 a . c 1 . g 4 . n i 1 . t r s 6 6 p e t S
e c e i u o l h a c V e c i v e d n o i t c e n n o c s i D
F x e n n A e e s ? g n i h c t i w s e l o p e l b u o d e v a h o t y r a s s e c e n
f e R t n ) e 1 m ( m o C
. t e k r a m e h t n o e l b a l i a v a s e l u a v d r a d n a t s e h t o t g n i d r o c c a e u l a v f f o d e d n u o R )
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TS 62257-7-1
© IEC:2010(E)
f n o o i e t l p a c i m l a p x p E a
y r e t t a b o N – 3 >
s g n i t r s l e l l a r a p f o r e b m u n h t i w y a r r a V L E : 3 e s a C
n o i t a r u g i f n o c g n i h t r a e m e t s y S
n o i i t t a u c c i r l i p c p A
m o o r l a c i n h c e T r o t a r e n e g V P
C D d s e d h a t r l a o e n U
d e h t r a e n U
d e h t r a e n U
– 69 –
p
m e t s y s g n i p m u p
W 0 8 6 = Y A R R A P
V 4 W 4 = 5 8 Y A = R p
y r e t t a B
n o i t p i r c s e d l a c i n f h o s c r g e e b n i T r t m s N u
o N a t a d y a r r A
4
D O M P
R A C O V
V 2 2 =
A 0 2 =
D O M C O V
e g l a a t n l i c o m o v V o V y L n E 4 a r V 4 r a 4 2 V P
A 5 = D O M C S I
Y A R R A C S I
A N = Y A R R A S C S I
0 1 / 9 9 0 2 C E I
) * ( A 8 s e l b a C
A 8 s e s u F
A 2 3 e l b a C
r s y e d t a t a o l b C o D n
*(
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– 70 –
e u l a v l a n i F
) * ( A 8
A N
A N
) * ( A 2 3
TS 62 6225 2577-77-1 1
. f e r F e x s e u n a n l C A
) * ( A 8
A N
© IEC:2010(E)
D O M C S I ×
2 ≤
G N I R T S P I R T I
g n i t a r g n s e i z l b i S a c d n a s e c i v e d n o i t c e t o r P
p e t s s s e c o r p g n i z i S
5 ×
2 ≤
G N I R T S ≤ P I D R O I T M
C S I ×
n o i t c e t o r p t n e r r
0 1 ≤
G N I R T S P I
≤ R T 5 I ×
≤
5 5 5 4 , 2 , , 4 1 1 7
) 3 3 1 > e l r e l u l i S g a r c i F a P p : e e n y s i ( g s l o g o n n o i n : r h t s c y r e e t f o t b V a n P B
A N
r c u e v o o N
×
Y A R R A C S I ×
2
A 9 2 = 0 2
≤
×
5 5 4 4 , , 1 1 = = y r e t t a b A o N N
e c e i u o l a h c V e c i v e d n o i t c e n n o c s i D
D O M C S I
G 5 G N I × N I 2 R R T T S ≤ 0 S P G 1 I N P I R I ≤ R T R T T G I I S N I ≤ = P I R D T E O R S L T B M I P A C I C S ≤ R T I G I 5 N I × × ≤ R 5 T 5 5 S 4 , 4 , 2 , I 1 1 7
E E L L B B A A C C Y Y A A R R R R A A I I
A N
6 e e l b l b a a T c – y 2 a . r r 1 . a 4 . b 1 u . s 6
6 e l b a T e l – b a 2 . c 1 . g 4 . n i r 1 . t s 6
5 p e t S
6 p e t S
n o i t c e t o r p 1 . g 4 . n i r 3 . t s 5
n o i t c e t o r p y a r r 2 . a 4 . b 3 u . s 5
n o i t c e t o r p 3 . y 4 . a r . r 3 a 5
6 e l b a T e – l b 2 a . c 1 . y 4 . a r . r 1 a 6
1 p e t S
2 p e t S
3 p e t S
4 p e t S
F x e n n A e e s ? g n i h c t i w s e l o p e l b u o d e v a h o t y r a s s e c e n
f e R t n ) e 1 m ( m o C
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TS 62257-7-1
© IEC:2010(E)
– 71 –
p
f n o o i e t l p a c i m l a p x p E a
y r e t t a b h t i W – 3
s g n i t r s l e l l a r a p f o r e b m u n h t i w y a r r a V L E : 4 e s a C
n o i t a r u g i f n o c g n i h t r a e m e t s y S
n o i i t t a u c c i r l i p c p A
m o o r l a c i n h c e T r o t a r e n e g V P
S E I l l a m S
W 0 8 6 = Y A R R A P
V 4 W 4 = 5 8 Y A = R p
d e h t r a E
d e h t r a E
d e h t r a E
y r e t t a B
n o i t p i r c s e d l a c i n f h o s c r g e e n T b i r t m s N u
s e y a t a d y a r r A
4
D O M P
R A C O V
V 2 2 =
A 0 2 =
D O M C O V
e g l a a t n l i c o m o v V o y L n V E 4 a r V 4 r a 4 2 V P
A 5 = D O M C S I
Y A R R A C S I
A N = Y A R R A S C S I
) * ( A 8 s e l b a C
A 8 s e s u F
A 2 3 e l b a C
A 2 3 e s u F
n o i t a t c i i l u p c r p i A c s d y r a h e o t i t l t w a C b D
0 1 / 0 0 1 2 C E I
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– 72 –
e u l a v l a n i F
) * ( A 8
A N
×
2
×
≤
2 ≤
p e t s s s e c o r p g n i z i S
G N I R T S P I R T I
×
2 ≤
D O M C S I ×
× ≤
5 5 5 4 , , 2 , 4 1 1 7 ) 3 3 1 > e r l u e l g l i i S a r c F a P e p : e s n y ( i g s s l e g o y n o i n : r h t y e r e c t f s o t t a V b n P B
n o i t c e t o r p 1 . g 4 n . i r 3 . t s 5 1 p e t S
Y 0 A 2 R × R 2 A ≤ P I Y R A T I R R ≤ A Y P A I R R T R I A
5 G 0 1 N I ≤ R T G S N I P I R R T T S I P ≤ R I T 5 I
≤
) * ( A 2 3
Y A R R A C S I
D O M C S I
g n i t g a n r i z s e i S l b a c d n a s e c i v e d n o i t c e t o r P
) * ( A 2 3
≤
C S 0 I 2 ×
×
0 4 ≤
Y A R R A
P I R T I
5 5 ≤ A 4 , 4 , 9 N 1 1 2
A N
n o i t c e t o r p y a r r 2 . a 4 . b 3 u . s 5 2 p e t S
y r e t t a B
n o i t c e t o r p 3 . y 4 . a r . r 3 a 5 3 p e t S
TS 62 6225 2577-77-1 1
. f e r F e s x u e a n l n C A
) * ( A 8
A N
e c i v e d n o i t c e t o r p t n e r r u c r e v o y a r r a V P e h t f o c t n e r r u c p i r T
= E L B A C Y A R R A I
e e u c l i a o V h c e c i v e d n o i t c e n n o c s i D
D O M C S I ×
2 ≤
G 5 G N I × N I 2 R R T T S ≤ 0 S P G 1 I N P I R I ≤ R T R T T G I I S N I ≤ = P I R T D E O R S L T B M I P A C I C S ≤ R T G I 5 I
A N
6 6 e e l e l b l b a b a T a T e – c – l b 2 y 2 a . a . r c 1 r 1 . a . y 4 . b 4 . a r . u 1 r 1 . a 6 s 6 4 5 p p e e t t S S
N I R T S I
×
×
© IEC:2010(E)
≤
5 5 5 4 , 2 , , 4 1 1 7
6 e l b a T e l – b a 2 . c 1 . g 4 n . i r 1 . t s 6 6 p e t S
F x e n n A e e s ? g n i h c t i w s e l o p e l b u o d e v a h o t y r a s s e c e n
f e R t n ) e 1 m ( m o C
. t e k r a m e h t n o e l b a l i a v a s e u l a v d r a d n a t s e h t o t g n i d r o c c a e u l a v f o d e d n u o R )
* (
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TS 62257-7-1
© IEC:2010(E)
– 73 – c
f n o o e i t l p a c i l m a p x p E a
y r e t t a b h t i W – s y a r r a b u s 2 – 3 s g n i r t s l e l l a r a p f o r e b m u n h t i w y a r r a V L E : 5 e s a C
n o i t a r u g i f n o c g n i h t r e a m e t s y S
n o i i t t a u c c i r l i p c p A
d s e d h a t r l a o e C n U D
m o o r l a c i n h c e T
d e h t r a e n U
r o t a r e n e g V P
n o i t p i r c s e d l a c i n h c e T
y r e t t a B
f o s r g e n b i r t m u s N
e g a t l o v y a r r a V P
d e h t r a e n U
S E C d i r b y H
W 0 6 3 1 = Y A R R A P
V 4 W 4 = 5 8 Y A = R c
s e Y
4
a t a d y a r r A
×
2
D O M P
R A C O V
V 2 2 =
A 0 4 =
D O M C O
V
l a n i c m o V o L n V E 4 V 4 4 2
A 5 = D O M C S I
Y A R R A C
I S
A 0 2 = Y A R R A S C S I
0 1 / 1 0 1 2 C E I
e l b a y e r g r c e w r h e u n e t n o e O r e s
A 8 s e s u F A 8 e l b a C
A 2 3 e l b a C
A 2 3 s e s u F
) * ( A 8 s e s u F
A 3 6 e l b a C
o r c d i i r M g
A 3 6 s e s u F
A
A
m o o r l
2 3 e l b a C
2 3 s e s u F
i a c n h c e T
s d a o l C A
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– 74 –
e u l a v l a n i F
) * ( A 2 3
) * ( A 8
) * ( A 3 6
S C S I
D O M C S I
×
2 ≤
×
2
5 G x N 2 I R
≤
T S P I R T I
Y A R R A C S I
≤
0 G 1 N
I R T S ≤ g n I D P i t R O g T a M I
≤
G N I R T S P I R T I
Y A R R A S P I R T I
≤
Y A R R A S
× A 2 0 ≤ 4
0 2 ×
2 ≤
Y A R R A S P I R T I
0 4 ≤
Y A R R A S
Y × A 2 R R ≤ A Y A A P I R 0 R R 8 T I A ≤ P ≤ I Y R Y T A A I R R R R ≤ A A A P I R C S T 0 4 I I
r i n ≤ P I C S C ≤ I 0 z S s e i 2 l S I 5 R × × T × ≤ b × ≤ × Y × I a 5 A 5 5 5 5 5 A ≤ 5 c 2 R 4 , 4 8 , R 4 , 2 , 4 , 9 4 , 4 d 1 1 7 1 A 1 2 1 1 5 n a s e 3 c i > v l e e l d l i S a n r c a P o i p t c n : y i e g s t s o e o g l r o y n P i n : r t h y y s c r r f t e t e e t o t t A a V a B N b n P B
p e t s s s e c o r p g n i z i S
n o i t c e t o r p 1 . g 4 . n i r 3 . t s 5
n o i t c e t o r p y a r r 2 . a 3 . b 4 u . s 5
n o i t c e t o r p 3 . y 3 . a r . r 4 a 5
1 p t e S
2 p t e S
3 p t e S
) * ( A 3 6
TS 62 6225 2577-77-1 1
) * ( A 2 3
) * ( A 8
. f e r F e x s e u n a n l C A
i e c v e d e n c i o i v t e c e d t o n r o p i t t c n e e t r o r r p u c t r n e e v r r o u y c r a e r r v a o b D O y u e e u a s c l M i C r V a o V a S h P I c V e P h × e c e t 2 i f h v t o ≤ e f t d G G 5 o n N I × t r e I N n n r R R 2 o i T e T u 0 t r S S r c ≤ 1 c u p P I G ≤ e I P i c R R N G n : p r n T T T I d i N I o e r = I I R T c d i T = ≤ S R T i s v = E S L E D P I o E D B L O R P r B M T I p L B A C I R A n C Y A C C T o S ≤ I i G I t Y A 5 c A R N ≤ × e R R I × R t 5 A T 5 o 4 4 2 r R A I S I S 1 , 7 , , 1 P I
6 6 e e l e l b l b a b a T a T e – c – l b 2 y 2 . a . a r c 1 r 1 . . a 4 y 4 . a b . r . . u 1 r 1 a 6 s 6 4 p t e S
5 p t e S
6 e l b a T e l – b a 2 . c 1 . g 4 . n i r 1 . t s 6 6 p t e S
© IEC:2010(E)
F x e n n A e e s ? g n i h c t i w s e l o p e l b u o d e v a h o t y r a s s e c e n
f e R t n ) e ( 1 m m o C
. t e k r a m e h t n o e l b a l i a v a s e u l a v d r a d n a t s e h t o t g n i d r o c c a e u l a v f f o d e d n u o R
)
* (
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TS 62257-7-1
© IEC:2010(E)
– 75 –
Annex F (informative) Double switching in PV array
F.1 F.1.1
Introductory remarks General
The reasons for requiring double pole switching on a PV array are dependent on the type of system. Two types of systems have to be considered: unearthed systems and earthed systems. F.1.2
Unearthed systems
For unearthed systems the requirement for switching in all active conductors comes from 536.2 Isolation, of IEC 60364-5-53. Subclause 536.2.1 states that “Every circuit shall be capable of being isolated from each of the live supply conductors.” Subclause 536.2.2.1 states that devices for isolation “shall effectively isolate all live supply conductors from the circuit concerned subject to the provisions of 536.1.2” (where this 536.1.2 does not apply to floating systems.) IEC 60364 states in the scope that it applies to all systems up to 1 000 V a.c. and 1 500 V d.c. This includes ELV and LV systems. F.1.3
Earthed systems
In the case of earthed systems a double pole switch has been mandated in the PV array standard and the earthing point for the system is shown on the system side of the PV array main switch. If an earth fault develops in the PV array, this switch is the only safe means of interrupting the flow of this fault current.
F.2 F.2.1
Earth fault analysis General
In this annex, the worst case PV array fault conditions are analysed for both earthed and floating PV arrays. The implications for overcurrent protection derived from the worst case fault current analysis are also discussed. The analysis is made for the case of PV strings with four series modules, however they are valid for any number of series connected PV modules. Also, the earth faults are considered to be zero impedance faults which is the case when the fault currents are the highest. F.2.2
Floating PV arrays
In floating PV arrays, there is no reference to earth; therefore a single earth fault does not produce any fault F.2).for What a single fault does produce earth reference forcurrents the PV (see arrayFigures circuit, F.1 andand a path earth fault current in the event isofan a second earth fault or a person touching the live conductors and earth simultaneously.
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– 76 –
I 2
I 3
m e t s y s g n i n o i t i d n o c r e w o P
−
© IEC:2010(E)
I 1 + I 2 + I 3
+
I 1
TS 62257-7-1
I 1 ≈ I 2 ≈ I 3 ≈ I M MP P MOD
IEC
2102/10
Figure F.1 – Floating PV array operating at maximum power point When a single earth fault develops, the PV array currents remain the same if the system is not shut down, provided that the power conditioning system does not allow fault currents to pass through its power circuits from the load side to the PV array side. If there is electrical isolation between PV array and a.c. loads, the system can continue operating in most cases but it becomes unsafe as the PV array is no longer floating, increasing the risk of electric shock and earth fault currents due to a second earth fault.
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TS 62257-7-1
© IEC:2010(E)
– 77 –
I 1
I 2 + I 3
+
+
I 1
I 2
I 3
I E =
0
I 1
I 2 ≈ I 3 ≈ I MP MOD
≈
m e t s y s g n i n o i t i d n o c r e w o P
−
IEC
2103/10
Figure F.2 – Floating PV array with single earth fault If a second fault develops in the PV array, the earth loop is closed allowing fault currents to flow in the PV array wiring (see Figure D.3). Under the fault conditions of Figure F.3, a three-module segment of string number 3 is shortcircuited, and the remaining PV m odule in string number 3 is connected in parallel with strings 1 and 2. This would cause the PV array voltage to drop significantly, most likely causing the power conditioning system to disconnect itself from the PV array, thus leaving the PV array open circuited.
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TS 62257-7-1
© IEC:2010(E)
I 1′ + I 2′ + I 3′
+
I E = I 1′ + I 2′ + I 3′ I 1′
I 2′
I 3′
I 1 ≈ I 2 ≈ I 3 ≈ I SC MOD
I E = I 1′ + I 2′ + I 3′
M3,1
I 1′ + I 2′ I = 0
−
IEC
2104/10
Figure F.3 – Floating PV array with double earth fault The most important observations from the node analysis of this fault case are the following: PV module M 3, 1 is forward biased with a voltage that is larger than its open circuit voltage. Thus the module is operating in the second quadrant of its I-V characteristic (i.e. the current through it is negative and it is forced to dissipate the power delivered by PV strings 1 and 2). As th the e volt vo ltag age e of str in ings gs 1 an and d 2 drop dr ops, s, the ir ou outp tput ut curr cu rren entt in incr crea eases ses to ap appr prox oxim imate ate ly thei th eirr short circuit value. If Standard Test Conditions are assumed, the reverse current through module M3, 1 is approximately twice I SC MOD . The current of the section of the string cable that connects module M 3,1 with the negative bus bar is also twice I SC MOD . The reverse current through PV module M 3,1 and through the segment of the string cable that connects it to the negative bus bar would increase by approximately I SC S C MOD for each additional parallel PV string in the circuit.
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TS 62257-7-1
© IEC:2010(E)
– 79 –
If the faults occurred in opposite locations of the PV array (see Figure F.4), then PV module M3, 4 would be forced to dissipate the power delivered by strings 1 and 2 and the segment that connects it to the positive bus bar would be overloaded. This implies that overcurrent protection in unearthed PV arrays, when required, has to be installed in both positive and negative cables of the corresponding circuit.
+
I = 0
I 1′ + I 2′
M3,4
I E = I 1′ + I 2′ + I 3′
I 1 ≈ I 2 ≈ I 3 ≈ I SC MOD
I 1′
I 2′
−
I 3′
I 1′ + I 2′ + I 3′
I = I ′ + I ′ + I ′
E
1 2 3 IEC
2105/10
Figure F.4 – Floating PV array with double earth fault
F.3
Earthed PV arrays
In earthed PV arrays, there is already a reference to earth and a path for earth fault currents; therefore a single earth fault, or a person touching an unearthed conductor and earth simultaneously will produce earth fault currents to flow in the PV array. Note that the worst-case earth fault scenario for earthed PV arrays is identical as that presented in Figure F.4, the only difference is that the connection to earth of the negative conductor of the PV array cable is not a fault, but an intentional connection. The node analysis and most of the observations made for the floating case hold true, except for the last one. In the earthed case, the PV string cable segments that connect to the negative busbar cannot be overloaded with one or multiple earth faults.
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F.4 F.4.1
– 80 –
TS 62257-7-1
© IEC:2010(E)
Implications for overcurrent protection General
The above discussion clearly shows that overcurrent protection for PV arrays is required in some cases to ensure a safe system in case of earth faults. F.4.2
Number of strings
If the earth fault characteristics are taken into account, it can be seen that overcurrent protection is irrelevant when there are less than three parallel strings in the circuit, and there is no battery storage system, provided that the PV modules are capabe of withstanding a reverse current equal to their short circuit current. Furthermore, when three parallel strings are connected and overcurrent protection devices are installed in each string, they will not trip if I TRIP is 2 times I SC MOD, unless there are increased irradiance conditions. Therefore, under this situation and the worst case earth fault situations presented above, PV modules would be subjected to reverse currents about twice their nominal short circuit current. F.4.3
Battery storage
When battery storage is present, the battery is capable of overloading the PV array wiring and components regardless of the location of the fault or the number of parallel-connected strings. F.4.4
Diodes
Blocking diodes are not a reliable protection against reverse current because they often fail in short circuit mode. The use of blocking diodes is currently restricted to prevent discharging the battery to an unenergised PV array at night. Their use should be avoided otherwise because they are sources of failures and power loss.
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TS 62257-7-1
© IEC:2010(E)
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Bibliography IEC 60050-151:2001, International Electrotechnical Vocabulary (IEV) – Part 151: Electrical and magnetic devices IEC 60050-195:1998, International Electrotechnical Vocabulary (IEV) – Part 195: Earthing and pr prot otec ecti tion on ag again ain st elec el ectr tric ic shock sh ock IEC 60050-442:1998, International Electrotechnical Vocabulary (IEV) – Part 442: Electrical accessories IEC 60050-461:1984, International Electro-technical Vocabulary (IEV) – Part 461: Electric cables IEC 60050-826:2004, International Electrotechnical Vocabulary (IEV) – Part 826: Electrical installations IEC 60364-5-53, Electrical installations of buildings –Selection and erection of electrical equipment – Isolation, switching and control IEC 60449, Voltage bands for electrical installations of buildings Part 2: Requirements for reference solar devices IEC 60904-2, Photovoltaic devices − Part IEC 60904-3, Photovoltaic devices − Part 3: Measurement principles phot ph otov ovol olta taic ic (P V) sola so larr de devic vic es with wi th re refe fere renc nce e s pe pectr ctr al irr ad adian ian ce da data ta
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IEC 61201, Use of conventional touch voltage limits – Application guide guide IEC 61829, Crystalline silicon photovoltaic (PV) array − On-site measurement of I-V characteristics characteristics IEC 61836:2007, Solar photovoltaic energy systems – Terms and symbols IEC 62246-2, Reed contact units – Part 2: Heavy-duty reed switches IEC 62257-2, Recommendations for small renewable energy and hybrid systems for rural electrification – Part 2: From requirements to a range of electrification systems IEC 62257-3, Recommendations for small renewable energy and hybrid systems for rural electrification – Part 3: Project development and management IEC 62257-4, Recommendations for small renewable energy and hybrid systems for rural electrification – Part 4: System selection and design
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