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'[EE]:: Superb paper - Review of Power Cable Standa'
2012\07\02@051836 by RussellMc

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Review of Power Cable Standard Rating Methods

Probably  part of
"Rating of Electric Power Cables in Unfavorable Thermal Environment"
By George J. Anders 1
ISBN 0-471-67909-7 © 2004 the Institute of Electrical and Electronics Engineers.

Aimed at non-standard and diffuclt cases where rote application of
relevant standards my not be adequate.





Calculation of the current-carrying capability, or ampacity, of
electric power cables
has been extensively discussed in the literature and is the subject of
several international and national standards. The main international
standards are those issued by
the International Electrotechnical Commission (IEC) and the Institute
of Electrical
and Electronic Engineers (IEEE). References at the end of this chapter
list the documents either issued or sponsored by these two
organizations. The calculation procedures in both standards are, in
principle, the same, with the IEC method incorporating several new
developments that took place after the publication of the Neher
and McGrath (NM) paper (1957). Similarities in the approaches are not
since during the preparation of the standard, Mr. McGrath was in touch with the
Chairman of Working Group 10 of IEC Subcommittee 20A (responsible for the
preparation of ampacity calculation standards). The major difference between the
two approaches is the use of metric units in IEC 60287 and imperial units in NM
paper (the same equations look completely different because of this).
Even though
the methods are similar in principle, the IEC document is more
comprehensive than
the NM paper. IEC 60287 not only contains all the formulas (with minor
listed in Appendix F of Anders, 1997) of the NM paper, but, in several cases, it
makes a distinction between different cable types and installation
conditions where
the NM paper does not make such a distinction. Also, the constants
used in the IEC
document are more up to date.

Nevertheless, the principles of heat transfer for buried cables applied in both
standards are the same, and the resulting equations will be reviewed
in this chapter.
The ampacity calculations are usually carried out in two different
ways. On the one
hand, steady-state or continuous ratings are sought; and, on the
other, time-dependent or transient calculations are performed. In both
cases, for cables buried underground, soil dry out caused by the heat
generated in the cable might be considered.
The calculation methods for cables in air are slightly different in
both standards
and, where applicable, the differences will be brought up in this
book. For cables installed in air, the presence of solar radiation and
wind may have profound effects on
Rating of Electric Power Cables in Unfavorable Thermal Environment. By
George J. Anders 1
ISBN 0-471-67909-7 © 2004 the Institute of Electrical and Electronics Engineers.

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