IEC TS 62257-7:2017

IEC TS 62257-7 ®
Edition 2.0 2017-09
REDLINE VERSION
TECHNICAL
SPECIFICATION
colour
inside
Recommendations for small renewable energy and hybrid systems for rural
electrification –
Part 7: Generators
All rights reserved. Unless otherwise specified, 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
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

IEC Central Office Tel.: +41 22 919 02 11
3, rue de Varembé Fax: +41 22 919 03 00
CH-1211 Geneva 20 info@iec.ch
Switzerland www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.

IEC Catalogue - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
The stand-alone application for consulting the entire The world's leading online dictionary of electronic and
bibliographical information on IEC International Standards, electrical terms containing 20 000 terms and definitions in
Technical Specifications, Technical Reports and other English and French, with equivalent terms in 16 additional
documents. Available for PC, Mac OS, Android Tablets and languages. Also known as the International Electrotechnical
iPad. Vocabulary (IEV) online.

IEC publications search - www.iec.ch/searchpub IEC Glossary - std.iec.ch/glossary
The advanced search enables to find IEC publications by a 65 000 electrotechnical terminology entries in English and
variety of criteria (reference number, text, technical French extracted from the Terms and Definitions clause of
committee,…). It also gives information on projects, replaced IEC publications issued since 2002. Some entries have been
and withdrawn publications. collected from earlier publications of IEC TC 37, 77, 86 and

CISPR.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Customer Service Centre - webstore.iec.ch/csc
details all new publications released. Available online and If you wish to give us your feedback on this publication or
also once a month by email. need further assistance, please contact the Customer Service
Centre: csc@iec.ch.
IEC TS 62257-7 ®
Edition 2.0 2017-09
REDLINE VERSION
TECHNICAL
SPECIFICATION
colour
inside
Recommendations for small renewable energy and hybrid systems for rural

electrification –
Part 7: Generators
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-4859-1

– 2 – IEC TS 62257-7:2017 RLV  IEC 2017
CONTENTS
FOREWORD . 3
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 8
4 General . 9
5 Generator boundaries . 9
6 Generators requirements . 10
6.1 General requirements . 10
6.2 Specific requirements for the different technologies . 10
6.2.1 Input requirements . 10
6.2.2 Output requirements . 12
6.2.3 Specific requirements for different generator technologies . 12
7 Generator design and sizing . 13
8 Hybrid generation . 13
Bibliography . 14

Figure 1 – General electrical configuration of a collective electrification system . 9

Table 1 – General inputs and outputs to be considered for generator specification . 10
Table 2 – Input requirements relative to the generator technology . 11
Table 3 – Output requirements relative to the generator technology . 12
Table 4 – Specific generators requirements considered in the IEC 62257 series . 13

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

Part 7: Generators
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 itself does not provide any attestation of conformity. Independent certification bodies provide 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 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.
This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition. A vertical bar appears in the margin wherever a change
has been made. Additions are in green text, deletions are in strikethrough red text.

– 4 – IEC TS 62257-7:2017 RLV  IEC 2017
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC 62257-7, which is a technical specification, has been prepared by IEC technical
committee 82: Solar photovoltaic energy systems.

This second edition cancels and replaces the first edition published in 2008. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Removed the word "small" from the description of the PV systems, and removed the power
limit (100 kVA).
b) Increased the relevant voltage levels to 1 000 V (AC) and 1 500 V (DC).
This technical specification is to be used in conjunction with other parts of this series.
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
82/1201/DTS 82/1258/RVDTS
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.
A list of all parts of IEC 62257 series, under the general title: Recommendations for
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 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 publication using a colour printer.

– 6 – IEC TS 62257-7:2017 RLV  IEC 2017
INTRODUCTION
The IEC 62257 series of documents 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 AC
voltage below 500 1 000 V and DC voltage below 750 1 500 V and 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 must 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 development mechanisms 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.
The purpose of this part of IEC 62257 is to provide project implementers with general
information about generators and to highlight the main characteristics relative to the different
technologies that can be used.

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

Part 7: Generators
1 Scope
The purpose of this part of IEC 62257 is to specify the general requirements for generators
(maximum power = 100 kVA) in decentralized rural electrification systems.
The aim is to point out the main items that must be considered when selecting, sizing,
installing, operating and maintaining this equipment.
This part of IEC 62257 specifies the general requirements for the generators in decentralized
rural electrification systems.
This document is a general introduction followed by more specific documents dedicated to the
generation technologies which are the most currently used in rural electrification projects.
2 Normative references
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 TS 62257-2:2004 2015, Recommendations for small renewable energy and hybrid
systems for rural electrification – Part 2: From requirements to a range of electrification
systems
IEC TS 62257-4, Recommendations for small renewable energy and hybrid systems for rural
electrification – Part 4: System selection and design
IEC TS 62257-5, Recommendations for small renewable energy and hybrid systems for rural
electrification – Part 5: Protection against electrical hazards
IEC TS 62257-7-1, Recommendations for small renewable energy and hybrid systems for
rural electrification – Part 7-1: Generators – Photovoltaic arrays generators
IEC TS 62257-7-3, Recommendations for small renewable energy and hybrid systems for
rural electrification – Part 7-3: Generating Generator set – Selection of generating generator
sets for rural electrification systems
IEC TS 62257-9-1 , Recommendations for small renewable energy and hybrid systems for
rural electrification – Part 9-1: Integrated systems – Micropower systems
___________
Third edition to be published. A second edition (dated 2010) already exists.
To be published.
– 8 – IEC TS 62257-7:2017 RLV  IEC 2017
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
generator
apparatus that converts one form of energy into electricity
[SOURCE: IEC TS 61836:2016, 3.3.2527, modified:"non-electric energy" changed to "one
form of energy"]
3.2
dispatchable power system
power system where delivered electricity is available as scheduled
(ex: a fossil-fuelled engine-powered generator is dispatchable. A renewable energy generator
is usually a non-dispatchable power system)
[SOURCE: IEC TS 61836:2016, 3.3.6467.1, modified to describe "dispatchable"]
3.3
non-dispatchable power system
non-dispatchable system is resource dependent; power might not be available at a specified
time
3.4
collective electrification system
small electric generating system and minigrid that supplies electricity to multiple consumption
points from a single or multiple energy sources
[SOURCE: IEC TS 61836:2016, 3.3.1012]
3.5
individual electrification system
small electric generating system that supplies electricity to one consumption point, such as a
household, usually from a single energy source
[SOURCE: IEC TS 61836:2016, 3.3.3234]
3.6
interface
boundary between two systems or the equipment facilitating the interconnection of two
systems
3.7
genset
colloquial term meaning “engine-generator set” consisting of a fossil-fuelled engine coupled to
an electric generator
[SOURCE: IEC TS 61836:2016, 3.3.2628]

3.8
microgrid
grid that operates at less than 100 kVA of capacity and is electrified by a micropower system
3.9
micropower system
generating system that produces less than 100 kVA through the use of a single source or a
multi-source system
3.10
user installation
electrical installation located in the user’s house, powering the user’s appliances and
connected to the interface with the microgrid
4 General
In an electrification system, a generator is a part of the energy production subsystem.
Different architectures of energy production subsystems are provided in IEC TS 62257-2
along with some recommendations for selecting the relevant energy production subsystems
matching both sources and demand requirements. (IEC TS 62257-2:2015, Annex D).
An energy production subsystem may include one or several generators of the same
technology or of different technologies (hybrid production). Recommendations to configure
hybrid power systems are provided in IEC TS 62257-9-1. According to the availability of the
primary resource, the generators can be classified as dispatchable or non-dispatchable.
5 Generator boundaries
Figure 1 illustrates the position of the generator in an electrification system.
Electrification system
Energy production Distribution Demand
subsystem subsystem subsystem
Micropower Microgrid Users installations
system
Loads
User interface
Other
Generators
equipment
Loads
Loads
IEC
Figure 1 – General electrical configuration of
a collective electrification system
NOTE 1 As explained in IEC TS 62257-4, a collective electrification systems is composed of 3 parts as shown in
Figure 1; an individual electrification system does not include a distribution subsystem, but could be powered by a
micropower system.
NOTE 2 Micropower systems are addressed in IEC TS 62257-9-1.

– 10 – IEC TS 62257-7:2017 RLV  IEC 2017
The generator embodies everything needed to produce electric power corresponding to the
necessary characteristics of voltage, frequency, harmonics, power and consumption of the
customers, according to the needed quality of service.
In the IEC 62257-7 series, “generator” means “installed generator”. Are included in a
generator:
– The generator itself, able to produce electricity from a primary source of energy (sun,
wind, fuel, water).
– The associated internal control devices.
– The associated protective devices.
– The associated connecting devices with other equipment of the micro power system
(busbars, etc.).
– The necessary infrastructure and civil engineering.
6 Generators requirements
6.1 General requirements
When defining the generator characteristics, the following “inputs” and “outputs” shall be
taken into consideration, as indicated in Table 1.
Table 1 – General inputs and outputs to be considered
for generator specification
Generator characteristics
Input requirements Output requirements
(constraints)          (results)

Technology
Primary energy resources Size Electrical performances

(sun, wind, water flow/head, (voltage, current, power,
Weight
fuel) frequency)
► ◄
Volume
Environmental conditions Protection Safety
(air pressure/humidity/ (people, equipment)
Housing
temperature)
Civil engineering
Signals Maintenance requirements Environmental impacts
(start/stop, synchronization) (exhaust, heat, noise)
Internal control
Regulations / Standards
Assessment of energy
demand
Assessment of energy
quality requirements
6.2 Specific requirements for the different technologies
6.2.1 Input requirements
Table 2 gives examples of issues that have to be addressed concerning the site
characteristics in order to assess whether the generator is relevant to the requirements of the
general specification.
Table 2 – Input requirements relative to the generator technology
Issues to be addressed
Input requirements
Micro hydro
(constraints)
PV array Wind turbine Genset
turbine
Resource Only during daylight High short-term Linked to site Day and night
availability and variable variability; accessibility and availability;
according to the seasonality and local storage seasonality and
season extreme conditions capabilities extreme conditions
(storm) (overflow)
Resource Possibility of Extrapolation of Easy evaluation of In most cases, no
assessment extrapolation of existing data sourcing and of existing data
existing data requires the use of possibility of available; on site
concerning a dedicated software transportation and measurement of
neighbouring area and a thorough recycling drums flow and
assessment of the observation of
site configuration seasonal variations
Resource level Production of a A minimum wind Specific A minimum water
given array could speed is required to consumption (l/kWh) flow or head is
vary by a factor of 4 start production  varies with load required
depending on site factor and altitude
Production is
solar irradiation and
strongly dependant
temperature
on wind resource
characteristics
speed, theoretically
on a cubic law
Possibility to install Yes, if room (mostly Not always practical Yes; but see Not always practical
the generator as unshaded) area is environmental
The wind resource The location is
close as possible to available impact
is dependant on the dependant on the
the energy
location Consider also noise water resource
utilisation
and vibration
In a few cases small
problems
wind turbines can
be installed directly
on roofs
Consider also noise
problems
Room Space The ratio surface / Space for setting up The ratio surface / The infrastructure is
availability for power installed is include the stays power is the very dependant of
installing the high for PV arrays installation and smallest the technology and
generator compared to other possibility to lay of the necessary
Additional space for
generator down the turbine for head
fuel storage is
maintenance
Small PV array can needed
be installed directly
on roofs
Site characteristics Shadowing Accessibility for fuel Accessibility to the
Roughness,
to be considered obstacles, etc. transportation water resource
Civil engineering Low to medium, Medium to high Low Could be high
constraint level depending on the depending on the depending on the
configuration of the configuration of the slope and width of
ground, the ground, the the river
consistency of the consistency of the
soil, the quality of soil or the quality of
the roofs the roof
Depends on the size
and technology of
the wind turbine
Needed operation Low Low, but high for Low, but high for Low, but medium for
skill maintenance heavy maintenance maintenance
operation operation operation
Operation Batteries storage or Batteries storage or To operate between To adjust the
constraints hybridation needed hybridation needed 50 % and 80 % of settings of the
to adapt the to adapt the the rated power to turbine in relation to
production to the production to the ensure the nominal the available flow
demand demand lifetime of the and the electricity
engine demand
Fuel storage needed
NOTE Different levels of accuracy to collect resources and demand data are given in IEC TS 62257-4.

– 12 – IEC TS 62257-7:2017 RLV  IEC 2017
6.2.2 Output requirements
Table 3 highlights the issues that have to be solved for each type of generator regarding the
different output requirements listed in the general specification (GS).
Table 3 – Output requirements relative to the generator technology
Issues to be solved
Output
requirements
Micro hydro
PV array Wind turbine Genset
(results)
turbine
Electrical Voltage forming Voltage and Internal voltage and Voltage and
performances needed (battery, frequency regulation frequency regulation frequency regulation
(loads and quality of hybridation) by an external mean by flow or demand
service) regulation
Storage to adapt Storage needed to
Storage needed in
production to adapt production to
some cases
demand demand
Energy conversion Energy conversion
Energy conversion
needed if a.c. needed when using
needed when using
demand wind turbines for
battery charging
battery charging
Safety issues Electrical Electrical Electrical Electrical
Mechanical Moving parts Moving parts Moving parts
(wind effect on PV Mechanical Heat Water pressure
array) (erection / laying
Fire hazard
down the machine)
Environmental Visual Visual Noise
Visual (especially
impact Ground occupation Noise and vibration Soil pollution due to
due to the weir and
Battery recycling Battery recycling oil and fuel
the penstock, if any)
(if battery storage) (if battery storage) Air pollution due to
exhaust Fauna and flora
Heat impact
Electrical performances shall be defined in order to supply the quality level as required in the
GS of the project. Supply quality indicators are given in IEC TS 62257-2:2015, Annex C,
Table C.1.
Safety recommendations include general electrical safety requirements from IEC TS 62257-5
(common to all generators) but attention shall be paid to the specific aspects related to each
technology (mechanical hazards, moving parts, fire hazards, high temperature, etc.).
The design of the generator shall take into account the characteristics of the appliances to be
supplied (e.g. a poor power factor implies the oversizing of the generator).
6.2.3 Specific requirements for different generator technologies
Specific requirements for different technologies are addressed in the following technical
specifications as indicated in Table 4.
...