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Topic Title: Why 433V
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Created On: 19 July 2013 08:45 AM
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 19 July 2013 08:45 AM
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On say a UK installed transformer 1000KVA 11kV/433V I see why we would need a rating above 400V to address volt drop but why the magic figure of 433V?
 19 July 2013 11:50 AM
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433V is the no load votlage at the transformer secondary terminals. It is industry practice to quote the no load voltage. When a load is connected there will be voltage drop within the transformer windings.
 19 July 2013 04:22 PM
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415V was the nominal voltage on full load...... 433V is the no load voltage which allows for 18V internal volt drop....
The % impedance or 'voltage impedance' of the transformer is related to the internal voltage drop.... therefore a 4% transformer would typically have a 4% internal volt drop or 18V. Overall it was 10% volt drop from source to final circuit..... 6% max at source, 4% in the sub-mains/ final circuit.

Distribution transformer typically had internal impedance rating of between 4~6%.
IET » Energy » Why 433V

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