Powerlines

From: Philip.Belben_at_pgen.com <(Philip.Belben_at_pgen.com)>
Date: Wed Apr 28 10:44:23 1999

[Power supplies with earth return]

> I have never looked but I suppose it might. I have a 400A service and
> sometimes I do a fair job of loading it. The transformer ped is out of the


Another difference! It is very unusual in the UK to give a domestic customer
more than 100A in the main incoming fuse. 400A on each side of your 115-0-115
supply is getting on for 100kW. Do you really use that? I would have thought
10kW would be more likely (my parents use 36kW at the winter peak, mostly
heating load. 50A from each of three phases at 240V)

Anyway, 400A on the 240V side corresponds to nearly 7A to be returned through
the earth at 14kV. Ouch! I wonder what the resistance of the earth connection
is. There will be a minimum resistance to prevent undue voltage rise under
short circuit conditions, but I don't know how this relates to earth return
circuits...

The only places where I've seen this sort of arrangement, there are still 2
conductors. One insulated to HV for the line, and one lightly insulated for the
(HV) neutral.


> way so I rarely go closer than 30 feet from it. They also must put the
> ground rod(s) inside the for safety (hate to think what it would be like if


ISTR that in the UK there is a minimum distance between LV and HV earth
electrodes.


> the ground got cut on the primary). I have never seen them but they have to
> be there somewhere.


Earth open circuit? Hmm. The entire HV winding rises to 13kV and the HV
neutral flashes over to the transformer tank? Assuming the tank is part of the
LV earth system. Otherwise the transformer tank rises too, and flashes over to
your house supply...



Philip.
Received on Wed Apr 28 1999 - 10:44:23 BST