Iec 60287 3 1 2017

IEC 60287 3 1 Edition 2 0 201 7 06 INTERNATIONAL STANDARD NORME INTERNATIONALE Electric cables – Calculation of the current rating – Part 3 1 Operating conditions – Site reference conditions Câbles él[.]

Operating conditions – Site reference conditions

In order to use the formulae given in the various parts of IEC 60287, numerical values for the physical quantities should be chosen relating to the operating conditions

It is obviously possible to compare the results of two calculations of current rating only when the assumptions made and the numerical values of the parameters are known

Operating conditions of cables vary significantly across different countries, as revealed by an international enquiry that gathered responses from multiple nations.

Annex A provides a summary of operating conditions across various countries, serving as a guide for cable installation designers when user data is incomplete It is important to avoid drawing unjustified conclusions from comparing values between countries, as each country's adopted values are influenced by multiple factors that may vary in significance elsewhere.

Values relating to the operating conditions are given in Annex A for the following countries:

France Oman United States of America

Procedure when values are not provided in national tables

General

When national tables do not specify values for reference ambient temperature, soil thermal resistivity, or solar radiation, it is recommended to use the values provided in sections 4.2.2, 4.2.3, and 4.2.4.

Ambient temperatures at sea level

Table 1 – Ambient temperatures at sea level

Ambient air temperature Ambient ground temperature at a depth of 1 m Min °C Max °C Min °C Max °C

It is crucial that current ratings are valid for the maximum specified temperatures, with lower values applicable for winter ratings when necessary These ratings align with temperature limits corresponding to seasonal variations, such as winter and summer or rainy and dry periods, ensuring accurate and reliable performance across different environmental conditions.

When no information about the depth of laying is given, the standard depth is to be taken as 1 m.

Thermal resistivity of soil

Table 2 – Thermal resistivity of soil

Very moist Moist Dry Very dry

Continuously moist Regular rainfall Seldom rains Little or no rain

Solar radiation

When no information about the intensity of solar radiation a value of 1 000 W/m 2 is adopted.

Australia

Thermal characteristics of the soil

Depth of laying of cables a

Voltage range 1 : L.V cables under footways under roadways

0,5 0,75 m m Voltage range 2: 1 1 kV cables under footways and roadways 0,8 m

Voltage range 3: 33 kV cables and higher voltages under footways and roadways 1 ,0 m

Maximum, winter +30 °C a Measured from the ground surface to the centre of the cable, or to the centre of a trefoil group.

Austria

Thermal resistivity, nominal, season 1 (wet) 1 ,0 Kã m/W

Thermal resistivity, dry zone, season 1 (dry) 2,5 Kã m/W

Depth of laying of cables

Voltage range 1 : up to 1 kV 0,7 m

Voltage range 2: > 1 kV up to 30 kV 0,8 m

Canada

Canada does not have standardized national values for soil thermal resistivity, temperature, or cable laying depth; however, typical values are available It is strongly recommended to conduct soil tests whenever possible to ensure accurate data for cable installations.

Thermal resistivity, nominal 0,5 to 3,0 Kã m/W

Depth of laying of cables (minimum cover)

Paper insulated, solid and non-draining cables for voltages up to 69 kV 1 ,1 m

Solid insulation (butyl, ethylene propylene rubber, p.v.c., cross- linked polyethylene, etc.) cables for voltages up to 46 kV 0,9 m

Oil filled cables for voltages up to 345 kV 1 ,1 m

Pipe-type (gas or oil pressure) cables for voltages up to 345 kV 1 ,1 m

Drying out is not considered for cables in concrete duct banks

When direct measurements of soil thermal resistivity are unavailable, a value of 0.9 K·m/W is typically assumed However, in situations where there may be gradual deterioration of the soil's thermal properties over time or significant seasonal climatic variations, it is advisable to base the current-carrying capacity calculations on a higher thermal resistivity of 1.2 K·m/W to ensure accuracy and reliability.

Reference is not made to lower values of resistivity, during winter, as a basis for system design to any significant extent.

China 1 0

Egypt 1 0

Intensity of solar radiation ≥1 000 W/m2 a Note at soil temperature 25 °C.

Finland 1 1

Average value to be used for rating calculations 1 ,0 Kã m/W

For submarine cables where the soil is completely saturated with water 0,4 Kã m/W

(average value 5 °C to 1 0 °C, exceptional maximum 20 °C)

All cables up to 36 kV 0,7 m

All cables up to 52 kV 1 ,0 m

All cables up to 1 23 kV 1 ,3 m

All cables up to 245 kV 1 ,5 m

The actual depth depends on local conditions

Reference value for rating calculations 25 °C

France 1 2

Thermal resistivity, nominal, summer 1 ,20 Kã m/W

Thermal resistivity, nominal, winter 0,85 Kã m/W

Thermal resistivity, dry zone a , summer 2,5 Kã m/W

Thermal resistivity, dry zone a , winter 2,5 Kã m/W

63 kV, 90 kV, 225 kV, 400 kV cables hot area 25 °C intermediate area 22 °C cold area 20 °C

63 kV, 90 kV, 225 kV and 400 kV cables hot region 1 7 °C intermediate region 1 5 °C cold region 1 3 °C

20 kV cables in Paris 1 ,0 to 1 ,2 m outside Paris city 0,8 m

63 kV, 90 kV, 225 kV and 400 kV cables 1 ,3 m

Intensity of solar radiation 1 000 W/m 2 a Drying out of the soil is only considered for high voltage systems.

Germany 1 3

The indicated values serve as standard references for current rating calculations, provided there are no specific requirements regarding soil thermal resistivity, ambient temperature, or cable laying depth.

Thermal resistivity, average value 1 ,0 Kã m/W

Thermal resistivity, for calculations considering a dry zone near the cable – for the dry zone 2,5 Kã m/W

Tem peratu re, maximum value 20 °C

Tem peratu re, minimum value 0 °C

Tem peratu re, average value 1 0 °C

Average value 1 0 °C a In spite of being calculated for 0,7 m, often cables at 20 kV to 30 kV are laid at 0,9 m to 1 ,0 m depth.

Italy 1 4

Thermal resistivity, maximum value 1 ,0 Kã m/W

If the soil exhibits poor thermal characteristics, an appropriate backfill material is used to improve conditions, with thermal resistivity values considered as an intermediate between the backfill and the surrounding soil.

Tem peratu re, maximum value (to be used in calculations) 20 °C

Tem peratu re, minimum value 5 °C

This depth is the maximum adopted unless otherwise specified

Maximum value (to be used in calculations) 30 °C

During summer, temperatures can occasionally exceed the typical maximum by up to 5 °C for a few hours each day, and in rare cases, even higher This temporary increase is generally considered acceptable due to its brief duration.

1 ,5 K⋅m/W, 1 ,0 K⋅m/W and 0,6 K m/W for dry, normal and wet soil respectively No distinction for seasons

Direct burial: 1 ,2 m for places where the pressure of vehicle or other heavy goods may be applied 0,6 m for other places

In duct: the use of duct which withstands the pressure of vehicle or other heavy goods is required (there is no regulation for the depth of duct)

The Japanese Cable Makers’ Association Standard JCS 0501 provides calculation formulas for the thermal resistance of soil using a two-layer model with distinct thermal resistivities separated by a boundary, such as the groundwater level Consequently, the groundwater level is a key factor influencing variations in soil thermal resistivity.

Thermal resistivity, nominal season 1 (summer)

Thermal resistivity, nominal season 2 (winter)

Thermal resistivity, dry zone season 1 (summer)

Thermal resistivity, dry zone season 2 (winter)

In the absence of direct measurements, soil thermal resistivity is commonly assumed to be 1.5 K·m/W; however, for critical cable installations, it is highly recommended to conduct a thorough survey of the soil's thermal properties to ensure accurate assessment and optimal performance.

When soil temperature measurements are not available a reference value of 25 °C is often used for rating calculations

Depth of laying of cables a b

Voltage range 1 : up to 1 kV cables (maximum 2 circuits)

Voltage range 2: > 1 kV up to 35 kV cables (5 kV, 1 5 kV, 25 kV and 35 kV, maximum 4 circuits)

Voltage range 3: > 35 kV up to1 38 kV cables (69 kV, 85 kV,

1 1 5 kV and 1 38 kV, maximum 2 circuits)

Only under roadways (normal terrain) 1 ,0 m

Only under roadways (phreatic zone or rock soils) 0,5 m

Voltage range 4: > 1 61 kV up to 230 kV cables (1 61 kV and

Voltage range 5: ≥ 400 kV cables (maximum 2 circuits)

Critical temperature or temperature rise 35 to 50 °C

The critical temperature significantly depends on soil composition and location, and it can also fluctuate due to seasonal changes and cyclic loading It is advisable to assess the critical temperature during a soil survey unless it is proven that the soil will not experience drying.

The soil thermal resistivity and temperature values presented are based on measurements taken at various locations in Mexico at different depths, including 0 m, 0.9 m, 1.2 m, and 1.5 m It is recommended to conduct soil measurements whenever possible for cable installations to ensure accuracy Measurements are typically taken from the ground surface to the top of the cable ducts or the top of a trefoil duct group, with cables always installed in HDPE ducts Depths may vary depending on underground obstacles along the cable route Additionally, direct normal irradiance or beam solar radiation values represent the maximum annual levels occurring over short time periods.

It is recommended that a survey of the thermal characteristics of the soil is carried out for critical cable links

Thermal resistivity, dry zone 2,5 Kã m/W

It is recommended that a survey of the thermal characteristics of the soil is carried out for critical cable links

The critical temperature varies significantly based on soil composition and geographic location, and it can also be influenced by seasonal changes and cyclic loading It is essential to determine the critical temperature during a soil survey unless it is proven that the soil will not experience drying.

The two-zone model is commonly employed to determine the current rating of medium voltage (MV) cable systems and, occasionally, high voltage (HV) systems This model defines the boundary between wet and dry zones based on the absolute temperature, specifically the isotherm at this boundary, which typically falls within a certain temperature range.

30 °C (MV cables) and 50 °C (HV cables)

Cable circuits are considered thermally independent when the separation between them is at least 3 meters For cables installed at depths greater than 3 meters, such as those placed using horizontal directional drilling, the minimum separation required to maintain thermal independence increases to 5 meters.

Depth of laying of cables a

This depth is the minimum adopted unless otherwise specified

Voltage range 1 : L.V under footways 0,5 m under roadways 0,75 M

Voltage range 2: 1 1 kV under footways and roadways 1 ,0 m

Voltage range 3: 33kV and higher under footways and roadways 1 ,0 m

Maximum winter +30 °C a Measured from the ground surface to the centre of the cable, or to the centre of a trefoil group

Thermal resistivity, average value to be used in calculations 1 ,0 Kã m/W

Temperature, Southern Norway m ax /m in 1 7/0 °C

Tem perature, Central Norway m ax /m in 1 5/0 °C

Tem perature, Northern Norway max /m in 1 3/-5 °C

Depth of laying of cables (minimum value)

Maximum value (to be used in calculations) 25 °C

Temperature, average value to be used in calculations 20 °C

Depth of laying of cables up to and including 36 kV 0,7 m above 36 kV 1 ,0 m

Average value to be used in calculations 25 °C

Thermal resistivity, nominal, winter 0,85 Kã m/W

Thermal resistivity, nominal, submarine cables 1 ,0 Kã m/W

This depth is the minimum adopted unless otherwise specified

Voltage range up to 1 kV 0,7 m

Voltage range up to 30 kV 1 ,0 m

Voltage range up to 400 kV 1 ,2 m

Air ambient temperature, summer (at sea level) 30 °C

Air ambient temperature, winter (at sea level) 20 °C

There are no recognized Spanish national values of soil thermal resistivities, ambient temperatures and depth of laying, the values shown below are typical

Thermal resistivity, Cables ≤0, 6/1 kV 1 Kã m/W

Thermal resistivity, Cables >0, 6/1 kV and ≤1 8/30 kV 1 ,5 Kã m/W

Thermal resistivity, Cables >1 8/30 kV 1 Kã m/W

Where concrete is used for the cable installation it should be considered for the calculation a value of 0,85 K m/W for the volume occupied by the concrete 0,85 Kã m/W

Voltage range 2: all higher voltages 0,8 m

Intensity of solar radiation (inland) 1 250 W/m 2

Intensity of solar radiation (coast) 1 000 W/m 2

Sweden

Where the soil is completely saturated with water and for submarine cables where the bottom is covered with sand 0,4 Kã m/W

Maximum value for submarine cables 1 ,0 Kã m/W

For important cables, a measurement of the resistivity and soil conditions on the sea bottom is recommended, otherwise: 0,6 Kã m/W

(for main part of the year between 5 °C and 1 0 °C)

For directly buried cables and for short road crossings by means of ducts

Paper-insulated cables up to 52 kV 0,7 m

Oil-filled cables up to 420 kV 1 ,0 to 1 ,5 a m a The depth depends on local conditions Less than 1 000 mm is not used.

Switzerland

Thermal resistivity, nominal, summer (May – October) 1 ,0 Kã m/W

Thermal resistivity, nominal, winter (November – April) 0,85 Kã m/W

Thermal resistivity, rocky soil, summer 1 ,3 Kã m/W

Thermal resistivity, rocky soil, winter 1 ,3 Kã m/W

Voltage range 1 0 kV to 30 kV 0,8 m

Voltage range 50 kV to 400 kV 1 ,0 m

Intensity of solar radiation, Swiss plateau (Mittelland) 1 000 W/m 2

Intensity of solar radiation, Alpine region (Alpenraum) 1 200 W/m 2

Cables are usually laid in HDPE pipes.

United Kingdom

HV

Thermal resistivity, nominal, winter 1 ,05 Kã m/W

Thermal resistivity, dry zone, winter 1 ,05 Kã m/W

Thermal resistivity, dry zone, summer

0,9 min (general) 0,75 min (substation sites) 0,825 min (Scotland) m m m Air ambient temperature

LV/MV

Thermal resistivity, nominal, season 2 No distinction for seasons Thermal resistivity, dry zone

Temperature, season 2 No distinction for seasons °C

Voltage range 2: 3 kV to 33 kV 0,8 m

Historically a 3 m circuit separation at normal cable depths is assumed to be thermally independent – under review.

United States of America

When circuits are separated 3,7 m (1 2 feet) or more they are considered thermally independent

IEC 60287 (all parts), Electric cables – Calculation of the current rating

This article provides reference ambient temperature values and soil thermal resistivities across various countries, detailing site-specific operating conditions and guidelines when national data is unavailable It covers general principles, sea-level ambient temperatures, soil thermal resistivity, and solar radiation factors An informative annex presents country-specific data for Australia, Austria, Canada, China, Egypt, Finland, France, Germany, Italy, Japan, Mexico, the Netherlands, New Zealand, Norway, Oman, Poland, Portugal, Spain, South Africa, Sweden, Switzerland, the United Kingdom (including high, low, and medium voltage conditions), and the United States Key tables include sea-level ambient temperatures and soil thermal resistivity, supporting accurate thermal assessments in diverse geographic contexts.

CÂBLES ÉLECTRIQUES – CALCUL DU COURANT ADMISSIBLE –

Conditions du site de référence

The International Electrotechnical Commission (IEC) is a global standardization organization composed of national electrotechnical committees Its primary objective is to promote international cooperation on standardization issues in the fields of electricity and electronics To achieve this, the IEC publishes international standards, technical specifications, technical reports, publicly available specifications (PAS), and guides, collectively known as IEC publications These documents are developed by study committees, with participation from any interested national committee and relevant international governmental and non-governmental organizations The IEC also works closely with the International Organization for Standardization (ISO) under mutually agreed terms to ensure coordinated efforts in standardization.

Official decisions or agreements by the IEC on technical matters represent, as much as possible, an international consensus on the topics studied, since the IEC National Committees involved are represented in each study committee.

IEC Publications are presented as international recommendations and are approved as such by the IEC National Committees Every reasonable effort is made to ensure the technical accuracy of IEC publications; however, the IEC cannot be held responsible for any misuse or misinterpretation by end users.

To promote international uniformity, IEC National Committees commit to transparently applying IEC Publications in their national and regional publications whenever possible Any discrepancies between IEC Publications and corresponding national or regional publications must be clearly stated in the latter.

The IEC itself does not provide any conformity certificates Independent certification bodies offer conformity assessment services and, in certain sectors, grant access to IEC conformity marks The IEC is not responsible for any services performed by these independent certification organizations.

6) Tous les utilisateurs doivent s'assurer qu'ils sont en possession de la dernière édition de cette publication

No liability shall be attributed to the IEC, its directors, employees, auxiliaries, or agents, including its experts and members of its study committees and National Committees, for any harm caused by bodily injury, material damage, or any other type of direct or indirect damage This also includes any costs (such as legal fees) and expenses arising from the publication or use of this IEC Publication or any other IEC Publication, or from the credit given to it.

8) L'attention est attirée sur les références normatives citées dans cette publication L'utilisation de publications référencées est obligatoire pour une application correcte de la présente publication

Attention is drawn to the fact that some elements of this IEC Publication may be subject to patent rights The IEC cannot be held responsible for failing to identify such patent rights or to indicate their existence.

La Norme internationale IEC 60287-3-1 Ed.2 a été établie par le comité d'études 20 de l’IEC: Câbles électriques

This second edition cancels and replaces the first edition published in 1995 and Amendment 1:1999 It represents a technical revision, including major technical changes compared to the previous edition Notably, the updated list of national installation conditions is now covered in Annex A, and Article 5, which required buyer information to select the appropriate cable type, has been removed.

Le texte de cette norme est issu des documents suivants:

Le rapport de vote indiqué dans le tableau ci-dessus donne toute information sur le vote ayant abouti à l'approbation de cette norme

Cette publication a été rédigée selon les Directives ISO/IEC, Partie 2

A comprehensive list of all parts of the IEC 60287 series, published under the general title "Electric Cables – Calculation of Current Rating," is available on the IEC website.

The reader's attention is drawn to Annex A, which lists all articles addressing less permanent differences inherent to certain countries related to the subject of this standard.

The committee has decided that the content of this publication will remain unchanged until the stability date specified on the IEC website at "http://webstore.iec.ch" within the data related to the searched publication On that date, the publication will be reviewed accordingly.

• remplacée par une édition révisée, ou

L'IEC 60287 a été divisée en trois parties de manière à faciliter les révisions et les adjonctions

Chaque partie est subdivisée en sous-parties qui sont publiées en tant que normes séparées

Partie 1 : Équations de l'intensité du courant admissible (facteur de charge 1 00 %) et calcul des pertes

Partie 2: Équations de la résistance thermique

La présente partie de l'IEC 60287-3 contient des valeurs des températures ambiantes de référence et des résistivités thermiques des sols dans divers pays

Operating conditions for cables can vary significantly from one country to another, particularly regarding ambient temperature and soil thermal resistivity, which are governed by different national standards Superficial comparisons of these values across countries may lead to incorrect conclusions if not based on common criteria, such as differing cable lifespan expectations Some countries design using maximum soil thermal resistivity values, while others use average values Notably, soil thermal resistivity is highly sensitive to moisture content and can fluctuate over time depending on soil type, topography, weather conditions, and cable load.

Il convient par conséquent d'adopter la méthode suivante pour le choix des valeurs des différents paramètres

It is recommended that numerical values be based on valid measurement results Such results are often included in national specifications as recommended values, allowing calculations to be performed using values commonly applied within the respective country An overview of these values is provided in this part of IEC 60287-3.

CÂBLES ÉLECTRIQUES – CALCUL DU COURANT ADMISSIBLE –

Conditions du site de référence

This part of IEC 60287-3 applies to the steady-state operating conditions of cables of all voltages, whether buried directly in the ground, placed in ducts, trenches, or steel tubes, with or without partial soil drying, as well as cables installed in open air Steady-state operation refers to the continuous flow of a constant current (100% load factor) sufficient to asymptotically produce the maximum conductor temperature, assuming ambient conditions remain constant.

Le présent document définit les conditions du site de référence, cependant les valeurs générales sont remplacées par les exigences spécifiques nationales

Le présent document ne contient aucune référence normative

Aucun terme n'est défini dans le présent document

L'ISO et l'IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en normalisation, consultables aux adresses suivantes:

• IEC Electropedia: disponible à l'adresse http://www.electropedia.org/

• ISO Online browsing platform: disponible à l'adresse http://www.iso.org/obp

4 Valeurs des températures ambiantes de référence et résistivités thermiques des sols dans divers pays

4.1 Conditions de fonctionnement – Conditions du site de référence

Afin d'utiliser les formules données dans les différentes parties de l'IEC 60287, il convient de choisir les valeurs numériques des grandeurs physiques en fonction des conditions de fonctionnement

Il n'est évidemment possible de comparer les résultats de deux calculs de courant admissible que si les hypothèses faites et les valeurs numériques des paramètres sont connues

Tiêu đề	IEC 60287-3-1:2017-06 - Calculation of current rating - Part 3-1: Operating conditions - Site reference conditions
Trường học	International Electrotechnical Commission
Chuyên ngành	Electrical Standards
Thể loại	Standard
Năm xuất bản	2017
Thành phố	Geneva

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Số trang	54
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