EN 60255-121:2014
(Main)Measuring relays and protection equipment - Part 121: Functional requirements for distance protection
Measuring relays and protection equipment - Part 121: Functional requirements for distance protection
IEC 60255-121:2014 specifies minimum requirements for functional and performance evaluation of distance protection function typically used in, but not limited to, line applications for effectively earthed, three-phase power systems. This standard also defines how to document and publish performance tests. This standard covers distance protection function whose operating characteristic can be defined on an impedance plane and includes specification of the protection function, measurement characteristics, phase selection, directionality, starting and time delay characteristics. The test methodologies for verifying performance characteristics and accuracy are included in this standard. The standard defines the influencing factors that affect the accuracy under steady state conditions and performance characteristics during dynamic conditions. It also includes the instrument transformer requirements for the protection function. The general requirements for measuring relays and protection equipment are defined in IEC 60255-1.
Messrelais und Schutzeinrichtungen - Teil 121: Funktionsanforderungen für den Distanzschutz
Relais de mesure et dispositifs de protection - Partie 121: Exigences fonctionnelles pour protection de distance
L'IEC 60255-121:2014 spécifie les exigences minimales relatives à l'évaluation fonctionnelle et à l'évaluation des performances de la fonction de protection de distance typiquement utilisée, sans s'y limiter à des applications de lignes dans des systèmes électriques triphasés avec mise à la terre directe. La présente norme définit également comment documenter et éditer des essais de qualification. La présente norme couvre la fonction de protection de distance dont la caractéristique de fonctionnement peut être définie sur un plan d'impédance et inclut la spécification de la fonction de protection, les caractéristiques de mesure, la sélection de phase, la directionnalité, les caractéristiques de démarrage et de temporisation. Les méthodologies d'essai pour vérifier les caractéristiques de performance et de précision sont incluses dans la présente norme. La norme définit les facteurs d'influence qui affectent la précision dans des conditions de régime établi et les caractéristiques de performance pendant des conditions dynamiques. Pour la fonction de protection, elle inclut aussi les exigences relatives aux transformateurs de mesure. Les exigences générales relatives aux relais de mesure et aux équipements de protection sont définies dans la norme CEI 60255-1.
Merilni releji in zaščitna oprema - 121. del: Funkcijske zahteve za daljinsko zaščito (IEC 60255-121:2014)
Standard EN IEC 60255-121 določa minimalne zahteve za ocenjevanje funkcij in delovanja daljinske zaščitne funkcije, ki se med drugim običajno uporablja za žice v učinkovito ozemljenih trifaznih napajalnih sistemih. Ta standard določa tudi, kako dokumentirati in objaviti preskuse delovanja. Ta standard zajema daljinsko zaščitno funkcijo, pri kateri so lahko lastnosti delovanja določene na impedančni ravnini, in vključuje določanje funkcije zaščite, značilnosti merjenja, izbiro faze, usmerjenost ter značilnosti vklopa in časovne zakasnitve. V tem standardu so zajete tudi preskusne metodologije za preverjanje lastnosti delovanja in točnosti. Standard določa dejavnike, ki vplivajo na točnost pri ustaljenih pogojih in lastnosti delovanja pri dinamičnih pogojih. Prav tako vključuje zahteve za instrumentne transformatorje za zaščitno funkcijo.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-september-2014
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Measuring relays and protection equipment - Part 121: Functional requirements for
distance protection
/
Relais de mesure et dispositifs de protection - Partie 121: Exigences fonctionnelles pour
protections de distance
Ta slovenski standard je istoveten z: EN 60255-121:2014
ICS:
29.120.70 Releji Relays
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EUROPEAN STANDARD EN 60255-121
NORME EUROPÉENNE
EUROPÄISCHE NORM
July 2014
ICS 29.120.70
English Version
Measuring relays and protection equipment - Part 121:
Functional requirements for distance protection
(IEC 60255-121:2014)
Relais de mesure et dispositifs de protection - Partie 121: Messrelais und Schutzeinrichtungen - Teil 121:
Exigences fonctionnelles pour protection de distance Funktionsanforderungen für den Distanzschutz
(CEI 60255-121:2014) (IEC 60255-121:2014)
This European Standard was approved by CENELEC on 2014-04-11. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2014 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 60255-121:2014 E
Foreword
The text of document 95/319/FDIS, future edition 1 of IEC 60255-121, prepared by IEC/TC 95
"Measuring relays and protection equipment" was submitted to the IEC-CENELEC parallel vote and
approved by CENELEC as EN 60255-121:2014.
The following dates are fixed:
– latest date by which the document has to be implemented at (dop) 2015-01-11
national level by publication of an identical national
standard or by endorsement
– latest date by which the national standards conflicting with (dow) 2017-04-11
the document have to be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such
patent rights.
Endorsement notice
The text of the International Standard IEC 60255-121:2014 was approved by CENELEC as a
European Standard without any modification.
- 3 - EN 60255-121:2014
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
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.
NOTE 1 When an International Publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available here:
www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60050 series International electrotechnical vocabulary - -
IEC 60255-1 - Measuring relays and protection equipment EN 60255-1 -
-- Part 1: Common requirements
IEC 61850 series Communication networks and systems for EN 61850 series
power utility automation
IEC 61869-2 2012 Instrument transformers -- Part 2: EN 61869-2 2012
Additional requirements for current
transformers
IEC 61869-5 2011 Instrument transformers -- Part 5: EN 61869-5 2011
Additional requirements for capacitor
voltage transformers
IEC 60255-121 ®
Edition 1.0 2014-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Measuring relays and protection equipment –
Part 121: Functional requirements for distance protection
Relais de mesure et dispositifs de protection –
Partie 121: Exigences fonctionnelles pour protection de distance
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XG
ICS 29.120.70 ISBN 978-2-8322-1399-5
– 2 – IEC 60255-121:2014 © IEC 2014
CONTENTS
FOREWORD . 9
1 Scope . 11
2 Normative references . 11
3 Terms and definitions . 12
4 Specification of the function . 13
4.1 General . 13
4.2 Input energizing quantities/energizing quantities . 13
4.3 Binary input signals . 14
4.4 Functional logic . 15
4.4.1 Faulted phase identification . 15
4.4.2 Directional signals . 15
4.4.3 Distance protection function characteristics . 15
4.4.4 Distance protection zone timers . 16
4.5 Binary output signals . 16
4.5.1 General . 16
4.5.2 Start (pickup) signals . 16
4.5.3 Operate signals . 17
4.5.4 Other binary output signals . 17
4.6 Additional influencing functions/conditions . 17
4.6.1 General . 17
4.6.2 Inrush current . 17
4.6.3 Switch onto fault/trip on reclose . 17
4.6.4 Voltage transformer (VT) signal failure (loss of voltage) . 17
4.6.5 Power swings . 18
4.6.6 Behavior during frequencies outside of the operating range . 18
5 Performance specifications . 18
5.1 General . 18
5.2 Effective and operating ranges . 18
5.3 Basic characteristic accuracy under steady state conditions . 19
5.3.1 General . 19
5.3.2 Determination of accuracy related to time delay setting . 19
5.3.3 Disengaging time . 20
5.4 Dynamic performance . 20
5.4.1 General . 20
5.4.2 Transient overreach (TO) . 20
5.4.3 Operate time and transient overreach (SIR diagrams) . 21
5.4.4 Operate time and transient overreach (CVT-SIR diagrams). . 21
5.4.5 Typical operate time . 21
5.5 Performance with harmonics . 22
5.5.1 General . 22
5.5.2 Steady-state harmonics tests . 23
5.5.3 Transient LC oscillation tests . 23
5.6 Performance during frequency deviation . 23
5.6.1 General . 23
5.6.2 Steady state testing during frequency deviation . 23
5.6.3 Transient testing during frequency deviation . 23
5.7 Double infeed tests . 24
IEC 60255-121:2014 © IEC 2014 – 3 –
5.7.1 General . 24
5.7.2 Single line, double infeed system . 24
5.7.3 Double line, double infeed system . 24
5.8 Instrument transformer (CT, VT and CVT) requirements . 25
5.8.1 General . 25
5.8.2 CT requirements . 25
6 Functional tests . 29
6.1 General . 29
6.2 Rated frequency characteristic accuracy tests . 29
6.2.1 General . 29
6.2.2 Basic characteristic accuracy under steady state conditions . 30
6.2.3 Basic directional accuracy under steady state conditions . 43
6.2.4 Determination of accuracy related to time delay setting . 48
6.2.5 Determination and reporting of the disengaging time . 48
6.3 Dynamic performance . 50
6.3.1 General . 50
6.3.2 Dynamic performance: operate time and transient overreach
(SIR diagrams) . 51
6.3.3 Dynamic performance: operate time and transient overreach
(CVT-SIR diagrams) . 61
6.3.4 Dynamic performance: transient overreach tests. 65
6.3.5 Dynamic performance: typical operate time . 69
6.4 Performance with harmonics . 74
6.4.1 Steady state harmonics tests . 74
6.4.2 Transient oscillation tests (network simulation L-C) . 75
6.5 Performance during off-nominal frequency . 82
6.5.1 Steady state frequency deviation tests . 82
6.5.2 Transient frequency deviation tests . 85
6.6 Double infeed tests . 90
6.6.1 Double infeed tests for single line . 90
6.6.2 Double infeed tests for parallel lines (without mutual
inductance) . 96
6.6.3 Reporting of double infeed test results . 100
7 Documentation requirements . 101
7.1 Type test report . 101
7.2 Documentation . 101
Annex A (informative) Impedance characteristics . 102
A.1 Overview. 102
A.1.1 General . 102
A.1.2 Non-directional circular characteristic . 102
A.1.3 MHO characteristic . 102
A.1.4 Quadrilateral/polygonal . 104
A.2 Example characteristics . 106
A.2.1 General . 106
A.2.2 Non-directional circular characteristic (ohm) . 106
A.2.3 Reactive reach line characteristic . 106
A.2.4 MHO characteristic . 107
A.2.5 Resistive and reactive intersecting lines characteristic . 107
A.2.6 Offset MHO characteristic. . 108
– 4 – IEC 60255-121:2014 © IEC 2014
Annex B (informative) Informative guide for the behaviour of timers in distance
protection zones for evolving faults . 110
Annex C (normative) Setting example . 112
Annex D (normative) Calculation of mean, median and mode. 115
D.1 Mean . 115
D.2 Median . 115
D.3 Mode . 115
D.4 Example. 115
Annex E (informative) CT saturation and influence on the performance of distance
relays . 116
Annex F (informative) Informative guide for testing distance relays based on CT
requirements specification . 119
F.1 General . 119
F.2 Test data . 120
F.3 CT data and CT model . 121
Annex G (informative) Informative guide for dimensioning of CTs for distance
protection . 125
G.1 General . 125
G.2 Example 1 . 126
G.3 Example 2 . 128
Annex H (normative) Calculation of relay settings based on generic point P expressed
in terms of voltage and current. 131
H.1 Settings for quadrilateral/polygonal characteristic . 131
H.2 Settings for MHO characteristic . 133
Annex I (normative) Ramping methods for testing the basic characteristic accuracy . 134
I.1 Relationship between simulated fault impedance and analog quantities . 134
I.2 Pre-fault condition . 134
I.3 Phase to earth faults . 134
I.4 Phase to phase faults. . 136
I.5 Ramps in the impedance plane . 139
I.5.1 Pseudo-continuous ramp . 139
I.5.2 Ramp of shots . 140
Annex J (normative) Definition of fault inception angle . 143
Annex K (normative) Capacitive voltage instrument transformer model . 145
K.1 General . 145
K.2 Capacitor voltage transformer (CVT) . 145
Figure 1 – Simplified distance protection function block diagram . 14
Figure 2 – Basic accuracy specification of an operating characteristic . 19
Figure 3 – Basic angular accuracy specifications of directional lines . 20
Figure 4 – SIR diagram – Short line average operate time . 22
Figure 5 – Fault positions to be considered for specifying the CT requirements . 26
Figure 6 – Test procedure for basic characteristic accuracy . 31
Figure 7 – Calculated test points A, B and C based on the effective range of U and I . 32
Figure 8 – Modified points B’ and C’ based on the limited setting range . 32
Figure 9 – Position of test points A, B, C, D and E in the effective range of U and I . 33
Figure 10 – Position of test points A, B’, C’, D and E in the effective range of U and I . 33
IEC 60255-121:2014 © IEC 2014 – 5 –
Figure 11 – Quadrilateral characteristic showing ten test points . 34
Figure 12 – Quadrilateral characteristic showing test ramps. 35
Figure 13 – Quadrilateral characteristic showing accuracy limits . 36
Figure 14 – Quadrilateral/polygonal characteristic showing accuracy limits . 37
Figure 15 – MHO characteristic showing nine test points . 37
Figure 16 – MHO characteristic showing test ramps . 38
Figure 17 – Accuracy limits for MHO characteristic . 39
Figure 18 – Basic directional element accuracy tests . 44
Figure 19 – Directional element accuracy tests in the second quadrant. 45
Figure 20 – Directional element accuracy tests in the second quadrant. 46
Figure 21 – Directional element accuracy tests in the fourth quadrant . 46
Figure 22 – Directional test accuracy lines in the fourth quadrant . 47
Figure 23 – Position of the three-phase fault for testing the disengaging time . 49
Figure 24 – Sequence of events for testing the disengaging time . 50
Figure 25 – Power system network with zero load transfer . 51
Figure 26 – Dynamic performance: operate time and dynamic overreach (SIR diagram) . 55
Figure 27 – SIR diagram for short line: minimum operate time . 56
Figure 28 – SIR diagram for short line: average operate time . 57
Figure 29 – SIR diagram for short line: maximum operate time . 57
Figure 30 – Dynamic performance tests (SIR diagrams). 59
Figure 31 – SIR diagram for long line: minimum operate time . 61
Figure 32 – SIR diagram for long line: average operate time . 62
Figure 33 – SIR diagram for long line: maximum operate time . 62
Figure 34 – Dynamic performance: operate time and dynamic overreach (CVT-SIR
diagram) . 64
Figure 35 – CVT-SIR diagram for short line: minimum operate time . 66
Figure 36 – CVT-SIR diagram for short line: average operate time . 66
Figure 37 – CVT-SIR diagram for a short line: maximum operate time . 67
Figure 38 – Fault statistics for typical operate time . 70
Figure 39 – Frequency distribution of operate time . 73
Figure 40 – Ramping test for harmonics . 75
Figure 41 – Steady-state harmonics test . 77
Figure 42 – Simulated power system network . 78
Figure 43 – Flowchart of transient oscillation tests . 79
Figure 44 – Simulated voltages (U , U , U ) and currents (I , I , I ) . 81
L1 L2 L3 L1 L2 L3
Figure 45 – Transient oscillation tests – Operate time . 82
Figure 46 – Test points for quadrilateral characteristics . 83
Figure 47 – Test points for MHO characteristic . 83
Figure 48 – Test ramp direction for quadrilateral characteristic . 83
Figure 49 – Test ramp direction for MHO characteristic . 84
Figure 50 – Steady-state frequency deviation tests . 86
Figure 51 – Short line model for frequency deviation test . 87
Figure 52 – Flowchart of transient frequency deviation tests . 89
– 6 – IEC 60255-121:2014 © IEC 2014
Figure 53 – SIR diagrams for frequency deviation tests – average operate time . 90
Figure 54 – Network model for single line tests . 91
Figure 55 – Line to earth fault . 92
Figure 56 – Line to line fault . 92
Figure 57 – Line to line to earth fault . 92
Figure 58 – Three-phase fault . 93
Figure 59 – Network model for parallel lines tests . 98
Figure 60 – Network model for current reversal test . 99
Figure A.1 – Non-directional circular characteristic with directional supervision . 102
Figure A.2 – MHO characteristic . 103
Figure A.3 – Quadrilateral/polygonal characteristics . 104
Figure A.4 – Non-directional circular characteristic (ohm) . 106
Figure A.5 – Reactive reach line characteristic . 107
Figure A.6 – MHO characteristics . 107
Figure A.7 – Resistive and reactive intersecting lines characteristics . 108
Figure A.8 – Offset MHO . 108
Figure B.1 – The same fault type evolving from time delayed zone 3 (position 1) into
time delayed zone 2 (position 2) after 200 ms . 110
Figure B.2 – Phase to earth fault in time delayed zone 3 (position 1) evolving into
three-phase fault in the same zone (position 2) after 200 ms . 111
Figure C.1 – Setting example for a radial feeder . 112
Figure C.2 – Phase to earth fault (LN) . 113
Figure C.3 – Phase to phase fault (LL) . 114
Figure E.1 – Fault positions to be considered for specifying the CT requirements . 117
Figure F.1 – Fault positions to be considered . 119
Figure F.2 – Double source network . 120
Figure F.3 – Magnetization curve for the basic CT . 122
Figure F.4 – Secondary current at the limit of saturation caused by AC component with
no remanent flux in the CT . 123
Figure F.5 – Secondary current in case of maximum DC offset . 123
Figure G.1 – Distance relay example 1 . 126
Figure G.2 – Distance relay example 2 . 128
Figure H.1 – Quadrilateral/polygonal characteristic showing test point P on the reactive
reach line . 131
Figure H.2 – Quadrilateral distance protection function characteristic showing test
point P on the resistive reach line. . 132
Figure H.3 – MHO characteristic showing test point P . 133
Figure I.1 – Three-line diagram showing relay connections and L1N fault . 135
Figure I.2 – Voltage and current phasors for L1N fault . 135
Figure I.3 – Voltages and currents for L1N fault, constant fault current . 136
Figure I.4 – Voltages and currents for L1N fault, constant fault voltage . 136
Figure I.5 – Three-line diagram showing relay connections and L1L2 fault . 137
Figure I.6 – Voltage and current phasors for L1L2 fault . 138
Figure I.7 – Voltages and currents for L1L2 fault, constant fault current . 138
Figure I.8 – Voltages and currents for L1L2 fault, constant fault voltage . 139
IEC 60255-121:2014 © IEC 2014 – 7 –
Figure I.9 – Pseudo-continuous ramp distance relay characteristic on an impedance
plane . 140
Figure I.10 – Pseudo-continuous ramp showing impedance step change and the time step 140
Figure I.11 – Ramp of shots distance relay characteristic on an impedance plane . 141
Figure I.12 – Ramp of shots showing impedance step change and the time step . 142
Figure I.13 – Ramp of shots with binary search algorithm . 142
Figure J.1 – Graphical definition of fault inception angle . 143
Figure K.1 – CVT equivalent electrical circuit . 145
Figure K.2 – Transient response of the 50 Hz version of the CVT model . 147
Table 1 – Example of effective and operating ranges of distance protection . 18
Table 2 – Recommended levels of remanence in the optional cases when remanence
is considered . 27
Table 3 – Basic characteristic accuracy for various points (quadrilateral/polygonal) . 42
Table 4 – Overall basic characteristic accuracy (quadrilateral/polygonal) . 42
Table 5 – Basic characteristics accuracy for various points (MHO) . 42
Table 6 – Overall basic characteristic accuracy (MHO) . 42
Table 7 – Basic directional accuracy for various fault types . 47
Table 8 – Basic directional accuracy e . 47
α
X
Table 9 – Results of disengaging time for all the tests . 50
Table 10 – Short line SIR and source impedance for selected rated current and
frequency . 53
Table 11 – Short line SIR and source impedances for other rated current and
frequency . 54
Table 12 – Long line SIR and source impedances for selected rated current and
frequency . 59
Table 13 – Long line SIR and source impedances for other rated current and frequency . 60
Table 14 – Short line CVT-SIR source impedance. 63
Table 15 – Transient overreach table for short line . 68
Table 16 – Transient overreach table for long line. 68
Table 17 – Transient overreach table for short line with CVTs . 69
Table 18 – Typical operate time . 71
Table 19 – Typical operate time . 71
Table 20 – Typical operate time . 72
Table 21 – Typical operate time (mode, median, mean) . 73
Table 22 – Steady state harmonics test . 75
Table 23 – Capacitance values . 78
Table 24 – Quadrilateral/polygonal basic characteristic accuracy at f and f . 85
min max
Table 25 – MHO basic characteristic accuracy at f and f . 85
min max
Table 26 – Tests without pre-fault load . 94
Table 27 – Tests with pre-fault load . 95
Table 28 – Current reversal test . 98
Table 29 – Evolving faults (only one line affected) . 99
Table 30 – Evolving faults (both lines affected) . 100
Table 31 – Double infeed test results . 101
– 8 – IEC 60255-121:2014 © IEC 2014
Table F.1 – Magnetization curve data . 122
Table G.1 – Fault currents . 127
Table G.2 – Fault currents . 128
Table J.1 – Fault type and reference voltage . 144
Table K.1 – Parameter values for the 50 Hz version of the CVT model . 146
Table K.2 – Parameter values for the 60 Hz version of the CVT model . 146
IEC 60255-121:2014 © IEC 2014 – 9 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MEASURING RELAYS AND PROTECTION EQUIPMENT –
Part 121: Functional requirements for distance protection
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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8) 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.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60255-121 has been prepared by IEC technical committee 95:
Measuring relays and protection equipment.
This standard cancels and replaces IEC 60255-16.
The text of this standard is based on the following documents:
FDIS Report on voting
95/319/FDIS 95/321/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.
– 10 – IEC 60255-121:2014 © IEC 2014
A list of all parts in the IEC 60255 series, published under the general title Measuring relays
and protection equipment, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC 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.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
IEC 60255-121:2014 © IEC 2014 – 11 –
MEASURING RELAYS AND PROTECTION EQUIPMENT –
Part 121: Functional requirements for distance protection
1 Scope
This part of IEC 60255 specifies minimum requirements for functional and performance
evaluation of distance protection function typically used in, but not limited to, line applications
for effectively earthed, three-phase power systems. This standard also defines how to
document and publish performance tests.
This standard covers distance protection function whose operating characteristic can be
defined on an impedance plane and includes specification of the protection function,
measurement characteristics, phase selection, directionality, starting and time delay
characteristics.
The test methodologies for verifying performance characteristics and accuracy are included in
this standard. The standard defines the influencing factors that affect the accuracy under
steady state conditions and performance characteristics during dynamic conditions. It also
includes the instrument transformer requirements for the protection function.
The distance protection functions covered by this standard are as follows:
IEC 61850-7-4
IEEE/ANSI C37.2
Function numbers Logical nodes
Phase distance protection 21 PDIS
Earth (ground) distance protection 21G PDIS
This standard does not specify the functional description of additional features often
associated with digital distance relays such as power swing blocking (PSB), out of step
tripping (OST), voltage transformer (VT) supervision, switch onto fault (SOTF), trip on reclose
(TOR), the logic for cross country faults in not effectively earthed networks, and trip
conversion logic. Only their influence on the distance protection function is covered in this
standard. The protection of series-compensated lines is beyond the scop
...
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