Re: Is this safe?

[David Johnson <trainman@ozemail.com.au>]

luis wrote:

> to all,
> Sorry about attaching a photo to the posting, what I was trying to show is how
> close these high voltage lines are to the rail line, the cables are attached to
> the wall of the railway tunnels.

In future, it would be far easier to simply put the photo on the web page mentioned
and put a link in the message.  (This goes for everyone, BTW).

> About the voltage these are not normal railway
> electricity lines, they are high voltage transmission lines (180MVA)

So...  What is the actual voltage of them?  The web page states the cable is rated
at >100kV DC with a current capacity of >300A. and a power capacity of 30MVA.
Therefore six parallel cables would be required to carry the current associated
with 180MVA.  What are they using for a negative return?  I assume that each HVDC
cable is concentric having the negative return in the same cable.  The diagram of
the Australian model shows three separate parallel connections, each with a +80kV
and a -80kV.  This makes for 160kV potential between the two cables, which at 300A
gives a capacity of 48MVA.  Multiply this by 3 and you get a total capacity of
144MVA - 36MVA short of the stated 180MVA.  Will they be over-rating the cable?

> that
> will connect NSW and Queensland power grids, these are very large capacity
> cables, instead of  using overhead power transmissions lines Northpower decided
> to use existing Right of Ways (like the railway corridor and roads ) to bypass
> all local approval processes with the local community. the community of
> Mullumbimby are very concerned  with the safety issues.
> We have a web page with more information and I can send more info if required.
> the web page is  www.rag.mullum.com.au

I would suggest that you don't walk too close to them with any floppy disks,
magnetic tapes, etc.   Are they magnetically shielded?  That sort of DC current
would make for some interesting magnetic fields.  TVs within close range would be
affected - Colour shifts and screen rotation would be noticable.

I cannot see why they would want to use DC to connect QLD & NSW grids.  AC is far
easier and cheaper to transmit I thought.  This DC system looks suitable for
alternative power sources where the input voltage is not stable.  The national grid
would be pretty stable.

In summation, I can't see why they are doing it, but I can't see too great a danger
for people if they are not too close to it all the time.

--
David Johnson
trainman@ozemail.com.au
http://www.ozemail.com.au/~trainman/
------------------------------------
These comments are made in a private
capacity and do not represent the
official view of State Rail.
C.O.W.S. Page 11.