Evaluation and qualification of electrical insulation systems

IEC 60505:2011 establishes the basis for estimating the ageing of electrical insulation systems (EIS) under conditions of either electrical, thermal, mechanical, environmental stresses or combinations of these (multifactor stresses). It specifies the principles and procedures that shall be followed, during the development of EIS functional test and evaluation procedures, to establish the estimated service life for a specific EIS. This standard should be used by all IEC technical committees responsible for equipment having an EIS. The contents of the corrigendum of March 2017 have been included in this copy.

Evaluation et qualification des systèmes d'isolation électrique

La CEI 60505:2011 établit les bases de l'estimation du vieillissement des systèmes d'isolation électrique (SIE) dans des conditions de contraintes électriques, thermiques, mécaniques, environnementales ou de combinaisons de ces contraintes (contraintes multifactorielles). Elle spécifie les principes et les procédures qui doivent être suivis, au cours du développement d'essais fonctionnels ou de procédures d'évaluation des SIE, pour établir la durée de vie estimée d'un SIE spécifique. Il convient que tous les comités d'études de la CEI responsables de matériels ayant un SIE utilisent la présente norme. Le contenu du corrigendum de mars 2017 a été pris en considération dans cet exemplaire.

Loading guide for dry-type power transformers

General Information

Status
Published
Publication Date
10-Jul-2011
Current Stage
PPUB - Publication issued
Start Date
11-Jul-2011
Completion Date
11-Jul-2011

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SLOVENSKI STANDARD
SIST IEC 60905:1997
01-oktober-1997
Loading guide for dry-type power transformers
Loading guide for dry-type power transformers
Guide de charge pour transformateurs de puissance du type sec
Ta slovenski standard je istoveten z: IEC 60505 Ed. 4.0
ICS:
29.180 Transformatorji. Dušilke Transformers. Reactors
SIST IEC 60905:1997 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST IEC 60905:1997
---------------------- Page: 2 ----------------------
SIST IEC 60905:1997
NORME
CEI
INTERNATIONALE IEC
905
INTERNATIONAL
Première
édition
STANDARD
First edition
1987
Le contenu du corrigendum d'avril 1991 a
été incorporé dans cette réimpression
The contents of the corrigendum of April 1991 has been included in this reprint
Guide de charge pour transformateurs
de puissance du type sec
Loading guide for dry-type power transformers
© CEI 1995 Droits de reproduction réservés — Copyright — all rights reserved

Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in

utilisée sous quelque forme que ce soit et par aucun pro- any form or by any means, electronic or mechanical,

cédé, électronique ou mécanique, y compris la photocopie et including photocopying and microfilm, without permission

les microfilms, sans l'accord écrit de l'éditeur. in writing from the publisher.

Bureau Central de la Commission Electrotechnique Internationale 3, rue de Varembé

Genève, Suisse
Commission Electrotechnique Internationale CODE PRIX
International Electrotechnical Commission PRICE CODE
IEC Mer+tgyuapoaHaa 3nelsrporexHH4ecnaa
HoMUCCUR
• Pour prix, voir
• catalogue en vigueur
For price, see current catalogue
---------------------- Page: 3 ----------------------
SIST IEC 60905:1997
— 3
905 © I E C 1987
CONTENTS
Page
FOREWORD 5
PREFACE 5
Clause
1. Scope 7
2. Object 7
3. Symbols 9
PART 1
4. Basis of guide
5. Algorithm for basic `use of life' calculations
6. Limitations 29
PART 2
29
7. Basis of establishing load curves
29
8. Selection of appropriate load curve with examples
---------------------- Page: 4 ----------------------
SIST IEC 60905:1997
905 ©IEC 1987 — 5 —
INTERNATIONAL ELECTROTECHNICAL COMMISSION
LOADING GUIDE
FOR DRY-TYPE POWER TRANSFORMERS
FOREWORD

1) The formal decisions or agreements of the I EC on technical matters, prepared by Technical Committees on which all the

National Committees having a special interest therein are represented, express, as nearly as possible, an international

consensus of opinion on the subjects dealt with.

2) They have the form of recommendations for international use and they are accepted by the National Committees in that

sense.

3) In order to promote international unification, the I E C expresses the wish that all National Committees should adopt the

text of the I E C recommendation for their national rules in so far as national conditions will permit. Any divergence

between the I E C recommendations and the corresponding national rules should, as far as possible, be clearly indicated in

the latter.
PREFACE

This guide has been prepared by IEC Technical Committee No. 14: Power transformers.

The text of this guide is based on the following documents:
Six Months' Rule Report on Voting
14(CO)60 14(CO)63

Full information on the voting for the approval of this guide can be found in the Voting Report

indicated in the above table.
The following 1 EC Publications are quoted in this guide:
Publications Nos. 76-1 (1976): Power transformers, Part 1: General.
726 (1982): Dry-type power transformers.
---------------------- Page: 5 ----------------------
SIST IEC 60905:1997
905 © I E C 1987 7
LOADING GUIDE
FOR DRY-TYPE POWER TRANSFORMERS
1. Scope

This guide is applicable to naturally cooled dry-type power transformers complying with

IEC Publication 726 and operated within the limitations referred to in Clause 6. Six different

insulation systems are taken into account, identified by their system temperatures.

Because there are numerous combinations of different insulation systems and constructions

it is possible to make loading recommendations only of a general nature. For this reason the

guide is in two parts:

— the first part makes no loading recommendations, but gives the method of calculating

loading conditions when the variable parameters are known as the result of prototype

testing of a particular construction and/or insulation system. The calculations are given in

the form of an algorithm from which computer programs can be written;

— the second part assumes constant values for the variable parameters, with the exception of

the insulation temperature limits (Table I) and the temperature of external cooling air,

irrespective of insulation system or construction, thereby enabling load curves to be

produced.

The guide indicates how dry-type transformers may be operated without exceeding the

acceptable limit of deterioration of insulation through thermal effects. The acceptable limit of

deterioration of insulation is defined as that which occurs when the dry-type transformer is

operating under rated conditions at the basic temperature of the external cooling air.

2. Object

The object of this guide is to permit the calculation of, and to indicate the permissible loading

under certain defined conditions in terms of rated current, for the guidance of users and to help

planners to choose the rated power of transformers required for new installations.

The basic temperature of the external cooling air is assumed to be 20 °C. Guidance is given

for this temperature, and also for external cooling air temperatures of 10 °C and 30 °C.

Deviations from these temperatures are provided for in such a way that the increased use of life

when operated with a higher external cooling air temperature is balanced by a reduced use of

life with a lower external cooling air temperature.

In practice, uninterrupted continuous operation at full rated current is unusual, and this

guide gives recommendations for cyclic daily loads, taking into account seasonal variations of

ambient temperature. The daily use of life due to thermal effects is compared with normal daily

use of life which results when the dry-type transformer is operating at rated voltage and

current, with an external cooling air temperature of 20 °C.
---------------------- Page: 6 ----------------------
SIST IEC 60905:1997
905 ©I E C 1987 — 9 —

Load curves, Figures 5 (1) to 5 (12) on pages 32 to 43, show the permissible load current

which will result in a normal daily use of life for winding insulation systems having insulation

system temperatures of 105, 120, 130, 155, 180 and 220 °C in the following two sets of

conditions:
continuous duty with different temperatures of external cooling air,
cyclic duty with different temperatures of external cooling air.
Note. —

It is assumed that the transformer is adequately ventilated and the increased losses resulting from an

overload do not significantly change the temperature of the cooling air.
Symbols
The following symbols are used in this guide:
a = subscript representing "ambient" (external cooling air)
c =
subscript representing the "hot spot of the winding" at rated current and basic
temperature of external cooling air
cc =

subscript representing the highest permissible "hot spot of the winding" according to

this guide
d =
subscript representing the doubling of the rate of using life
e =

subscript representing the final "average of winding" for any value of load current

= subscript representing the initial "average of winding" for any value of load current

= integer variable representing the number of the day in the year (1^j-.365)
K1, K2i ... K, .. K
N = load currents as fractions of rated currents

m = subscript representing maximum "average of winding". (Thus for continuous rated

current,
A0c/Z, and for a short time in excess of rated current, D°
m = 08cc/
AOmr =
resulting in a greater than normal rate of using life during this period)
= subscript representing any one period during the daily load cycle
q = exponent of K
by which the average temperature rise varies with load current
r =
subscript representing rated value
t = time
tb =
duration, in hours, at any load current K 1 (tb , 24 — tp)
tp =
maximum permissible duration, in hours, at any load current
t1 , t2, ... tn
, ... tN = duration of each load condition period
w =
subscript representing the winding
subscript representing the "hot spot of winding"

= amplitude of annual variations in the daily average ambient temperature (sinusoidal

variation is assumed)
B =

amplitude of daily variations in the ambient temperature (sinusoidal variation is

assumed)
I =
load current in amperes (any value); I r = rated current

subscript representing any individual load period prior to the start of the load period

to for which the calculation is being made
---------------------- Page: 7 ----------------------
SIST IEC 60905:1997
905 © I E C 1987 – 11 –
L = life consumption in hours
calculated annual use of life
Lan
LR = relative rate of using life
N = number of different load periods for a day

T = sum of the individual load periods tk prior to the start of the load period t„ for which

the calculation is being made

Z = ratio between hot spot and average winding temperature rises (see also explanations

to subscript m)
arbitrary variable used in determining the relative rate of using life
AO =
temperature rise in kelvins

accuracy factor for estimation of the hot-spot temperature at the beginning of the 24 h

E =
period
8 = temperature in degrees Celsius
Dad = daily average ambient temperature
0a,, = annual average ambient temperature
r = thermal time constant of windings at rated current, in hours
PART 1
4. Basis of guide
4.1.
Introduction

The life of a dry-type transformer is related to the deterioration of its insulation through

thermal ageing. Experience indicates that the normal life of a transformer is some tens of years.

It cannot be stated more precisely, because it may vary even between identical units, owing in

particular to operating factors which may differ from one transformer to another.

In practice, uninterrupted continuous operation at full load current is unusual and so account

should be taken of the various operating conditions and the subsequent fluctuation of the rate

of thermal deterioration of the transformer insulation.
It is necessary therefore:

a) To define "normal" expectation of life as a function of the rated load current and the rated

hot spot temperature of the winding insulation.

b) To relate the increase in hot spot winding temperature to the increase in the rate of

insulation deterioration.

c) To devise a method of calculating the net effect of variation in the winding hot spot

temperature due to changes in load period, load current and ambient temperature, on the

thermal ageing of the insulation.

d) To then compare the net "use of life" due to the sum of the different factors in the load

cycle, with the definition of "normal use of life". Hence, any of the parameters in the load

cycle can be adjusted to give a normal expectation of transformer life.
---------------------- Page: 8 ----------------------
SIST IEC 60905:1997
905 © I E C 1987 – 13 –
4.2 Parameters used in the calculations
4.2.1
Temperature limits
TABLE I
Temperature limits
Hot spot winding Average winding
Insulation
temperature temperature-rise
system
temperature (°C) limits at rated current
(K)
(IEC Publi-
rated highest
(I EC Publication 726)
cation 726)
permissible
(40,r)
(°C) (Bcc)
(Bc)
105 (A) 95 140 60
120 (E) 110 155
120 165 80
130 (B)
145 190 100
155 (F)
220 125
180 (H) 175
210 250 150
220(C)
is used to calculate normal life consumption. Under certain operating
4.2.2 The parameter 0,

conditions in which it is permissible to exceed this normal consumption level, high overloads

may be applied, resulting in a hot spot temperature considerably higher than O. Thus a

parameter 0 cn representing the absolute limit of the hot spot temperature has been introduced.

This temperature is that beyond which the rate of deterioration of the insulation becomes

and 8cc.)
inadmissible. (See Table I for values of 0,

4.2.3 The value of parameter 0d is taken as the increase in hot spot temperature which doubles the

rate of using life.

4.2.4 The basic value required for calculating the life consumption level is the temperature at the

hottest spot. For this purpose, it is necessary to know the temperature rise at this position for

each load condition and the ambient temperature. There are at least two methods of obtaining

the hot spot temperature rise:
Kn;
a) can be determined by performing temperature-rise tests with various loads
AOWhn
b) by using the formula:
= Z  OBwr  Knq (1)
OBwhn
In this case, it is necessary to know the values of Z, AO, and q.

It is preferable to use, whenever possible, the results of tests giving thus removing any

AOWhn,

uncertainty regarding the validity of the factor Z and the value of q. Experience shows that q

and Z assume different values depending on the type of transformer and the level of the load

current at which it operates.
wh„ may be possible only on prototype
Note. — With some types of winding construction determination of AB
transformers.
AOWh = f (K), which can be used to
On the basis of the test results, a curve can be plotted of
for each K n necessary for the calculation.
determine the corresponding
AOwhn
---------------------- Page: 9 ----------------------
SIST IEC 60905:1997
905©IEC1987 — 15 —

4.2.5 Values obtained during temperature-rise tests carried out on a prototype under different load

conditions:
z = thermal time constant in hours;

Note. — The winding to be taken into consideration is that with the shortest time constant.

40wr
= average winding temperature rise at the assigned rating;
4B =

f (K): temperature rise at the hottest spot, under the established conditions, as a

function of the load.

4.2.6 Values obtained by means of ageing tests carried out on models of insulating systems:

Bc =
...

IEC 60505
Edition 4.0 2011-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Evaluation and qualification of electrical insulation systems
Évaluation et qualification des systèmes d'isolation électrique
IEC 60505:2011
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 60505
Edition 4.0 2011-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Evaluation and qualification of electrical insulation systems
Évaluation et qualification des systèmes d'isolation électrique
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XC
ICS 29.080.30 ISBN 978-2-88912-539-5
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – 60505 © IEC:2011
CONTENTS

FOREWORD ........................................................................................................................... 5

INTRODUCTION ..................................................................................................................... 7

1 Scope ............................................................................................................................... 9

2 Normative references ....................................................................................................... 9

3 Terms and definitions ....................................................................................................... 9

3.1 General terms ....................................................................................................... 10

3.2 Terms related to service stresses and ageing ........................................................ 10

3.3 Terms related to testing ......................................................................................... 11

4 Ageing ............................................................................................................................ 12

4.1 Ageing mechanism ................................................................................................ 12

4.2 Assessment of ageing mechanisms ....................................................................... 14

4.3 Electrical ageing .................................................................................................... 15

4.4 Thermal ageing ..................................................................................................... 17

4.5 Mechanical ageing ................................................................................................ 19

4.6 Environmental ageing ............................................................................................ 21

4.7 Accelerated ageing ................................................................................................ 22

4.8 Multifactor ageing .................................................................................................. 23

5 Basic evaluation considerations ...................................................................................... 23

5.1 Elements for preparing an evaluation method ........................................................ 23

5.1.1 Object ....................................................................................................... 23

5.1.2 Service conditions ..................................................................................... 23

5.1.3 Life values ................................................................................................. 24

5.2 Types of evaluation procedures ............................................................................. 24

5.3 Choice of the test object ........................................................................................ 26

5.4 Experimental test procedures ................................................................................ 26

5.5 Conclusions for standardization practices .............................................................. 27

6 Functional ageing tests................................................................................................... 27

6.1 Test objects........................................................................................................... 27

6.1.1 Construction of test objects ....................................................................... 27

6.1.2 Number of test objects ............................................................................... 28

6.1.3 Quality assurance tests ............................................................................. 28

6.1.4 Preconditioning subcycle ........................................................................... 28

6.1.5 Initial diagnostic tests ................................................................................ 28

6.1.6 Reference EIS ........................................................................................... 28

6.2 Test conditions ...................................................................................................... 28

6.2.1 Continuous and cyclic testing .................................................................... 28

6.2.2 Levels of test stresses, ageing factors and diagnostic factors .................... 29

6.3 Determination of EIS service life ........................................................................... 29

6.3.1 Extrapolation of life test results ................................................................. 29

6.3.2 Comparison of life test data ....................................................................... 29

6.4 Diagnostics ........................................................................................................... 30

6.4.1 Diagnostic tests – End point criteria........................................................... 30

6.4.2 Additional specific tests ............................................................................. 31

6.5 Analysing the data ................................................................................................. 31

6.6 Test report ............................................................................................................ 31

Annex A (informative) Glossary ............................................................................................ 32

---------------------- Page: 4 ----------------------
60505 © IEC:2011 – 3 –

Bibliography .......................................................................................................................... 71

Figure 1 – Ageing of an EIS .................................................................................................. 13

Figure 2 – Intrinsic/extrinsic electrical ageing of practical EIS ............................................... 15

Figure 3 – Intrinsic/extrinsic thermal ageing of practical EIS ................................................. 17

Figure 4 – Intrinsic/extrinsic mechanical ageing of practical EIS ........................................... 20

Figure 5 – Intrinsic/extrinsic environmental ageing of practical EIS ....................................... 22

Figure 6 – Elements of evaluation methods ........................................................................... 23

Figure 7 – Type of evaluation procedure ............................................................................... 25

Figure 8 – Selection of test object ......................................................................................... 26

Figure 9 – Establishing the test method ................................................................................ 27

Figure A.1 – Surface abrasion damage ................................................................................. 32

Figure A.2 – Surface enamel peeling like string ................................................................... 32

Figure A.3 – Scheme of the measurement set-up for the charging/discharging current .......... 33

Figure A.4 – Example of sample preparation ......................................................................... 33

Figure A.5 – Charging/discharging current on HDPE film ...................................................... 34

Figure A.6 – Property versus time behaviour, detection of threshold (end point, p )

and maintenance time ........................................................................................................... 35

Figure A.7 – Correspondence between the ageing plots of the property p (in red),

obtained at different stress levels, and the resulting life line ................................................. 35

Figure A.8 – Example of charge injection of positive carriers (holes) from the anode

and of negative charge carriers (electrons) from the cathode in a PE flat specimen,

detected by space charge measurement performed by PEA method ..................................... 36

Figure A.9 – Stress-strain curve for a typical material ........................................................... 37

Figure A.10 – Scheme of measurement set- up for charging/discharging current .................. 38

Figure A.11 – Example of sample preparation ....................................................................... 38

Figure A.12 – Charging/discharging current on HDPE film .................................................... 38

Figure A.13 – Charging current at 135 °C and different values of DC electrical field ............. 39

Figure A.14 – Charging current at 120 °C and different values of DC electrical field ............. 39

Figure A.15 – Corona at post insulator head ........................................................................ 40

Figure A.16 – Corona on top and arcing to ground ................................................................ 40

Figure A.17 – Stages of mechanical ductile fracture (cracking) (Source unknown) ............... 41

Figure A.18 – Photo showing orderings in epoxy structure and void ...................................... 42

Figure A.19 – Discharge between conductors through air...................................................... 44

Figure A.20 – Paper insulation degraded by electrical surface discharges ............................ 44

Figure A.21 – Example of electric strength test on XLPE sample 0,2 mm thick ..................... 45

Figure A.22 – Two parameters Weibull plot electric strength results performed on

seven XLPE specimens, 0,2 mm thick .................................................................................. 45

Figure A.23 – Loss angle of a dielectric ................................................................................ 47

Figure A.24 – Loss factor for pre-treated and thermally aged (at 110 °C and 130 °C)

XLPE cables measured at 90 °C plotted vs. frequency .......................................................... 47

Figure A.25 – Field lines from a positive charge above a plane conductor ............................. 48

Figure A.26 – Electrical tree.................................................................................................. 49

Figure A.27 – EPDM ashing and erosion on fitting ................................................................ 50

Figure A.28 – Failing external insulation ............................................................................... 51

---------------------- Page: 5 ----------------------
– 4 – 60505 © IEC:2011

Figure A.29 – Failing external insulation ............................................................................... 51

Figure A.30 – Critical failure of solid cable insulation (XLPE) by electrical breakdown ......... 52

Figure A.31 – Example flashover .......................................................................................... 53

Figure A.32 – Substation – Outdoor installation .................................................................... 54

Figure A.34 – Internal interfaces in epoxy structure and void ................................................ 56

Figure A.35 – Example of craze and crack development in an inter-lamellar space

under mechanical tension T .................................................................................................. 57

Figure A.36 – Water treeing .................................................................................................. 58

Figure A.37 – After 11 years in service UV and moisture impact ........................................... 59

Figure A.38 – Random (amorphous) structure of a molecular chain ...................................... 59

Figure A.39 – Oriented structure (semi-crystalline) of a molecular chain ............................... 59

Figure A.40 – Typical morphology of melt-grown polyethylene spherulites ............................ 60

Figure A.41 – Areas in which PD generally occur .................................................................. 61

Figure A.42 – Classes of defect – Internal, surface and corona PD ....................................... 61

Figure A.43 – Basic PD measurement circuit ........................................................................ 62

Figure A.44 – Examples of PD patterns relevant to internal, surface and corona PD ............. 62

Figure A.45 – GIS research – Metal conductor protrusion ..................................................... 63

Figure A.46 – Internally strained epoxy – Frozen in strains in epoxy resin due to

thermal stress, measured by TMA curves ............................................................................. 64

Figure A.47 – Externally strained parts in an on-load tap changer (OLTC) .......................... 64

Figure A.48 – A material being loaded in a) compression, b) tension, c) shear ...................... 65

Figure A.49 – Effect of thermal-mechanical stresses leading to interfacial electrical

tracking ................................................................................................................................. 66

Figure A.50 – Stress-strain curve for a typical material ......................................................... 66

Figure A.51 – Over crimped rod; breaks during tensile test ................................................... 67

Figure A.52 – Typical installation fault .................................................................................. 68

Figure A.53 – Surface tracking on sheds and fitting end ........................................................ 68

Figure A.54 – Vented trees – Initiate at interface .................................................................. 69

Figure A.55 – Tape wrinkling ................................................................................................ 70

Table 1 – Ageing temperatures ............................................................................................. 19

Table 2 – Cyclical and continuous procedures ...................................................................... 30

---------------------- Page: 6 ----------------------
60505 © IEC:2011 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
EVALUATION AND QUALIFICATION
OF ELECTRICAL INSULATION SYSTEMS
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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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.

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

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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

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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 60505 has been prepared by IEC technical committee 112:

Evaluation and qualification of electrical insulating materials and systems.

This fourth edition cancels and replaces the third edition, published in 2004, and constitutes a

technical revision.

The main change with respect to the previous edition is the addition of a Glossary in the form

of Annex A to this standard.
The text of this standard is based on the following documents:
FDIS Report on voting
112/174/FDIS 112/184/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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– 6 – 60505 © IEC:2011

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.
The contents of the corrigendum of March 2017 have been included in this copy.

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.
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60505 © IEC:2011 – 7 –
INTRODUCTION

The life of an electrical insulation system (EIS) or systems frequently determines the life of

electrical equipment which can be affected by electrical, thermal, mechanical or
environmental stresses acting either individually or in combination.

Intended, estimated or proven service life times are essential parameters for describing the

life of electrical insulation systems. In the early days of electrotechnical engineering, life

figures were rather vague. The limitation of the life of the insulation under thermal stress was

one of the first indicators of the effect of ageing in some equipment in service. As experience

in using EIS increased, it was appreciated that there was a need to select specific materials

having satisfactory life time at a given temperature, to enable the required service life to be

achieved and to allow for the calculation of the thermal capability of equipment.

The user of this standard may evaluate existing test methods and provide correlation with his

equipment. Therefore, the user of this standard is responsible for demonstrating the validity of

the existing test method in accordance with the principles of this standard.

The determination of the prospective life is a fundamental task when developing and

designing an EIS. Estimated service life of an EIS needs to be established for several

reasons:
– for type testing when introducing a new EIS into production;
– for quality assurance of production;
– for estimating the life expectancy of new equipment;
– for estimating the remaining life for maintenance purposes.

“Ageing” focuses on the mechanisms affecting the EIS performance. “Evaluation” links these

potential mechanisms by “Analysis” and “Diagnostics” to the design of a specific kind of

evaluation test procedure.

The keyword structure below meets such requirements and allows an easier choice of the

parts of interest.
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60505 © IEC:2011 – 9 –
EVALUATION AND QUALIFICATION
OF ELECTRICAL INSULATION SYSTEMS
1 Scope

This International Standard establishes the basis for estimating the ageing of electrical

insulation systems (EIS) under conditions of either electrical, thermal, mechanical,

environmental stresses or combinations of these (multifactor stresses).

It specifies the principles and procedures that shall be followed, during the development of

EIS functional test and evaluation procedures, to establish the estimated service life for a

specific EIS.

This standard should be used by all IEC technical committees responsible for equipment

having an EIS.
2 Normative references

The following referenced documents are indispensable for the application 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 60216-2, Electrical insulating materials – Thermal endurance properties – Part 2:

Determination of thermal endurance properties of electrical insulating materials – Choice of

test criteria

IEC 60216-3, Electrical insulating materials – Thermal endurance properties – Part 3:

Instructions for calculating thermal endurance characteristics

IEC 60216-5, Electrical insulating materials – Thermal endurance properties – Part 5:

Determination of relative thermal endurance index (RTE) of an insulating material

IEC 60493-1, Guide for the statistical analysis of ageing test data – Part 1: Methods based on

mean values of normally distributed test results

IEC 60544-1, Electrical insulating materials – Determination of the effects of ionizing radiation

– Part 1: Radiation interaction and dosimetry

IEC/TS 61251, Electrical insulating materials – AC voltage endurance evaluation –

Introduction

IEC 62539, Guide for the statistical analysis of electrical insulation breakdown data

3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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– 10 – 60505 © IEC:2011
3.1 General terms
3.1.1
electrical insulation system
EIS

insulating structure containing one or more electrical insulating materials (EIM) together with

associated conducting parts employed in an electrotechnical device
3.1.2
electrical insulating material
EIM

material with negligibly low electric conductivity, used to separate conducting parts at different

electrical potentials
[IEC 60050-212:2010, 212-11-01, modified]
3.1.3
reference EIS

established EIS evaluated on the basis of either a known service experience record or a

known comparative functional evaluation
3.1.4
candidate EIS

EIS under evaluation to determine its service capability (with regard to electrical, thermal,

mechanical, environmental or multifactor stresses)
3.1.5
intended life
design life of an EIS under service conditions
3.1.6
estimated life

expected service life derived from either service experience or the results of tests performed

in accordance with appropriate evaluation procedures, or both, as established by the

responsible organization or technical committee
3.1.7
evaluation
establishment of rela
...

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