[BC] Electrical Code

[PeterH5322@aol.com]

>In other words, just how high does the line voltage have to be before it
>cannot be buried? Or, if that isn't the issue, then what is the reason for
>having so many overhead lines vs underground?

The limit for solid dielectric insulated underground lines is about 138 
kV.

The limit for oil underground lines is about 230 kV.

The limit for gas (sulfur hexafluoride, SF6) underground lines is about 
345 kV.

We had air-insulated lines of 500 kV ac and +/- 500 kV dc (1,000 kV 
line-to-line).

In the 230 kV range, which was the maximum which my former employer, this 
nation's largest municipal utility, employed underground, the cost for 
such underground transmission was ten to fourteen times the cost, per 
unit distance, of overhead, air-insulated lines.

It is a little less than that for underground distribution.

But, ten to fourteen times is still ten to fourteen times, and who is 
going to pay for that difference?

Plus, the the time to diagnose and repair a failure in such an 
underground line can be (and usually is) much greater than for a failure 
in an air-insulated line, measured in time-to-diagnose, in 
time-to-repair, and in cost.