prEN IEC 60255-167:2026

• Status: Not Published
• Publication Date: 01-Feb-2028
• Technical Committee: CLC/TC 95X - Measuring relays and protection equipment
• Drafting Committee: CLC/TC 95X - Measuring relays and protection equipment
• Current Stage: 4020 - Enquiry circulated - Enquiry
• Start Date: 28-Aug-2026
• Due Date: 20-Dec-2024
• Completion Date: 28-Aug-2026
• Ref Project: oSIST prEN IEC 60255-167:2026 - Measuring relays and protection equipment - Part 167: Functional requirements for directional overcurrent protection

prEN IEC 60255-167:2026 is a CLC draft in the IEC 60255 series for measuring relays and protection equipment. It specifies the functional and performance requirements, test methods, and reporting rules for a.c. directional overcurrent protection, for use by relay manufacturers, test laboratories, and engineers who need to specify or assess this function.

What does prEN IEC 60255-167:2026 specify?

prEN IEC 60255-167:2026 specifies the minimum requirements for functional and performance evaluation of an a.c. directional overcurrent protection function, and how to document the declared performance. It focuses on the directional element, while referring to IEC 60255-151 for the overcurrent element.

The standard covers directional phase, positive-sequence, negative-sequence, zero-sequence, and neutral overcurrent protection functions. It does not cover directional elements embedded in other protection functions such as distance protection or power protection.

Annex	What it covers
Annex A	Informative examples of directional characteristics
Annex B	Normative requirements for digitally interfaced directional overcurrent protection using IEC 61850
Annex C	Informative ramping methods for angular accuracy tests
Annex D	Normative calculation of mean, median, and mode
Annex E	Normative definition of fault inception angle

The document is organized into clauses for scope, normative references, terms, functional specification, performance specification, functional tests, and documentation requirements. In practice, that means it tells the manufacturer what to declare, how to test it, and what evidence to include in the type test report and technical documentation.

What are the key requirements of prEN IEC 60255-167:2026?

prEN IEC 60255-167:2026 requires the manufacturer to describe the function clearly, declare its performance, and support those claims with standardized tests. The clauses are written so that users can compare protection functions on the same basis and understand how the directional element behaves in real faults.

Functional description and declared behaviour

Clause 4 requires a functional block diagram of the implemented directional overcurrent protection function. The manufacturer must describe the input energizing quantities, the polarizing quantities and operating quantities used by the directional element, any binary input signals, binary output signals, and any additional influencing functions or conditions.

This matters because directional overcurrent protection depends on how the relay derives fault direction. Clause 4.2 allows different combinations of currents and voltages, including neutral current, memory quantities, and compensation methods, so the user must know exactly what the product uses. Clause 4.3 also makes clear that any blocking or control input must be described and must meet timing requirements in the actual application.

Clause 4.7 requires the manufacturer to state the instrument transformer or merging unit constraints that affect performance, including accuracy class, connection, earthing, and relevant settings. It also asks for declared effects from capacitor voltage transformer response and current transformer saturation, which are practical issues in substation and feeder protection.

Performance declarations

Clause 5 requires the manufacturer to declare effective and operating ranges, angular accuracy, reset hysteresis where applicable, operate time, disengage time, and dynamic performance. The effective range is where the accuracy requirements are met; the operating range is wider and covers the intended operating region.

This matters because a relay may work outside its most accurate range, but the user needs to know where the declared accuracy applies. Clause 5.2 also expects declaration of behaviour at high fault current conditions, so the user can judge whether the relay remains suitable during severe faults.

Clause 5.3 requires declaration of the angular accuracy of the directional element, and if relevant, its angular reset hysteresis. Clause 5.4 and 5.5 require declared operate time and disengage time. Clause 5.6 addresses dynamic performance, including prefault load, fault resistance, evolving faults, and current reversal.

Testing and reporting

Clause 6 defines the functional tests used to verify the claims in Clause 5. The angular accuracy and reset hysteresis tests use ramp methods, and Annex C explains the supported ramping approaches. The operate time and disengage time tests use repeated injections and require the results to be reported as complete test data plus typical values.

This matters in practice because the standard does not rely on a single test point. It asks for repeated measurements, so users see the spread of response times and can judge consistency, not just a best case result.

Clause 6.5 adds dynamic performance tests based on a two-source equivalent network. It covers prefault load, fault resistance, evolving faults, and current reversal, which are common situations where directional supervision can be challenged. Annex E gives the fault inception angle definition used for these tests.

Clause 7 requires the type test report to include the equipment under test, test equipment, block diagram, energizing quantities, polarizing and operating quantities, additional features, test methods and settings, complete test results, and the final claims with pass/fail conclusions. It also requires the user-facing technical documentation to carry the same claims and core descriptions.

What terms does prEN IEC 60255-167:2026 define?

• Directional overcurrent protection - protection that operates only for a fault in one direction from the installation point, and only when current exceeds a set value for a given time.
• Operating quantity - the electric quantity whose phase angle is compared with the polarizing quantity to determine fault direction.
• Polarizing quantity - the electric quantity that provides the angular reference for directional decision.
• Characteristic angle - the angle between operating quantity and polarizing quantity where the directional element is most sensitive.
• Effective range - the range of an input or characteristic quantity where the accuracy requirements are met.
• Angular reset hysteresis - the angle difference between the operate value and the reset value of the directional element.
• GOOSE - Generic Object Oriented System Event, used in Annex B for digital outputs over IEC 61850.
• SV - Sampled Values, used in Annex B as the digital input stream carrying analogue measurements.

Who uses prEN IEC 60255-167:2026?

prEN IEC 60255-167:2026 is used by protection relay manufacturers, digital protection system designers, test laboratories, utility protection engineers, and technical buyers who need to specify or verify directional overcurrent protection. It is also relevant to quality managers and certification teams that review type test reports and technical documentation.

In practice, users apply it when designing relays, choosing test methods, comparing declared performance, and checking how a protection function behaves with instrument transformers, merging units, or IEC 61850 digital interfaces. It is especially relevant for transmission and distribution protection, including systems with solidly earthed, impedance earthed, resonant earthed, or isolated neutral arrangements.

What changed in prEN IEC 60255-167:2026 from the previous edition?

prEN IEC 60255-167:2026 partially replaces IEC 60255-12:1980. The foreword states these main technical changes:

• the document applies only to the directional overcurrent protection function;
• the operating quantity and polarizing quantity of the directional element are defined;
• the operating characteristic, performance, and corresponding test methods are specified in detail;
• digitally interfaced directional overcurrent protection is included.

Which standards are used with prEN IEC 60255-167:2026?

• IEC 60255-1 - gives the common requirements for measuring relays and protection equipment.
• IEC 60255-151 - covers the over/under current element that forms the overcurrent part of the function.
• IEC TS 60255-216-1:2025 - sets the general requirements and tests for protection functions using digital communication as input and output.
• IEC 61850-7-1, IEC 61850-7-4, IEC 61850-8-1, IEC 61850-9-2, and IEC/IEEE 61850-9-3 - provide the communication framework, logical node structure, service mapping, sampled values, and time synchronization used in Annex B.
• IEC 61869-9 and IEC 61869-13 - cover digital interfaces for instrument transformers and stand-alone merging units.

What does the prEN IEC 60255-167:2026 document contain?

The document contains tables for designations, settings, test results, performance declarations, IEC 61850 settings, and reporting formats. It also includes a functional block diagram example, directional characteristic examples, test sequence figures, and network models for dynamic performance testing.

Annex C describes three angular-accuracy ramping methods: pseudo-continuous ramp, ramp of shots, and ramp of shots with a binary search algorithm. Annex D gives the statistical rules for mean, median, and mode, which are used when summarizing repeated operate or disengage time results.

The dynamic test section uses a two-source equivalent network with specified source and line models, defined fault locations, fault types, and fault inception angles. Annex E defines that angle relative to the nearest preceding positive-going zero-crossing, which matters when test results are compared across different systems and fault conditions.

For digitally interfaced functions, Annex B adds SV and GOOSE-based requirements, digital performance checks, and IEC 61850-based settings. That annex is the part to read when the relay takes measurements and sends trip signals over a digital network rather than through conventional analogue wiring.

SLOVENSKI STANDARD
01-oktober-2026
Merilni releji in zaščitna oprema - 167. del: Funkcionalne zahteve za smerno
nadtokovno zaščito
Measuring relays and protection equipment - Part 167: Functional requirements for
directional overcurrent protection
Relais de mesure et dispositifs de protection - Partie 167: Exigences fonctionnelles pour
la protection directionnelle de surintensité
Ta slovenski standard je istoveten z: prEN IEC 60255-167:2026
ICS:
29.120.70 Releji Relays
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

95/644/CDV
COMMITTEE DRAFT FOR VOTE (CDV)
PROJECT NUMBER:
IEC 60255-167 ED1
DATE OF CIRCULATION: CLOSING DATE FOR VOTING:
2026-08-28 2026-11-20
SUPERSEDES DOCUMENTS:
95/610/CD, 95/643/CC
IEC TC 95 : MEASURING RELAYS AND PROTECTION EQUIPMENT
SECRETARIAT: SECRETARY:
France Mr Thierry BARDOU
OF INTEREST TO THE FOLLOWING COMMITTEES: HORIZONTAL FUNCTION(S):

TC 8,TC 13,TC 57
ASPECTS CONCERNED:
Electricity transmission and distribution,Energy Efficiency
SUBMITTED FOR CENELEC PARALLEL VOTING NOT SUBMITTED FOR CENELEC PARALLEL VOTING
Attention IEC-CENELEC parallel voting
The attention of IEC National Committees, members of
CENELEC, is drawn to the fact that this Committee Draft
for Vote (CDV) is submitted for parallel voting.
The CENELEC members are invited to vote through the
CENELEC online voting system.
This document is still under study and subject to change. It should not be used for reference purposes.
Recipients of this document are invited to submit, with their comments, notification of any relevant patent rights of
which they are aware and to provide supporting documentation.
Recipients of this document are invited to submit, with their comments, notification of any relevant “In Some
Countries” clauses to be included should this proposal proceed. Recipients are reminded that the CDV stage is the
final stage for submitting ISC clauses. (SEE AC/22/2007 OR NEW GUIDANCE DOC).

TITLE:
Measuring relays and protection equipment - Part 167: Functional requirements for directional
overcurrent protection
PROPOSED STABILITY DATE: 2032
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IEC CDV 60255-167 © IEC 2026
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IEC CDV 60255-167 © IEC 2026
CONTENTS
CONTENTS . 3
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 10
2 Normative references . 10
3 Terms, definitions and abbreviations . 11
3.1 Terms and definitions. 11
3.2 Symbols and abbreviated terms . 14
4 Specification of directional overcurrent protection function . 15
4.1 General . 15
4.2 Input energizing quantities . 15
4.2.1 General . 15
4.2.2 Connections . 16
4.2.3 Polarizing quantities and operating quantities of directional element . 16
4.3 Binary input signals. 17
4.4 Functional logic . 17
4.4.1 Directional element . 17
4.4.2 Operating logic . 19
4.5 Binary output signals . 19
4.5.1 General . 19
4.5.2 Start (pickup) signals . 19
4.5.3 Operate (trip) signals . 19
4.5.4 Other output signals . 20
4.6 Additional influencing functions and conditions . 20
4.6.1 General . 20
4.6.2 Input energizing quantity failure . 20
4.6.3 Load encroachment . 20
4.7 Instrument transformer requirements . 21
5 Performance specification . 21
5.1 General . 21
5.2 Effective and operating ranges. 21
5.3 Accuracy related to directional element . 22
5.4 Operate time of directional element . 22
5.5 Disengage time of directional element . 22
5.6 Dynamic performance . 22
5.6.1 General . 22
5.6.2 Typical operate time of directional element . 23
5.6.3 Impacts of prefault load and fault resistance . 23
5.6.4 Evolving faults . 23
5.6.5 Current reversal condition . 23
6 Functional tests . 23
6.1 General . 23
6.1.1 Purpose of the tests. 23
6.1.2 Injection of input energizing quantities . 24
6.1.3 Binary outputs to be monitored . 25
6.1.4 Test Settings and configuration . 25
IEC CDV 60255-167 © IEC 2026
6.1.5 Test methods and procedures . 25
6.2 Determination of accuracy related to directional element . 25
6.2.1 General . 25
6.2.2 Angular accuracy of directional element . 26
6.2.3 Reset hysteresis of directional element . 2
6.3 Determination of operate time of directional element . 6
6.4 Determination of disengage time of directional element . 9
6.5 Dynamic performance tests . 12
6.5.1 General . 12
6.5.2 Determination of typical operate time . 14
6.5.3 Impacts of prefault load and fault resistance . 17
6.5.4 Evolving fault tests . 21
6.5.5 Current reversal tests . 22
7 Documentation requirements . 24
7.1 Type test report . 24
7.2 Technical documentation . 24
Annex A (informative) Examples of directional characteristics of directional
overcurrent protection functions. 25
Annex B (normative) Requirements for a directional overcurrent protection function
using digital communication as inputs and outputs. 27
B.1 General . 27
B.2 Requirements . 27
B.2.1 General requirements for digitally interfaced directional overcurrent
protection functions . 27
B.2.2 Specific requirements for digitally interfaced directional overcurrent
protection functions . 28
B.3 Performance requirements . 31
B.4 Functional tests . 31
B.4.1 Injection of input energizing quantities . 31
B.4.2 Tests for nominal conditions of digitally interfaced protection functions. 31
B.4.3 Performance under abnormal SV and GOOSE . 32
B.5 IEC 61850 based settings . 34
Annex C (informative) Ramping methods for testing the angular accuracy . 36
C.1 General . 36
C.2 Pseudo-continuous ramp . 36
C.3 Ramp of shots. 38
C.4 Ramp of shots with binary search algorithm . 40
Annex D (normative) Calculation of mean, median and mode. 43
D.1 Mean . 43
D.2 Median . 43
D.3 Mode . 43
D.4 Example . 43
Annex E (normative) Definition of fault inception angle . 44
Bibliography . 46

Figure 1 – An example of simplified protection functional block diagram . 15
Figure 2 – Example of operating characteristic for a directional element . 18
Figure 3 – Phase angle ramp of operating quantity for angular accuracy test of
directional element . 27
IEC CDV 60255-167 © IEC 2026
Figure 4 – Example test sequence for angular accuracy of directional element . 28
Figure 5 – Phase angle ramp of operating quantity for reset hysteresis test of
directional element . 2
Figure 6 – Example test sequence for reset hysteresis of directional element . 3
Figure 7 – Example test sequence for operate time of directional element . 7
Figure 8 – Example test sequence for Disengage time of directional element. 10
Figure 9 – Single line, double-infeed system . 12
Figure 10 – Double lines, double-infeed system . 13
Figure 11 – Example test sequence for typical operate time . 16
Figure 12 – Fault resistance of phase-to-earth fault . 17
Figure 13 – Fault resistance of phase-to-phase fault . 18
Figure 14 – Fault resistances of phase-to-phase-to-earth fault . 18
Figure 15 – Three-phase fault . 18
Figure 16 – Example test sequence for impacts of prefault load and fault resistance . 19
Figure C.1 – Pseudo-continuous ramp showing phase angle step change and the time
step 37
Figure C.2 – Ramp of shots showing phase angle step change and the time step . 40
Figure C.3 – Ramp of shots with binary search algorithm . 42
Figure E.1 – Graphical definition of fault inception angle . 44

Table 1 – Directional overcurrent protection designations . 10
Table 2 – Example of effective and operating ranges of directional overcurrent
protection function . 21
Table 3 – Settings associated with the directional element for type tests . 26
Table 4 – Operate angle of directional element . 1
Table 5 – Angular accuracy of directional element . 2
Table 6 – Reset angle of directional element . 5
Table 7 – Angular reset hysteresis of directional element. 6
Table 8 – Injected quantities for operate time test . 6
Table 9 – Operate time test results of directional element . 8
Table 10 – Typical operate time for directional element . 9
Table 11 – Injected quantities for disengage time test . 9
Table 12 – Disengage time test results of directional element . 11
Table 13 – Typical disengage time of directional element . 12
Table 14 – Operate time of directional element . 17
Table 15 – Test cases for impacts of prefault load and fault resistance . 19
Table 16 – Test report for impacts of prefault load and fault resistance . 21
Table 17 – Evolving faults at the same fault location . 21
Table 18 – Evolving faults at different locations . 22
Table 19 – Test report for evolving fault tests . 22
Table 20 – Current reversal tests . 23
Table 21 – Test report for current reversal tests. 23
Table A.1 – Examples of directional characteristic . 25
Table B.1 – Requirements for digitally interfaced functions . 27
IEC CDV 60255-167 © IEC 2026
Table B.2 – Specification of the expected behaviour of the directional overcurrent
protection function receiving abnormal SV as energizing quantities . 30
Table B.3 – Performance requirements for digitally interfaced directional overcurrent
protection functions . 31
Table B.4 – Rated primary quantities to be used for functional test of digitally
interfaced directional overcurrent protection functions . 31
Table B.5 – Test requirements for abnormal GOOSE and SV conditions for digitally
interfaced directional overcurrent protection functions . 32
Table B.6 – Test results for abnormal GOOSE and SV conditions for digitally interfaced
directional overcurrent protection functions . 33
Table B.7 – IEC 61850 settings for directional overcurrent protection . 34
Table E.1 – Fault type and reference voltage . 44

IEC CDV 60255-167 © IEC 2026
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Measuring relays and protection equipment -
Part 167: Functional requirements for directional overcurrent protection

FOREWORD
The International Electrotechnical Commission (IEC) is a worldwide organization for
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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.
IEC draws attention to the possibility that the implementation of this document may involve the
use of (a) patent(s). IEC takes no position concerning the evidence, validity or applicability of
any claimed patent rights in respect thereof. As of the date of publication of this document, IEC
had not received notice of (a) patent(s), which may be required to implement this document.
However, implementers are cautioned that this may not represent the latest information, which
IEC CDV 60255-167 © IEC 2026
may be obtained from the patent database available at https://patents.iec.ch. IEC shall not be
held responsible for identifying any or all such patent rights.
IEC 60255-167 has been prepared by IEC technical committee 95: Measuring relays and
protection equipment. It is an International Standard.
This document partially replaces the standard IEC 60255-12:1980 [1] (Directional relays and
power relays with two input energizing quantities) published in 1980. This edition constitutes a
technical revision for the directional overcurrent protection function.
This edition includes the following significant technical changes with respect to the previous
edition:
a) this document is applicable to the directional overcurrent protection function only.
b) operating quantity and polarizing quantity of the directional element are defined.
c) the operating characteristic, the performance of the directional overcurrent protection
function and corresponding test methods are specified in detail.
d) digitally interfaced directional overcurrent protection function is included.
The text of this International Standard is based on the following documents:
Draft Report on voting
95/XX/FDIS 95/XX/RVD
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 International Standard 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.
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, or
• revised.
IEC CDV 60255-167 © IEC 2026
INTRODUCTION
This document is part of the IEC 60255-1xx series of functional standards, which functionally
describes protection functions and provides a framework for testing and assessing the
performance of protection functions. It defines various technical features for protection function
whose performance is declared, as well as the corresponding requirements for testing and
reporting the performance.
For the standardized definitions of a protection function technical feature (such as operate time
or start time) and for the standardized testing methods to evaluate it (e.g., test methods for
assessing accuracy using pseudo-continuous ramp or ramp of shots), Clause 5 defines the
standardized technical features of the protection function. Clause 6 and the related annexes
detail how the performance of this technical feature is tested, evaluated, and reported.
In cases where a protection function technical feature is standardized but lacks a standardized
testing method (for example, effective range , operating range , or the procedure to determine
accuracy), Clause 5 defines the technical feature and requires the manufacturer to provide a
report on the performance of this technical feature in a standardized format.
When neither a standardized definition of the technical feature nor a standardized testing
method exists but the document needs to address a particular behaviour or application, Clause
4 offers a general description of the topic. In such cases, the manufacturer is required to provide
a declaration explaining how they address the topic. This is a requirement in a broad sense.
All the declarations and test results from Clause 5 and Clause 6 are expected to be part of the
protection function type tests according to this document. Declarations from Clause 4 are
expected to be included in technical manuals or any other relevant technical documents related
to the protection function. A note in the type test report, confirming that these declarations have
been addressed, is also expected to be available.
Clause 7 provides a comprehensive list of the declarations and tests that are to be included in
the type test report.
Overall, the presence of the term "shall" throughout the document indicates a requirement.
While these requirements do not always relate strictly to the performance, they ensure
transparency and consistency in testing and reporting the functionality. The p erformance
measurement methods specified in this document reflect international consensus and provide
a consistent framework for protection function testing and evaluation throughout the industry.
The mention of "minimum requirements" in this document refers to the standardized technical
features as well as performance measurement methods where consensus has been reached
on their definitions. Protection functions can have additional proprietary technical features not
covered in this document, but their performance is also part of the product’s type tests. As such,
at a minimum, a type test report for the protection function specified in this document is
expected to provide the information to support and validate the declarations.
This document focuses on the directional overcurrent protection function, which is a
combination of a directional element and an overcurrent element. This standard defines the
specific performance characteristics, requirements and testing methods for the directional
element. The requirements and testing methods for the overcurrent element are already
specified in IEC 60255-151. Therefore, full compliance with IEC 60255-151 is a prerequisite for
evaluating the overcurrent element as part of a directional overcurrent protection function.
Users of this document are expected to refer to IEC 60255-151 for the overcurrent element
aspects, making both documents necessary for complete application of the function.
IEC CDV 60255-167 © IEC 2026
1 Scope
This part of IEC 60255 specifies the minimum requirements for functional and performance
evaluation of an a.c. directional overcurrent protection function. This document also defines
how to document and publish performance test results.
The directional overcurrent protection function comprises an overcurrent element combined
with a directional element. The directional element supervises the operation of the overcurrent
element based on the direction of the fault current. This document specifies the requirements
that apply to the directional element, and refers to IEC 60255-151where relevant to the
overcurrent element. This document defines factors that influence the accuracy and dynamic
performance of the directional overcurrent protection function. The test methods for verifying
the declared performance are also included in this document.
This document covers directional phase, positive-sequence, negative-sequence, zero-
sequence, and neutral overcurrent protection functions, as listed in Table 1. Annex A provides
commonly used operating characteristics of these functions.
Table 1 – Directional overcurrent protection designations
Protection function IEEE/ANSI C37.2-2022 [2] IEC 61850-7-
4:2010/AMD1:2020
Applicable Function Numbers
Applicable Logical
Nodes
Directional phase overcurrent protection 67
a
Directional positive-sequence overcurrent 67
PTOC
protection
a
RDIR+PTOC
Directional negative-sequence overcurrent
protection
Directional zero-sequence overcurrent protection 67N a
PTOC
Directional neutral overcurrent protection 67G
a
RDIR+PTOC
ab
PSDE
a
The direction information of protection Logical Nodes can be available in Data Attribute 'dirGeneral' of its Data
Object 'Str', 'Dir' or 'Op'.
b
The Logical Node PSDE can be used for directional earth fault protection in resonant earthed (neutral) system
and isolated neutral system.
Additional restraint or blocking elements may be part of the directional overcurrent protection
function. This document does not specify the functional description of these additional restraint
or blocking elements.
This document does not cover directional elements integrated into other protection functions,
such as distance protection and power protection.
The general requirements for measuring relays and protection equipment are defined in IEC
60255-1. For digitally interfaced directional overcurrent functions via IEC 61850, Annex B
contains the associated requirements based on IEC TS 60255-216-1:2025.
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 CDV 60255-167 © IEC 2026
IEC 60255-1, Measuring relays and protection equipment - Part 1: Common requirements
IEC 60255-151:2009, Measuring relays and protection equipment - Part 151: Functional
requirements for over/under current protection
IEC 60255-151, Measuring relays and protection equipment - Part 151: Functional requirements
for over/under current protection
IEC TS 60255-216-1:2025, Measuring relays and protection equipment - Part 216-1: Digital
Interface - General Requirements and Tests for Protection Functions using digital
communication as input and output
IEC 61850-7-1:2011/AMD1:2020, Communication networks and systems for power utility
automation - Part 7-1: Basic communication structure - Principles and models
IEC 61850-7-4:2010/AMD1:2020, Communication networks and systems for power utility
automation - Part 7-4: Basic communication structure - Compatible logical node classes and
data object classes
IEC 61850-8-1:2011/AMD1:2020, 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, 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 61869-9:2016, Instrument transformers - Part 9: Digital interface for instrument
transformers
IEC 61869-9, Instrument transformers - Part 9: Digital interface for instrument transformers
IEC 61869-13, Instrument transformers - Part 13: Stand-alone merging unit (SAMU)
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions 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
directional overcurrent protection
protection designed to operate only for a fault located in one direction from the installation point,
and when the current as an energizing quantity exceeds a predetermined value for a given time
IEC CDV 60255-167 © IEC 2026
3.1.2
characteristic quantity
electric quantity, or one of its parameters, the name of which characterizes a protection function
and the value of which are the subject of accuracy requirement
[SOURCE: IEC 60050-447:2020 [3], 447-07-01, modified — "measuring relay or protection
equipment" has been replaced with "protection function", and the original examples have been
deleted.]
3.1.3
operating range
interval for which the measuring relay or
protection equipment under specified conditions is able to perform its intended function(s) in
accordance with the specified requirements
Note 1 to entry: When accuracy requirements have to be met, see "effective range (3.1.4) ".
[SOURCE: IEC 60050-447:2020 [3], 447-03-16]
3.1.4
effective range
interval of an input energizing quantity or a characteristic quantity (3.1.2) within which the
accuracy requirements are met
[SOURCE: IEC 60050-447:2020 [3], 447-07-08]
3.1.5
rated value
value of a quantity used for specification purposes, established for a specified set of operating
conditions of a component, device, equipment, or system
[SOURCE: IEC 60050-151:2001 [4] , 151-16-08]
3.1.6
operating quantity
electric quantity, the phase angle of which with respect to the polarizing
quantity (3.1.7) is recognized by the directional element to determine the fault direction
3.1.7
polarizing quantity
electric quantity that provides an angular reference to the directional element to determine the
fault direction
3.1.8
characteristic angle
maximum sensitivity angle
φ
RCA
angle between the phasor representing operating quantity (3.1.6) and the phasor representing
polarizing quantity (3.1.7) at which the directional element achieves maximum sensitivity
3.1.9
operate value
value of the characteristic quantity (3.1.2) at which a protection
function operates
IEC CDV 60255-167 © IEC 2026
[SOURCE: IEC 60050-447:2020 [3], 447-02-10, modified — "measuring relay or protection
equipment" has been replaced with "protection function", and the original figure has been
deleted.]
3.1.10
reset value
value of the characteristic quantity (3.1.2) at which a protection function resets
[SOURCE: IEC 60050-447:2020 [3], 447-02-12, modified — "measuring relay or protection
equipment" has been replaced with "protection function", and the original figure has been
deleted.]
3.1.11
angular reset hysteresis
absolute value of the angle difference between a reset value (3.1.10) and an operate value
(3.1.9) of directional element
3.1.12
zero-sequence current
one of the three symmetrical sequence components which exists
only in an unsymmetrical three-phase system of sinusoidal quantities and which is defined by
the following complex mathematical expression:
𝐼 = (𝐼 + 𝐼 + 𝐼 )
0 𝐿1 𝐿2 𝐿3
where I , I and I are the complex expressions of the phase current phasors
L1 L2 L3
[SOURCE: IEC 60050-448:1995 [5], 448-11-29, modified — "component" has been replaced
with "current" in term and its definition.]
3.1.13
zero-sequence voltage
one of the three symmetrical sequence components which exists
only in an unsymmetrical three-phase system of sinusoidal quantities and which is defined by
the following complex mathematical expression:
𝑈 = (𝑈 + 𝑈 + 𝑈 )
0 𝐿1 𝐿2 𝐿3
where U , U and U are the complex expressions of the phase voltage phasors
L1 L2 L3
[SOURCE: IEC 60050-448:1995 [5], 448-11-29, modified — "component" has been replaced
with "voltage" in term and its definition.]
3.1.14
neutral current
electric current in the neutral conductor of a polyphase line
[SOURCE: IEC 60050-141:2004 [6], 141-03-05]
3.1.15
neutral overcurrent protection
ground overcurrent protection (US)
overcurrent protection in the earthing connection of the neutral of transformers, reactors or
generators
[SOURCE: IEC 60050-448:1995 [5], 448-14-30, modified — "current protection" has been
replaced with "overcurrent protection " in term and its definition.]
IEC CDV 60255-167 © IEC 2026
3.2 Symbols and abbreviated terms
CT Current Transformer
DG Distributed Generation; Dispersed Generation
I Positive-sequence current
I Negative-sequence current
I zero-sequence current
I Feeder zero sequence current , from busbar to a feeder
0feeder
IED Intelligent Electronic Device
Phase currents
I , I , I
L1 L2 L3
I neutral current, from a neutral-to-earth path CT
neu
G Measured value of the characteristic quantity of overcurrent element
GOOSE Generic Object Oriented System Event
G Setting value (start value) of the characteristic quantity of overcurrent element
S
L-E Phase-to-earth Fault
L-L-E Phase-to-phase-to-earth Fault
RMS Root Mean Square
SAMU Stand- Alone Merging Unit
S operating quantity of directional element
OPD
S Minimum magnitude of the operating quantity required for fault direction
OPD_min
determination
S polarizing quantity of directional element
POL
S Minimum magnitude of the polarizing quantity required for fault direction
POL_min
determination
SV Sampled Values
U Positive-sequence voltage
U Negative-sequence voltage
U , zero-sequence voltage
U , U , Positive-sequence voltages (referenced to each phase-to-earth voltage
1(L1) 1(L2)
respectively), or the memory prefault phase-to-earth voltages
U
1(L3)
U , U , U Phase-to-earth voltages
L1 L2 L3
Phase-to-phase voltages
U , U ,
L1 L2 L2 L3
U
L3 L1
VT Voltage Transformer
VTS Voltage Transformer Signal Supervision
σ Declared accuracy of comparator limit angle
φ
φ Comparator limit angle for forward direction, which defines the forward operate
B
boundary of directional element
φ Comparator limit angle for reverse direction, which defines the reverse operate
BR
boundary of directional element
φ Phase angle of operating quantity
OPD
φ characteristic angle
RCA
IEC CDV 60255-167 © IEC 2026
4 Specification of directional overcurrent protection function
4.1 General
Clause 4 lists the minimum features that shall be described in the product documentation of the
directional overcurrent protection function.
The manufacturer shall provide the functional block diagram of the directional overcurrent
protection function implemented. An example of the expected functional block diagram is shown
in Figure 1.
Figure 1 – An example of simplified protection functional block diagram
The overcurrent element is covered by IEC 60255-151. The requirements for the directional
element is specified in this document.
According to the algorithm implemented by the manufacturer, additional features should be
described in the product documentation.
4.2 Input energizing quantities
4.2.1 General
The product documentation shall state the type of input energizing quantities used by the
directional overcurrent protection function. For example:
– single or three-phase current(s): I (, I , I );
L1 L2 L3
– neutral current, from a neutral-to-earth path CT: I ;
neu
– zero-sequence current (I );
– single or three phase-to-earth voltage(s): U (,U , U );
L1 L2 L3
– multiple phase-to-phase voltage(s): U , U , U ;
L1 L2 L2 L3 L3 L1
– zero-sequence voltage(U ) .
Ratings and relevant requirements for input energizing quantities are specified in IEC 60255 -1.
Input energizing quantities can be presented to the directional overcurrent protection either
hardwired from instrument transformers or transmitted as data received over communication
ports using a data communication protocol, such as IEC 61850-9-2 or, more specifically, IEC
61869-9, which is a profile of IEC 61850-9-2. In the latter case, the directional overcurrent
IEC CDV 60255-167 © IEC 2026
protection function is considered as digitally interfaced function. Annex B provides requirements
for a directional overcurrent protection function using IEC 61850 signals as inputs and outputs.
4.
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