-=> Jay Emrie said to Greg Mayman
 -=> about "HVDC TRANSMISSION LINES" on 12-30-02  21:04.....

 JE> I'm a bit puzzled. How is the hollow core  going to
 JE> dissipate heat when the hollow itself traps the heat inside
 JE> itself?

A hollow conductor of the same current carrying capacity as a
solid one has a greater surface area per unit length.

Compare these two:
                               SOLID  HOLLOW
Outer diameter                  2.5     4.0     inches
Overall area                    2.0    12.6     sq.inches
diameter of hollow centre       0       3.67    inches
area of hollow centre           0      10.6     sq.inches
area of conductor               2.0     2.0     sq.inches
outside circumpherence          7.85    12.56   inches
surface area per 1 ft. length  94.2    150.7    sq.inches

So the hollow conductor has an outer surface area, and hence the
ability to dissipate heat, more than 50% greater than the solid
one.

This has used no extra metal, hence no increase in weight, since
the cross sectional area of the metallic part is the same.

The only penalty is an increase in wind resistance, but that can
be reduced by flattening the hollow tube into an oval. If the
height of the oval is the same as the diameter of the solid
conductor, the resistance to wind from the side is actually less
than the round solid conductor due to streamlining effect of the
oval shape.

From Greg Mayman, in beautiful Adelaide, South Australia

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