[Amps] Benefits of 3-phase power?

[Ian White, G3SEK]

G3RZP wrote:
>
>It's not usual to provide 3 phase mains in the UK to domestic premises.
>Some country areas have 2 phase - that's what I have. There's an 11kV 3
>phase line to a transformer near the house, and the output from that is 2
>phases and neutral; with 440 between phase and 230 between neutral and
>phase.

In Britain the system varies according to the population density, and 
also the old regional Electricity Boards did things in slightly 
different ways.

In towns and villages, distribution is almost always 440V 3-phase from 
transformers every quarter to half a mile. 3 phases plus neutral run 
along the road, either in a buried cable or as 4 wires on poles. 
Individual homes get one of those phases plus neutral, with the load 
roughly spread along all three phases as you go along the road. This has 
interesting consequences if you're putting RF into the mains - the RFI 
tends to skip a house or two, either side!

Generally, only industrial premises get all three phases. For example a 
farm might have 3-phase into the barns, but even then that's not 
necessarily for 3-phase equipment - they might connect different 
buildings to a different single phase. The farmhouse would certainly be 
connected to only one of those phases, because there's no need for all 
three.

Distribution in very rural areas tends to be 3-phase 11kV as far as they 
can go, but as they come near the end of the network there's nowhere 
left to spread the load on different phases. Then they fall back to 
single-phase HV for the last few miles, with two wires on poles and a 
transformer to 230V at the far end. If there were two separate buildings 
to supply, they might use a 230-0-230V transformer and supply a 
different single phase to each... but still an individual home would 
only be single-phase.

So it's chicken-and-egg - in Britain, no homes are supplied with 3-phase 
because 3-phase household electrical equipment doesn't exist... so no 
homes are supplied with 3-phase.


-- 
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
                            Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek