IEC TS 62257-7-3:2018

Recommendations for renewable energy and hybrid systems for rural electrification - Part 7-3: Generator set - Selection of generator sets for rural electrification systems

IEC TS 62257-7-3:2018(E) specifies the general requirements for the selection, sizing, erection and operation of generator sets in decentralized rural electrification systems. It applies to all low voltage combustion engine electricity generator sets energized by renewable energy such as biomass gasifier or biogas, or fossil fuel such as gasoline or diesel fuel, and designed for supplying electrical power to isolated sites used in systems as described in IEC TS 62257-2. The aim of this document is to provide users with the appropriate guide to select generator sets for using in micropower plant with different configurations and levels of reliability and safety of the equipment during its estimated service lifespan. This document describes the minimum requirement of generator set functionality and safety requirements and does not claim to be an exhaustive instruction manual or design specification.
The main technical changes of this new edition with regard to the previous edition are as follows:
- Increased the voltage and power levels to which this TS applies.
- Added descriptions of four different types of micropower systems and their relevant requirements.

General Information

• Status: Published
• Publication Date: 12-Mar-2018
• ICS: 27.160 - Solar energy engineering
• Technical Committee: TC 82 - Solar photovoltaic energy systems
• Drafting Committee: JWG 1 - TC 82/JWG 1
• Current Stage: PPUB - Publication issued
• Start Date: 13-Mar-2018
• Completion Date: 06-Apr-2018

Relations

• Revises: IEC TS 62257-7-3:2008 - Recommendations for small renewable energy and hybrid systems for rural electrification - Part 7-3: Generator set - Selection of generator sets for rural electrification systems
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC TS 62257-7-3 ®
Edition 2.0 2018-03
TECHNICAL
SPECIFICATION
Recommendations for renewable energy and hybrid systems for rural
electrification –
Part 7-3: Generator set – Selection of generator sets for rural electrification
systems
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IEC TS 62257-7-3 ®
Edition 2.0 2018-03
TECHNICAL
SPECIFICATION
Recommendations for renewable energy and hybrid systems for rural

electrification –
Part 7-3: Generator set – Selection of generator sets for rural electrification

systems
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-5455-4

– 2 – IEC TS 62257-7-3:2018 © IEC 2018
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 10
3 Terms and definitions . 11
4 Introduction to generator sets . 14
4.1 Generator set system . 14
4.2 Generator set application in rural electrification systems . 14
4.2.1 General. 14
4.2.2 Single generator set (micropower plant Type A) . 14
4.2.3 Multiple generator sets (micropower plant Type B) . 14
4.2.4 Single generator set with a power conditioning sub-system (micropower
plant Type C). 15
4.2.5 Multiple generator sets with multiple power conditioning sub-systems
(micropower plant Type D) . 15
4.3 Resource assessment . 16
5 Selection and erection . 16
5.1 General . 16
5.2 Selection requirements . 17
5.2.1 Power quality. 17
5.2.2 Generator set sizing . 17
5.2.3 Generator set type . 18
5.2.4 Derating factors . 19
5.2.5 Starting system . 19
5.2.6 Control systems . 20
5.2.7 Noise issues . 20
5.2.8 Environmental issues . 20
5.3 Erection . 21
5.3.1 Shipping . 21
5.3.2 Design of the erection site . 21
5.3.3 Installation requirements. 23
6 Safety. 25
6.1 General . 25
6.2 Electrical issues . 25
6.2.1 General requirements . 25
6.2.2 Connection system to the application . 25
6.2.3 Power cables . 26
6.2.4 Neutral system . 26
6.2.5 Earthing . 26
6.2.6 Overcurrent protection . 27
6.2.7 Residual Current Protection Device (RCD) . 27
6.2.8 Isolating devices . 27
6.3 Mechanical issues . 27
6.3.1 Vibration . 27
6.3.2 Protection from mechanical damage . 27
6.3.3 Protection from moving parts . 28
6.4 Thermal issues . 28

6.5 Fire risk . 28
7 Acceptance . 28
7.1 General . 28
7.2 Conformity of the generator set to the identification file . 28
7.3 Conformity of the generator set system to the generator set specification
(GS) . 28
7.4 Acceptance process . 28
7.4.1 Preparation of the generator set for commissioning . 28
7.4.2 Commissioning inspection of the generator set system . 29
7.4.3 Commissioning tests of the generator set system . 29
7.4.4 Test file . 30
8 Operation and maintenance . 30
8.1 Access to the generator set . 30
8.2 Operation process . 30
8.3 Monitoring . 31
8.4 Maintenance schedule. 31
9 Replacement . 31
10 Marking . 32
10.1 General . 32
10.2 Generator set . 32
10.3 Engine . 32
10.4 Alternator . 33
10.5 Shutdown apparatus . 33
11 Documentation . 33
11.1 General . 33
11.2 Installation . 33
11.3 Operation. 34
11.4 Inspection and maintenance . 34
Annex A (informative) Generator set classification criteria . 35
A.1 General . 35
A.2 Functioning mode . 35
A.3 Services provided . 35
A.4 Application classes . 35
A.5 Lifespan . 36
A.6 Generator set components design . 36
A.6.1 Engine . 36
A.6.2 Alternator . 37
A.6.3 Starting systems . 37
A.7 Configuration types . 37
A.8 Installation modes. 38
Annex B (informative) Identification file . 39
B.1 General . 39
B.2 Electrical construction characteristics . 39
B.3 Mechanical construction characteristics . 39
Annex C (informative) Maintenance schedule . 40
Annex D (informative) Example of commissioning records sheet. 41

Figure 1 – General functional configuration of micropower plant in micropower system . 9

– 4 – IEC TS 62257-7-3:2018 © IEC 2018
Figure 2 – Micropower plant Type A: single generator set . 14
Figure 3 – Micropower plant Type B: multiple generator sets in micropower plant . 15
Figure 4 – Micropower plant Type C: single generator set with a power conditioning
sub-system in micropower plant . 15
Figure 5 – Micropower plant Type D: Multiple generator sets with multiple power
conditioning sub-systems micropower plant . 16

Table 1 – Examples of derating factors for generator sets. 19
Table 2 – Generator set permitted noise levels . 20
Table 3 – Cross-section of power cables . 26
Table A.1 – Classification of generator set services . 35
Table A.2 – Common lifespan values . 36
Table C.1 – Example of maintenance schedule . 40

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

Part 7-3: Generator set – Selection of generator sets
for rural electrification systems

FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC 62257-7-3, which is a technical specification, has been prepared by IEC technical
committee 82: Solar photovoltaic energy systems.

– 6 – IEC TS 62257-7-3:2018 © IEC 2018
This second edition cancels and replaces the first edition, issued in 2008. It constitutes a
technical revision.
The main technical changes with regard to the previous edition are as follows:
• Increased the voltage and power levels to which this TS applies.
• Added descriptions of four different types of micropower systems and their relevant
requirements.
This technical specification is to be used in conjunction with other parts of this series or future
parts as and when they are published.
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
82/1329/DTS 82/1383A/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 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.
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.

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 1 000 V, and DC 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 off-grid rural electrification concentrating on, but not
specific to, developing countries. They are not 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
possible. One of the main objectives is to provide the minimum sufficient requirements,
relevant to the field of application, that is, renewable energy and hybrid off-grid systems.

– 8 – IEC TS 62257-7-3:2018 © IEC 2018
RECOMMENDATIONS FOR RENEWABLE ENERGY AND
HYBRID SYSTEMS FOR RURAL ELECTRIFICATION –

Part 7-3: Generator set – Selection of generator sets
for rural electrification systems

1 Scope
This part of IEC 62257 specifies the general requirements for the selection, sizing, erection
and operation of generator sets in decentralized rural electrification systems.
It applies to all low voltage combustion engine electricity generator sets energized by
renewable energy such as biomass gasifier or biogas, or fossil fuel such as gasoline or diesel
fuel, and designed for supplying electrical power to isolated sites used in systems as
described in IEC TS 62257-2.
This document is not an exhaustive resource for the design, installation, operation or
maintenance of generator sets, but is more focused on recommendations to provide strategies
on selection and criteria which may affect the use of such generation systems in a rural
electrification project.
Four cases of micropower plant will be considered as illustrated by Figure 1 to power a
collective electrification system (microgrid) or an individual electrification system.
– the micropower plant is composed of one generator set;
– the micropower plant is composed of multiple generator sets, which may have a single
energy source or multiple energy sources;
– the micropower plant which is a hybrid energy system between one generator set and a
Power Conditioning Sub-system (PCS) which is powered by other energy source including
renewable energy source or energy storage;
– the micropower plant which is a hybrid energy system between multiple generator sets and
multiple Power Conditioning Sub-systems (PCSs) which are powered by other energy
sources including renewable energy sources or energy storage systems.

Figure 1 – General functional configuration of micropower plant
in micropower system
The aim of this document is to provide users with the appropriate guide to select generator
sets for using in micropower plant with different configurations and levels of reliability and
safety of the equipment during its estimated service lifespan.
It describes the minimum requirement of generator set functionality and safety requirements
and does not claim to be an exhaustive instruction manual or design specification.

– 10 – IEC TS 62257-7-3:2018 © IEC 2018
Compliance with this document does not exempt any person, organization or corporation from
the responsibility to comply with all other relevant requirements including what is indicated in
maker user manuals and local electrical regulations.
This document gives recommendations for the following types of generator sets:
a) single phase;
b) three phase;
c) LV range up to 500 V – 50/60 Hz (see IEC TS 62257-9-2).
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 60034-1, Rotating electrical machines – Part 1: Rating and performance
IEC 60034-9, Rotating electrical machines – Part 9: Noise limits
IEC 60034-22, Rotating electrical machines – Part 22: AC generators for reciprocating internal
combustion (RIC) engine driven generating sets
IEC 60364 (all parts), Low-voltage electrical installations
IEC 60529, Degrees of protection provided by enclosures (IP code)
IEC 61009-1, Residual current operated circuit-breakers with integral overcurrent protection
for household and similar uses (RCBOs) – Part 1: General rules
IEC TS 62257-2:2015, Recommendations for renewable energy and hybrid systems for rural
electrification – Part 2: From requirements to a range of electrification systems
IEC TS 62257-5, Recommendations for renewable energy and hybrid systems for rural
electrification – Part 5: Protection against electrical hazards
IEC TS 62257-6, Recommendations for renewable energy and hybrid systems for rural
electrification – Part 6: Acceptance, operation, maintenance and replacement
IEC TS 62257-9-2, Recommendations for renewable energy and hybrid systems for rural
electrification – Part 9-2: Microgrid
IEC TS 62257-9-4, Recommendations for renewable energy and hybrid systems for rural
electrification – Part 9-4: Integrated systems – User installation
ISO 8528-1, Reciprocating internal combustion engine driven alternating current generating
sets – Part 1: Application, ratings and performance
ISO 8528-5, Reciprocating internal combustion engine driven alternating current generating
sets – Part 5: Generating sets
ISO 8528-7, Reciprocating internal combustion engine driven alternating current generating
sets – Part 7: Technical declarations for specification and design

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
environmental conditions
environment characteristics (altitude, temperature, humidity, etc.) which may affect the
performance
3.2
generator set
equipment producing electricity from a fossil fuel; it consists basically of an internal
combustion engine producing mechanical energy and a generator which converts the
mechanical energy into electrical energy and mechanical transmission, support and assembly
components
3.3
identification file
IF
document provided by the manufacturer which guarantees the conformity of the equipment
supplied with that which has undergone the type tests
3.4
lifespan
effective period of functioning taking into account the probability of a catastrophic failure
3.5
non-routine maintenance
maintenance necessary in addition to that pre-planned
3.6
rated frequency
frequency at which the generator set is designed to operate
3.7
routine maintenance
preventive maintenance carried out to an established plan
3.8
rated electrical power
nominal power
rated capacity
maximum continuous power supplied by a generator set in compliance with its specifications,
and under standard operating conditions
Note 1 to entry: This is expressed in VA (volt-ampere), or more usually in kVA.
3.9
rated rotation speed
alternator rotation speed necessary to produce the voltage at the rated frequency

– 12 – IEC TS 62257-7-3:2018 © IEC 2018
3.10
rated voltage
voltage between phases on the alternator terminals at the rated frequency and rated power
3.11
extra low voltage
ELV
voltage not exceeding a limit which is generally accepted to be 50 V a.c. and 120 V d.c. ripple
free
3.12
safety extra-low voltage
SELV
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
3.13
protected extra-low voltage
PELV
extra-low voltage system which is not electrically separated from earth, but which otherwise
satisfies all the requirements for SELV
3.14
live conductive part
conductor or conductive part intended to be energized in normal operation, including a neutral
conductor, but by convention not a PE or a PEN conductor
3.15
power factor
ratio of real power to apparent power in an a.c. circuit
3.16
real power
for a.c. circuits, the product of voltage, current and power factor, also equal to the rate of flow
of electrical energy
Note 1 to entry: Real power is measured in watts (W).
3.17
apparent power
for a.c. circuits, the product of voltage by current
Note 1 to entry: Measured in volt-amperes (VA).
3.18
nominal power of the generator set
maximum apparent power that can be provided by the generator set according to the
manufacturer’s specification
3.19
minor fuel storage
fuel storage located in the generator set room
3.20
main fuel storage
fuel storage located outside the generator set room and able to provide fuel filling the minor
fuel storage
3.21
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 upper limits of extra-low voltage, but not exceeding
1 000 V a.c. or 1 500 V d.c.
c) High voltage: exceeding upper limits of low voltage
3.22
protective conductor
(identification: PE)
conductor provided for purposes of safety, for example protection against electric shock
[SOURCE: IEC 60050-195:1998, 195-02-09]
3.23
PEN conductor
conductor combining the functions of both a protective earthing conductor and a neutral
conductor
[SOURCE: IEC 60050-195:1998, 195-02-12]
3.24
generator power plant
multiple generator sets operate together to provide higher power than single generator set
operation or provide higher reliability of electrical power generation
3.25
individual electrification system
IES
micropower plant system that supplies electricity to one consumption point usually with a
single energy resource point
3.26
collective electrification system
CES
micropower plant and micro-grid that supplies electricity to multiple consumption points using
a single or multiple energy resource points
3.27
power conditioning sub-system
component(s) that convert(s) electricity from one form into another form that is suitable for the
intended application. Such a sub-system could include the charge regulator that converts d.c.
to d.c., the inverter that converts d.c. to a.c., or the charger or rectifier that converts a.c. to
d.c.
3.28
micropower system
electrical power system that consists of micropower plant, distribution network and load which
is not part of national utility grid network
3.29
micropower plant
electrical power generator plant that supplies stable voltage and frequency to micropower
system
– 14 – IEC TS 62257-7-3:2018 © IEC 2018
4 Introduction to generator sets
4.1 Generator set system
In the present document a generator set system includes the installed generator set itself, the
related civil works or prefabricated enclosure if any and all relative ancillaries, such as fuel
tank, pipes, earthing systems, etc., necessary for the operation of the generator set.
4.2 Generator set application in rural electrification systems
4.2.1 General
The usage of generator sets in rural electrification systems application, are described in IEC
TS 62257-2 for T3, T4, T5 and T6 categories of systems.
In these system categories the generator sets are used to supply a.c power with stable
voltage and frequency to distribution system, recharge batteries and/or provide a backup
power supply to all or part of the a.c. distribution system, or to supply a.c. dedicated
equipment.
The type of use of the generator set shall be identified by the project developer and notified to
the supplier.
For rural electrification the generator set can be operated as a single unit or can be operated
in multiple units. Multiple generator sets known collectively as the generator power plant are
operated in order to increase total power or increase reliability of micropower plant. The
generator set or generator power plant can also operate with other power conditioning sub-
system(s) to form hybrid power/energy system in micropower plant.
Power generation in micropower plant with generator set(s) can be in one of the following
configurations.
4.2.2 Single generator set (micropower plant Type A)
This type of micropower plant (refer to Figure 2) has one generator to supply power to user
whether it is IES or CES.
• The selection of generator set is based on peak load of IES or CES. The starting/stopping
of the generator is set by manual or an automatic control device.

Figure 2 – Micropower plant Type A: single generator set
4.2.3 Multiple generator sets (micropower plant Type B)
This type of micropower plant (refer to Figure 3) has more than one generator set in
micropower plant and the generator sets can operate as follows:
• One generator set is put to operate at any time. The selection of generator set is based on
peak load of IES or CES. The starting/stopping of the generator is set by manual or an
automatic control device.
• Parallel a.c. operation of more than one generator set to supply larger load of IES or CES.
The micropower plant shall have measuring instruments to indicate that electrical a.c.
output of the running generators are synchronized before they enter into parallel operation
together. The combination of a.c. output can be done by manual or automatic control
devices.
Figure 3 – Micropower plant Type B: multiple generator sets
in micropower plant
4.2.4 Single generator set with a power conditioning sub-system (micropower plant
Type C)
This type of micropower plant (refer to Figure 4) has a generator set operating with a power
conditioning sub-system which can be a.c power source such as PV converter, converter with
energy storage system (ESS), wind turbine, hydro turbine or other energy sources with
converter to condition a.c. at output. The micropower plant can operate as follows:
• The generator set or power conditioning sub-system with ESS is alternately operated by
manual or an automatic control device. When the generator set is operating it may charge
the ESS through the power conditioning sub-system.
• The generator set and power conditioning sub-system are operated in parallel on a.c.
output by manual or an automatic control device. To operate in parallel the generator set
and the power conditioning sub-system need to have capability to synchronize their a.c.
output together. The power conditioning sub-system may have power sources such as PV,
wind turbine, ESS, or energy sources. To operate in this mode the micropower plant shall
be capable of preventing electrical current back feed to the alternator of the generator set.

Figure 4 – Micropower plant Type C: single generator set with
a power conditioning sub-system in micropower plant
4.2.5 Multiple generator sets with multiple power conditioning sub-systems
(micropower plant Type D)
This type of micropower plant (refer to Figure 5) has more than one generator set operating
with more than one power conditioning sub-system. It also covers the cases where single
generator set works with multiple power conditioning sub-systems, or where multiple
generator sets are working with a single power conditioning sub-system. The power
conditioning sub-system may be AC power sources such as PV converters, converters with

– 16 – IEC TS 62257-7-3:2018 © IEC 2018
energy storage systems (ESS), wind turbines, hydro turbines or other energy sources with
converters to condition a.c. at output. The micropower plant can operate as follows:
• One or multiple generator sets and one or multiple power conditioning sub-systems are
either operated by manual or an automatic control devices.
In this operation a bus tie switch is not required.
• One or multiple generator sets and one or multiple power conditioning sub-systems are
operated in parallel on a.c. output by manual or an automatic control device. In this
operation the bus tie switch is required when a group of multiple generator sets
synchronized together before it is tied with the bus which has a group of multiple power
conditioning sub-systems that are synchronized together.

Figure 5 – Micropower plant Type D: Multiple generator sets with
multiple power conditioning sub-systems micropower plant
4.3 Resource assessment
Before choosing a generator set as the generator in an electrification system, it is important to
check the availability of the fuel supply on the installation site and whether it is possible to be
supplied throughout the year. For example in some countries it could be impossible to deliver
fuel to the site during the rainy season.
The project implementer also shall take into account that the cost of fuel may vary with the
price of the oil market and also with changes in local subsidies.
5 Selection and erection
5.1 General
A lot of technologies are available on the market for engines, from the most simple to the
most sophisticated.
For small size (~below 5 kVA) the most commonly used technology is gasoline engines.
For larger size, the most commonly used technology is diesel engines while the biofuel engine
and biomass gasification engine in the range of lower than 1 000 kVA are also used.

Other fuels can be used, such as fuel oil, or ethanol.
The engines are designed either for 3 000 rpm (generally for small machines) or 1 500 rpm
(generally for larger machines) at 50 Hz and 3 600 rpm or 1 800 rpm for 60 Hz.
Other technologies like small fuel turbines may also be available.
The project implementer shall select the appropriate technology corresponding to the required
level of quality of the service, the skill of the maintenance staff, the level of equipment
available at the maintenance centre, the spare parts than can be easily sourced, and all
specific constraints of the project. Annex A provides some information about the classification
of different types of generator sets as they are available on the market.
5.2 Selection requirements
5.2.1 Power quality
Type and configuration of generator set shall be selected in relation with the requirements of
the power supply to the end user as given in the General Specification (GS) of the project.
These requirements shall refer to the different figures expressed in IEC TS 62257-2:2015,
Annex C.
The control system of the generator set shall be able to provide information necessary to
assess that the level of quality of service provided is in accordance with the requirements of
the generator set (at least voltage, current and frequency).
5.2.2 Generator set sizing
Generator set sizing has two primary requirements:
a) that the alternator is capable of supplying the continuous and surge load apparent power
(VA);
b) that the engine is capable of providing the power requirements of the alternator and the
mechanical losses of the whole system (alternator + coupling system).
It is for the project developer to precisely define the generator set minimum operating
conditions:
• the environmental conditions;
• the maximum nominal outputs, the corresponding durations and load factor;
• the electrical load characteristics (power factor, permitted voltage range, current harmonic
content, high starting currents, etc.).
The selection and sizing of generator set should be done with consideration of the supplied
electrical load and the structure of the microgrid (single phase / three phase, see IEC
TS 62257-9-2).
Important rating of the generator set shall be considered:
• rated voltage;
• rated frequency;
• rated power and corresponding operating speed in conformity with ISO 8528-1;
• the application class, as defined in ISO 8528-1(see Annex A);
• rated current;
• rated power factor.
– 18 – IEC TS 62257-7-3:2018 © IEC 2018
NOTE When considering the power rating it is important to consider the application class and the service to be
provided. Refer to Annex A.
Care needs to be taken with respect to application classes defined in ISO 8528-1 as these
classes of operation take into account only predominantly linear loads. In many microgrid and
hybrid system applications, considerable harmonic current flows (particularly in battery
charger loads) may cause excessive voltage distortion if not taken into account early in the
design and specification.
The sizing of the generator set shall be made such as the engine works between 50 % and
80 % of its maximum nominal power in normal operating conditions. Functioning at maximum
nominal power shall not exceed manufacturer’s recommendations as well as overload periods
of functioning.
The project implementer shall draw the daily load curve and its variation along the year in
order to determine the maximum and minimum power. This makes it possible to determine the
nominal power of the engine to ensure that it operates between 50 % and 80 % of its
maximum nominal power.
The project implementer shall also assess if there is any peak power or very low power period
during the year whose duration may affect the generator set lifespan. A solution could be to
install multiple generator sets (micropower plant Type B or Type D) and operate them in two
options:
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