Help w/ power losses on transmission lines

[pipeliner]

I'm not a power engineer, but I've been asked to provide another group in my company a "rule of thumb" they could use to characterize power loss on a high voltage power line, i.e. what's a reasonable power loss (%) per 100 miles on a well designed transmission line?

 

[dspell]

Maybe the GO-98 standard has a power loss specification. Typically, electrical distribution systems are designed for a maximum Voltage Drop, with 3-5% being the target.

 

[kraigb]

Dielectric losses can depend on whether the line is installed overhead or underground. If it is underground, the choice of insulation can make some difference based on the dielectric constant of the insulation material.

The equation for dielectric loss from the Neher McGrath paper on calculation of temperature rise of cables (IEEE Transactions Oct. 1957 - there have been some updates to this, too) is:

Wd = 0.00276(E^2)(SIC)(insulation PF) / log[(2T+Dc)/Dc]

Where:
Wd is dielectric loss in watts per conductor foot,
E is phase to neutral voltage in kV,
SIC is relative dielectric constant of the insulation material,
Insulation PF is the power factor of the insulation material (also called tangent delta),
T is the insulation thickness,
Dc is the diameter of the conductor (over the semicon shield).

 

[jbartos]

Transmission lines are built with the intent to have less than 5% loss or 10% loss. All hardware is adjusted to these baseline losses. If you happen to calculate it, the following equations may be used:
Loss = 3R x squareI, in Watts
where
R is total resistance of one conductor
I is conductor current
or
Percent Loss = 173 x r x s x I/(E x cos(phi))
where
r is conductor resistance per mile
s is transmission distance in miles
I is conductor current
E is line voltage at receiving end
cos(phi) is power factor at receiving end
Reference:
Electrical Transmission and Distribution Reference Book, Westinghouse Electric Corporation, 777 Penn Center Blvd, Pittsburgh, PA 15235, 4th Edition, 12th Printing, page 271