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Reliability of underground power lines? - Page 4

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Posted by John Gilmer on August 18, 2010, 2:47 am
 




Pretty sure.   I often "chat" with the guys installing/repairing equipment.
That's the number I remember.

Semi-rural east central Virginia.




Posted by Josepi on August 19, 2010, 2:15 am
 


That should give 66kV phase to phase. Very HV for underground system,
especially in older installations as the insulations were quite expensive,
at that level.





Pretty sure.   I often "chat" with the guys installing/repairing equipment.
That's the number I remember.

Semi-rural east central Virginia.




Posted by hubops on August 19, 2010, 9:42 pm
 

  4800  maybe ?  

John T.





Posted by Josepi on August 20, 2010, 12:19 am
 

We ran a lot of 2400/4160 through subdivisions underground. That was
switched over to 8.0/13.8kV later in an effort to save transformer and line
losses.

I have heard of some utilities running 16.1/27.6kV but mostly overhead
except for u/g dips to avoid obstacles. 27.6kV starts a whole new
technology. Corona problems start and faults result in massive explosions so
once at that level the sky is the limit. 44kV is talked about but I have not
seen it used u/g.

Lots of 115kV, 230kV and 500kV is used here for cross country transmission
on towers. These voltages are rumoured to have some u/g cryo circuits in
use, somewhere??


  4800  maybe ?

John T.





Posted by John Gilmer on August 20, 2010, 1:01 pm
 



What difference does it make?

The HV cables are individually  "shielded."   You can see this at any  place
the HV "goes underground."    It doesn't really matter whether another phase
is in the same trench.    The highest voltage to ground/neutral is the 38kV.

The important questions are:   1)  Can nominal 50/1 turns ratio transformers
at that voltage be designed to be relative cheap and reliable?;  2)  Can
cable systems (to include field repair splicing & repair) be designed to
cheaply and reliably handle the 38kV to ground?

At those voltages the currents would typically be less than 10 amps.
Faults are quickly cleared so the high voltage doesn't present any extra
public risk.



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