Quote:
Originally Posted by Street Pharmacist
Probably a really stupid question, but is it that much more expensive to bury? I mean, we bury freaking giant pipelines...
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Not a stupid question. I get it all the time. Really depends on length, voltage and capacity.
240kV and up you are looking at ~3 to 8x. Low end being direct bury, high end being duct bank or conduit install.
They are a b*tch to manufacture (only a few globally), install (manufacturer has to do the splicing) and maintain (super expensive to spare and you need the splice crew back). An overhead wire is about 1 inch in diameter, an equivalent underground cable 5 or 6 inches for the insulation and jacket. That means less on a reel for transportation purposes which means more splices. More splices means more chances for failure.
AC transmission lines make crazy amounts of heat, and kinda like to catch on fire. If anyone lives in the west end of downtown, you'll remember when Enmax lost a cable. That outage was weeks long.
They really are a last resort. High voltage underground are typically found in only the largest cities. Tokyo has a 500kV underground line (and substation for that matter).