A method of temperature-rise verification of low-voltage switchgear and controlgear assemblies by calculation

IEC TR 60890:2014 specifies a method of temperature-rise verification of low-voltage switchgear and controlgear ASSEMBLIES by calculation. The method is applicable to enclosed ASSEMBLIES or partitioned sections of ASSEMBLIES without forced ventilation. It is not applicable where temperature rise verification to the relevant product standard of the IEC 61439 series has been established. This second edition cancels and replaces the first edition published in 1987 and its Amendment 1:1995. It constitutes a technical revision. This edition includes the following significant technical changes with respect to the last edition:
- alignment with IEC 61439-1:2011;
- revision of Annex B;
- general editorial review.

Méthode de vérification par calcul des échauffements pour les ensembles d'appareillage à basse tension

L'IEC TR 60890:2014 décrit une méthode de vérification par calcul des échauffements pour les ENSEMBLES d'appareillage à basse tension. La méthode est applicable aux ENSEMBLES sous enveloppe ou aux sections compartimentées des ENSEMBLES sans ventilation forcée. Elle n'est pas applicable lorsque la vérification de l'échauffement a été réalisée conformément à la norme produit de la série IEC 61439. Cette deuxième édition annule et remplace la première édition parue en 1987 et son Amendement 1:1995. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à la dernière édition:
- harmonisation avec l'IEC 61439-1:2011;
- révision de l'Annexe B;
- revue éditoriale générale.

General Information

Status
Published
Publication Date
06-May-2014
Current Stage
PPUB - Publication issued
Start Date
07-May-2014
Completion Date
07-May-2014
Ref Project

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IEC TR 60890
Edition 2.0 2014-05
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
A method of temperature-rise verification of low-voltage switchgear and
controlgear assemblies by calculation
Méthode de vérification par calcul des échauffements pour les ensembles
d’appareillage à basse tension
IEC TR 60890:2014-05(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TR 60890
Edition 2.0 2014-05
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
A method of temperature-rise verification of low-voltage switchgear and
controlgear assemblies by calculation
Méthode de vérification par calcul des échauffements pour les ensembles
d’appareillage à basse tension
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX V
ICS 29.130.20 ISBN 978-2-8322-1566-1

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 – IEC TR 60890:2014 © IEC 2014
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 7

3 Terms and definitions ...................................................................................................... 7

4 Conditions for application ................................................................................................ 7

5 Calculation ...................................................................................................................... 8

5.1 Necessary information ............................................................................................ 8

5.2 Calculation procedure ............................................................................................. 8

5.2.1 General ........................................................................................................... 8

5.2.2 Determination of the effective cooling surface A of the enclosure ................... 8

5.2.3 Determination of the internal temperature rise ∆t of the air at mid-
0,5

height of the enclosure .................................................................................... 8

5.2.4 Determination of the internal temperature rise ∆t of air at the top of
1,0

the enclosure ................................................................................................... 9

5.2.5 Characteristic curve for temperature rise of air inside enclosure ...................... 9

6 Evaluation of the design ................................................................................................ 11

Annex A (informative) Examples for the calculation of the temperature-rise of air

inside the enclosures ..................................................................................................... 20

A.1 Example 1 ............................................................................................................. 20

A.2 Example 2 ............................................................................................................. 23

Annex B (informative) Operating current and power losses of conductors ............................ 27

Bibliography .......................................................................................................................... 32

Figure 1 – Temperature-rise characteristic curve for enclosures with

A exceeding 1,25 m ........................................................................................................... 10

Figure 2 – Temperature-rise characteristic curve for enclosures with A

not exceeding 1,25 m .......................................................................................................... 10

Figure 3 – Enclosure constant k for enclosures without ventilation openings, with an

effective cooling surface A > 1,25 m ................................................................................... 13

Figure 4 – Temperature distribution factor c for enclosures without ventilation openings

and with an effective cooling surface A > 1,25 m ............................................................... 14

Figure 5 – Enclosure constant k for enclosures with ventilation openings and an

effective cooling surface A > 1,25 m .................................................................................. 15

Figure 6 – Temperature distribution factor c for enclosures with ventilation openings

and an effective cooling surface A > 1,25 m ...................................................................... 16

Figure 7 – Enclosure constant k for enclosures without ventilation openings and with

an effective cooling surface A ≤ 1,25 m ............................................................................. 17

Figure 8 – Temperature distribution factor c for enclosures without ventilation openings

and with an effective cooling surface A ≤ 1,25 m ............................................................... 18

Figure 9 – Calculation of temperature rise of air inside enclosures ........................................ 19

Figure A.1 – Example 1, calculation for an enclosure with exposed side faces without

ventilation openings and without internal horizontal partitions ............................................... 20

Figure A.2 – Example 1, calculation for a single enclosure .................................................... 22

Figure A.3 – Example 2, calculation for an enclosure for wall-mounting with ventilation

openings ............................................................................................................................... 23

---------------------- Page: 4 ----------------------
IEC TR 60890:2014 © IEC 2014 – 3 –

Figure A.4 – Example 2, calculation for one enclosure half ................................................... 24

Figure A.5 – Example 2, calculation for an enclosure for wall-mounting with ventilation

openings ............................................................................................................................... 26

Table 1 – Method of calculation, application, formulae and characteristics ............................ 11

Table 2 – Symbols, units and designations ........................................................................... 12

Table 3 – Surface factor b according to the type of installation .............................................. 12

Table 4 – Factor d for enclosures without ventilation openings and with an effective

cooling surface A >1,25 m .................................................................................................. 12

Table 5 – Factor d for enclosures with ventilation openings and an effective cooling

surface A >1,25 m .............................................................................................................. 12

Table B.1 – Operating current and power loss of single-core copper cables with a

permissible conductor temperature of 70 °C (ambient temperature inside the

enclosure: 55 °C) .................................................................................................................. 28

Table B.2 – Reduction factor k for cables with a permissible conductor temperature

of 70 °C (extract from IEC 60364-5-52:2009, Table B.52-14) ................................................ 29

Table B.3 – Operating current and power loss of bare copper bars with rectangular

cross-section, run horizontally and arranged with their largest face vertical (ambient

temperature inside the enclosure: 55 °C, temperature of the conductor 70 °C) ...................... 30

Table B.4 – Factor k for different temperatures of the air inside the enclosure and/or

for the conductors ................................................................................................................. 31

---------------------- Page: 5 ----------------------
– 4 – IEC TR 60890:2014 © IEC 2014
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
A METHOD OF TEMPERATURE-RISE VERIFICATION OF LOW-VOLTAGE
SWITCHGEAR AND CONTROLGEAR ASSEMBLIES BY CALCULATION
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

this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,

Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC

Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested

in the subject dealt with may participate in this preparatory work. International, governmental and non-

governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely

with the International Organization for Standardization (ISO) in accordance with conditions determined by

agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence

between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

the latter.

5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

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.

The main task of IEC technical committees is to prepare International Standards. However, a

technical committee may propose the publication of a technical report when it has collected

data of a different kind from that which is normally published as an International Standard, for

example "state of the art".

IEC/TR 60890, which is a technical report, has been prepared by subcommittee 17D: Low-

voltage switchgear and controlgear assemblies, of IEC technical committee 17: Switchgear

and controlgear.

This second edition cancels and replaces the first edition published in 1987 and its

Amendment 1:1995. It constitutes a technical revision.

This edition includes the following significant technical changes with respect to the last

edition:
– alignment with IEC 61439-1:2011;
– revision of Annex B;
– general editorial review.
---------------------- Page: 6 ----------------------
IEC TR 60890:2014 © IEC 2014 – 5 –
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
17D/490/DTR 17D/499/RVC

Full information on the voting for the approval of this technical report 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.

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.
---------------------- Page: 7 ----------------------
– 6 – IEC TR 60890:2014 © IEC 2014
INTRODUCTION

In IEC 61439-1, in the series of design verifications, a temperature-rise verification of low-

voltage power switchgear and controlgear assemblies (hereafter called ASSEMBLIES) is

specified. This may be by test, however, alternatives are acceptable in defined circumstances.

Selection of the method used for temperature rise verification is the responsibility of the

original manufacturer. Where applicable this technical report may also be used for

temperature rise verification of similar products in accordance with other standards. The

factors and coefficients, set out in this report have been derived from measurements on

numerous ASSEMBLIES and the method has been verified by comparison with test results.

---------------------- Page: 8 ----------------------
IEC TR 60890:2014 © IEC 2014 – 7 –
A METHOD OF TEMPERATURE-RISE VERIFICATION OF LOW-VOLTAGE
SWITCHGEAR AND CONTROLGEAR ASSEMBLIES BY CALCULATION
1 Scope

This Technical Report specifies a method of temperature-rise verification of low-voltage

switchgear and controlgear ASSEMBLIES by calculation.

The method is applicable to enclosed ASSEMBLIES or partitioned sections of ASSEMBLIES

without forced ventilation. It is not applicable where temperature rise verification to the

relevant product standard of the IEC 61439 series has been established

NOTE 1 The influence of the materials and wall thicknesses usually used for enclosures can have some effect on

the steady state temperatures. However, the generalised approach used in this technical report ensures it is

applicable to enclosures made of sheet steel, sheet aluminium, cast iron, insulating material and the like.

The proposed method is intended to determine the temperature rise of the air inside the

enclosure.

NOTE 2 The air temperature within the enclosure is equal to the ambient air temperature outside the enclosure

plus the temperature rise of the air inside the enclosure caused by the power losses of the installed equipment.

Unless otherwise specified, the ambient air temperature outside the ASSEMBLY is the air temperature indicated for

the installation (average value over 24 h) of 35 °C. If the ambient air temperature outside the ASSEMBLY at the

place of use exceeds 35 °C, this higher temperature is deemed to be the ambient air temperature.

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 61439-1:2011, Low-voltage switchgear and controlgear assemblies – Part 1: General

rules
3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 61439-1 apply.

4 Conditions for application

This method of calculation is only applicable if the following conditions are fulfilled:

– the power loss data for all built in components is available;

– there is an approximately even distribution of power losses inside the enclosure;

– the installed equipment is so arranged that air circulation is not significantly impeded;

– the equipment installed is designed for direct current or alternating current up to and

including 60 Hz with the total of supply currents not exceeding 3 150 A;

– conductors carrying currents in excess of 200 A, and the adjacent structural parts are so

arranged that eddy-current and hysteresis losses are minimised;

– for enclosures with natural ventilation, the cross-section of the air outlet openings is at

least 1,1 times the cross-section of the air inlet openings;
---------------------- Page: 9 ----------------------
– 8 – IEC TR 60890:2014 © IEC 2014

– there are no more than three horizontal partitions in the ASSEMBLY or in a section of it;

– where enclosures with external ventilation openings have compartments, the surface of

the ventilation openings in each horizontal partition shall be at least 50 % of the horizontal

cross-section of the compartment.
5 Calculation
5.1 Necessary information

The following data is needed to calculate the temperature rise of the air inside an enclosure:

– dimensions of the enclosure: height/width/depth;
– the type of installation of the enclosure according to Figure 4;
– design of enclosure, i.e. with or without ventilation openings;
– number of internal horizontal partitions;
– effective power loss of equipment installed in the enclosure;
– effective power losses (P ) of conductors according to Annex B.

NOTE The effective power losses of the equipment installed in the circuits of the ASSEMBLY used for this

calculation are the power losses at the rated currents of the various circuits.
5.2 Calculation procedure
5.2.1 General

For the enclosures specified in columns 4 and 5 of Table 1, the calculation of the temperature

rise of the air inside the enclosures is carried out using the formulae laid down in columns 1 to

3 of Table 1.

The pertinent factors and exponents (characteristics) are obtained from columns 6 to 10 of

Table 1.
The symbols, units and designations are to be taken from Table 2.

For enclosures having more than one section with vertical partitions the temperature rise of

the air inside the enclosure shall be determined separately for each section.

Where enclosures without vertical partitions or individual sections have an effective cooling

surface greater than 11,5 m or a width greater than about 1,5 m, they should be divided for

the calculation into fictitious sections, whose dimensions approximate to the foregoing values.

NOTE The form (see Figure 9) can be used as a calculation aid.
5.2.2 Determination of the effective cooling surface A of the enclosure
The calculation is carried out according to Formula (1) in column 1 of Table 1.

The effective cooling surface A of an enclosure is the sum of the individual surfaces A

e o

multiplied by the surface factor b. This factor takes into account the heat dissipation of the

individual surfaces according to the type of installation of the enclosure.

5.2.3 Determination of the internal temperature rise ∆t of the air at mid-height of

0,5
the enclosure
The calculation is carried out according to Formula (2) in column 2 of Table 1.
---------------------- Page: 10 ----------------------
IEC TR 60890:2014 © IEC 2014 – 9 –

In Formula (2) the enclosure constant k allows for the size of the effective cooling surface for

enclosures without ventilation openings and, in addition, for the cross-section of the air inlet

openings for enclosures with ventilation openings.

The dependence of the temperature rises occurring in the enclosure on the effective power

loss P is expressed by the exponent x.

The factor d allows for the dependence of the temperature rise on the number of internal

horizontal partitions.
5.2.4 Determination of the internal temperature rise ∆t of air at the top of the
1,0
enclosure
The calculation is made according to Formula (3) in column 3 of Table 1.

Factor c allows for the temperature distribution inside an enclosure. Its determination varies

with the design and installation of the ASSEMBLY as follows:
The factor c from Figure 4, depends on the
a) For enclosures without ventilation

openings and with an effective cooling type of installation and the height/base factor

surface: f, where:
1,35
A > 1,25 m

b) For enclosures with ventilation openings The factor c from Figure 6, depends on the

and with an effective cooling surface:
cross-section of air inlet openings and the
height/base factor f, where:
1,35
A > 1,25 m

c) For enclosures without ventilation The factor c from Figure 8, depends on the

openings and with an effective cooling height/width factor g, where:
surface:
A ≤ 1,25 m g=
where
h is the enclosure height, in m;
A is the surface area of the enclosure base, in m ;
w is the enclosure width, in m.
5.2.5 Characteristic curve for temperature rise of air inside enclosure
5.2.5.1 General

To evaluate the design according to Clause 6, it is necessary to apply the calculated results of

5.2.3 and 5.2.4 with the proper characteristic curve for temperature rise of air inside the

enclosure as a function of the enclosure height. The air temperatures within horizontal levels

are practically constant.
5.2.5.2 Temperature-rise characteristic curve for enclosures with an effective
cooling surface A exceeding 1,25 m

As a general rule, the characteristic curve of temperature rise is adequately well defined by a

straight line which runs through the points ∆t and ∆t (see Figure 1).
1,0 0,5
---------------------- Page: 11 ----------------------
– 10 – IEC TR 60890:2014 © IEC 2014

The internal air temperature rise at the bottom of the enclosure is close to zero, i.e. the

characteristic curve flattens out towards zero. In practice, the dotted part of the characteristic

curve is of secondary importance.
IEC 1428/14
Figure 1 – Temperature-rise characteristic curve
for enclosures with A exceeding 1,25 m
5.2.5.3 Temperature rise characteristic curve for enclosures with an effective
cooling surface A not exceeding 1,25 m

For this type of enclosure, the maximum temperature rise in the upper quarter is constant and

the values for ∆t and ∆t are identical (see Figure 2).
1,0 0,75

The characteristic curve is obtained by connecting the temperature-rise values at an

enclosure level of 0,75 and 0,5 (see Figure 2).

The internal air temperature rise at the bottom of the enclosure is close to zero, i.e. the

characteristic curve flattens out towards zero. In practice, the dotted part of the characteristic

curve is of secondary importance.
IEC 1429/14
Figure 2 – Temperature-rise characteristic curve
for enclosures with A not exceeding 1,25 m
---------------------- Page: 12 ----------------------
IEC TR 60890:2014 © IEC 2014 – 11 –
6 Evaluation of the design

It shall be determined whether the equipment within the ASSEMBLY can operate satisfactorily at the relevant calculated temperature rise.

If it is not so, the parameters will have to be changed and the calculation repeated.

Table 1 – Method of calculation, application, formulae and characteristics
1 2 3 4 5 6 7 8 9 10 11
Calculation formulae Enclosure Characteristics Characteristic curve
Temperature rise of air Factors Exponent
Plotting of
Effective cooling Effective cooling
temperature-rise
At mid-height of At (int
...

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