Measuring relays and protection equipment - Part 149: Functional requirements for thermal electrical relays

IEC 60255-149:2013 specifies minimum requirements for thermal protection relays. This standard includes specification of the protection function, measurement characteristics and test methodologies. The object is to establish a common and reproducible reference for evaluating dependent time relays which protect equipment from thermal damage by measuring a.c. current flowing through the equipment. Complementary input energizing quantities such as ambient, coolant, top oil and winding temperature may be applicable for the thermal protection specification set forth in this standard. This standard covers protection relays based on a thermal model with memory function.

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

La CEI 60255-149:2013 spécifie les exigences minimales relatives aux relais de protection thermique. Cette norme inclut la spécification de la fonction de protection, les caractéristiques de mesure et les méthodes d'essais. L'objet est d'établir une référence commune et reproductible pour des relais à temps dépendant qui protègent un dispositif contre les détériorations thermiques par la mesure du courant alternatif circulant dans le dispositif. Des grandeurs d'alimentation d'entrée complémentaire, telles que la mesure de la température ambiante, du liquide de refroidissement, de l'huile isolante, des enroulements, peuvent être applicables pour la spécification de protection thermique définie dans la présente norme. La présente norme couvre les relais de protection basés sur un modèle thermique à fonction de mémoire.

General Information

Status
Published
Publication Date
29-Jul-2013
Current Stage
PPUB - Publication issued
Start Date
30-Jul-2013
Completion Date
30-Jul-2013
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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
IEC 60255-149:2013
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
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

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 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

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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

to the ambient temperature (T ) ............................................................................................ 40

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– 4 – 60255-149 © IEC:2013
INTERNATIONAL ELECTROTECHNICAL COMMISSION
______________
MEASURING RELAYS AND PROTECTION EQUIPMENT –
Part 149: Functional requirements for thermal electrical relays
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

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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 60255-149 has been prepared by IEC technical committee 95:

Measuring relays and protection equipment.
This first edition cancels and replaces IEC 60255-8, published in 1990.
The text of this standard is based on the following documents:
FDIS Report on voting
95/313/FDIS 95/317/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.

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60255-149 © IEC:2013 – 5 –

A list of all parts of IEC 60255 series, under the general title Measuring relays and protection

equipment, can be found on the IEC website.

Future standards in this series will carry the new general title as cited above. Titles of existing

standards in this series will be updated at the time of the next edition.

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.
---------------------- Page: 7 ----------------------
– 6 – 60255-149 © IEC:2013
MEASURING RELAYS AND PROTECTION EQUIPMENT –
Part 149: Functional requirements for thermal electrical relays
1 Scope

This part of the IEC 60255 series specifies minimum requirements for thermal protection

relays. This standard includes specification of the protection function, measurement

characteristics and test methodologies.

The object of this standard is to establish a common and reproducible reference for evaluating

dependent time relays which protect equipment from thermal damage by measuring a.c.

current flowing through the equipment. Complementary input energizing quantities such as

ambient, coolant, top oil and winding temperature may be applicable for the thermal protection

specification set forth in this standard. This standard covers protection relays based on a

thermal model with memory function.

The test methodologies for verifying performance characteristics of the thermal protection

function and accuracy are also included in this Standard.

This standard does not intend to cover the thermal overload protection trip classes indicated

in IEC 60947-4-1 and IEC 60947-4-2, related to electromechanical and electronic protection

devices for low voltage motor-starters.
The thermal protection functions covered by this standard are as follows:
Protection function IEC 61850-7-4 IEEE C37.2
PTTR
Thermal overload protection 49
Rotor thermal overload protection PROL 49R
Stator thermal overload protection PSOL 49S

General requirements for measuring relays and protection equipment are specified in

IEC 60255-1.
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.
IEC 60050 (all parts), International Electrotechnical Vocabulary (available at
http://www.electropedia.org)
IEC 60085, Electrical insulation – Thermal evaluation and designation

IEC 60255-1, Measuring relays and protection equipment – Part 1: Common requirements

IEC 61850-7-4, Communication networks and systems for power utility automation – Part 7-4:

Basic communication structure – Compatible logical node classes and data classes
---------------------- Page: 8 ----------------------
60255-149 © IEC:2013 – 7 –
3 Terms and definitions

For the purpose of this document, the terms and definitions given in IEC 60050-447, as well

as the following apply.
3.1
hot curve

for a thermal electrical relay with a total memory function, characteristic curve representing

the relationship between specified operating time and current, taking into account thermal

effect of a specified steady-state load current before the overload occurs

Note 1 to entry: Hot curve is a plot of a particular time-current solution for a first-order thermal system differential

equation, assuming a specific constant overload current and a specific preload current.

3.2
cold curve

for a thermal electrical relay, characteristic curve representing the relationship between

specified operating time and current, with the relay at reference and steady-state conditions

with no-load current flowing before the overload occurs

Note 1 to entry: Cold curve is a plot of a particular time-current solution for a first-order thermal system

differential equation, assuming a specific constant overload current when there is no preload.

3.3
basic current

specified limiting (nominal) value of the current for which the relay is required not to operate

at steady-state conditions of the equipment to be thermally protected

Note 1 to entry: The basic current serves as a reference for the definition of the operational characteristics of

thermal electrical relays. The basic settings of a thermal electrical protection function are made in terms of this

basic current (I ) and the thermal time constant (τ) of the protected equipment.
3.4
equivalent heating current

current which takes into account the additional heating sources such as imbalance currents

and/or harmonics
3.5
factor k

factor by which the basic current (I ) is multiplied to obtain the maximum permissible

continuous operating current value of the equipment to be thermally protected, which is used

in the thermal characteristic function

Note 1 to entry: The factor k indicates the maximum permissible constant between phase current (full load) and

the basic (nominal) current of the protected equipment.
3.6
previous load ratio

ratio of the load current preceding the overload to basic current under specified conditions

3.7
reference limiting error
limiting error determined under reference conditions
[SOURCE: IEC 60050:2010, 447-08-07]
---------------------- Page: 9 ----------------------
– 8 – 60255-149 © IEC:2013
3.8
temperature rise

difference between the temperature of the part under consideration and a reference

temperature

Note 1 to entry: The reference temperature may be for example the ambient air temperature or the temperature of

a cooling fluid.
[SOURCE: IEC 60050:2001, 151-16-26]
3.9
thermal equilibrium

thermal state reached when the temperature rise of the several parts of the machine do not

vary by more than a gradient of 2 K per hour
[SOURCE: IEC 60050:1996, 411-51-08]
3.10
thermal time constant

time required for the temperature rise of the protected equipment relative to its initial

temperature, to reach 63,2 % of its final, asymptotic value following a step increase in current

Note 1 to entry: The initial temperature for example can be ambient temperature.
3.11
thermal level

ratio expressed in percentage between the estimated actual temperature of the equipment

and the temperature of the equipment when the equipment is operating at its maximum

current (k × I ) for a long period, enough to allow equipment to reach its thermal equilibrium

4 Specification of the function
4.1 General

An example of a thermal protection function with its input energizing quantities, binary input

signals, operate (trip), alarm and other binary outputs, and functional logic which includes

measuring element, thermal level calculation, settings, and thresholds are shown in Figure 1.

The manufacturer shall provide the functional block diagram of the specific thermal protection

implementation.
---------------------- Page: 10 ----------------------
60255-149 © IEC:2013 – 9 –
Thermal protection functional logic
Thresholds
Operate (trip)
Settings
(trip, alarm) signal
Input
Energizing
Measuring
energizing
quantities
quantites element
(signal
(equivalent
processing)
heating
current)
Thermal
Alarm (pre-
operate) signal
level
calculation
Ambient / winding
To other
temperature
protection
measuring
functions
Binary
(option)
input
signals
Other binary
The exact and complete contents of this functional logic block diagram area
output signals
depends upon the implementation
IEC 1846/13
Figure 1 – Simplified thermal protection function block diagram
4.2 Input energizing quantities/energizing quantities

The input energizing quantities are the measuring signals, such as phase (or line) currents,

and ambient/environmental or winding temperatures (if required or applicable). Their ratings

and relevant requirements are specified in IEC 60255-1.

Input energizing quantities can be presented to the thermal protection functional logic either

hardwired from current transformers and any additional input quantities such as ambient or

winding temperature, or as a data packet over a communication ports using an appropriate

data communication protocol, such as IEC 61850-9-2.

The input energizing quantities used by the thermal protection function need not be the

current directly taken from the secondary side of the current transformers. Therefore the

protection relay documentation shall state the type of energizing quantities used by the

thermal protection function.
Examples of input energizing quantities are:
– single-phase current measurement;
– three-phase current measurement;
– positive and negative sequence current measurement;
– winding or ambient temperature sensor.

NOTE The ambient temperature, coolant temperature, top oil temperature or winding temperature of the

equipment to be thermally protected can be measured by temperature sensors, such as resistance temperature

detector (RTD), the values of which can be used for biasing the calculation of the thermal level replica specified in

this standard. Output signals or values of these temperature sensors can be taken into account for the first-order

thermal model algorithm, which can influence and compensate the calculated thermal level (based on the

equivalent heating current and heating thermal time constant values).
4.3 Binary input signals

If any binary input signals (externally or internally driven) are used, their influence on the

thermal protection function shall be clearly described on the functional logic diagram or in the

protective device manufacturer documentation. Additional textual description may also be

provided if this can further clarify the functionality of the input signals and their intended

application or implementation.
---------------------- Page: 11 ----------------------
– 10 – 60255-149 © IEC:2013

Binary input signals to this function may emanate from a number of different sources.

Examples include:
• traditionally wired to physical inputs;
• via a communications port from external devices;

• via internal logical connections from other functional elements within the relay.

The method of receiving the signal is largely irrelevant except to conform to operational

requirements.

Definitions, ratings and standards for physical binary input signals are specified in

IEC 60255-1.

The following are examples of binary input signal application in thermal protection.

1) When the thermal protection function is imp
...

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