A couple 3phase questions...

[Bud--]

True [will be the same loss if one 1000W load is turned off]

Also true [will probably also be the same loss with any total load of 2000W]

If you can ignore the neutral also true. (But not counting the neutral is cheating.)

Beachcomber's post was the power delivered per per pound of copper, in which case 3 phase provides more power per wire (and per pound of copper).

For efficiency, if we use your example ignoring the neutral, 3 phase is still more efficient since the losses per wire are the same but the losses are divided by a larger power delivered for 3 phase. Thus the percent losses are lower for 3 phase making the efficiency per wire higher. (Actually losses should have been divided by the power supplied to the wire.)

If neutrals are included in calculating loss per wire, the 3 phase efficiency is improved.

bud--

[Jeff Wisnia]

At the risk of making a total PIA of myself over this, bud, I was showing that the losses per wire (In my example 8.33 Watts per wire.) were the same for each wire, in both the single phase (2 wires) and three phase (3 wires) examples.

The power in the three phase example (3000 Watts) was 1.5 times the power of the single phase one (2000 watts) as were the losses in both examples.

So, I still can't agree that the losses expressed as a percentage of the delivered power (or the supplied power, which as you point out below is "correcter".) would be different for the two examples I gave.

Agreed, three phase will take less pounds of copper per unit of delivered power, at the same voltage of course.

Peace,

Jeff

[Bud--]

Yea that works, but only if you ignore the neutrals. It also requires the loads to have the same I-V characteristic. In the real world that is unlikely which would result in too high a voltage on the lower wattage loads (which is why it is a code violation unless designed as part of a listed apparatus).

Ignoring the code, the real world connection would likely be all 240V loads supplied by single phase 240V 2 wire, or 3 phase 240V 3 wire delta. Load matching would not be an issue then. In that case the 3 phase delivers more power per wire.

bud--

[Edwin Pawlowski]

It would be great if the world used 3 phase power. All the wires could then be the same color. Out system now has black, white, green, sometimes red. It just gets so confusing.