Recommendations for small renewable energy and hybrid systems for rural electrification - Part 9-2: Microgrids

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.

Priporočila za sisteme malih obnovljivih virov energije in hibridne sisteme za elektrifikacijo podeželja - 9-2. del: Mikro omrežja

General Information

Status
Not Published
Current Stage
PPUB - Publication issued
Start Date
09-Oct-2006

Buy Standard

Technical specification
-TS IEC/TS 62257-9-2:2008
English language
52 pages
sale 10% off
Preview
sale 10% off
Preview

e-Library read for
1 day

Standards Content (sample)

SLOVENSKI STANDARD
SIST-TS IEC/TS 62257-9-2:2008
01-november-2008
3ULSRURþLOD]DVLVWHPHPDOLKREQRYOMLYLKYLURYHQHUJLMHLQKLEULGQHVLVWHPH]D
HOHNWULILNDFLMRSRGHåHOMDGHO0LNURRPUHåMD

Recommendations for small renewable energy and hybrid systems for rural electrification

- Part 9-2: Microgrids
Ta slovenski standard je istoveten z: IEC/TS 62257-9-2
ICS:
27.190 Biološki viri in drugi Biological sources and
alternativni viri energije alternative sources of energy
SIST-TS IEC/TS 62257-9-2:2008 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST-TS IEC/TS 62257-9-2:2008
---------------------- Page: 2 ----------------------
SIST-TS IEC/TS 62257-9-2:2008
TECHNICAL IEC
SPECIFICATION TS 62257-9-2
First edition
2006-10
Recommendations for small renewable energy
and hybrid systems for rural electrification –
Part 9-2:
Microgrids
© IEC 2006 ⎯ Copyright - all rights reserved

No part of this publication may be reproduced or utilized in any form or by any means, electronic or

mechanical, including photocopying and microfilm, without permission in writing from the publisher.

International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland

Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch

PRICE CODE
Commission Electrotechnique Internationale XA
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
For price, see current catalogue
---------------------- Page: 3 ----------------------
SIST-TS IEC/TS 62257-9-2:2008
– 2 – TS 62257-9-2 © IEC:2006(E)
CONTENTS

FOREWORD...........................................................................................................................4

INTRODUCTION.....................................................................................................................6

1 Scope...............................................................................................................................7

2 Normative reference .........................................................................................................7

3 Terms and definitions .......................................................................................................7

4 General ............................................................................................................................9

4.1 Limits of a microgrid ................................................................................................9

4.2 Voltage drops..........................................................................................................9

4.3 Composition of a microgrid......................................................................................9

5 Protection against electric shocks...................................................................................11

6 Protection against overcurrents ......................................................................................11

7 Selection and erection of equipment...............................................................................11

7.1 Equipment installation ...........................................................................................11

7.2 Operational conditions and external influences......................................................11

7.3 Characteristics of lines ..........................................................................................13

7.4 Cables...................................................................................................................14

7.5 Poles.....................................................................................................................14

7.6 Cable anchorage ...................................................................................................17

7.7 Connections and accessories ................................................................................17

7.8 Where poles are used for other purposes ..............................................................19

7.9 Isolation and switching ..........................................................................................19

7.10 Earthing arrangement, protective conductors and protective bonding

conductors ............................................................................................................20

8 Verification and acceptance............................................................................................22

8.1 General .................................................................................................................22

8.2 Supervision of works .............................................................................................22

8.3 Verification before commissioning (on site acceptance).........................................22

8.4 Operation tests......................................................................................................23

Annex A (informative) Characteristics of cables ....................................................................24

Annex B (informative) Maximum circuit length.......................................................................26

Figure 1 – Microgrid limits.......................................................................................................9

Figure 2 – Microgrid consisting of a single-phase feeder.......................................................10

Figure 3 – Three phase system output, single phase distribution or three phase

service provided where needed.............................................................................................10

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 .............................................................16

Figure 7 – Example of an overhead line ................................................................................16

Figure 8 – Connection mode diagram....................................................................................19

Figure 9 – Microgrid earthing scheme ...................................................................................21

---------------------- Page: 4 ----------------------
SIST-TS IEC/TS 62257-9-2:2008
TS 62257-9-2 © IEC:2006(E) – 3 –

Table 1 – Maximum values of voltage drops............................................................................9

Table 2 – Fuse ratings for protection from short-circuiting in 230 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

---------------------- Page: 5 ----------------------
SIST-TS IEC/TS 62257-9-2:2008
– 4 – TS 62257-9-2 © IEC:2006(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
RECOMMENDATIONS FOR SMALL RENEWABLE ENERGY
AND HYBRID SYSTEMS FOR RURAL ELECTRIFICATION
Part 9-2: Microgrids
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote

international co-operation on all questions concerning standardization in the electrical and electronic fields. To

this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,

Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC

Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested

in the subject dealt with may participate in this preparatory work. International, governmental and non-

governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely

with the International Organization for Standardization (ISO) in accordance with conditions determined by

agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence

between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

the latter.

5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any

equipment declared to be in conformity with an IEC Publication.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

The main task of IEC technical committees is to prepare International Standards. In

exceptional circumstances, a technical committee may propose the publication of a technical

specification when

• the required support cannot be obtained for the publication of an International Standard,

despite repeated efforts, or

• The subject is still under technical development or where, for any other reason, there is

the future but no immediate possibility of an agreement on an International Standard.

Technical specifications are subject to review within three years of publication to decide

whether they can be transformed into International Standards.

IEC 62257-9-2, which is a technical specification, has been prepared by IEC technical

committee 82: Solar photovoltaic energy systems.

This part of IEC 62257-9 is based on IEC/PAS 62111 (1999); it cancels and replaces the

relevant parts of IEC/PAS 62111.
---------------------- Page: 6 ----------------------
SIST-TS IEC/TS 62257-9-2:2008
TS 62257-9-2 © IEC:2006(E) – 5 –
This part of IEC 62257-9 is to be used in conjunction with the IEC 62257 series.
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
82/412/DTS 82/443/RVC

Full information on the voting for the approval of this technical specification can be found in

the report on voting indicated in the above table.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts of the IEC 62257 series, under the general title Recommendations for small

renewable energy and hybrid systems for rural electrification, can be found on the IEC

website.

The committee has decided that the contents of this publication will remain unchanged until

the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in

the data related to the specific publication. At this date, the publication will be

• 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.
---------------------- Page: 7 ----------------------
SIST-TS IEC/TS 62257-9-2:2008
– 6 – TS 62257-9-2 © IEC:2006(E)
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 500 V, d.c. nominal voltage below 750 V and nominal power below 100 kVA.

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 (DRES) 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.
---------------------- Page: 8 ----------------------
SIST-TS IEC/TS 62257-9-2:2008
TS 62257-9-2 © IEC:2006(E) – 7 –
RECOMMENDATIONS FOR SMALL RENEWABLE ENERGY
AND HYBRID SYSTEMS FOR RURAL ELECTRIFICATION
Part 9-2: Microgrids
1 Scope

The purpose this part of IEC 62257-9 is to specify 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 62257-9 applies to microgrids for decentralized rural electrification purposes.

The microgrids covered by this part of IEC 62257-9 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

micropowerplant and do not include voltage transformation.

The low-voltage levels covered under this part of IEC 62257-9 are the 230 V 1-Ø/400 V 3-Ø

systems, 220 V 1-Ø/380 V 3-Ø, the 120 V 1-Ø/208 V 3-Ø, 60 Hz or 50 Hz systems.

This part of IEC 62257-9 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 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 62257 (all parts), Recommendations for small renewable energy and hybrid systems for

rural electrification
IEC 60439 (all parts), Low-voltage switchgear and controlgear assemblies
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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
---------------------- Page: 9 ----------------------
SIST-TS IEC/TS 62257-9-2:2008
– 8 – TS 62257-9-2 © IEC:2006(E)
3.3
earth

conductive mass of the earth, whose electric potential at any point is conventionally taken as

equal to zero
3.4
microgrid

subsystem of a DRES intended for power distribution of which the capacity does not exceed

100 kVA

NOTE The prefix «micro» is intended to express the low level of transmitting capacity.

3.5
micropowerplant
subsystem of a DRES for power generation up to 100 kVA

NOTE The prefix «micro» is intended to express the low power level generated (from a few kVA to a few tens of

kVA).
3.6
protective conductor
identification: PE

conductor provided for purposes of safety, for example protection against electric shock

[IEV 195-02-09]
3.7
PEN conductor

conductor combining the functions of both a protective earthing conductor and a neutral

conductor
[IEV 195-02-12]
3.8
power line

overhead or underground line installed to convey electrical energy for any purpose other than

communication
3.9
section of an overhead line
part of a line between two tension poles
NOTE A section generally includes several spans.
3.10
selectivity (or protection coordination)

ability of a protection to identify the faulty section and/or phase(s) of a power system

[IEV 448-11-06]
3.11
service connection line
conductors between the supplier’s mains and the customer’s installation

NOTE In the case of an overhead service connection, this means the conductor between a supply-line pole and the

customer’s installation.
3.12
span
part of a line between two consecutive poles
---------------------- Page: 10 ----------------------
SIST-TS IEC/TS 62257-9-2:2008
TS 62257-9-2 © IEC:2006(E) – 9 –
3.13
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

micropowerplant and the input terminals of the user’s interface as illustrated in Figure 1.

Production Distribution User
sub-system sub-system sub-system
Micropowerplant Microgrid Installation
Other
User interface
Generator
equipment
IEC 1909/06
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.
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 62257-9 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).
---------------------- Page: 11 ----------------------
SIST-TS IEC/TS 62257-9-2:2008
– 10 – TS 62257-9-2 © IEC:2006(E)
PEN
PEN 1 PEN 1 PEN 1
IEC 1910/06
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.

1) Case 1: Three-phase power system output; one three-phase feeder with three phase or

single phase distribution.
PEN
PEN 2 PEN PEN 1 PEN 3
IEC 1911/06
Figure 3 – Three phase system output, single phase distribution
or three phase service provided where needed
---------------------- Page: 12 ----------------------
SIST-TS IEC/TS 62257-9-2:2008
TS 62257-9-2 © IEC:2006(E) – 11 –
2) Case 2: Three-phase power system output; single phase distribution is used
throughout the community.
PEN
PEN 3 PEN 2 PEN 1
IEC 1912/06
Figure 4 – Three phase system output, single phase distribution
5 Protection against electric shocks
The microgrid shall be designed as a TN-C system (refer to IEC 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 micropowerplant

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 0,4 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 installation

All switch gear and control equipment shall be installed in cabinets or cases which allow

access only to authorized personnel. The cabinets shall comply with the IEC 60439 series.

7.2 Operational conditions and external influences
7.2.1 Ambient temperature

The conductors shall be chosen and installed so as to suit the highest local ambient

temperature.
---------------------- Page: 13 ----------------------
SIST-TS IEC/TS 62257-9-2:2008
– 12 – TS 62257-9-2 © IEC:2006(E)

The microgrid sections, including conductors and accessories, shall be installed within the

temperature limits specified by the product manufacturers and according to the manufacturers

instructions (see cable characteristics in Annex A).
7.2.2 Sources of heat

To avoid the effects of heat emitted by outside sources, the following methods or equally

efficient methods may be used to protect the cables:
• sufficient distance from sources of heat,
• protection screen,

• choice of line to allow for detrimental effects that may occur, local strengthening or change

of insulating material.

NOTE The heat given off by outside sources may be transmitted by convection, conduction or radiation.

7.2.3 Presence of water

The microgrid conductors and equipment shall be selected and installed to avoid damage by

water. Special precautions may be necessary for microgrid sections frequently exposed to

water or are liable to be immersed.
7.2.4 Risk of penetration of solid bodies

The microgrid conductors and equipment shall be selected and installed to minimize hazards

caused by the penetration of solid bodies. The cables and equipment shall ensure that the IP

protection degree is appropriate to the chosen location.

For locations where large quantities of dust appear, additional precautions shall be taken to

prevent the buildup of substances in quantities that are liable to affect the dissipation of heat

from the conductors.
7.2.5 Corrosive or polluting substance presence

When there is a possibility of corrosive substances occurring, including water, which are liable

to cause degradation or corrosion, all the parts of the line shall be suitably protected or

manufactured from material that resists such substances.

Different materials that may form electrolytic couples shall not be brought into contact with the

conductors unless special steps are taken to avoid the consequences of such contacts.

The materials that may cause mutual individual degradation or hazardous degradation shall

not be allowed to come into contact with other materials.
7.2.6 Mechanical requirements

For fixed installations in which medium, high or very high impact may occur, protection shall

be performed by any of the following arrangements:
• mechanical characteristics of the cables,
• chosen location,
• provision of complementary local or general mechanical protection,
or by any combination thereof.

The requirements provided in this part of IEC 62257-9 allow the project implementer to erect

microgrids matching the needs of consumers in rural areas and also matching normal climatic

conditions. If harsh conditions are expected, specific design studies shall be performed.

---------------------- Page: 14 ----------------------
SIST-TS IEC/TS 62257-9-2:2008
TS 62257-9-2 © IEC:2006(E) – 13 –
7.2.7 Equipment and supporting structures

Equipment and supporting structure, including their foundations, shall withstand the

anticipated mechanical stresses.
7.2.8 Vibration

The conductors and/or equipment supported by or attached to structures affected by medium

or high vibration conditions shall be appropriate to such conditions.
7.2.9 Other mechanical constraints for underground microgrid sections

The interior sizes of conduits and connecting accessories shall permit easy pulling or removal

of conductors or cables.

The curve radius shall be such that conductors or cables are undamaged (see cable

characteristics in Annex A).

The lines through which conductors or cables have to be pulled shall include suitable means

of access for pulling.
7.2.10 Presence of flora, mold or fauna

When any known or foreseen conditions represent a hazard because of the presence of flora,

mold or fauna, the microgrid equipment shall be selected and installed to include mitigation

measures against inherent damage.
Such protection measures include:
• choice of materials with appropriate mechanical properties,
• appropriate choice of location,
• prevention of access to animals.
7.2.11 Solar radiation

Insulated conductors and cables for overhead lines shall be rated to withstand U.V. exposure.

7.3 Characteristics of lines
7.3.1 General

The microgrid is in general designed with overhead lines made of insulated twisted

conductors.
7.3.2 Installation modes
There are two possible modes depending on the type of cable being used:

• cable without carrier neutral: the spans shall be as regular as possible. To prevent

festoons from forming, the maximum length of the spans is 30 m for 16 mm cable, and

25 m for 25 mm cable. An installation block is limited to 4 spans.
• cable with carrier neutral: the maximum span length is limited to 50 m.
7.3.3 Minimum height of conductors

The installation tensions shall be determined according to the graphs supplied by the cable

manufacturer.
---------------------- Page: 15 ----------------------
SIST-TS IEC/TS 62257-9-2:2008
– 14 – TS 62257-9-2 © IEC:2006(E)

For alignment along a road, and depending on the constraints due to nearby dwellings, cables

shall be at a minimum height of 3,5 m or 4,5 m above ground.

For road crossings, and depending on the type of traffic using the road, cables shall be at a

minimum height of 4,5 m or 6 m above ground.

The poles shall be chosen so as to limit the sag to a value compatible with the height and in

accordance with the setup conditions specified in 7.5.2.3.
7.3.4 Proximity to other services

Where insulated cables cross or are near to communication cables, gas, water, or other pipes,

an appropriate clearance shall be maintained between cables and the pipelines. Where this

clearance cannot be maintained, contact between the cables and the pipelines shall be

prevented.
7.4 Cables

For cables with or without a carrier, the phase conductor(s) and the PEN conductor shall have

the same section.

Considering the technology used for light fittings (electronic ballasts), public lighting

conductors shall only be used as private wires to transmit controls. Energy shall be drawn off

the distribution network.
The characteristics of the cables are given in Annex A.

Minimum cross sectional areas of conductors for overhead lines are given in Table 2,

depending on the rating of the protection devices.

The graphs in Annex B indicate the maximum possible length of the circuit dependin

...

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.