National foreword

This British Standard reproduces verbatim IEC 60853‑3:2002 and implements it as the UK national standard.

The UK participation in its preparation was entrusted by Technical Committee GEL/20, Electric cables, to Subcommittee GEL/20/16, Medium/high voltage cables, which has the responsibility to:

aid enquirers to understand the text;
present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed;
monitor related international and European developments and promulgate them in the UK.

A list of organizations represented on this subcommittee can be obtained on request to its secretary.

Cross-references

The British Standards which implement international publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online.

This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.

Compliance with a British Standard does not of itself confer immunity from legal obligations.

This British Standard, having been prepared under the direction of the Electrotechnical Sector Policy and Strategy Committee, was published under the authority of the Standards Policy and Strategy Committee on 23 September 2002

Summary of pages

This document comprises a front cover, an inside front cover, the IEC title page, pages 2 to 15 and a back cover.

The BSI copyright date displayed in this document indicates when the document was last issued.

FOREWORD

The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of the 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, the IEC publishes International Standards. 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. The IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
The formal decisions or agreements of the 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 National Committees.
The documents produced have the form of recommendations for international use and are published in the form of standards, technical specifications, technical reports or guides and they are accepted by the National Committees in that sense.
In order to promote international unification, IEC National Committees undertake to apply IEC International Standards transparently to the maximum extent possible in their national and regional standards. Any divergence between the IEC Standard and the corresponding national or regional standard shall be clearly indicated in the latter.
The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment declared to be in conformity with one of its standards.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 60853‑3 has been prepared by IEC technical committee 20: Electric cables.

The text of this standard is based on the following documents:

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 3.

Annexes A and B are for information only.

The committee has decided that the contents of this publication will remain unchanged until 2007. At this date, the publication will be

reconfirmed;
withdrawn;
replaced by a revised edition, or
amended.

INTRODUCTION

Methods for calculating cyclic ratings for cables installed in the ground are given in IEC 60853‑1 and IEC 60853‑2. Part 1 is applicable to cables having negligible thermal capacitance; Part 2 is applicable to cables where their thermal capacitance cannot be neglected.

A fundamental assumption in Part 1 and Part 2 is that the thermal properties of the soil are uniform throughout the thermal field of the cable. For many installations, such an assumption is acceptable and further refinement is unnecessary.

However, higher working temperatures increase the probability that the soil immediately around a cable may lose so much of its moisture that it dries out to a significantly higher value of thermal resistivity than that corresponding to its normal site condition. The reduction in permissible current-carrying capacity of a cable, necessary to avoid overheating, can be significant.

1 Scope

This part of IEC 60853 gives a method for calculating the cyclic rating factor, for cables of all voltages, where partial drying out of the surrounding soil is anticipated. The method is based on one of the three methods published in a CIGRE¹ document. The method is applicable to any type of cable, but it is recommended that it should be applied only to installations of one multi-core cable or to three single-core cables or to groups of circuits where the intercircuit spacing is sufficient to permit free vertical movement of soil moisture between the zones of dry soil associated with each circuit. This standard does not preclude the use of other methods of calculation where full details of the load cycle are not known.

The method assumes that the entire region surrounding a cable or cables has uniform thermal characteristics prior to drying out; the only non-uniformity being that caused by drying. As a consequence the method should not be applied, without further consideration, to installations where special backfills, having properties different from the site soil, are used.

2 Normative references

3 Symbols

4 Description of method

4.1 General description

4.2 Principles

4.3 Formulae

BS IEC 60853-3:2002

Calculation of the cyclic and emergency current rating of cables - Cyclic rating factor for cables of all voltages, with partial drying of the soil

Current

Published:

23 Sep 2002