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Topic Title: 132/11 KV Transformer Cables
Topic Summary: Sizing of 11 KV Cables
Created On: 12 October 2013 03:15 PM
Status: Read Only
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 12 October 2013 03:15 PM
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Joined: 10 November 2009


I have done electrical installation of 132/11 KV substation in UAE in the past.

As per drawings, there are 6 runs of 1C X 800 mm2 XLPE copper cables per phase from transformer 11 KV side to 11 KV switchgear panel. This totals 18 runs for three phases.

I doubt the system is over designed. Can anybody guide me?

Transformer particulars are 50 MVA, 132/11 KV, 37.5% impedance, YdN, ONAF.

 24 October 2013 04:33 AM
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What is the short circuit rating for switchgear and distance of cable run between switchgear panel and transformer?
 24 October 2013 05:50 AM
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Well and truly over engineered.

Three of the secondary tails per phase would suffice and that's being cautious.

Although it's not a part of the original question, what is the fault rating of the 11KV switchgear? Sorry I've only dealt with up to 20MVA @ 11KV.

Could there be a better way?

In theory yes, but in practice?
 29 October 2013 10:17 AM
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Not necessarily, the installation details have not been given. As a rough example:

ABB XLPE Cable Systems User Guide (available from the ABB website) gives rating for 800 Cu in trefoil with solid bonding as 930 A for buried.

But this is at 20°C, UAE will be hotter say 40°C - derating 0.84.

3 groups with 400 mm between each trefoil group would derate by 0.77; 6 groups by 0.66.

So rating for 3 is 601 A x 3 = 1803 A or 34 MVA (i.e. too little); rating for 6 is 515 A x 6 = 3090 A or 59 MVA (i.e. a little to spare).

There are other factors that will apply but this suggests that it could be reasonable depending on the installation.



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