IEC 60255-149:2013

IEC 60255-149 ®
Edition 1.0 2013-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Measuring relays and protection equipment –
Part 149: Functional requirements for thermal electrical relays

Relais de mesure et dispositifs de protection –
Partie 149: Exigences fonctionnelles pour relais électriques thermiques

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IEC 60255-149 ®
Edition 1.0 2013-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Measuring relays and protection equipment –

Part 149: Functional requirements for thermal electrical relays

Relais de mesure et dispositifs de protection –

Partie 149: Exigences fonctionnelles pour relais électriques thermiques

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX X
ICS 29.120.70 ISBN 978-2-8322-1005-5

– 2 – 60255-149 © IEC:2013
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Specification of the function . 8
4.1 General . 8
4.2 Input energizing quantities/energizing quantities . 9
4.3 Binary input signals . 9
4.4 Functional logic . 10
4.4.1 Equivalent heating current . 10
4.4.2 Basic (setting) and operating current values for thermal protection . 10
4.4.3 Thermal level calculation . 11
4.4.4 Time-current limit characteristic equations and curves . 12
4.4.5 Thermal level alarm threshold . 14
4.5 Binary output signals . 15
4.5.1 General . 15
4.5.2 Operate (trip) output signal . 15
4.5.3 Alarm signal . 15
4.5.4 Other binary output signals . 15
4.6 Additional influencing factors on thermal protection . 16
4.6.1 General . 16
4.6.2 Influence of ambient temperature on thermal protection . 16
4.6.3 Thermal reset facilities . 16
4.7 Behaviour of thermal protective device during auxiliary power supply failure . 17
5 Performance specification . 17
5.1 Accuracy related to the characteristic quantity . 17
5.2 Accuracy related to the operate time . 17
5.3 Performance during frequency variations . 18
6 Functional test methodology . 18
6.1 General . 18
6.2 Determination of steady-state errors related to the operating current value . 19
6.3 Determination of steady-state errors related to the characteristic quantity and
the operate time . 19
6.3.1 Accuracy determination of the cold curve . 19
6.3.2 Accuracy determination of the hot curves . 20
6.4 Performance with specific cooling thermal time constant . 21
6.5 Performance with harmonics . 22
6.6 Performance during frequency variations . 22
6.7 Performance during different ambient temperatures . 23
7 Documentation requirements . 24
7.1 Type test report . 24
7.2 Other user documentation . 24
Annex A (informative) Simple first-order thermal model of electrical equipment. 26
Annex B (informative) Thermal electrical relays which use temperature as setting
parameters . 41
Bibliography . 46

60255-149 © IEC:2013 – 3 –
Figure 1 – Simplified thermal protection function block diagram . 9
Figure 2 – Typical examples of characteristic curves for cold state of a first-order
thermal system with no previous load before overload occurs . 13
Figure 3 – Typical examples of characteristic curves for hot states of a first-order
thermal system for different values of previous load before overload occurs . 14
Figure A.1 – An electrical equipment to be thermally protected represented as a
simple first-order thermal system . 26
Figure A.2 – Equivalence between a first-order thermal system and an electric parallel
RC circuit . 30
Figure A.3 – Analogue thermal circuit representation of a simple first-order thermal
system . 31
Figure A.4 – Analogue thermal circuit representation of a simple first-order thermal
system – motor starting condition . 31
Figure A.5 – Analogue thermal circuit representation of a simple first-order thermal
system – motor stopped condition . 31
Figure A.6 – Dynamic step response of a simple first-order thermal system algorithm to
a current below pickup . 33
Figure A.7 – Dynamic step response of a first-order thermal system (cold initial state) . 34
Figure A.8 – Dynamic step response of a first-order thermal system (hot initial state) . 34
Figure A.9 – Dynamic step response of a first-order thermal system to a load current
followed by an overload current (initial state: cold) . 35
Figure A.10 – Dynamic step response of a first-order thermal system to a load current
followed by an overload current (initial state: hot) . 35

Table 1 – Limiting error as multiples of assigned error . 18
Table 2 – Test points of the cold curve . 20
Table 3 – Test points of the hot curve . 21
Table 4 – Test points of the cold curve with harmonics . 22
Table 5 – Test points of the cold curve during frequency variations . 22
Table A.1 – Thermal and electrical models . 30
Table A.2 – Thermal insulation classes and maximum temperatures, according to
IEC 60085. 40
Table A.3 – Example of correction factor values (F ) for class F equipment according
a
to the ambient temperature (T ) . 40
a
– 4 – 60255-149 © IEC:2013
INTERNATIONAL ELECTROTECHNICAL COMMISSION
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MEASURING RELAYS AND PRO
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