Microgrids - Part 2: Guidelines for operation

IEC TS 62898-2:2018 provides guidelines for operation of microgrids. Microgrids considered in this document are alternating current (AC) electrical systems with loads and distributed energy resources (DER) at low or medium voltage level. This document does not cover direct current (DC) microgrids.
IEC TS 62898-2 applies to operation and control of microgrids, including:
• operation modes and mode transfer;
• energy management system (EMS) and control of microgrids;
• communication and monitoring procedures;
• electrical energy storage;
• protection principle covering: principle for non-isolated microgrid, isolated microgrid, anti-islanding, synchronization and reclosing, power quality;
• commissioning, maintenance and test.

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IEC TS 62898-2

Edition 1.0 2018-09


Microgrids –
Part 2: Guidelines for operation

IEC TS 62898-2:2018-09(en)

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IEC TS 62898-2


Edition 1.0 2018-09





Microgrids –

Part 2: Guidelines for operation




ICS 29.240.01 ISBN 978-2-8322-6042-5

  Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission

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– 2 – IEC TS 62898-2:2018 © IEC 2018
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 8
4 Operation modes . 13
4.1 General . 13
4.2 Non-isolated microgrid . 13
4.2.1 General . 13
4.2.2 Grid-connected mode . 13
4.2.3 Island mode . 14
4.2.4 Mode transfer of non-isolated microgrids . 14
4.3 Isolated microgrid . 15
4.3.1 General . 15
4.3.2 Structure of the isolated microgrids . 15
4.3.3 Voltage response characteristics . 16
4.3.4 Frequency response characteristics . 16
5 Control of microgrids . 16
5.1 General . 16
5.2 Control of the non-isolated microgrid . 18
5.2.1 Control of the grid-connected mode . 18
5.2.2 Control of the island mode . 19
5.3 Control of the isolated microgrid . 20
6 Communication and monitoring . 21
6.1 General . 21
6.2 Communications of microgrids . 22
6.2.1 General . 22
6.2.2 Communications between non-isolated microgrids and the utility grid . 22
6.2.3 Communications inside the microgrids . 22
6.3 Monitoring the DER . 22
6.4 Monitoring the switching devices for non-isolated microgrids . 22
6.5 Monitoring the switching devices for isolated microgrids . 23
7 Electrical energy storage . 23
7.1 General . 23
7.2 EES in non-isolated microgrids . 23
7.2.1 Requirements for EES in grid-connected mode . 23
7.2.2 Requirements for EES in island mode . 23
7.2.3 Requirements for EES in mode transfer . 24
7.3 EES management . 24
8 Protection principle for microgrids. 24
8.1 General . 24
8.2 Principle for protection in a non-isolated microgrid . 25
8.3 Reclosing with synchronization in a non-isolated microgrid . 25
8.4 Principle for protection in an isolated microgrid . 25
9 Power quality and EMC of microgrids . 25
9.1 Power quality in non-isolated microgrids . 25

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IEC TS 62898-2:2018 © IEC 2018 – 3 –
9.2 Power quality in isolated microgrids . 26
9.3 EMC in microgrids . 26
10 Maintenance and test of microgrids . 26
10.1 General . 26
10.2 Maintenance . 26
10.3 Test . 27

Annex A (informative) Business use case A: Improving reliability and securing the
energy supply by islanding . 28
Annex B (informative) Business use case B: Electrifying remote areas and using
renewable energy sources . 31
Annex C (informative) Business use case C: Reducing energy costs for microgrid
users . 33
Annex D (informative) Business use case D: Optimizing local resources to provide
services to the grid/disaster preparedness . 35
Annex E (informative) Example of power factor requirements cited in some standards . 36
Bibliography . 37

Figure 1 – Example for a non-isolated microgrid . 17
Figure 2 – Example for an isolated microgrid . 18
Figure 3 – The P-f control in isolated microgrid . 20
Figure B.1 – One of the actual examples of mainly-isolated microgrids used for
electrification in far rural area . 32
Figure C.1 – Principle scheme of customer energy management and information
exchange with upstream grid . 34

Table 1 – Example for the isolated microgrid frequency response of 50 Hz . 21
Table E.1 – Power factor requirements . 36

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Part 2: Guidelines for operation

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Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC TS 62898-2, which is a technical specification, has been prepared by subcommittee 8B:
Decentralized Electrical Energy Systems, of IEC technical committee 8: Systems aspects of
electrical energy supply.

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IEC TS 62898-2:2018 © IEC 2018 – 5 –
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting

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 62898 series, published under the general title Microgrids, 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
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understanding of its contents. Users should therefore print this document using a
colour printer.

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– 6 – IEC TS 62898-2:2018 © IEC 2018
Microgrids can serve different purposes depending on the primary objectives of their
applications. They are usually seen as means to facilitate the management of grid
contingency and the local optimization of energy supply by controlling distributed energy
resources (DER). Microgrids also present a way to provide electricity supply in remote areas
and to use clean and renewable energy as a systemic approach for rural electrification.
IEC TS 62898 series is intended to provide with comprehensive guidelines and requirements
for microgrid projects.
IEC TS 62898-1 mainly covers the following issues:
1) determination of microgrid purposes and application;
2) preliminary study necessary for microgrid planning, including resource analysis, load
forecast, DER planning and power system planning;
3) principles of microgrid technical requirements that should be specified during planning
4) microgrid evaluation to select an optimal microgrid planning scheme.
IEC TS 62898-2 mainly covers the following issues:
a) response characteristic requirements of microgrids under different operation modes;
b) the basic control strategies and methods under different operation modes;
c) the requirements of electrical energy storage (EES), communication and monitoring under
different operation modes;
d) the principle of relay protection under different operation modes;
e) basic requirements of synchronization and reclosing during mode transfer;
f) principle for power quality, EMC, maintenance and test of microgrid.
Microgrids can be stand-alone or be the sub-system of the smart grid. The technical
requirements in this document are intended to be consistent and in line with:
• system requirements from IEC System Committee Smart Energy (e.g. Use Cases
“microgrid” to come);
• IEC 62786 requirements for connection of generators intended to be operated in parallel
with the grid;
• basic rules from IEC TC 64 and TC 99 for safety and quality of power distribution within
installations (essentially through coordination of protective devices in the different
operation modes);
• IEC TS 62257 series (IEC TC 82) with respect to rural electrification;
• IEC TS 62749 with respect to power quality.

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IEC TS 62898-2:2018 © IEC 2018 – 7 –

Part 2: Guidelines for operation

1 Scope
The purpose of this document is to provide guidelines for operation of microgrids. Microgrids
considered in this document are alternating current (AC) electrical systems with loads and
distributed energy resources (DER) at low or medium voltage level. This document does not
cover direct current (DC) microgrids.
Microgrids are classified into isolated microgrids and non-isolated microgrids.
Isolated microgrids have no electrical connection to a larger electric power system and
operate in island mode only.
Non-isolated microgrids may act as controllable units to the electric power system and can
operate in the following two modes:
• grid-connected mode;
• island mode.
The 62898 series is intended to provide guidelines and the basic technical requirements to
ensure the security, reliability and stability of microgrids.
IEC TS 62898-2 applies to operation and control of microgrids, including:
• operation modes and mode transfer;
• energy management system (EMS) and control of microgrids;
• communication and monitoring procedures;
• electrical energy storage;
• protection principle covering: principle for non-isolated microgrid, isolated microgrid, anti-
islanding, synchronization and reclosing, power quality;
• commissioning, maintenance and test.
NOTE 1 Safety for personnel is outside the scope of this document, and such information is referred to in
IEC TC 64 and TC 99 publications.
NOTE 2 Local laws and regulations can overrule the requirements of this document.
NOTE 3 The principles for main types of protections in microgrid, fault analysis for converter type and rotating
machines type, protection type selection, general technical requirements, setting value principles and so forth are
intended to be developed in IEC TS 62898-3-1 .
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.
 Under preparation. Stage at the time of publication: IEC/CD TS 62898-3-1:2018.

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– 8 – IEC TS 62898-2:2018 © IEC 2018
IEC TR 61000-1-7:2016, Electromagnetic compatibility (EMC) – Part 1-7: General – Power
factor in single-phase systems under non-sinusoidal conditions
IEC 61000-4-7:2002, Electromagnetic compatibility (EMC) – Part 4-7: Testing and
measurement techniques – General guide on harmonics and interharmonics measurements
and instrumentation, for power supply systems and equipment connected thereto
IEC 61000-4-7:2002/AMD1:2008
IEC 61000-4-30:2008 , Electromagnetic compatibility (EMC) – Part 4-30: Testing and
measurement techniques – Power quality measurement techniques
IEC 61968-1, Application integration at electric utilities – System interfaces for distribution
management – Part 1: Interface architecture and general recommendations
IEC 61850-3, Communication networks and systems for power utility automation – Part 3:
General requirements
IEC 61850-4, Communication networks and systems for power utility automation – Part 4:
System and project management
IEC 61850-5, Communication networks and systems for power utility automation – Part 5:
Communication requirements for functions and device models
IEC TS 62749, Assessment of power quality – Characteristics of electricity supplied by public
IEC TS 62786, Distributed energy resources connection with the grid
IEC TS 62898-1, Microgrids – Part 1: Guidelines for microgrid projects planning and
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
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
anti-islanding protection
protection function(s) or combination of protection functions preventing distributed energy
resources from supplying electricity to an unintentional island
Note 1 to entry: The protection function includes the detection of system characteristics which can lead to an
unintentional island.
[SOURCE: IEC 60050-617:2017, 617-04-19, modified – "an unintentional island to be
supplied with electrical energy by distributed energy resources" has been replaced by
"distributed energy resources from supplying electricity to an unintentional island" and Note 1
to entry has been changed]
nd rd
 This 2 edition was replaced in 2015 by a 3 Edition.

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IEC TS 62898-2:2018 © IEC 2018 – 9 –
black start
start-up of an electric power system from a blackout through internal energy resources
[SOURCE: IEC 60050-617:2017, 617-04-24]
device for changing one or more characteristics associated with electrical energy
Note 1 to entry: Characteristics associated with energy are for example voltage, number of phases and frequency
including zero frequency.
[SOURCE: IEC 60050-151:2001, 151-13-36]
distributed energy resources
generators, including loads having a generating mode (such as electrical energy storage
systems), connected to the low or medium voltage network, with their auxiliaries, protection
and connection equipment, if any
[SOURCE: IEC 60050-617:2017, 617-04-20, modified – "including loads having a generating
mode" and "with their auxiliaries, protection and connection equipment, if any" have been
distributed generation
generation of electric energy by multiple sources which are connected to the low or medium
voltage network
[SOURCE: IEC 60050-617:2009, 617-04-09, modified – "power distribution system" has been
replaced by "low or medium voltage network"]
distribution network
electrical facility and its components including poles, transformers, disconnects, relays,
isolators, cables and wires that are owned by an electrical utility for the purpose of distributing
electrical energy from substations to customers
Note 1 to entry: Usually, the distribution network operates up to a nominal voltage of 35 kV.
distribution system operator
party operating a distribution system
[SOURCE: IEC 60050-617:2009, 617-02-10]
electrical energy storage
installation that is able to absorb electrical energy, store it and release it for a certain amount
of time during which energy conversion processes may be included
EXAMPLE A device that absorbs AC electrical energy to produce hydrogen by electrolysis, stores the hydrogen,
and uses that gas to produce AC electrical energy is an EES.
Note 1 to entry: EES may be used also to indicate the activity of an apparatus described in the definition while
performing its own functionality.

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– 10 – IEC TS 62898-2:2018 © IEC 2018
electromagnetic compatibility
ability of an equipment or system to function satisfactorily in its electromagnetic environment
without introducing intolerable electromagnetic disturbances to anything in that environment
[SOURCE: IEC 60050-161:2017 161-01-07, modified – "apparatus or system" has been
replaced by "equipment or system"]
electromagnetic disturbance
any electromagnetic phenomenon which may degrade the performance of a device,
equipment or system, or adversely affect living or inert matter
high voltage
voltage having a value above a conventionally adopted limit
[SOURCE: IEC 60050-151:2001, 151-15-05]
intentional island
island resulted from planned action(s) of automatic protections, or from deliberate action(s) by
the responsible network operator, or both, in order to keep supplying electrical energy to a
section of an electric power system
[SOURCE: IEC 60050-617:2017, 617-04-17]
single or multiple transmission link between transmission systems
enabling electric power and energy to be exchanged between these networks by means of
electric circuits and/or transformers
[SOURCE: IEC 60050-617:2009, 617-03-08]
part of an electric power system, that is disconnected from the
remainder of the interconnected system, but remains energized
Note 1 to entry: An island can be either the result of the action of automatic protections or the result of a
deliberate action.
Note 2 to entry: The generation and loads can be any combination of customer-owned and utility-owned.
[SOURCE: IEC 60050-617:2017, 617-04-12, modified – "electrically disconnected" has been
changed to "disconnected", "interconnected electric power system" has been changed to
"interconnected system", "from the local electric power sources" has been deleted, Note 2 to
entry has been changed]
isolated microgrid
group of interconnected loads and distributed energy resources forming a local electric power
system at distribution voltage levels not currently capable of being connected to a wider
electric power system
Note 1 to entry: Isolated microgrids are usually designed for geographical islands or for rural electrification.

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IEC TS 62898-2:2018 © IEC 2018 – 11 –
Note 2 to entry: Microgrids capable of being connected to a wider electric power system are also called non-
isolated microgrids.
[SOURCE: IEC 60050-617:2017, 617-04-23, modified – "with defined electrical boundaries"
has been deleted, Note 2 to entry has been added]
low voltage
a set of voltage levels used for the distribution of electricity and

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