Improving energy efficiency via proper cable sizig

[Avish]

Can someone please describe to me the various factors affecting cable
sizing, and the step-by-step procedures how to do it, with examples if
possible. This has to do with one-size up cabling in a textile manufacturing plant, and to analuse what effect this will have on the cost, and also about the payback.

 

Thanks.

[Spir Georges GHALI]

Avish said:

Can someone please describe to me the various factors affecting cable
sizing, and the step-by-step procedures how to do it, with examples if
possible. This has to do with one-size up cabling in a textile manufacturing plant, and to analuse what effect this will have on the cost, and also about the payback.

 

Thanks.

---

Dear Avish ;

 

I answered many time about the section of cables calculation and how should be done, noting that the last one was before about one week where the name of Topic is ” Cable Size ” with an example about it.

 

In all case, the factors that affect the cable's size accordignly to ” IEC… ” are :

     – The type of cable :

          – Single Core  or  Multi Cores

          – Cu   or  Alu 

          – PVC  or  XLPE

     – The number of cables per phase

     – The Method of Installation ” Unburied  or  Buried ” with the relevant ways for each one

     – The numer of layers

     – The ambient temperature

     – The number of cables have been laid together.

     – The Harmonics

 

After doing the necessary calculation and definingthe section of cable according to the above factors, we should take into consideration the following points :

– Calculate the percentage of ” Total Voltage Drop ” from the Source to the Load that should be compliance with the standard percentages, if not, the cable's section should be over sized.

– At the 1sf and the 2nd levels of the networks where the short circuit currents values are important, we should calculate the Thermal Stress to know if that cable can withstand it during the tripping time of the protection device, if not, the cable's section should be over sized.

 

Regards

[admin]

The earlier response gives you a good idea on how to correctly size the cable to work reliably and comply with standards. However there was another element to your question ant that was energy efficiency and payback which was not  really addressed.

This is a question of whether to oversize cables or not. Any cable has an loss due to its resistance. The correct selection of cable will result is a given loss. If you then select a cable of larger cross section, the resistance will be lower and thus the loss lower. To answer your question, you need to calculate the resitance of the minimum cable which will do the job. From this and the load current you can calculate the loss in the cable. From the operating cycle of the load over time you can calculate the kWHr consumption and from the $/kWhr cost you pay for electricity you can calculate how much it will cost over a period of time.

Do exactly the same for the cable of the next size up or even two sizes up.

You can then compare the two and you will know how much the bigger cables save you in energy costs and you can compare this with the capital cost of the larger cable to see if it is a value for money proposition. You have all the info that you need to run various payback scenarios on which to make a decision.

When you upsize cables make sure that the equipment you are feeding can accommodate the larger cables as equipment these days is often very tightly sized. Check what the fault current will now be because the larger cable will give less resistance and thus higher fault current. The cable wiill most probably handle it but will all other equipment in the chain.

Another aspect as to whether to choose aluminium or copper cable. You will need larger cross section aluminium cables than copper to achieve the same losses but often aluminium, even in the larger size is cheaper. Remember though here it is not just the cable cost to consider. The terminations are also more expensive as you often need bimetalic lugs, you need to make sure that the equipment you have is able to accommodayte the larger cross section on its teminations and the aluminium cables will occupy more area on your ladders or in conduits. Some atmospheres are also injurious to aluminium but not copper.

Hope that this satifactorily addresses your question.

[Author]

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