IEC TS 62786:2017

Distributed energy resources connection with the grid

IEC TS 62786:2017(E) provides principles and technical requirements for distributed energy resources (DERs) connected to the distribution network. It applies to the planning, design, operation and connection of DERs to distribution networks. It includes general requirements, connection scheme, choice of switchgear, normal operating range, immunity to disturbances, active power response to frequency deviation, reactive power response to voltage variations and voltage changes, EMC and power quality, interface protection, connection and start to generate electrical power, active power management, monitoring, control and communication, and conformance tests.
This document specifies interface requirements for connection of generating plants with the distribution network operating at a nominal frequency of 50 Hz or 60 Hz.
DERs include distributed generation and permanently connected electrical energy storage in the form of synchronous generators, asynchronous generators, converters, etc., connected to the medium voltage (MV) or low voltage (LV) distribution network.

General Information

• Status: Published
• Publication Date: 10-Apr-2017
• ICS: 29.240.01 - Power transmission and distribution networks in general
• Technical Committee: TC 8 - System aspects of electrical energy supply
• Drafting Committee: JWG 10 - TC 8/JWG 10

Relations

• Replaced By: IEC TS 62786-1:2023 - Distributed energy resources connection with the grid - Part 1: General requirements
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC TS 62786 ®
Edition 1.0 2017-04
TECHNICAL
SPECIFICATION
Distributed energy resources connection with the grid

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IEC TS 62786 ®
Edition 1.0 2017-04
TECHNICAL
SPECIFICATION
Distributed energy resources connection with the grid

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.240.01 ISBN 978-2-8322-4218-6

– 2 – IEC TS 62786:2017 © IEC 2017
CONTENTS
FOREWORD . 4
1 Scope and object . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Requirements on generating plants . 11
4.1 General . 11
4.2 Connection scheme . 12
4.3 Choice of switchgear . 12
4.3.1 General . 12
4.3.2 Interface switch . 12
4.4 Normal operating range . 12
4.4.1 General . 12
4.4.2 Operating frequency range . 12
4.4.3 Operating voltage range . 13
4.5 Immunity to disturbances . 13
4.5.1 General . 13
4.5.2 Rate of change of frequency (ROCOF) immunity . 13
4.5.3 Under voltage ride through (UVRT) requirements . 13
4.5.4 Over voltage ride through (OVRT) requirements . 14
4.6 Active power response to frequency deviation . 14
4.7 Reactive power response to voltage variations and voltage changes . 15
4.7.1 General . 15
4.7.2 Reactive power control . 15
4.7.3 Dynamic reactive power support capabilities . 15
4.8 EMC and power quality . 15
4.8.1 General . 15
4.8.2 Direct current (DC) injection . 16
4.9 Interface protection . 16
4.10 Connection and start to generate electrical power . 17
4.10.1 General . 17
4.10.2 Connection of synchronous generators . 17
4.10.3 Auto reclose of distribution lines . 17
4.11 Active power management . 18
4.12 Monitoring, control and communication . 18
4.12.1 Monitoring and control . 18
4.12.2 Communication . 18
5 Conformance tests . 18
Annex A (normative)  Operating frequency range . 19
Annex B (normative)  Operating voltage range . 20
Annex C (normative)  Under voltage ride through capability of DERs . 21
Annex D (normative)  Over voltage ride through parameters . 22
Bibliography . 23

Figure 1 – Electricity generating plant connected to a distribution network (schematic
view of switches) . 10
Figure 2 – Under voltage ride through capability requirements of DER . 14

Table 1 – Operating frequency requirements of DERs . 13
Table 2 – Operating voltage requirements of DERs . 13
Table 3 – Interface protection functions . 17
Table A.1 – Continuous operating frequency range . 19
Table A.2 – Limited operating frequency range . 19
Table B.1 – Continuous operating voltage range . 20
Table B.2 – Limited operating voltage range . 20
Table C.1 – UVRT capability of DERs with an interface to the grid based on a
synchronous generator . 21
Table C.2 – UVRT capability of DERs with an interface to the grid based on non-
synchronous generators (eg. converters, DFIG, etc.) . 21
Table D.1 – Medium voltage OVRT requirements . 22

– 4 – IEC TS 62786:2017 © IEC 2017
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DISTRIBUTED ENERGY RESOURCES
CONNECTION WITH THE GRID
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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The main task of IEC technical committees is to prepare International Standards. In
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• 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 TS 62786 has been prepared by IEC Technical Committee 8: System aspects for
electrical energy supply.
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
8/1439/DTS 8/1457/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.
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.

– 6 – IEC TS 62786:2017 © IEC 2017
DISTRIBUTED ENERGY RESOURCES
CONNECTION WITH THE GRID
1 Scope and object
This technical specification provides principles and technical requirements for distributed
energy resources (DERs) connected to the distribution network. It applies to the planning,
design, operation and connection of DERs to distribution networks. It includes general
requirements, connection scheme, choice of switchgear, normal operating range, immunity to
disturbances, active power response to frequency deviation, reactive power response to
voltage variations and voltage changes, EMC and power quality, interface protection,
connection and start to generate electrical power, active power management, monitoring,
control and communication, and conformance tests.
This document specifies interface requirements for connection of generating plants with the
distribution network operating at a nominal frequency of 50 Hz or 60 Hz.
DERs include distributed generation and permanently connected electrical energy storage in
the form of synchronous generators, asynchronous generators, converters, etc., connected to
the medium voltage (MV) or low voltage (LV) distribution network.
NOTE Mobile electrical energy storage devices (e.g. electrical vehicles) are under consideration for future
editions.
The requirements of this document can be superseded by laws and regulations where
applicable.
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 61000 (all parts), Electromagnetic compatibility (EMC)
IEC TS 62749, Assessment of power quality – Characteristics of electricity supplied by public
networks
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
black start
start up of an electric power system from a blackout through internal energy resources

3.2
converter-type generator
generator that produces electrical power and is connected to the distribution network via a
converter, including doubly-fed induction machines
3.3
distributed energy resource
DER
generators, including loads having a generating mode (such as electrical energy storage
systems) connected to the low or medium voltage distribution network, with their auxiliaries,
protection and connection equipment
3.4
distribution network
electric power network for the distribution of electric power from and to network users for
which a distribution system operator (DSO) is responsible
3.5
distribution system operator
DSO
party operating a distribution network
Note 1 to entry: In some countries, a DSO is also referred to as DNO (distribution network operator).
[SOURCE: IEC 60050-617:2009, 617-02-10, modified – Note 1 to entry has been added]
3.6
flicker
impression of unsteadiness of visual sensation induced by a light stimulus whose luminance
or spectral distribution fluctuates with time
Note 1 to entry: Flicker can be calculated by short term indicator P and long term indicator P .
st lt
[SOURCE: IEC 60050-161:1990, 161-08-13, modified – Note 1 to entry has been added]
3.7
fundamental frequency
frequency of the fundamental component of a periodic quantity
Note 1 to entry: For the purpose of this document, the fundamental frequency is the same as the power supply
frequency, e.g. 50 Hz or 60 Hz.
[SOURCE: IEC 60050-103, 103-07-21, modified – Note 1 to entry has been added]
3.8
fundamental component
sinusoidal component of Fourier series of periodic quantity having the frequency of the
quantity itself
[SOURCE: IEC 60050-103,103-07-19]
3.9
generating unit
indivisible set of equipment whose primary purpose is to generate electrical power
3.10
generating plant
group of generating units including auxiliaries connected to one POC

– 8 – IEC TS 62786:2017 © IEC 2017
3.11
harmonic frequency
frequency of a harmonic component
[SOURCE: IEC 60050-103:2009, 103-07-26]
3.12
harmonic component
sinusoidal component of Fourier series of a periodic quantity, the harmonic order of which is
an integer number greater than one
th
Note 1 to entry: A component of harmonic n (with n>1) is generally designated n harmonic. the designation of

st
the fundamental component as “1 harmonic” is not recommended.
[SOURCE: IEC 60050-103:2009, 103-07-25]
3.13
interface protection
combination of protection relay functions which opens the interface switch of a generating unit
and prevents its closure, whichever is appropriate, in the case of:
• a fault on the electric power network;
• an unintentional islanding situation;
• voltage and frequency being outside continuously operating ranges
3.14
interharmonic frequency
frequency which is a non-integer multiple of the reference fundamental frequency
Note 1 to entry: By extension from harmonic order, the interharmonic order is the ratio of an interharmonic
frequency to the fundamental frequency. This ratio is not an integer (recommended notation: "m").
Note 2 to entry: In the case where m<1, the term subharmonic frequency may be used.
[SOURCE: IEC 60050-551:2001, 551-20-06, modified – Note 1 to entry and Note 2 to entry
have been added]
3.15
interharmonic component
sinusoidal component of a periodic quantity having an interharmonic frequency
Note 1 to entry: Its value is normally expressed as an r.m.s. value.
Note 2 to entry: For brevity, such a component may be referred to simply as an "interharmonic".
[SOURCE: IEC 60050-551:2001, 551-20-08, modified – The existing note has been deleted
and Note 1 to entry and Note 2 to entry have been added]
3.16
long-term flicker indicator
measure of flicker evaluated over a specified time interval of a relatively long duration, using
successive values of the short-term flicker indicator
Note 1 to entry: The duration is typically 2 hours, using 12 successive values of P , in accordance with
st
IEC 61000-4-15.
[SOURCE: IEC 60050-161:1990, 161-08-19]

3.17
low voltage
LV
set of voltage levels used for the distribution of electricity and whose upper limit is generally
accepted to be 1 000 V for alternating current
[SOURCE: IEC 60050-601:1985, 601-01-26]
3.18
medium voltage
MV
any set of voltage levels lying between low and high voltage
Note 1 to entry: The boundaries between medium and high voltage levels that overlap and depend on local
circumstances as well as history or common usage. Nevertheless the band 1 kV to 35 kV is considered as the
accepted medium voltage boundary.
Note 2 to entry: Because of existing network structures, boundary between MV and HV can be different from
country to country.
[SOURCE: IEC 60050-601:1985, 601-01-28, modified – The existing note has been modified
and Note 2 to entry has been added]
3.19
point of connection
POC
physical connection point on the distribution network where a generating plant is connected
3.20
power factor
under periodic conditions, ratio of the absolute value of the active power P to the apparent
power S:
IPI
λ =
S
Note 1 to entry: Under sinusoidal conditions, the power factor is the absolute value of the active factor.
[SOURCE: IEC 60050-131:2002, 131-11-46]
3.21
rapid voltage changes
RVC
quick transition (that may last several cycles) in r.m.s. voltage between two steady-state
conditions while the voltage stays within the thresholds defined for voltage swells and dips
Note 1 to entry: RVC is expressed by the relative steady state voltage change or by a maximum r.m.s. voltage
change aggregated over several cycles.
3.22
short term flicker indicator
measure of flicker evaluated over a specified time interval of a relatively short duration
Note 1 to entry: The duration is typically 10 minutes, in accordance with IEC 61000-4-15.
[SOURCE: IEC 60050-161:1990, 161-08-18]
3.23
short-time withstand current
the current that a circuit or a switching device in the closed position can carry during a
specified short time under prescribed conditions of use and behaviour

– 10 – IEC TS 62786:2017 © IEC 2017
[SOURCE: IEC 60050-441:2000, 441-17-17]
3.24
system operator
party responsible for safe and reliable operation of a part of the electric power system in a
certain area and for connection to other parts of the electric power system
[SOURCE: IEC 60050-617:2009, 617-02-09]
3.25
switch
device for changing the electric connections among its terminals
[SOURCE: IEC 60050-151:2001, 151-12-22]
Distribution network
Point of connection (POC)
Producer's network
Main switch
Interface protection relay
Producer's non-island
operation
Interface switch
Producer's island
operation
Generating unit switch
IEC
Figure 1 – Electricity generating plant connected to a distribution network
(schematic view of switches)
3.26
main switch
switch installed as close as possible to the point of connection, for protection against internal
faults and disconnection of the whole plant from the distribution network
Note 1 to entry: See also Figure 1.
3.27
interface switch
switch (circuit breaker, switch or contactor) installed in the producer’s network, for separating
the part(s) of the producer’s network containing at least one generation unit from the
distribution network
Note 1 to entry: See also Figure 1.
Note 2 to entry: In some situations, the interface switch may be used to enable island operation of part of the
producer’s network, if technically feasible.

3.28
generating unit switch
switch installed electrically close to the terminals of each generating unit of the generating
plant, for protection and disconnection of that generating unit
Note 1 to entry: See also Figure 1.
3.29
voltage deviation
difference between the supply voltage at a given instant and the declared supply voltage
[SOURCE: IEC 60050-614:2016, 614-01-04]
3.30
voltage dip
sudden voltage reduction at a point in an electric power system, followed by voltage recovery
after a short time interval, from a few periods of the sinusoidal wave of the voltage to a few
seconds
[SOURCE: IEC 60050-614:2016, 614-01-08]
3.31
voltage fluctuation
series of voltage changes or a continuous variation of the r.m.s. or peak value of the voltage
Note 1 to entry: Whether the r.m.s. or peak value is chosen depends upon the application.
[SOURCE: IEC 60050-161:1990, 161-08-05, modified – Note to entry 1 has been modified]
3.32
voltage swell
sudden increase of voltage at a point in an electrical system followed by voltage reduction
after a short period of time from a few cycles to a few seconds
3.33
voltage unbalance
condition in a polyphase system in which the r.m.s. values of the phase element voltages
(fundamental component), or the phase angles between consecutive phase element voltages,
are not all equal
Note 1 to entry: The degree of the inequality is usually expressed as the ratios of the negative- and zero-
sequence component to the positive-sequence component.
Note 2 to entry: In this standard, voltage unbalance is considered in relation to 3-phase systems.
[SOURCE: IEC 60050-614:2016, 614-01-32, modified – Note 1 to entry and Note 2 to entry
have been added]
4 Requirements on generating plants
4.1 General
When connecting a DER t
...