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Topic Title: Transmission/Distribution Voltages
Topic Summary: Why multiples of eleven?
Created On: 21 February 2014 08:04 AM
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 21 February 2014 08:04 AM
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awaygood

Posts: 9
Joined: 25 July 2008

Does anyone have a definitive answer to why (in the UK, at least) transmission/distribution voltages are multiples of eleven. There are numerous answers to this question on the internet (e.g. due to form factor -if so, why? Or to allow for a 10% voltage drop), but these seem to represent opinions rather than facts.

Is there a definitive answer?
 21 February 2014 07:10 PM
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Zuiko

Posts: 521
Joined: 14 September 2010

Originally posted by: awaygood

Does anyone have a definitive answer to why (in the UK, at least) transmission/distribution voltages are multiples of eleven.


Except 400V and 400 kV....?

So, some declared, nominal, line-voltages are divisible by 11 and some are not. I've seen the form factor explantion (which is 1.111 for a sine wave, although transmission line voltages are never pure sine waves). Its tenuous - what would be the real-world benefit?

I'm more inclined to think it was a 10% volt-drop safety-factor back in the day, which given the distances involved, and the lack of decent on-load voltage regulation, seems reasonable.

Edited: 21 February 2014 at 07:38 PM by Zuiko
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