IEC , Electric cables – Calculation of the current rating – Part 2: Thermal resistance – Section 1: Calculation of thermal resistance. IEC Electric cables – Calculation of the current rating – Part 1: Current rating equations (% load factor) and calculation of losses – Section 1: General . IEC Standard ().  Electric Cables – Calculation of the current rating – Part 2: Thermal resistance – Section 2A: A method for calculating.
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Before you continue reading this note, if you have not done so already we would suggest first reading our IEC introduction note:.
In the previous note we looked at the approach taken by the standard to the sizing of cables and illustrated this with an example. We then looked at one method of applying the standard and identified resources enabling the calculation of all the various parameters involved. In the note we are going to put everything together and reveal the necessary equations for actually calculating the cable maximum current rating.
Some or all of this heat is dissipated through the cable insulation, bedding, serving and into the surrounding medium. 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.
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. It can probably be appreciated by now, that in typical real life situations, this can be quite a complicated calculation.
For cables which have varying or cyclic loads, the current rating could possibly be increased. Change in temperature across a material is equal to the heat input multiplied by the thermal resistance of the material. In terms of the thermal model and for a simple a.
Within the standard this above is used to derive the equations for current rating. It is simplified for d. 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:.
IEC 60287 Current Capacity of Cables – Rated Current
The calculation 27-2-1 each element needs some explanation and these have been split across several notes with each note dealing with one topic.
For details, please refer to the first note in this serieswhich lists the other related notes. Steven has over twenty five years experience working on some of the largest construction projects. He has a deep technical understanding of electrical engineering and is keen to share this knowledge.
I dont know how i can thank you for the great information’s you provide,and its really appreciated. Just to notify you, but correct me if I’m wrong. I need to use your calculation but there is a mistake with the factorisation of 28-2-1 denominator in the formula for buried cables where drying-out of the soil occur for AC cable. It looks logical, otherwise we would have been a squared resistance in the denominator.
Thanks for the feedback. I’ve modified the drying out equations slightly. Let me know if you have still think something is wrong. Just another thing I’ve just noticed still easy to figure out because of unexpected results in the section “Buried cables where drying-out of the soil is to be avoided”, AC part, in the numerator, it should be a subtraction instead of an addition.
To let a positive comment, I find your website very helpful. Paul, please feel free to keep pointing out problems. Feedback is one way I can improve the articles. IECitself does have the correct equation. When significant, it becomes a factor to be considered in the sizing of cables. This note looks at how to obtain the necessary loss factors for use within This formulas really helpful, but my question is what is the limit of overcurrent carrying capacity of cable?
Arjijit, I’m not to sure exactly what you are asking. The equations give a safe steady state rated current 287–2-1 a cable.
If you exceed this value of current, you could be affecting the life of the cable. The more you exceed the greater the effect. My view is that you should used the equations to select the cable based on your anticipated current rating. You then select an approppropriate protective device to isolated the cable should you exceed this value.
If you have a load current which is genuinely varying, you could use IEC “Calculation of the cyclic and emergency current rating of cables. Have an opinion or something to say, want to ask or answer questions, share your knowledge then 287-21- our site to do it. As a community of ief interested A UPS is an uninterruptible power supply.
It is a device which maintains a continuous supply of electrical power, even iwc the event of failure of the Dielectrics insulating materials for example when subjected to a varying electric field, will have some energy loss.
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They have started applying this at the Louisville The European Union is implementing a voluntary code of practice ice participants with the aim of improving the overall efficiency of data centres. It a good demonstration of innovative The standard aims to consolidate AC and traction voltages within the industry and defines the following bands: Electric motors are one lec the most widely used items of electrical equipment.
Improving motor efficiency benefits include, reduced power demand, lower While software is a great asset, many times If you have some expert knowledge or experience, why not consider sharing this with our community. Steven McFadyen Steven has over twenty five years experience working on some of the largest construction projects. About the author myElectrical Engineering. View 8 Comments old system. Comments are closed for this post: Contribute to 28-72-1 Have an opinion or something to say, want to ask or answer questions, share your knowledge then use our site to do it.
Dielectric loss in cables Dielectrics insulating materials for example when subjected to a varying electric field, will have some energy loss. EU Code of Conduct on Data Centres – Best Practices The European Union is implementing a voluntary code of practice for participants with the aim of improving the overall efficiency of data centres. Meeting room of the future The IET site has a video of a visit showing of a high tech meeting room developed at Napier University in Edinburgh.
Voltage Levels to IEC The standard aims to consolidate AC and traction voltages within the industry and defines the following bands: Motor Efficiency Classification Electric motors are one of the most widely used items of electrical equipment.
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Have some knowledge oec share If you have some expert knowledge or experience, why not consider sharing this with our community. Copyright c myElectrical. Click here to view the notes indexed by tag.