IEC 61869-1:2007

IEC 61869-1
Edition 1.0 2007-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Instrument transformers –
Part 1: General requirements
Transformateurs de mesure –
Partie 1: Exigences générales
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IEC 61869-1
Edition 1.0 2007-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Instrument transformers –
Part 1: General requirements
Transformateurs de mesure –
Partie 1: Exigences générales
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XB
CODE PRIX
ICS 17.220.20 ISBN 2-8318-9322-4

– 2 – 61869-1 © IEC:2007
CONTENTS
FOREWORD.6

1 Scope.9
2 Normative references .9
3 Terms and definitions .10
3.1 General definitions .11
3.2 Definitions related to dielectric ratings.11
3.3 Definitions related to current ratings .13
3.4 Definitions related to accuracy .13
3.5 Definitions related to other ratings.14
3.6 Definitions related to gas insulation.14
3.7 Index of abbreviations .15
4 Normal and special service conditions .15
4.1 General .15
4.2 Normal service conditions .16
4.2.1 Ambient air temperature .16
4.2.2 Altitude.16
4.2.3 Vibrations or earth tremors .16
4.2.4 Other service conditions for indoor instrument transformers .16
4.2.5 Other service conditions for outdoor instrument transformers .17
4.3 Special service conditions .17
4.3.1 General .17
4.3.2 Altitude.17
4.3.3 Ambient temperature .17
4.3.4 Vibrations or earth tremors .17
4.3.5 Earthquakes .17
4.4 System earthing .18
5 Ratings.18
5.1 General .18
5.2 Highest voltage for equipment .18
5.3 Rated insulation levels .20
5.3.1 General .20
5.3.2 Rated primary terminal insulation level .20
5.3.3 Other requirements for primary terminals insulation.20
5.3.4 Between-section insulation requirements.21
5.3.5 Insulation requirements for secondary terminals .21
5.4 Rated frequency.21
5.5 Rated output .21
5.6 Rated accuracy class .21
6 Design and construction .21
6.1 Requirements for liquids used in equipment .21
6.1.1 General .21
6.1.2 Liquid quality .21
6.1.3 Liquid level device .21
6.1.4 Liquid tightness .21
6.2 Requirements for gases used in equipment .21

61869-1 © IEC:2007 – 3 –
6.2.1 General .21
6.2.2 Gas quality .22
6.2.3 Gas monitoring device .22
6.2.4 Gas tightness .22
6.2.5 Pressure relief device.23
6.3 Requirements for solid materials used in equipment .23
6.4 Requirements for temperature rise of parts and components .23
6.4.1 General .23
6.4.2 Influence of altitude on temperature-rise.24
6.5 Requirements for earthing of equipment .25
6.5.1 General .25
6.5.2 Earthing of the enclosure.25
6.5.3 Electrical continuity .25
6.6 Requirements for the external insulation.25
6.6.1 Pollution .25
6.6.2 Altitude.26
6.7 Mechanical requirements.27
6.8 Multiple chopped impulse on primary terminals .28
6.9 Internal arc fault protection requirements .28
6.10 Degrees of protection by enclosures.29
6.10.1 General .29
6.10.2 Protection of persons against access to hazardous parts and
protection of the equipment against ingress of solid foreign objects.29
6.10.3 Protection against ingress of water.29
6.10.4 Indoor instrument transformers.30
6.10.5 Outdoor instrument transformers .30
6.10.6 Protection of equipment against mechanical impact under normal
service conditions.30
6.11 Electromagnetic Compatibility (EMC) .30
6.11.1 General .30
6.11.2 Requirement for Radio Interference Voltage (RIV) .30
6.11.3 Requirements for immunity .31
6.11.4 Requirement for transmitted overvoltages.31
6.12 Corrosion .32
6.13 Markings .33
6.14 Fire hazard.33
7 Tests .33
7.1 General .33
7.1.1 Classification of tests .33
7.1.2 List of tests.34
7.1.3 Sequence of tests.35
7.2 Type tests .35
7.2.1 General .35
7.2.2 Temperature-rise test .36
7.2.3 Impulse voltage withstand test on primary terminals .37
7.2.4 Wet test for outdoor type transformers.38
7.2.5 Electromagnetic Compatibility (EMC) tests .38
7.2.6 Test for accuracy.40
7.2.7 Verification of the degree of protection by enclosures.40

– 4 – 61869-1 © IEC:2007
7.2.8 Enclosure tightness test at ambient temperature .41
7.2.9 Pressure test for the enclosure .41
7.3 Routine tests .41
7.3.1 Power-frequency voltage withstand tests on primary terminals .41
7.3.2 Partial discharge measurement .42
7.3.3 Power-frequency voltage withstand tests between sections .44
7.3.4 Power-frequency voltage withstand tests on secondary terminals .44
7.3.5 Test for accuracy.44
7.3.6 Verification of markings .44
7.3.7 Enclosure tightness test at ambient temperature .45
7.3.8 Pressure test for the enclosure .45
7.4 Special tests .45
7.4.1 Chopped impulse voltage withstand test on primary terminals .45
7.4.2 Multiple chopped impulse test on primary terminals .46
7.4.3 Measurement of capacitance and dielectric dissipation factor .47
7.4.4 Transmitted overvoltage test .47
7.4.5 Mechanical tests.49
7.4.6 Internal arc fault test.50
7.4.7 Enclosure tightness tests at low and high temperatures.51
7.4.8 Gas dew point test.52
7.4.9 Corrosion test.52
7.4.10 Fire hazard test .52
7.5 Sample tests .52
8 Rules for transport, storage, erection, operation and maintenance .53
9 Safety.53
10 Influence of products on the natural environment .53

Annex A (normative) Identification of test specimen .54
Annex B (informative) Rules for transport, storage, erection, operation and
maintenance .55
Annex C (informative) Fire hazard .60
Annex D (informative) Sample test.61

Bibliography.62

Figure 1 – Altitude correction factor for the temperature rise.25
Figure 2 – Altitude correction factor .27
Figure 3 – Transmitted overvoltages measurement: Test impulse waveforms.32
Figure 4 – RIV measuring circuit .39
Figure 5 – Test circuit for partial discharge measurement .42
Figure 6 – Alternative circuit for partial discharge measurement .42
Figure 7 – Example of balanced test circuit for partial discharge measurement.43
Figure 8 – Example of calibration circuit for partial discharge measurement.43
Figure 9 – Transmitted overvoltages measurement: general test configuration.48
Figure 10 – Transmitted overvoltages measurement: test circuit and GIS Test
configuration (CT).48

61869-1 © IEC:2007 – 5 –
Table 1 – Temperature categories .16
Table 2 – Rated primary terminal insulation levels for instrument transformers .19
Table 3 – Partial discharge test voltages and permissible levels .20
Table 4 – Permissible temporary leakage rates for gas systems .22
Table 5 – Limits of temperature rise for various parts, materials and dielectrics of
instrument transformers .24
Table 6 – Creepage distances .26
Table 7 – Static withstand test loads.28
Table 8 – Arc fault duration and performance criteria.29
Table 9 – Transmitted over voltage limits.31
Table 10 – List of tests .34
Table 11 – Gas type and pressure during type, routine and special tests .35
Table 12 – Modalities of application of the test loads to be applied to the line primary
terminals.50
Table C.1 – Fire hazard of electro technical products.60

– 6 – 61869-1 © IEC:2007
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSTRUMENT TRANSFORMERS –
Part 1: General requirements
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 provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall be attached 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
essential 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 61869-1 has been prepared by IEC technical committee 38:
Instrument transformers.
TC 38 decided to restructure the whole set of stand-alone Standards in the IEC 60044 series
and transform it into a new set of standards composed of general requirements documents
and specific requirements documents.
This Standard is the first issue of this new series and can be regarded as a Product Family
standard. It contains the general requirements for instrument transformers and shall be read
in conjunction with the relevant specific requirements standard for the instrument transformer
concerned.
61869-1 © IEC:2007 – 7 –
An overview of the planned set of standards is given below:
PRODUCT FAMILY STANDARDS PRODUCT PRODUCTS OLD STANDARD
STANDARD
61869-2 CURRENT 60044-1
TRANSFORMERS
61869-3 INDUCTIVE VOLTAGE 60044-2

TRANSFORMERS
61869-4 COMBINED 60044-3
TRANSFORMERS
61869-5 CAPACITIVE VOLTAGE 60044-5

TRANSFORMERS
61869-1
61869-6 CURRENT 60044-6
GENERAL
TRANSFORMERS FOR
REQUIREMENTS FOR
TRANSIENT
INSTRUMENT
PERFORMANCE
TRANSFORMERS
61869-9 61869-7 ELECTRONIC VOLTAGE 60044-7
TRANSFORMERS
ADDITIONAL
REQUIREMENTS AND 61869-8 ELECTRONIC
60044-8
DIGITAL INTERFACE
CURRENT
FOR ELECTRONIC
TRANSFORMERS
INSTRUMENT
TRANSFORMERS
61869-10 LOW-POWER STAND-
ALONE CURRENT
SENSORS
This Standard covers all general requirements formerly found in the stand-alone standards of
the IEC 60044 series. Additionally, it introduces some technical innovations:
• requirements for gas-insulated instrument transformers
• additional special tests
• requirements for internal arc fault protection
• requirements for degrees of protection by enclosure
• requirements for resistance to corrosion
• requirements for safety and environmental concerns
The text of this standard is based on the following documents:
FDIS Report on voting
38/360/FDIS 38/364/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.

– 8 – 61869-1 © IEC:2007
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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.
61869-1 © IEC:2007 – 9 –
INSTRUMENT TRANSFORMERS –
Part 1: General requirements
1 Scope
This International Standard is applicable to newly manufactured instrument transformers with
analogue or digital output for use with electrical measuring instruments or electrical protective
devices having rated frequencies from 15 Hz to 100 Hz.
This standard is a product family standard and covers general requirements only. For each
kind of instrument transformer the product standard is composed by this standard and the
relevant specific standard.
2 Normative references
The following referenced documents are essential 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 60060-1: High-voltage test techniques – Part 1: General definitions and test requirements
IEC 60068-2-11: Basic environmental testing procedures – Part 2: Tests – Test Ka: Salt mist
IEC 60068-2-17: Basic environmental testing procedures – Part 2: Tests - Test Q: Sealing
IEC 60068-2-75: Environmental testing – Part 2-75: Tests – Test Eh: Hammer tests.
IEC 60071-1: Insulation co-ordination – Part 1: Definitions, principles and rules
IEC 60085: Electrical insulation – Thermal classification
IEC 60270: High-voltage test techniques – Partial discharge measurements
IEC 60296: Fluids for electrotechnical applications – Unused mineral insulating oils for
transformers and switchgear
IEC 60376: Specification of technical grade sulfur hexafluoride (SF ) for use in electrical
equipment
IEC 60417: Graphical symbols for use on equipment
IEC 60455 (all parts): Resin based reactive compounds used for electrical insulation
IEC 60480: Guidelines for the checking and treatment of sulphur hexafluoride (SF ) taken
from electrical equipment and specification for its re-use
IEC 60529: Degrees of protection provided by enclosures (IP code)
IEC 60567: Oil-filled electrical equipment – Sampling of gases and of oil for analysis of free
and dissolved gases – Guidance

– 10 – 61869-1 © IEC:2007
IEC 60694: Common specifications for high-voltage switchgear and controlgear standards
IEC 60695-1-1: Fire hazard testing – Part 1-1: Guidance for assessing the fire hazard of
electrotechnical products - General guidelines
IEC 60695-1-30: Fire hazard testing – Part 1-30: Guidance for assessing the fire hazard of
electrotechnical products – Use of preselection testing procedures
IEC 60695-7-1: Fire hazard testing – Part 7-1: Toxicity of fire effluent - General guidance
IEC 60721-3-3: Classification of environmental conditions – Part 3-3: Classification of groups
of environmental parameters and their severities – Stationary use of weatherprotected
locations
IEC 60721-3-4: Classification of environmental conditions – Part 3: Classification of groups of
environmental parameters and their severities – Section 4: Stationary use at non-
weatherprotected locations
IEC 60815, Guide for the selection of insulators in respect of polluted conditions
IEC 60867: Insulating liquids – Specifications for unused liquids based on synthetic aromatic
hydrocarbons
IEC 61462: Composite hollow insulators – Pressurized and unpressurized insulators for use in
electrical equipment with rated voltage greater that 1 000 V – Definitions, test methods and
acceptance criteria and design recommendations
IEC 61634: High-voltage switchgear and controlgear – Use and handling of sulphur
hexafluoride (SF ) in high-voltage switchgear and controlgear
IEC 62155: Hollow pressurized and unpressurized ceramic and glass insulators for use in
electrical equipment with rated voltages greater than 1 000 V
IEC 62262: Degree of protection IK code
IEC 62271-2: High-voltage switchgear and controlgear – Part 2: Seismic qualification for rated
voltages of 72,5 kV and above.
IEC 62271-203: High-voltage switchgear and controlgear – Part 203: Gas-insulated metal-
enclosed switchgear for rated voltages above 52 kV
CISPR 18-2: Radio interference characteristics of overhead power lines and high-voltage
equipment – Part 2: Methods of measurement and procedure for determining limits
IEC Guide 109: Environmental aspects – Inclusion in electrotechnical product standards
ISO 3231: Paints and varnishes – Determination of resistance to humid atmospheres
containing sulphur dioxide
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

61869-1 © IEC:2007 – 11 –
3.1 General definitions
3.1.1
instrument transformer
transformer intended to transmit an information signal to measuring instruments, meters and
protective or control devices or similar apparatus
[IEV 321-01-01, modified]
3.1.2
enclosure
housing affording the type and degree of protection suitable for the intended application
[IEV 826-12-20]
3.1.3
primary terminals
terminals to which the voltage or current to be transformed is applied
3.1.4
secondary terminals
terminals which transmit an information signal to measuring instruments, meters and
protective or control devices or similar apparatus
3.1.5
secondary circuit
the external circuit receiving the information signals supplied by the secondary terminals of an
instrument transformer
[IEV 321-01-08, modified]
3.1.6
section
electrically conductive part of an instrument transformer insulated from other similar parts and
equipped with terminals
3.2 Definitions related to dielectric ratings
3.2.1
highest voltage of a system (Usys)
highest value of the phase-to-phase operating voltage (r.m.s. value) which occurs under
normal operating conditions at any time and at any point in the system
[IEV 601-01-23, modified]
3.2.2
highest voltage for equipment (U )
m
the highest r.m.s. value of phase-to-phase voltage for which the equipment is designed in
respect of its insulation as well as other characteristics which relate to this voltage in the
relevant equipment standards
[IEV 604-03-01 ]
3.2.3
rated insulation level
combination of voltage values which characterizes the insulation of a transformer with regard
to its capability to withstand dielectric stresses

– 12 – 61869-1 © IEC:2007
3.2.4
isolated neutral system
system where the neutral point is not intentionally connected to earth, except for high
impedance connections for protection or measurement purposes
[IEV 601-02-24]
3.2.5
resonant earthed system (a system earthed through an arc-suppression coil)
system in which one or more neutral points are connected to earth through reactances which
approximately compensate the capacitive component of a single-phase-to-earth fault current
[IEV 601-02-27]
NOTE With resonant earthing of a system, the residual current in the fault is limited to such an extent that an
arcing fault in air is self-extinguishing.
3.2.6
earth fault factor
at a given location of a three-phase system, and for a given system configuration, the ratio of
the highest r.m.s. phase-to-earth power frequency voltage on a healthy phase during a fault to
earth affecting one or more phases at any point on the system to the r.m.s. value of phase-to-
earth power frequency voltage which would be obtained at the given location in the absence
of any such fault
[IEV 604-03-06]
3.2.7
earthed neutral system
system in which the neutral is connected to earth either solidly or through a resistance or
reactance of sufficiently low value to reduce transient oscillations and to give a current
sufficient for selective earth fault protection.
a) A three-phase system with effectively earthed neutral at a given location is a system
characterized by an earth fault factor at this point which does not exceed 1,4.
NOTE This condition is obtained approximately when, for all system configurations, the ratio of zero-
sequence reactance to the positive-sequence reactance is less than 3 and the ratio of zero-sequence
resistance to positive sequence reactance is less than one.
b) A three-phase system with non-effectively earthed neutral at a given location is a system
characterized by an earth fault factor at this point that may exceed 1,4.
3.2.8
solidly earthed neutral system
system whose neutral point(s) is(are) earthed directly
[IEV 601-02-25]
3.2.9
impedance earthed neutral system
system whose neutral point(s) is(are) earthed through impedances to limit earth fault currents
[IEV 601-02-26]
3.2.10
exposed installation
installation in which the apparatus is subject to overvoltages of atmospheric origin
NOTE Such installations are usually connected to overhead transmission lines either directly or through a short
length of cable.
61869-1 © IEC:2007 – 13 –
3.2.11
non-exposed installation
installation in which the apparatus is not subject to overvoltages of atmospheric origin
NOTE Such installations are usually connected to underground cable networks.
3.3 Definitions related to current ratings
See specific requirements standard.
3.4 Definitions related to accuracy
3.4.1
actual transformation ratio (k)
ratio of the actual primary voltage or current to the actual secondary voltage or current
3.4.2
rated transformation ratio (k )
r
ratio of the rated primary voltage or current to the rated secondary voltage or current
3.4.3
ratio error (ε)
the error which an instrument transformer introduces into the measurement and which arises
from the fact that the actual transformation ratio is not equal to the rated transformation ratio
3.4.4
phase displacement (Δφ)
difference in phase between the primary voltage or current and the secondary voltage or
current phasors, the direction of the phasors being so chosen that the angle is zero for an
ideal transformer.
The phase displacement is said to be positive when the secondary voltage or current phasors
leads the primary voltage or current phasors. It is usually expressed in minutes or
centiradians.
NOTE 1 This definition is strictly correct for sinusoidal voltages or currents only.
NOTE 2 Electronic instrument transformers may introduce a delay time due to a digital data transmission and by
digital signal processing.
[IEV 321-01-23, modified]
3.4.5
accuracy class
a designation assigned to an instrument transformer, the ratio error and phase displacement
of which remain within specified limits under prescribed conditions of use
[IEV 321-01-24, modified]
3.4.6
burden
admittance (or impedance) of the secondary circuit expressed in siemens (or ohms) and
power factor
NOTE The burden is usually expressed as the apparent power in volt-amperes absorbed at a specified power-
factor and at the rated secondary voltage or current.
3.4.7
rated burden
value of the burden on which the accuracy requirements of this specification are based.

– 14 – 61869-1 © IEC:2007
3.4.8
rated output (S )
r
value of the apparent power (in voltamperes at a specified power factor) which the
transformer is intended to supply to the secondary circuit at the rated secondary voltage or
current and with rated burden connected to it
3.5 Definitions related to other ratings
3.5.1
rated frequency (f )
R
value of the frequency on which the requirements of this standard are based
3.5.2
mechanical load (F)
forces on different parts of the instrument transformer as a function of four main forces:
– forces on the terminals due to the line connections,
– forces due to the wind,
– seismic forces,
– electro dynamic forces due to short circuit current
3.5.3
internal arc fault protection instrument transformer
instrument transformer designed in such a way to ensure an assigned protection level against
internal arc fault
3.6 Definitions related to gas insulation
3.6.1
pressure relief device
a device suitable to limit dangerous over-pressures inside the instrument transformer
3.6.2
gas-insulated metal-enclosed instrument transformer
metal-enclosed instrument transformer intended to be mounted on Gas-Insulated Switchgear
(GIS), inside or outside the switchgear enclosure
3.6.3
closed pressure system
volume that is replenished only periodically by manual connection to an external gas source
3.6.4
rated filling pressure
pressure referred to the standard atmospheric air conditions (20 °C and 101,3 kPa) to which
the gas-insulated instrument transformer is filled before being put in service, or periodicaly
replenished
3.6.5
minimum functional pressure
pressure referred to the standard atmospheric air conditions (20 °C and 101,3 kPa) at which,
and above which, rated insulation and other characteristics of the gas-insulated instrument
transformer are maintained and at which gas replenishment becomes necessary
3.6.6
design pressure of the enclosure
pressure used to determine the thickness of the enclosure. It is at least equal to the maximum
pressure of the enclosure at the highest temperature that the gas used for insulation can
reach under maximum service conditions.

61869-1 © IEC:2007 – 15 –
3.6.7
design temperature of the enclosure
highest temperature that can be reached by the enclosure under service conditions
3.6.8
absolute leakage rate
amount of gas escaped by time unit, expressed in Pa.m /s
3.6.9
relative leakage rate (F )
rel
absolute leakage rate related to the total amount of gas in the instrument transformer at rated
filling pressure (or density). It is expressed in percentage per year.
3.7 Index of abbreviations
IT Instrument Transformer
CT Current Transformer
CVT Capacitive Voltage Transformer
VT Voltage Transformer
AIS Air-Insulated Switchgear
GIS Gas-Insulated Switchgear
k actual transformation ratio
k rated transformation ratio
r
ε ratio error
Δφ phase displacement
S rated output
r
Usys highest voltage for system
U highest voltage for equipment
m
f rated frequency
R
F mechanical load
F relative leakage rate
rel
4 Normal and special service conditions
4.1 General
Unless otherwise specified, instrument transformers are intended to be used at their rated
4.2.
characteristics under the normal service conditions listed in
If the actual service conditions differ from these normal service conditions, instrument
transformers shall be designed to comply with any special service conditions required by the
purchaser, or appropriate arrangements shall be made (see 4.3).

– 16 – 61869-1 © IEC:2007
Detailed information concerning classification for environmental conditions is given in
IEC 60721-3-3 (indoor) and IEC 60721-3-4 (outdoor).
For gas-insulated metal-enclosed instrument transformers, Clause 2 of IEC 62271-203 is
applicable.
4.2 Normal service conditions
4.2.1 Ambient air temperature
Instrument transformers are classified in three categories as given in Table 1.
Table 1 – Temperature categories
Category Minimum temperature Maximum temperature
°C °C
–5/40 –5 40
–25/40 –25 40
–40/40 –40 40
NOTE 1 In the choice of the temperature category, storage and transportation conditions should also be
considered.
NOTE 2 In case of instrument transformers integrated within other equipment (e.g. GIS, circuit breaker) the
instrument transformer should be specified for the temperature conditions for the respective equipment.

4.2.2 Altitude
The altitude does not exceed 1 000 m.
4.2.3 Vibrations or earth tremors
Vibrations due to causes external to the instrument transformers or earth tremors are
negligible.
4.2.4 Other service conditions for indoor instrument transformers
Other considered service conditions are as follows:
a) the influence of solar radiation may be neglected;
b) the ambient air is not significantly polluted by dust, smoke, corrosive gases, vapours or
salt;
c) the conditions of humidity are as follows:
1) the average value of the relative humidity, measured for a period of 2
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