3 ms·

Does anyone know if transmission lines can be buried? Some high voltage DC can be in the hundreds of kV, is there a limit to what can be buried in moist ground

Does anyone know if transmission lines can be buried? Some high voltage DC can be in the hundreds of kV, is there a limit to what can be buried in moist ground even remotely efficiently? You’d need a good amount of electrical insulation, but also thermal conductivity (I assume these lines heat up?). Any experts here?

snagglegaggle 7y ago
The issue is more with burying AC as I'm aware, the ground takes energy out by interacting with the magnetic field. With DC there is only a static field and less parasitic loss and you can add enough insulation. There shouldn't be appreciable heat generation in either. Consider the fact that we lay oceanic cables.
Robotbeat 7y ago
Absolutely they can be buried. They must be insulated, but that's not particularly expensive. There are thermal limits, as you mentioned, but that simply requires appropriate engineering. It costs $1 million per mile (roughly) to bury transmission lines. PG&E has about 18,000 miles of transmission lines. That's about $18 billion to bury the lines. Sounds like a lot, but... ...the estimate price of these multi-day blackouts is on the order of $1 billion per blackout. Given multiple blackouts per year, and we're talking just a few years to pay back the price of burying the transmission lines. https://www.sfchronicle.com/business/article/A-cool-billion-Economists-estimate-PG-E-14505047.php https://www.sfchronicle.com/business/article/A-cool-billion-...
- dehrmann 7y ago
  > the estimate price of these multi-day blackouts is on the order of $1 billion per blackout But that's not the cost to PG&E. PG&E (or the state) would have to find a way to get some of that somewhat hidden opportunity cost.
  - Robotbeat 7y ago
    The state already does that through regular, economy-wide taxes. (Maybe this is why it's a bad idea to grant a monopoly to a for-profit company like PG&E that doesn't take into account the externalities of power outages... Then again, Texas' very deregulated but non-monopoly ERCOT seems to do pretty well. So either state-owned OR deregulated may be optimums compared to PG&E...)
- xadhominemx 7y ago
  $1m/mile is off by like a factor if 10. PG&E thinks it costs $3-5m/mile to bury _distribution_ lines: http://www.pgecurrents.com/2017/10/31/facts-about-undergrounding-electric-lines/ http://www.pgecurrents.com/2017/10/31/facts-about-undergroun...
  - Robotbeat 7y ago
    Good argument for burying PG&E, then, and starting over.
jchulce 7y ago
It is physically impossible to have long distance underground high voltage AC transmission lines due to capacitance: http://www.puc.nh.gov/2008IceStorm/ST&E%20Presentations/NEI%20Underground%20Presentation%2006-09-09.pdf http://www.puc.nh.gov/2008IceStorm/ST&E%20Presentations/NEI%... HVDC wouldn't have that issue, but there's not much experience with HVDC in North America.

snagglegaggle 7y ago

The issue is more with burying AC as I'm aware, the ground takes energy out by interacting with the magnetic field. With DC there is only a static field and less parasitic loss and you can add enough insulation. There shouldn't be appreciable heat generation in either. Consider the fact that we lay oceanic cables.

Robotbeat 7y ago

Absolutely they can be buried. They must be insulated, but that's not particularly expensive. There are thermal limits, as you mentioned, but that simply requires appropriate engineering. It costs $1 million per mile (roughly) to bury transmission lines. PG&E has about 18,000 miles of transmission lines. That's about $18 billion to bury the lines. Sounds like a lot, but... ...the estimate price of these multi-day blackouts is on the order of $1 billion per blackout. Given multiple blackouts per year, and we're talking just a few years to pay back the price of burying the transmission lines. https://www.sfchronicle.com/business/article/A-cool-billion-Economists-estimate-PG-E-14505047.php https://www.sfchronicle.com/business/article/A-cool-billion-...

dehrmann 7y ago
> the estimate price of these multi-day blackouts is on the order of $1 billion per blackout But that's not the cost to PG&E. PG&E (or the state) would have to find a way to get some of that somewhat hidden opportunity cost.
- Robotbeat 7y ago
  The state already does that through regular, economy-wide taxes. (Maybe this is why it's a bad idea to grant a monopoly to a for-profit company like PG&E that doesn't take into account the externalities of power outages... Then again, Texas' very deregulated but non-monopoly ERCOT seems to do pretty well. So either state-owned OR deregulated may be optimums compared to PG&E...)
xadhominemx 7y ago
$1m/mile is off by like a factor if 10. PG&E thinks it costs $3-5m/mile to bury _distribution_ lines: http://www.pgecurrents.com/2017/10/31/facts-about-undergrounding-electric-lines/ http://www.pgecurrents.com/2017/10/31/facts-about-undergroun...
- Robotbeat 7y ago
  Good argument for burying PG&E, then, and starting over.

jchulce 7y ago

It is physically impossible to have long distance underground high voltage AC transmission lines due to capacitance: http://www.puc.nh.gov/2008IceStorm/ST&E%20Presentations/NEI%20Underground%20Presentation%2006-09-09.pdf http://www.puc.nh.gov/2008IceStorm/ST&E%20Presentations/NEI%... HVDC wouldn't have that issue, but there's not much experience with HVDC in North America.