IEC TS 62257-9-2:2016

IEC TS 62257-9-2 ®
Edition 2.0 2016-09
TECHNICAL
SPECIFICATION
colour
inside
Recommendations for renewable energy and hybrid systems for rural
electrification –
Part 9-2: Integrated systems – Microgrids

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IEC TS 62257-9-2 ®
Edition 2.0 2016-09
TECHNICAL
SPECIFICATION
colour
inside
Recommendations for renewable energy and hybrid systems for rural

electrification –
Part 9-2: Integrated systems – Microgrids

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-3586-7

– 2 – IEC TS 62257-9-2:2016 © IEC 2016
CONTENTS
FOREWORD. 5
INTRODUCTION . 7
1 Scope . 8
2 Normative reference . 8
3 Terms and definitions . 8
4 General . 10
4.1 Limits of a microgrid . 10
4.2 Voltage drops . 10
4.3 Composition of a microgrid . 10
5 Protection against electric shocks . 12
6 Protection against overcurrents . 12
7 Selection and erection of equipment. 12
7.1 Equipment installation . 12
7.2 Operational conditions and external influences . 12
7.2.1 Ambient temperature . 12
7.2.2 Sources of heat . 12
7.2.3 Presence of water . 12
7.2.4 Risk of penetration of solid bodies . 13
7.2.5 Corrosive or polluting substance presence . 13
7.2.6 Mechanical requirements . 13
7.2.7 Equipment and supporting structures . 13
7.2.8 Vibration . 13
7.2.9 Other mechanical constraints for underground microgrid sections . 13
7.2.10 Presence of flora, mold or fauna . 14
7.2.11 Solar radiation . 14
7.3 Characteristics of lines . 14
7.3.1 General . 14
7.3.2 Installation modes . 14
7.3.3 Minimum height of conductors . 14
7.3.4 Proximity to other services . 14
7.4 Cables . 14
7.5 Poles . 15
7.5.1 General . 15
7.5.2 Characteristics of poles . 15
7.6 Cable anchorage . 17
7.7 Connections and accessories . 18
7.7.1 General . 18
7.7.2 Connections between conductors, connections to other equipment . 18
7.7.3 Connection points for individual service connections . 18
7.7.4 Connection equipment . 18
7.8 Where poles are used for other purposes . 19
7.8.1 Public lighting points . 19
7.8.2 Telecommunication lines . 19
7.9 Isolation and switching . 20
7.9.1 Overcurrent protection device . 20

7.9.2 Isolating devices . 21
7.10 Earthing arrangement, protective conductors and protective bonding
conductors . 21
8 Verification and acceptance . 22
8.1 General . 22
8.2 Supervision of works . 22
8.3 Verification before commissioning (on site acceptance) . 23
8.4 Operation tests . 23
Annex A (informative) Characteristics of cables . 24
Annex B (informative) Maximum circuit length . 26

Figure 1 – Microgrid limits . 10
Figure 2 – Microgrid consisting of a single phase feeder . 11
Figure 3 – Three phase system output, single phase distribution or three phase
service provided where needed . 11
Figure 4 – Three phase system output, single phase distribution . 11
Figure 5 – Diagram showing installation of twinned wooden poles forming an angle . 16
Figure 6 – Examples of different pole arrangements . 17
Figure 7 – Example of an overhead line . 17
Figure 8 – Connection mode diagram . 19
Figure 9 – Microgrid earthing scheme . 21
Figure B.1 – Maximum lengths as a function of active power (1 phase) for 16 mm
cable and 6 % voltage drop with loads at end of cable . 27
Figure B.2 – Maximum lengths as a function of active power (1 phase) for 16 mm
cable and 6 % voltage drop with loads spread across cable . 28
Figure B.3 – Maximum lengths as a function of active power (1 phase) for 25 mm
cable and 6 % voltage drop with loads at end of cable . 29
Figure B.4 – Maximum lengths as a function of active power (1 phase) for 25 mm
cable and 6 % voltage drop with loads spread across cable . 30
Figure B.5 – Maximum lengths as a function of active power (3 phase) for 35 mm
cable and 6 % voltage drop with loads at end of cable . 31
Figure B.6 – Maximum lengths as a function of active power (3 phase) for 35 mm
cable and 6 % voltage drop with loads spread across cable . 32
Figure B.7 – Maximum lengths as a function of active power (3 phase) for 35 mm
cable and 3 % voltage drop with loads at end of cable . 33
Figure B.8 – Maximum lengths as a function of active power (3 phase) for 50 mm
cable and 6 % voltage drop with loads at end of cable . 34
Figure B.9 – Maximum lengths as a function of active power (3 phase) for 50 mm
cable and 6 % voltage drop with loads spread across cable . 35
Figure B.10 – Maximum lengths as a function of active power (3 phase) for 50 mm
cable and 3 % voltage drop with loads at end of cable . 36
Figure B.11 – Maximum lengths as a function of active power (3 phase) for 70 mm
cable and 6 % voltage drop with loads at end of cable . 37
Figure B.12 – Maximum lengths as a function of active power (3 phase) for 70 mm
cable and 6 % voltage drop with loads spread across cable . 38
Figure B.13 – Maximum lengths as a function of active power (3 phase) for 70 mm
cable and 3 % voltage drop with loads at end of cable . 39

– 4 – IEC TS 62257-9-2:2016 © IEC 2016
Table 1 – Maximum values of voltage drops . 10
Table 2 – Fuse ratings for protection from short-circuiting in 230 V (and 240 V) a.c.
microgrids (overhead lines) . 20
Table 3 – Fuse ratings for protection from short-circuiting in 120 V a.c. microgrids
(overhead lines) . 20
Table 4 – Circuit breaker ratings for protection from short-circuiting in microgrids
(overhead lines) . 20
Table 5 – Characteristics of earthing components . 22
Table A.1 – Example of characteristics of grid conductors for overhead lines (insulated
twisted conductors without carrier neutral) . 24

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
RECOMMENDATIONS FOR RENEWABLE ENERGY
AND HYBRID SYSTEMS FOR RURAL ELECTRIFICATION –

Part 9-2: Integrated systems – Microgrids

FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC 62257-9-2, which is a technical specification, has been prepared by IEC technical
committee 82: Solar photovoltaic energy systems.

– 6 – IEC TS 62257-9-2:2016 © IEC 2016
This second edition cancels and replaces the fist edition issued in 2006. It constitutes a
technical revision.
The main technical changes with regard to the previous edition are as follows:
• Changing the voltage range covered by the technical specification to a.c. nominal voltage
below 1 000 V and d.c. nominal voltage below 1 500 V (introduction).
• Including 240 V 1-Ø/415 V 3-Ø, in the voltage levels (scope).
• Deleted microgrid and micropowerplants from terms and definitions.
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
82/1029/DTS 82/1088/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 document has been drafted in accordance with the ISO/IEC Directives, Part 2.
This part of IEC 62257 is to be used in conjunction with the IEC 62257 series.
A list of all parts in the IEC 62257 series, published under the general title Recommendations
for renewable energy and hybrid systems for rural electrification, can be found on the IEC
website.
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

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.
INTRODUCTION
The IEC 62257 series 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. nominal
voltage below 1 000 V and d.c. nominal voltage below 1 500 V.
These documents are recommendations:
• to choose the right system for the right place,
• to design the system,
• to operate and maintain the system.
These documents are focused only on rural electrification concentrating on but not specific to
developing countries. They should not be considered as all inclusive to rural electrification.
The documents try to promote the use of renewable energies in rural electrification; they do
not deal with clean mechanisms developments at this time (CO emission, carbon credit, etc.).
Further developments in this field could be introduced in future steps.
This consistent set of documents is best considered as a whole with different parts
corresponding to items for safety, sustainability of systems and at the lowest life cycle cost as
possible. One of the main objectives is to provide the minimum sufficient requirements,
relevant to the field of application that is: small renewable energy and hybrid off-grid systems.
Decentralized Rural Electrification Systems (DRESs) are designed to supply electric power for
sites which are not connected to a large interconnected system, or a national grid, in order to
meet basic needs.
The majority of these sites are:
• isolated dwellings,
• village houses,
• community services (public lighting, pumping, health centres, places of worship or cultural
activities, administrative buildings, etc.),
• economic activities (workshops, microindustry, etc.).
The DRE systems fall into three categories:
• process electrification systems (for example for pumping),
• individual electrification systems (IES) for single users,
• collective electrification systems (CES) for multiple users.
Process or individual electrification systems exclusively consist of two subsystems:
• an electric energy generation subsystem,
• the user's electrical installation.
Collective electrification systems, however, consist of three subsystems:
• an electric energy generation subsystem,
• a distribution subsystem, also called microgrid,
• user’s electrical installations including interface equipment between the installations and
the microgrid.
– 8 – IEC TS 62257-9-2:2016 © IEC 2016
RECOMMENDATIONS FOR RENEWABLE ENERGY
AND HYBRID SYSTEMS FOR RURAL ELECTRIFICATION –

Part 9-2: Integrated systems – Microgrids

1 Scope
This part of IEC 62257, which is a technical specification, specifies the general requirements
for the design and the implementation of microgrids used in decentralized rural electrification
to ensure the safety of persons and property and their satisfactory operation according to the
scheduled use.
This part of IEC 62257 applies to microgrids for decentralized rural electrification purposes.
The microgrids covered by this part of IEC 62257 are low voltage a.c., three-phase or single-
phase, with rated capacity less than or equal to 100 kVA. They are powered by a single
micropower plant and do not include voltage transformation. The rated capacity is at the
electrical output of the micropower plant, that is, the upstream terminals of the main switch
between the micropower plant and the microgrid.
The voltage levels covered under this specification are voltages of the 240 V 1-Ø/415 V 3-Ø,
the 230 V 1-Ø/400 V 3-Ø, the 220 V 1-Ø/380 V 3-Ø, and the 120 V 1-Ø/208 V 3-Ø systems at
60 Hz or 50 Hz; or obeyed by local code.
This part of IEC 62257 specifies microgrids made of overhead lines because of technical and
economical reasons in the context of decentralized rural electrification. In particular cases,
underground cables can be used.
The requirements cover microgrids with radial architecture.
2 Normative reference
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements 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 61439 (all parts), Low-voltage switchgear and controlgear assemblies
IEC 62257 (all parts), Recommendations for renewable energy and hybrid systems for rural
electrification
IEC TS 62257-5, Recommendations for renewable energy and hybrid systems for rural
electrification – Part 5: Protection against electrical hazards
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
carrier
messenger
wire or a rope, the primary function of which is to support the cable in aerial installations,
which may be separate from or integral with the cable it supports
3.2
block
part of a line between two consecutive stoppage poles
3.3
earth
conductive mass of the earth, whose electric potential at any point is conventionally taken as
equal to zero
3.4
protective conductor
identification: PE
conductor provided for purposes of safety, for example protection against electric shock
[SOURCE: IEC 60050-195:1998, 195-02-09]
3.5
PEN conductor
conductor combining the functions of both a protective earthing conductor and a neutral
conductor
[SOURCE: IEC 60050-195:1998, 195-02-12]
3.6
power line
overhead or underground line installed to convey electrical energy for any purpose other than
communication
3.7
section of an overhead line
part of a line between two tension poles
Note 1 to entry: A section generally includes several spans.
3.8
selectivity
protection coordination
ability of a protection to identify the faulty section and/or phase(s) of a power system
[SOURCE: IEC 60050-448:1995, 448-11-06]
3.9
service connection line
conductors between the supplier’s mains and the customer’s installation

– 10 – IEC TS 62257-9-2:2016 © IEC 2016
Note 1 to entry: In the case of an overhead service connection, this means the conductor between a supply-line
pole and the customer’s installation.
3.10
span
part of a line between two consecutive poles
3.11
stay
steel wire, rope or rod, working under tension, that connects a point of a support to a separate
anchor
4 General
4.1 Limits of a microgrid
The microgrid is defined between the output terminals of the isolating device of the
micropower plant and the input terminals of the user’s interface as illustrated in Figure 1.
Production Distribution User
sub-system sub-system sub-system
Microgrid Installation
Micropowerplant
Other
User interface
Generator
equipment
IEC
Figure 1 – Microgrid limits
4.2 Voltage drops
The maximum values of the voltage drops in the microgrid shall not exceed the values
indicated in Table 1 or the values regulated by local code.
Table 1 – Maximum values of voltage drops
Microgrid Voltage drop
%
Main line 6
Individual service connection line 1

4.3 Composition of a microgrid
Three microgrid schemes are specified in this part of IEC 62257 depending on the maximum
active power value required and the topography of the areas to be served.
• Single phase power system output: one single phase feeder with multiple single phase
distribution (see Figure 2).
G
PEN
~
PEN 1 PEN 1 PEN 1
IEC
Figure 2 – Microgrid consisting of a single phase feeder
NOTE A community could be served by multiple single phase distribution driven by different single phase
generators.
• three phase system output: depending on the power needs of the customers, the layout of
the area to be served and the cost, two different distribution architectures can be used, as
shown in Figure 3 and Figure 4.
a) Case 1: Three phase power system output; one three phase feeder with three phase or
single phase distribution.
G
~
PEN
PEN 2 PEN PEN 1 PEN 3
IEC
Figure 3 – Three phase system output, single phase distribution
or three phase service provided where needed
b) Case 2: Three phase power system output; single phase distribution is used
throughout the community.
G
~
PEN
PEN 3 PEN 2 PEN 1
IEC
Figure 4 – Three phase system output, single phase distribution

– 12 – IEC TS 62257-9-2:2016 © IEC 2016
5 Protection against electric shocks
The microgrid shall be designed as a TN-C system (see IEC TS 62257-5).
6 Protection against overcurrents
The microgrid shall be provided with a device to protect against overcurrent. It shall be placed
at the interface with the micropower plant
The characteristics of the device shall ensure that, at any point, negligible impedance faults
between phase conductor and protection conductor or earth will cause automatic
disconnection within a period of time of 0,3 s.
Special attention shall be paid to the selectivity with respect to the overcurrent protective
device of the user’s installation. The selectivity between protective devices in series should
ensure that any faulty section is interrupted.
7 Selection and erection of equipment
7.1 Equipment installat
...