+500kV installed underground and indoors 1

[buddy91082]

Anyone have expwrince with installing +500kV lines underground and the pros and cons? Is it something that is typcially done?

Also, can the gear that accomodates the 500kv lines be installed indoors?

Thanks.

 

[davidbeach]

I'd love to have your kind of budget if you can afford to even think about the possibility of underground/indoor 500kV. I'm sure that anything can be done if enough money is thrown at the project.

 

[itsmoked]

500kV underground?! That's plumb crazy talk!

Boys get a rope.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[rcw retired EE]

We were looking at it in some tight locations for a power plant - using underground 500kV cables and GIS switchgear. Cost was prohibitive. We are doing it at 345 kV, but not running the lines very far underground, 200 meters max.

HV underground cables and indoor switchgear is common in Japan where real estate is at a premium.

We saw one installation that used SF6 bus to carry the 500 kV lines into the congested substation from the overhead line termination point on the outskirts of the station.

 

[dpmac]

We performed acceptance testing on some SCFF 500KV DC lines about 10 years ago. They were installed in a tunnel bored under the St. Lawrence River. Three circuits, two cables each about 2 miles long encased in concrete. I was not involved in the construction, only testing, but I recall some very interesting pictures showing long sections of serpentine sections of cables seriously clamped to allow for thermal expansion. All terminations were air terminals.

 

[bacon4life]

Seems like there are a number of 500+ kV DC lines around such as:

http://tdworld.com/underground_transmission_distribution/nexans-finland-sweden-submarine-cable/

Check out page 2 for a discussion of Solid Dielectric (Cross-Linked Polyethylene or XLPE), Gas Insulated Transmission Line (GIL), and Self-Contained Fluid Filled (SCFF) for use at 500 kV AC.

http://www.sdge.com/sunrisepowerlink/info/CPUC ED DR9 ALT-79 5-18-07.doc

 

[tlrols]

Look at the third powerhouse at Grand Coulee...it is probably the biggest (on a MW basis) 500 kV (AC) cable in the world. Sumitomo worked their magic on the cables serving the large units leaving Grand Coulee...they go through the dam and up the hill/mountain to the spreaderyard--it shows that if you have enough money you CAN do just about anything...

 

[rcw retired EE]

Running 500 kV cables through Grand Coulee Dam was not an engineering nor an economic decision.

Lady Bird Johnson, wife of then US President Lyndon B. Johnson, visited the site during early construction and saw the mock-up model with transmission lines across the face of the dam. She commented that the wires spoiled a beautiful view of the spill way and couldn't something else be done to beautify this American landmark. HV oil-filled cables through the interior dam access tunnels was the answer.

The big engineering challenge was the difference in elevation between the step-up transformers at the base of the third power house and the new 500 kV yard at the top of the bluff overlooking the dam. I'm guessing it is > 250 meters elevation difference. That height put excessive hydraulic pressure on the bushings at the transformer end and required some interesting cooling system designs.

One side benefit, the dam spillway now is the viewing screen for a spectacular laser light show every summer evening. It is ironic, that with the third powerhouse the spectacular rush of water over the spillway is no longer present except during fish water spills and a minimal trickle for nightly shows.

(Information is from lectures by Dr. Eugene Greenfield, who consulted on the cable design.)

 

[dpc]

As to your question -- the biggest con to 500 kV underground is that it is incredibly expensive. Plus requires much more O&M cost than 500 kV overhead.

I guess it's a little like wondering about the pros and cons of flying a helicopter to work and back versus driving a car.



"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg

 

[WhiteyWhitey]

Pro:

Less clearing and Access Track Management Required.

No arial surveys required.

 

[tlrols]

Yep, the Coulee 500 kV cable was part of Lady Bird's "Beautify America" project...so, it is a true example of what can be done with just money, there was certainly no technical reason why the 500 kV cable had to be used (other than 500 kV lines across the face of the dam were deemed to be "ugly"). The Coulee 500 kV cables are, however, a rather "cool" use of technology. I personally like the interesting 500 kV structures that go up the hill from Coulee, very angular...

At the end of the day the original question still gets answered as yes you can do 500 kV cables, they can be installed indoors, the pro isn't really definable, and the con is that 500 kV cables cost a bunch of money...