T 4 * - external thermal resistance (free air) adjusted for solar radiation, K.All current amendments available at time of purchase are included with the purchase of this document. T 4 - thermal resistance of surrounding medium, K.m/W T 3 - thermal resistance of external serving, K.m/W T 2 - thermal resistance between sheath and armour, K.m/W T 1 - thermal resistance per core between conductor and sheath, K.m/W resistance of the conductor per unit length, О©/m V - ratio of thermal resistivity of dry and moist soils For details, please refer to the first note in this series, which lists the other related notes. The calculation of each element needs some explanation and these have been split across several notes (with each note dealing with one topic). Note: when calculating a cable where some drying of the soil may occur, it is also necessary to perform the calculation for no drying out of soil and take the worse case (lower) rating. I = 0.5Д¬ables directly exposed to solar radiation I = ] 0.5Д«uried cables where drying-out of the soil is to be avoided The standard gives the following equations for the calculation of the cable current rating (for all alternating current voltages and direct current up to 5 kV):Д«uried cables where drying out of the soil does not occur or cables in airД«uried cables where partial drying-out of the soil occurs only effects and modified for partial drying of soil and solar radiation where appropriate. Within the standard this above is used to derive the equations for current rating. cable, the heat balance equation is given by (a list of symbols is given at the end of the note): In terms of the thermal model and for a simple a.c. For example, if a cable is run along a refrigerated gas pipe, we can hazard that this will reduce the О”О and hence the cable will be able to carry more current.Д¬hange in temperature across a material is equal to the heat input multiplied by the thermal resistance of the material.

Tip: the thermal model is worth remembering as enables us to intuitively understand how a cable is likely to behave in conditions which are not normally encountered. For cables which have varying or cyclic loads, the current rating could possibly be increased. Note: rated current capacity found by the method assumes that the cable is fully loaded for 100% of it's operation time. It can probably be appreciated by now, that in typical real life situations, this can be quite a complicated calculation. In thermal equilibrium, when all these factors have balanced and the temperature of the conductor is the maximum allowable for the insulation we have the maximum rated current for the cable. This is why we give the ebook compilations in this website. The rate of heat flow is related to the temperature difference across the cable and affected by the ambient temperature, temperature rises due to other cables and any critical temperature rise of the soil above ambient. iec-6-ed-4-0-b-2009-semiconductor-converters 1/1 Downloaded from 45.33.112.142 on Novemby guest Book Iec 60146 1 1 Ed 4 0 B 2009 Semiconductor Converters When people should go to the book stores, search introduction by shop, shelf by shelf, it is in fact problematic. Some or all of this heat is dissipated through the cable insulation, bedding, serving and into the surrounding medium. Heat is generated within the cable by various mechanisms - conductor I 2R loss, dielectric loss, sheath loss, armour loss and direct solar radiation. The image illustrates the thermal model for a cable. rated load are still in service, recommendations that are specific to this equipment are also included.

In the note we are going to put everything together and reveal the necessary equations for actually calculating the cable maximum current rating. We then looked at one method of applying the standard and identified resources enabling the calculation of all the various parameters involved. In the previous note we looked at the approach taken by the standard to the sizing of cables and illustrated this with an example. IEC 60287 Current Capacity of Cables - An Introduction Before you continue reading this note, if you have not done so already we would suggest first reading our IEC 60287 introduction note:

This note looks at the formulae used to calculate the rated current capacity of a cable in line with IEC 60287 'Calculation of the continuous current rating of cables (100% load factor)'.

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