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Topic Title: 33/11kV Star - Star Transformer Earthing
Topic Summary: Cable Requirements
Created On: 27 January 2012 02:07 PM
Status: Read Only
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 27 January 2012 02:07 PM
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Joined: 25 July 2008

Dear Sirs

The 33kV side of the transformer is designed to be solidly earthed.

Please could someone correctly advise if a bare or sheathed copper conductor can be used or if the cable needs to be 33kV rated between the neutral and main earth connection?

Kind Regards
 28 January 2012 12:06 PM
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Would the basic principle adopted for 11kV generator to a NER be applicable?
ie. the star point (neutral) is a 6.35kV rated single core cable for 11kV and therefore for 33kV a cable rated at 19kV
 28 January 2012 02:48 PM
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I have seen it done several ways. Copper tape from the earth bar to the star point. Green yellow cable or Insulated cable as used for the phases.
If there is an NER you have to use insulated cable due to the volt drop across the resistor, but for solidly earthed you can use LV insulated cable or tape.
 28 January 2012 09:26 PM
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I agree. If it is solidly earthed (no NER), then you could run copper tape up to it. However, depending on where you are, these days there may be some merit in making it appear live to the untrained eye. We quite often put CTs on the neutral for the transformer protection, so this is another reason to keep it insulated. We often find that there is sufficient cable that we have used for the phases to make off the neutral, then take the end of this to the earth tape.



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