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To calculate the cross-sectional area of the copper busbar, it is necessary to calculate the permissible current of the busbar. One of the correction coefficients that must be multiplied in this current is "the copper busbar surface temperature correction coefficient". How should I find this coefficient? Is there a table for this purpose?

Icont = Itable × k1 × k2 × k3 × k4 × k5

Calculation of the cross-sectional area of the tire The calculation ofthe permissible current that can pass through the busbar is done using the following formula and applying correction coefficients:

(1-6) Icont = Itable × k1 × k2 × k3 × k4 × k5

Icont: allowed continuous busbar current (final)

Itable: allowed continuous busbar current according to table (6-9) or (6-10)

k1: the correction factor related to the conductivity of the busbar if the conductivity of the copper busbar used is not 56 m/Ωmm2 or the conductivity of the aluminum busbar is not 35.1 m/Ωmm2. Figure (6-11)

k2: correction factor related to ambient temperature other than 35 degrees Celsius and tire surface temperature other than 65 degrees Celsius (Figure 12-6)

k3: correction factor related to the installation of tires in a flat or vertical installation with a length of more than 2 meters (Table 7-6)

k4: correction factor related to skin effect in alternating current up to 60HZ according to the layout of the busbars, if no branch is taken at a distance of more than 2 meters from the busbar (Figures 13-6 and 14-6)

k5: the correction factor related to the reduction of the current capacity of the tire at a height of more than 1000 meters above sea level (Table 8-6)

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  • \$\begingroup\$ Where did you come across this term you refer to (copper busbar surface temperature correction coefficient)? \$\endgroup\$
    – Andy aka
    Commented Jan 21 at 12:02
  • \$\begingroup\$ @Andyaka This formula was written in a PDF file. I really searched a lot for this topic, but I couldn't find anything to guide me. \$\endgroup\$
    – Bahman.MD
    Commented Jan 21 at 12:07
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    \$\begingroup\$ You need to link the pdf file. \$\endgroup\$
    – Andy aka
    Commented Jan 21 at 12:08
  • \$\begingroup\$ The PDF file is not in English and I will edit the question and put a part of it. \$\endgroup\$
    – Bahman.MD
    Commented Jan 21 at 12:14
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    \$\begingroup\$ There may be an English translation. Or, find an equivalent document that talks about the terms you mention. \$\endgroup\$
    – Andy aka
    Commented Jan 21 at 12:15

2 Answers 2

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Assuming you are asking about the k2 factor, first order power dissipation (ignoring radiation, conduction, etc) is driven by the temperature difference between the busbar and ambient.

The standard tables often (but not always) assume 35C ambient, and a maximum busbar surface temperature of 65C. If you can allow higher surface temperatures (ignoring burn risk) or lower ambient (reliable cooling or simply cold environment) the busbar will be able to carry more current. If the opposite is the case, capacity will be less.

Again to a first order, the power dissipation is proportional to busbar-ambient delta, so if the tables assume a 30C delta, then limiting surface temperature to 55C would equate to a correct factor of 0.67, whilst allowing 75C would give a factor of 1.33.

However, most tables will include those correction factors under a range of conditions.

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  • \$\begingroup\$ Are the items you mentioned available somewhere like a table in the IEC standards? \$\endgroup\$
    – Bahman.MD
    Commented Jan 21 at 13:48
  • \$\begingroup\$ And another question, is it better to always consider the maximum temperature of 65 degrees Celsius to calculate the sizing of the cross section of the busbar, or does it depend on specific conditions? \$\endgroup\$
    – Bahman.MD
    Commented Jan 21 at 13:56
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    \$\begingroup\$ @Bahman.MD "Standard tables" always give the assumptions they assume such as ambient temperature and even correction factors away from that value. \$\endgroup\$
    – Solar Mike
    Commented Jan 21 at 17:11
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There are an amazing number of effects on what current, in practice, a given busbar can support. I recommend the extremely complete monograph:

  • Copper for Busbars – Guidance for Design and Installation, David Chapman and Prof. Toby Norris, The Copper Alliance Pub. 22, (2014 ed., 103 pp)

You can find this online (free) at Leonardo Energy.

Also of interest are the tables and materials listed at the Copper Development Asasociation's busbar page.

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  • \$\begingroup\$ Agree well worth a read. One of my favourite effects is the increase in capacity with age; due to increased emmesivity as the bars oxidize. \$\endgroup\$
    – colintd
    Commented Jan 21 at 23:00

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