IEC TS 62786-3:2023

Distributed energy resources connection with the grid - Part 3: Additional requirements for stationary battery energy storage system

IEC TS 62786-3:2023, which is a Technical Specification, provides principles and technical requirements for interconnection of distributed Battery Energy Storage System (BESS) to the distribution network. It applies to the design, operation and testing of BESS interconnected to distribution networks. It includes the additional requirements for BESS, such as connection scheme, choice of switchgear, normal operating range, immunity to disturbance, 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 electric power, active power management, monitoring, control and communication, and grid-connected tests.
The stationary BESSs considered within the scope of this document include electrical forms such as lead-acid, lithium-ion, liquid flow and sodium-sulfur batteries, interconnected to medium voltage (MV) or low voltage (LV) distribution networks via bidirectional DC to AC power converters. This document will specify active and reactive power response and grid-connected testing for distributed BESS, as a supplement for IEC TS 62786-1:2023.
This document specifies interface requirements for connection of distributed BESS with the distribution network operating at a nominal frequency of 50 Hz or 60 Hz.

General Information

• Status: Published
• Publication Date: 27-Nov-2023
• 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
• Current Stage: PPUB - Publication issued
• Start Date: 28-Nov-2023
• Completion Date: 17-Nov-2023

Standards Content (Sample)

IEC TS 62786-3 ®
Edition 1.0 2023-11
TECHNICAL
SPECIFICATION
colour
inside
Distributed energy resources connection with the grid –
Part 3: Additional requirements for stationary battery energy storage
system
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IEC TS 62786-3 ®
Edition 1.0 2023-11
TECHNICAL
SPECIFICATION
colour
inside
Distributed energy resources connection with the grid –
Part 3: Additional requirements for stationary battery energy storage
system
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.240.01 ISBN 978-2-8322-7667-9
– 2 – IEC TS 62786-3:2023 © IEC 2023
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions, abbreviated terms and symbols . 6
3.1 Terms and definitions . 6
3.2 Abbreviated terms and symbols . 9
3.2.1 Abbreviated terms . 9
3.2.2 Symbols . 9
4 Requirements for distributed BESS . 11
4.1 General . 11
4.2 Connection scheme . 11
4.3 Choice of switchgear . 11
4.3.1 General . 11
4.3.2 Interface switch . 11
4.4 Normal operating range . 11
4.4.1 General . 11
4.4.2 Operating frequency range . 11
4.4.3 Operating voltage range . 12
4.5 Immunity to disturbances . 12
4.5.1 General . 12
4.5.2 Rate of change of frequency (ROCOF) immunity . 12
4.5.3 Under voltage ride through (UVRT) requirements . 12
4.5.4 Over voltage ride through (OVRT) requirements . 12
4.5.5 Rapid phase angle change immunity . 12
4.6 Active power response to frequency deviation . 13
4.6.1 General . 13
4.6.2 Active power response to over frequency . 14
4.6.3 Active power response to underfrequency . 14
4.7 Power response to voltage changes . 15
4.7.1 General . 15
4.7.2 Voltage support by reactive power . 15
4.7.3 Reactive power control modes . 15
4.7.4 Voltage related active power control . 15
4.7.5 Voltage related reactive power response . 16
4.7.6 Additional reactive current requirements on BESS . 16
4.8 EMC and power quality . 16
4.8.1 General . 16
4.8.2 Direct current (DC) injection . 16
4.9 Interface protection . 17
4.9.1 General . 17
4.9.2 Requirements on voltage and frequency protection . 17
4.9.3 Means to detect islanding situation . 17
4.9.4 Digital input to the interface protection . 17
4.10 Connection and starting to generate electrical power . 17
4.10.1 General . 17
4.10.2 Connection of BESS . 17
4.10.3 Auto reclose of distribution lines . 17

4.10.4 Black start capability and intentional islanding control . 17
4.11 Ceasing and reduction of active power on set point. 17
4.12 Remote information exchange . 17
4.12.1 General . 17
4.12.2 Monitoring and control . 18
4.12.3 Communication . 18
5 Conformance tests . 18
Annex A (normative) Operating frequency range . 19
Annex B (normative) Operating voltage range . 20
Annex C (normative) Summary of power thresholds to be defined by individual
countries . 21
Bibliography . 22

Figure 1 – Example of the interconnection interface concept . 8
Figure 2 – Typical power-frequency response curve for BESS charging and discharging

modes under operating frequency range . 13
Figure 3 – Example of reactive power capability range of BESS in per unit at nominal
voltage . 15
Figure 4 – Typical voltage related active power regulation of BESS . 16

Table 1 – Operating frequency requirements of BESS. 11
Table 2 – Operating voltage requirements of BESS with LV distribution network . 12
Table A.1 – Continuous operating frequency range . 19
Table A.2 – Limited operating frequency range . 19
Table A.3 – Limited charging/discharging time . 19
Table B.1 – Continuous operating POC voltage range . 20
Table B.2 – Limited operating voltage range . 20

– 4 – IEC TS 62786-3:2023 © IEC 2023
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DISTRIBUTED ENERGY RESOURCES CONNECTION WITH THE GRID –

Part 3: Additional requirements for stationary
battery energy storage system
FOREWORD
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IEC TS 62786-3 has been prepared by IEC Technical Committee 8: System aspects of electrical
energy supply. It is a Technical Specification.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
8/1663/DTS 8/1680/RVDTS
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Specification is English.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts in the IEC 62786 series, published under the general title Distributed energy
resources connection with the grid, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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– 6 – IEC TS 62786-3:2023 © IEC 2023
DISTRIBUTED ENERGY RESOURCES CONNECTION WITH THE GRID –

Part 3: Additional requirements for stationary
battery energy storage system
1 Scope
This part of IEC 62786, which is a Technical Specification, provides principles and technical
requirements for interconnection of distributed Battery Energy Storage System (BESS) to the
distribution network. It applies to the design, operation and testing of BESS interconnected to
distribution networks. It includes the additional requirements for BESS, such as connection
scheme, choice of switchgear, normal operating range, immunity to disturbance, 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 electric
power, active power management, monitoring, control and communication, and grid-connected
tests.
The stationary BESSs considered within the scope of this document include electrical forms
such as lead-acid, lithium-ion, liquid flow and sodium-sulfur batteries, interconnected to medium
voltage (MV) or low voltage (LV) distribution networks via bidirectional DC to AC power
converters. This document will specify active and reactive power response and grid-connected
testing for distributed BESS, as a supplement for IEC TS 62786-1:2023.
This document specifies interface requirements for connection of distributed BESS with the
distribution network operating at a nominal frequency of 50 Hz or 60 Hz.
NOTE Mobile electrical energy storage devices (e.g., electrical vehicles) are under consideration for future editions.
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 62786-1:2023, Distributed energy resources connection with the grid – Part 1: General
requirements
IEC TS 62898-2: Microgrids – Part 2: Guidelines for operation
3 Terms and definitions, abbreviated terms and symbols
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC TS 62786-1:2023 and
the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp

3.1.1
battery energy storage system
BESS
electrical energy storage system with an accumulation subsystem based on batteries with
secondary cells
Note 1 to entry: A battery energy storage system includes a flow battery energy system.
3.1.2
battery storage subsystem
BSS
BESS subsystem, comprising at least one battery energy storage unit, where energy is stored
in the battery
Note 1 to entry: Generally, the battery storage subsystem is connected to the power conversion subsystem that
performs the necessary power conversion to electrical energy; however, in some cases, a power converter can be
embedded in the battery storage subsystem.
3.1.3
charging mode
operating mode during a required time in which the BESS is supplied with electrical energy from
the POC in a controllable way
3.1.4
charging regulation time
time interval from the time when the BESS receives the control signal or when the grid
parameter changes in a way to trigger the system response to the time when the power deviation
is controlled within a specified percentage of the set point value after charging power firstly
reaches to the set point value
3.1.5
charging response time
time interval from the time when the BESS receives the control signal or the grid parameter
changes in a way to trigger the system response to the time when the charging power firstly
reaches the set point value
3.1.6
charging to discharging transition time
under normal operation conditions, time when the BESS transits from a specified percentage
of rated power charging mode to a specified percentage of rated power discharging mode
3.1.7
discharging mode
operating mode during a required time in which the BESS supplies electrical energy to the POC
in a controllable way
3.1.8
discharging to charging transition time
under normal operation conditions, time when the BESS transits from a specified percentage
of rated power discharging mode to a specified percentage of rated power charging mode
3.1.9
discharging regulation time
time interval from the time when the BESS receives the control signal or the grid parameter
changes in a way to trigger the system response to the time when the power deviation is
controlled within a specified percentage of the set point value after discharging power reaches
to the set point value
– 8 – IEC TS 62786-3:2023 © IEC 2023
3.1.10
discharging response time
time interval from the time when the BESS receives the control signal or the grid parameter
changes in a way to trigger the system response to the time when the discharging power firstly
reaches the set point value
3.1.11
interconnection interface
single device or a collection of multiple devices connecting the BESS with the grid, which
includes the interface switchgear, interface control, interface protection, interface
communication, auxiliary subsystem etc.
Note 1 to entry: Figure 1 gives an example of interconnection interface between BESS and distribution network.

Figure 1 – Example of the interconnection interface concept
3.1.12
power conversion subsystem
subsystem generally connected to the battery storage subsystem and to the POC through the
interconnection interface, which converts power bi-directionally between the battery storage
subsystem and AC power system
[SOURCE: IEC 62933-1:2018, 5.2.2, modified − The definition has been rewritten and the Note
to entry removed.]
3.1.13
rated power charging response time
special state of charging response time, which refers to the time interval from the time when
the BESS receives the control signal in standby mode to the time when the charging power
firstly reaches the rated power
3.1.14
rated power charging regulation time
special state of charging regulation time, which refers to the time interval from the time when
the BESS receives the control signal in standby mode to the time when the power deviation is
controlled within a specified percentage of the rated power after charging power firstly reaches
the rated power
3.1.15
secondary battery
assembly of battery cell(s) which can include associated safety and control circuits and
case/enclosure, ready for use as a source of electrical energy characterized by its voltage, size,
terminal arrangement, capacity and rate capability
Note 1 to entry: This includes single cell batteries.
[SOURCE: IEC 62485-2:2010, 3.5, modified − The definition has been rewritten.]
3.1.16
standby mode
operation mode of the BESS that connected to the POC without any intentional power flow and
providing for immediate operation upon demand
[SOURCE: IEC 62933-1:2018, 6.1.7, modified − The definition has been rewritten.]
3.1.17
state of charge
SOC
ratio between the available energy from a battery storage subsystem and the actual energy
capacity, typically expressed as a percentage
[SOURCE: IEC 62933-1:2018, 6.2.4, modified – "EES system" has been replaced by "battery
storage system".]
3.1.18
stationary battery
secondary battery which is designed for service in a fixed location and is not habitually moved
from place to place during the operating life
Note 1 to entry: It is permanently connected to the DC power supply (fixed installation) or part of a complete battery
storage system.
[SOURCE: IEC 62485-2:2010, 3.8, modified – "or part of a complete battery storage system"
has been added and the second sentence has been changed to a Note to entry.]
3.2 Abbreviated terms and symbols
3.2.1 Abbreviated terms
BESS battery energy storage system
BSS battery storage subsystem
DER distributed energy resources
DSO distributed system operator
EMC electromagnetic compatibility
OVRT over voltage ride through
POC point of connection
ROCOF rate of change of frequency
SO system operator
SOC state of charge
UVRT under voltage ride through
3.2.2 Symbols
F operating frequency
– 10 – IEC TS 62786-3:2023 © IEC 2023
f under frequency dead zone value
dz1
f over frequency dead zone value
dz2
f upper threshold of continuous operation frequency range
max1
f upper threshold of limited ope
...