4 Feb
2011
4 Feb
'11
12:08 p.m.
On Friday, February 04, 2011, Frej Drejhammar wrote:
Philip Belben <philip at axeside.co.uk> writes:
Remember that it's three phase with a 2pi/3 phase difference. Your
calculations are only correct if we were considering three separate
single-phase supplies: 3*240*16=11.5kW and 3*240*25=18kW
respectively.
If we consider a resistive load in a delta connection, which is the
case in a typical Swedish electrically heated house with 380V (the
voltage between two phases) radiators, the maximum power available
is sqrt(3)*380*16*3=32kW and 49kW respectively.
You've got an extra x3 in there...
16A, 220V to ground service would give you 16A *220V * 3 = 16A * 380V
*sqrt(3) = 10.5kW. (you can treat them as 3 separate single phase
circuits if you use their voltage to ground).
They don't act like 3 x 380V single phase circuits, you actually get
less power out of them, because the currents between each leg add up
(with a phasor, so you get 1.7 x instead of 2 x the current).
Pat
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>
Swedish houses have electric heating, run off 3-phase. A house
> will have at least 16A, sometimes 25A meter fuses; Sweden is
> quite cold in winter.
Are you sure? 16A 3 phase is only 11kW, 25A 18kW. I would expect
60A or 100A fuses.