IEC 61869-9:2016

Instrument transformers - Part 9: Digital interface for instrument transformers

IEC 61869-9:2016 is a product family standard applicable to instrument transformers with digital output. The product standard is composed of IEC 61869-1 and IEC 61869-6, in addition to this standard and the relevant product specific standards in the IEC 61869 series (Part 7, Part 8, Part 12, Part 13, Part 14, and Part 15). This standard defines requirements for digital communications of instrument transformer measurements. It is based on the IEC 61850 series, UCA international users group document Implementation guideline for digital interface to instrument transformers using IEC 61850-9-2, and the relevant parts of IEC 60044-8 that are replaced by this standard. It includes additional improvements including the IEC 61588 network based time synchronization. This first edition replaces the corresponding specific requirements previously contained in IEC 60044-8, published in 2002. This International Standard contains specific requirements for electronic low power instrument transformers (LPIT) having a digital output. However, the reader is encouraged to use its most recent edition. This publication contains an attached file in the form of a .xml file. This file is intended to be used as a complement and does not form an integral part of the publication.

Transformateurs de mesure - Partie 9: Interface numérique des transformateurs de mesure

L'IEC 61869-9:2016 est une norme de familles de produits applicable aux transformateurs de mesure à sortie numérique. La norme de produit est composée de l'IEC 61869 1 et de l'IEC 61869 6, en plus de la présente norme et des normes spécifiques aux produits correspondants dans la série IEC 61869 (Partie 7, Partie 8, Partie 12, Partie 13, Partie 14 et Partie 15). La présente norme définit les exigences en matière de communication numérique des mesurages de transformateurs de mesure. Elle repose sur la série IEC 61850, sur le document Implementation guideline for digital interface to instrument transformers using IEC 61850-9-2 de l’UCA International Users Group et sur les parties correspondantes de l'IEC 60044-8 qui sont remplacées par la présente norme. Elle inclut des améliorations supplémentaires, notamment la synchronisation basée sur le réseau de l'IEC 61588. Cette première édition remplace les exigences spécifiques correspondantes de l'IEC 60044-8, parue en 2002. La présente Norme internationale contient les exigences spécifiques relatives aux transformateurs de mesure électroniques de faible puissance (LPIT) équipés d’une sortie numérique. La présente publication contient un fichier joint sous la forme de fichier .xml. Ce fichier est destiné à être utilisé en complément de la présente publication et n’en fait pas partie intégrante.

General Information

• Status: Published
• Publication Date: 26-Apr-2016
• ICS: 17.220.20 - Measurement of electrical and magnetic quantities
• Technical Committee: TC 38 - Instrument Transformers
• Drafting Committee: WG 37 - TC 38/WG 37
• Current Stage: PPUB - Publication issued
• Start Date: 27-Apr-2016
• Completion Date: 31-May-2016

Standards Content (Sample)

IEC 61869-9 ®
Edition 1.0 2016-04
INTERNATIONAL
STANDARD
colour
inside
Instrument transformers –
Part 9: Digital interface for instrument transformers

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IEC 61869-9 ®
Edition 1.0 2016-04
INTERNATIONAL
STANDARD
colour
inside
Instrument transformers –
Part 9: Digital interface for instrument transformers

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.220.20 ISBN 978-2-8322-3331-3

– 2 – IEC 61869-9:2016  IEC 2016
CONTENTS
FOREWORD . 4
INTRODUCTION . 7
1 Scope . 12
2 Normative references . 12
3 Terms and definitions . 13
3.5 Terms and definitions related to other ratings . 13
3.7 Index of abbreviations . 13
4 Normal and special service conditions . 14
5 Ratings . 14
5.6 Rated accuracy class . 14
5.901 Performance requirements . 15
6 Design and construction . 16
6.901 Technological boundaries . 16
6.901.1 Interface point . 16
6.901.2 Digital output interface . 16
6.901.3 Human-machine interface . 16
6.902 Electrical requirements . 17
6.902.1 Frequency response requirements . 17
6.902.2 Maximum processing delay time requirement . 17
6.903 Specification of the communications profile . 19
6.903.1 General . 19
6.903.2 Variants . 19
6.903.3 Digital output sample rates . 20
6.903.4 Logical devices . 21
6.903.5 Logical nodes LPHD . 21
6.903.6 Logical nodes LLN0 . 21
6.903.7 Logical nodes TCTR . 21
6.903.8 Logical nodes TVTR . 24
6.903.9 Quality . 25
6.903.10 Dataset(s) . 26
6.903.11 Multicast sampled value control block(s) . 27
6.903.12 Configuration of the merging unit . 27
6.903.13 Rated conformance classes . 28
6.904 Synchronization . 34
6.904.1 General . 34
6.904.2 Precision time protocol synchronization . 34
6.904.3 1PPS synchronization . 35
6.904.4 Sample value message SmpSynch attribute . 35
6.904.5 Holdover mode . 36
6.904.6 Free-running mode . 37
6.904.7 Time adjustments . 37
7 Tests . 38
7.2 Type tests . 38
7.2.6 Test for accuracy . 38
7.2.901 Digital output conformance tests . 38
7.2.902 Maximum processing delay time test . 38

7.2.903 Loss of synchronization tests . 39
7.2.904 1PPS test . 39
Annex 9A (informative) Dynamic range considerations . 40
Annex 9B (informative) Time synchronization and management example . 43
Annex 9C (informative) Example merging unit ICD file . 45
Annex 9D (informative) Test circuits for accuracy measurement . 56
Annex 9E (informative) Electronic nameplate . 59
Bibliography . 60

Figure 901 – General block diagram of an electronic LPIT with digital output . 8
Figure 902 – General illustration of the objects within a merging unit (example) . 9
Figure 903 – Electronic LPIT with digital output (concept example) . 10
Figure 904 – Standalone merging unit . 11
Figure 905 – Duplex LC connector . 16
Figure 906 – Maximum processing delay time . 17
Figure 907 – Output message timestamp point . 19
Figure 908 – TCTR naming example . 23
Figure 909 – 1PPS signal waveform at the merging unit clock input . 35
Figure 910 – Time adjustment example (6 ASDU example) . 37
Figure 9A.1 – Nomogram for current . 41
Figure 9A.2 – Nomogram for voltage . 42
Figure 9B.1 – Sampled value signal processing example showing 2ASDUs per
message (F4800S2I4U4 example) . 43
Figure 9D.1 – Example test circuit . 56
Figure 9D.2 – Example test circuit . 58

Table 901 – Maximum processing delay time limits . 18
Table 902 – Standard sample rates . 20
Table 903 – Extensions to the LPHD class . 21
Table 904 – AmpSv object attribute values . 23
Table 905 – Extensions to the TCTR class . 24
Table 906 – VolSv object attribute values . 25
Table 907 – Extensions to the TVTR class . 25
Table 908 – Configuration parameters of the merging unit . 28
Table 909 – Basic conformance statement . 29
Table 910 – ACSI models conformance statement . 29
Table 911 – ACSI service conformance statement . 31
Table 912 – PICS for A-Profile support . 33
Table 913 – PICS for T-Profile support . 34

– 4 – IEC 61869-9:2016  IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSTRUMENT TRANSFORMERS –
Part 9: Digital interface for instrument transformers

FOREWORD
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61869-9 has been prepared by IEC technical committee 38:
Instrument transformers.
This first edition replaces the corresponding specific requirements previously contained in
IEC 60044-8, published in 2002.
The text of this standard is based on the following documents:
FDIS Report on voting
38/502/FDIS 38/508/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts in the IEC 61869 series, published under the general title Instrument
transformers, can be found on the IEC website.
This publication contains an attached file in the form of a .xml file. This file is intended to be
used as a complement and does not form an integral part of the publication.
This International Standard contains specific requirements for electronic low power instrument
transformers (LPIT) having a digital output.
This Part 9 is to be read in conjunction with, and is based on, IEC 61869-1:2007, General
Requirements and IEC 61869-6:2016. However, the reader is encouraged to use its most
recent edition.
This Part 9 follows the structure of IEC 61869-6 and IEC 61869-1 and supplements or
modifies their corresponding clauses/subclauses.
When a particular clause/subclause of Part 6 is not mentioned in this Part 9, that
clause/subclause applies. When this standard states “addition”, “modification” or
“replacement”, the relevant text in Part 6 is to be adapted accordingly.
When a particular clause/subclause of Part 1 is not mentioned in Part 6, that
clause/subclause applies. When part 6 states “addition”, “modification” or “replacement”, the
relevant text in Part 1 is to be adapted accordingly.
For additional clauses, subclauses, figures, tables, annexes or note, the following numbering
system is used:
– clauses, subclauses, tables, figures and notes that are numbered starting from 901 are
additional to those in Part 1;
– additional annexes are lettered 9A, 9B, etc.
An overview of the planned set of standards at the date of publication of this document is
given below. The updated list of standards issued by IEC TC38 is available at the website:
www.iec.ch
– 6 – IEC 61869-9:2016  IEC 2016
PRODUCT FAMILY STANDARDS PRODUCT PRODUCTS OLD
STANDARD STANDARD
IEC IEC
61869-2 ADDITIONAL REQUIREMENTS FOR 60044-1
CURRENT TRANSFORMERS
60044-6
61869-3 ADDITIONAL REQUIREMENTS FOR 60044-2
INDUCTIVE VOLTAGE TRANSFORMERS
61869-4 ADDITIONAL REQUIREMENTS FOR 60044-3
COMBINED TRANSFORMERS
61869-5 ADDITIONAL REQUIREMENTS FOR 60044-5
CAPACITOR VOLTAGE
TRANSFORMERS
61869-7 ADDITIONAL REQUIREMENTS FOR 60044-7
ELECTRONIC VOLTAGE
TRANSFORMERS
61869-8 ADDITIONAL REQUIREMENTS FOR 60044-8
ELECTRONIC CURRENT
TRANSFORMERS
61869-1
GENERAL 61869-9 DIGITAL INTERFACE FOR INSTRUMENT
REQUIREMENTS TRANSFORMERS
FOR
61869-10 ADDITIONAL REQUIREMENTS FOR
INSTRUMENT
LOW POWER PASSIVE CURRENT
61869-6
TRANSFORMERS
TRANSFORMERS
ADDITIONAL
61869-11 ADDITIONAL REQUIREMENTS FOR 60044-7
GENERAL
LOW POWER VOLTAGE
REQUIREMENTS
TRANSFORMERS
FOR LOW POWER
INSTRUMENT
61869-12 ADDITIONAL REQUIREMENTS FOR
TRANSFORMERS
COMBINED ELECTRONIC INSTRUMENT
TRANSFORMERS AND COMBINED
STAND ALONE INSTRUMENT
TRANSFORMERS
61869-13 STAND ALONE MERGING UNIT
61869-14 ADDITIONAL REQUIREMENTS FOR DC
CURRENT TRANSFORMERS
61869-15 ADDITIONAL REQUIREMENTS FOR DC
VOLTAGE TRANSFORMERS FOR DC
APPLICATIONS
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

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INTRODUCTION
General
This standard is a product family standard for instrument transformers. It provides an
application of the standard series IEC 61850, which details layered substation communication
architecture in the world of instrument transformers.
By providing tutorial material such as examples and explanations, it also provides access for
instrument transformer, protective relay and meter experts to concepts and methods applied
in the IEC 61850 series.
Compared to instrument transformers, digital communication technology is subject to on-going
changes which are expected to continue in the future. Significant experience with electronics
integrated directly into instrument transformers has yet to be gathered on a broader basis, as
this type of equipment is not widely spread in the industry and a change of paradigm has not
yet occurred.
Position of this standard in relation to the IEC 61850 series
The IEC 61850 series is a standard intended to be used for communication networks and
systems for power utility automation. The most important parts of this series define:
a) information models for the substation automation system;
b) these information models include both the models of the instrument transformers and
other process equipment (like circuit-breakers and disconnectors), and the models of the
substation automation system (like protection relays and meters). The models are defined
in IEC 61850-7-3 and IEC 61850-7-4;
c) the communication between intelligent electronic devices (IEDs) of the substation
automation system. The abstract models are defined in IEC 61850-7-2 and the mappings
on communication stacks are defined in IEC 61850-8-1 and IEC 61850-9-2;
d) a configuration language used to describe the configuration aspects of the substation
automation system is described in IEC 61850-6;
e) conformance testing of the communication interfaces of the IEDs of the power utility
automation system including their data models. The conformance testing is defined in
IEC 61850-10.
Typically, in a traditional system, IEDs like bay level controllers or protection relays interface
directly through analogue signals to instrument transformers. In that case, the data models of
the instrument transformers are implemented in these bay level devices. However, this is not
the only realization. In the case where electronics are integrated directly into electronic LPIT,
the above-mentioned data models should be implemented within the instrument transformer
and the instrument transformer needs to support a communication interface. The part of an
electronic LPIT that does this is known as the merging unit.
IEC 61850, being a system oriented standard series, leaves many options open in order to
support present and future requirements of all sizes of substations at all voltage levels.
To reduce the engineering amount required to achieve interoperability for the digital interface
between instrument transformers and equipment that uses the digital signal (like protective
relays, meters or bay level controllers), this standard specifies additional constraints on
implementing a digital communication interface.
The IEC 61869-9 standard:
– replaces the IEC 60044-8 digital solution;

– 8 – IEC 61869-9:2016  IEC 2016
– provides a product standard for instrument transformers with a digital interface according
to the IEC 61850 series; similar to what IEC 62271-3 offers for switchgear;
– includes backward compatibility for the UCA International Users Group Implementation
Guideline for Digital Interface to Instrument Transformers Using IEC 61850-9-2;
– uses IEC 61588 based time synchronization in accordance with IEC/IEEE 61850-9-3, with
an option for 1PPS (pulse per second).
Overview of the digital interface for instrument transformers
An illustrative general block diagram of an instrument transformer with digital output is shown
in Figure 901. It shows multiple current and/or voltage information coming from the secondary
converters (SC in Figure 901) and fed into a common block labelled “merging unit”. The
merging unit performs all the data processing (sampling, analogue to digital conversion,
scaling, message formatting, etc.) necessary to produce a time-coherent output data stream
according to this standard. For the purposes of this standard a merging unit is a physical unit
(hardware subsystem) used to assemble and transmit digital output data frames.
SC of ECTa (meas.)
SC of ECTb (meas.)
SC of ECTc (meas.)
SC of ECTa (prot.)
Digital
SC of ECTb (prot.)
output
SC of ECTc (prot.)
Merging unit
SC of ECT neutral Clock
input
SC of EVTa
SC of EVTb
SC of EVTc
SC of EVT neutral
Power
supply
SC of EVT busbar
IEC
Figure 901 – General block diagram of an electronic
LPIT with digital output
A merging unit is modelled as one or more logical devices that contain multiple logical nodes
as illustrated in Figure 902.
Merging unit (physical device)
Logical device "xxxxMUnn"
LPHD
PhyNam
Logical node LLN0
PhyHealth
InnATCTR1
MSVCB03
I AmpSv.instMag.i
A
SvEna = TRUE
AmpSv.q
DatSet = PhsMeas1
Dataset PhsMeas1
samples
InnBTCTR2
InnATCTR1.AmpSv.instMag.i
SmpRate = 4 800
I 4 800
AmpSv.instMag.i InnATCTR1.AmpSv.q
B
APPID = 0 x 4003
samples
AmpSv.q
InnBTCTR2.AmpSv.instMag.i
noASDU = 2
per
InnBTCTR2.AmpSv.q
second
InnCTCTR3.AmpSv.instMag.i
InnCTCTR3
InnCTCTR3.AmpSv.q
I AmpSv.instMag.i
C
InnNTCTR4.AmpSv.instMag.i
AmpSv.q
InnNTCTR4.AmpSv.q
UnnATVTR1.VolSv.instMag.i
InnNTCTR4
UnnATVTR1.VoSvl.q
I AmpSv.instMag.i
N
UnnBTVTR2.VolSv.instMag.i
MSVCB04
AmpSv.q
UnnBTVTR2.VoSvl.q
SvEna = TRUE
UnnCTVTR3.VolSv.instMag.i
DatSet = PhsMeas1
UnnATVTR1
UnnCTVTR3.VolSv.q
U VolSv.instMag.i
A
UnnNTVTR4.VolSv.instMag.i samples
SmpRate = 14 400
VolSv.q
UnnNTVTR4.VolSv.q
APPID = 0 x 4 004
14 400
noASDU = 6
UnnBTVTR2
samples
U VolSv.instMag.i per
B
VolSv.q
second
UnnCTVTR3
U VolSv.instMag.i
C
VolSv.q
UnnNTVTR4
U VolSv.instMag.i
N
VolSv.q
Instantiate to UnnNTVTR4 Instantiate to MSVCB04
LN TVTR Standard MSVCB Standard
LN class CB class
VolSv SvEna
NamPlt DatSet
SmpRate
APPID
noASDU
IEC
Figure 902 – General illustration of the objects within a merging unit (example)
Current and voltage measurements in the example merging unit in Figure 902 are modelled
per IEC 61850-7-1 by using the following logical nodes:
• Class TCTR per IEC 61850-7-4, instantiated individually for each of the three current
transformer phases, and for the neutral current measurement.
• Class TVTR per IEC 61850-7-4, instantiated individually for each of the three voltage
transformer phases, and for the neutral voltage measurement.
• Logical node zero LLN0 containing instances of the sampled value control blocks
(MSVCB03 and MSVCB04 in this example) controlling simultaneous publishing of
IEC 61850-9-2 data streams (in this example one with 4 800 samples per second and
2 samples per frame yielding a frame rate of 2 400 per second, the other with
14 400 samples per second and 6 samples per frame also yielding a frame rate of

– 10 – IEC 61869-9:2016  IEC 2016
2 400 per second), and a dataset that controls the content of the sampled value digital
output messages.
Applicable sample rates, time synchronization, control blocks and dataset are defined in this
standard.
Physical realization of the above concepts may vary with the applied technology determining
which parts are necessary for the realization of an actual instrument transformer. One such
realization showing an electronic LPIT with built-in digital data output is shown in Figure 903
and further described in the relevant product specific standards in the IEC 61869 series
(Part 7, Part 8, Part 12, Part 14, Part 15).
sensor converter transmitting system converter
A Phase Current
Instrument
Transformer
sensor converter transmitting system converter
System
B Phase Current
sensor converter transmitting system converter
C Phase Current
sensor converter transmitting system converter
Neutral Current Merging
unit
Digital
sensor converter transmitting system converter
output
A Phase Voltage
sensor converter transmitting system converter
B Phase Voltage
sensor converter transmitting system converter
C Phase Voltage
Synchronizing
sensor converter transmitting system converter
signal
Neutral Voltage
IEC
Figure 903 – Electronic LPIT with digital output (concept example)
It is not absolutely necessary that all parts shown in Figure 903 be included. For clarity, power
supplies are not shown here. An instrument transformer may be implemented in a single
physical unit or in multiple physical units. For example, there may be a separate physical unit
for each phase containing the primary voltage and/or current sensors, primary converters and
primary insulation, with all secondary converters and the merging unit in a separate physical
unit located in the control house. The number of primary inputs and their type (voltage or
current) in a single instrument transformer may be other than shown here.
For comparison, an illustrative general block diagram of an installation using a stand-alone
merging unit (SAMU) is shown in Figure 904. Unlike the merging unit in an instrument
transformer, a SAMU is a separate product covered in IEC 61869-13. It accepts as inputs the
outputs of instrument transformers, said outputs conforming to the specifications of one of the
product standards in the IEC 61869 series. The number of inputs and their type (voltage or
current) may be other than shown in Figure 904. Output produced by a SAMU and output
produced by an electronic LPIT with built in merging unit should in principle be
indistinguishable from each other (excluding the fact that SAMU output will typically have
lower accuracy due to cascading the separately given instrument transformer and SAMU
accuracy specifications).
Instrument Transformer
A Phase Current
Instrument Transformer
B Phase Current
Instrument Transformer
C Phase Current
Stand
Instrument Transformer
alone
Neutral Current
merging
Digital
unit
Instrument Transformer
output
(SAMU)
A Phase Voltage
Instrument Transformer
B Phase Voltage
Instrument Transformer
C Phase Voltage
Instrument Transformer Synchronizing
Neutral Voltage signal
IT output signals
(analogue or digital)
IEC
An example will be presented in IEC 61869-13 , as soon as this standard will be available.
Figure 904 – Standalone merging unit

______________
Under consideration.
– 12 – IEC 61869-9:2016  IEC 2016
INSTRUMENT TRANSFORMERS –
Part 9: Digital interface for instrument transformers

1 Scope
This part of IEC 61869 is a product family standard applicable to instrument transformers with
digital output. The product standard is composed of IEC 61869-1 and IEC 61869-6, in addition
to this standard and the relevant product specific standards in the IEC 61869 series (Part 7,
Part 8, Part 12, Part 13, Part 14, and Part 15).
This standard defines requirements for digital communications of instrument transformer
measurements. It is based on the IEC 61850 series, UCA international users group document
Implementation guideline for digital interface to instrument transformers using IEC 61850-9-2,
and the relevant parts of IEC 60044-8 that are replaced by this standard. It includes additional
improvements including the IEC 61588 network based time synchronization.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
Clause 2 of IEC 61869-6:2016 is applicable with the following additions:
IEC 61588:2009, Precision clock synchronization protocol for networked measurement and
control systems
IEC 61850-6:2009, Communication networks and systems for power utility automation –
Part 6: Configuration description language for communication in electrical substations related
to IEDs
IEC 61850-7-1:2011, Communication networks and systems for power utility automation –
Part 7-1: Basic communication structure – Principles and models
IEC 61850-7-2:2010, Communication networks and systems for power utility automation –
Part 7-2: Basic information and communication structure – Abstract communication service
interface (ACSI)
IEC 61850-7-3:2010, Communication networks and systems for power utility automation –
Part 7-3: Basic communication structure – Common data classes
IEC 61850-8-1:2011, Communication networks and systems for power utility automation –
Part 8-1: Specific communication service mapping (SCSM) – Mappings to MMS (ISO 9506-1
and ISO 9506-2) and to ISO/IEC 8802-3
IEC 61850-9-2:2011, Communication networks and systems for power utility automation –
Part 9-2: Specific communication service mapping (SCSM) – Sampled values over
ISO/IEC 8802-3
IEC/IEEE 61850-9-3:2016, Communication networks and systems for power utility
automation – Part 9-3: Precision time protocol profile for power utility automation

IEC 61850-10:2012, Communication networks and systems for power utility automation –
Part 10: Conformance testing
IEC 61869-6:2016, Instrument transformers – Part 6: Additional general requirements for
low-power instrument transformers
UCA (International Users Group), Implementation guideline for digital interface to instrument
transformers using IEC 61850-9-2
3 Terms and definitions
3.5 Terms and definitions related to other ratings
For the purposes of this document, the terms and definitions in IEC 61869-6:2016 apply, with
the following additions:
3.5.901
rated holdover time
rated duration over which the merging unit continues to send samples maintaining the sample
timing required for the measuring accuracy class following loss of the time signal
3.5.902
processing delay time
t
pd
difference between the time encoded by the field SmpCnt in a digital output message and the
time this message appears at the digital output
3.5.903
maximum processing delay time
longest processing delay time (t ) under all rated operating conditions
pd
3.5.904
free running mode
operating mode where sampled values issued by the merging unit are not synchronised to an
external clock to the degree required to meet the measuring accuracy class phase error limit
Note 1 to entry: The values are based on an internal clock oscillator.
3.7 Index of abbreviations
Index of abbreviations of IEC 61869-6:2016 is extended by the addition of the following:
9-2LE The sampled value protocol defined by UCA International Users Group document
Implementation Guideline for Digital Interface to Instrument Transformers using
IEC 61850-9-2, modification Index R2-1 dated 2004-07-07
ASDU Application Service Data Unit
ACSI Abstract Communications Service Interface
SCSM Specific Communication Service Mapping
SAV Common data class defined in IEC 61850-7-3:2010, 7.4.4 for modelling sampled
values.
TCTR Logical node defined in IEC 61850-7-4:2010, 5.15.4 for modelling sampled values
from current transformers
TVTR Logical node defined in IEC 61850-7-4:2010, 5.15.20 for modelling sampled values
from voltage transformers
– 14 – IEC 61869-9:2016  IEC 2016
SCL System Configuration description Language according to IEC 61850-6:2009,
Clause 4
ICD IED Capability Description file according to IEC 61850-6:2009, 5.3
IED Intelligent Electronic Device
SAS Substation Automation System
MU Merging Unit
SAMU Stand Alone Merging Unit
EMC ElectroMagnetic Compatibility
4 Normal and special service conditions
Clause 4 of IEC 61869-1:2007 applies.
5 Ratings
5.6 Rated accuracy class
Accuracy classes for electronic LPIT with digital output are defined in the applicable
IEC 61869 series product standards Part 7, Part 8, Part 12, Part 13, Part 14, and Part 15.
Accuracy class specifications apply end-to-end, representing all errors introduced between
the instrument transformer primary and the properly time-stamped message created at the
digital output.
Accuracy specifications directly incorporate all errors associated with time synchronization.
Time synchronization requirements are as described in 6.904.
With regard to accuracy classes, instrument transformers with digital output shall be classified
in two groups:
• measuring instrument transformers,
• protection instrument transformers.
To make best use of the dynamic range enabled by the 32-bit message format specified in
this standard, all protection instrument transformers and protection capable SAMU channels
shall be specified with dual accuracy class ratings. Dual rating is intended to precisely
document the measuring and protection accuracy class applicable to a given channel.
The dual rating requirement acknowledges the fact that protection rated instrument
transformers are commonly also used for measurement and indication purposes. It
establishes a proven, well understood method for documenting this performance.
The protection instrument transformer accuracy class shall be given as a slash “/” symbol
separated pair, with measuring accuracy class taking the first position and the protection
at the end. Dual specification shall
accuracy class followed by the accuracy limit factor K
ALF
be reported on the digital instrument transformer nameplate.
Rating examples:
0,2S 0,2S class measuring instrument transformer (not rated for protection)
0,2S/5P20 5P20 protection instrument transformer meeting class 0,2S measuring
accuracy class requirements
5.901 Performance requirements
Electronic LPIT with digital output shall meet all the requirements defined in IEC 61869
specific product standards Part 7, Part 8, Part 12, Part 13, Part 14, and Part 15, if applicable.
This requirement therefore extends to the merging unit component which is an integral part of
the instrument transformer apparatus, and is therefore subject to the same environmental and
EMC conditions.
Depending on the device conformance class defined in 6.903.13, the merging unit component
may be exposed to various levels of Ethernet network traffic. Although it is impossible to
foresee all operating environments, the following recommendations are provided based on
real life field experience:
• merging unit behaviour should be well defined under all operating conditions;
• if present, the test signal generating capability should be disabled by default;
• all data included in the same ASDU (including quality bits) should be mutually consistent
and represent the same time instant as required by the applicable accuracy class
specification;
• data shall be synchronized to a common time reference as described in 6.904.
Merging units should have well defined behaviour under all operating conditions. This
especially applies during power-up, power-down and self-diagnostic system failure indications
(as required by IEC 61869-6:2016, 6.604). While the merging unit output (data stream) may
become unavailable at any time (through component failure), when present, quality bits within
the stream should faithfully represent the electronic LPIT operating state in accordance with
the built-in self-check, diagnostic capabilities or external alarm inputs (when present). Quality
bits are used by protective relays, and are relied upon to prevent protective scheme mal-
operation.
For example, when powering up, an optical current transformer may need to activate
thermoelectric coolers, perform carefully controlled laser start-up, and wait until the system
has stabilized to allow operation within stated accuracy. During this process, merging unit
(digital) output should be disabled. If data output is enabled, all affected data values should
be tagged as ‘invalid’, and detailed quality set to either ‘failure’ or ‘inaccurate’ in accordance
with 6.903.9. The same requirement applies during power-down (loss of power) and self-
diagnostic system activation (i.e. DSP subsystem failure). The merging unit should guarantee
no un-flagged bad sampled value data is output.
Built in test signal generating capability is generally encouraged, but should be considered at
the substation system level. It should be disabled by default. This applies to shipping and to
all active power system installations. When present, test values shall be accompanied by the
associated test bit activation as described in 6.903.9.
External Ethernet traffic received by the merging unit should not interfere with the sampled
value transmission. This requirement applies regardless of the type of traffic, destination
address range or the receive channel loading (100 % loading and full duplex communications
are assumed).
A data consistency requirement applies to all data values within the same ASDU. Quality bit
updates should be atomic (shall be updated at the same time and shall be consistent with the
SV data point they describe), and are not allowed to lag behind their associated data values.
For example; the outOfRange quality bit should be set as soon as clipping occurs, and it
should stay set until the input value is back within clipping limits and output returns within the
accuracy class. While the outOfRange bit is true, the associated data value should be
reported as being at some value between the clipping limit and the actual input value. The
output behaviour, while the input is outside the clipping limits, should be monotonic, with the
output value not allowed to change sign without a corresponding change at the device input
(no polarity inversion).
– 16 – IEC 61869-9:2016  IEC 2016
6 Design and construction
6.901 Technological boundaries
6.901.1 Interface point
An electronic LPIT with built in merging unit has two signal interface boundaries, plus an
auxiliary power supply interface. The first signal boundary is the instrument transformer high
voltage primary, while the second is the merging unit’s digital output connector interface. The
merging unit output connector should also define the split of responsibility between the
electronic LPIT manufacturer and the system integrator. Additional interface boundaries such
as interfaces between the primary and secondary converter are considered to be integral
parts of the electronic LPIT. Additional interface points, such as 1PPS time synchronization
input, may also be present in some installations.
The cables and connections that are internal to the electronic LPIT assembly including
connections between a merging unit and the primary side sensor are outside the scope of this
standard. The system integrator should supply all cables and connections that form part of the
connection to the substation automation system (SAS). Where any cables or connections are
run external to enclosures, they should be supplied with suitable mechanical protection.
6.901.2 Digital output interface
A fibre optic digital transmission system 100BASE-FX (1 300 nm, multimode, full duplex, two
strand fibre optic cable) according to
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