Re: [IRCA] Now that's a ground system! (OT)

[Charles A Taylor <MWDXer@xxxxxxx>]

At 12:17 PM 4/21/2007 -0600, you wrote:
>A while back I became aware of something called the Pacific DC Intertie.
>It is a high voltage DC power system that transports hydroelectric power
>from the Columbia River in northern Oregon to the Los Angeles area. It
>provides enough electricity to power up to three million homes in the
>L.A. area. They use DC instead of AC for several reasons that I won't
>get into here. We're talking about 500,000 VDC at gigawatt power levels!
>They normally use two sets of double wires for transmission. One set is
>positive and the other is negative. This is called bipolar mode. But
>what I found very interesting is that if there is a fault on one of the
>lines they can use a single line for the power feed and use the earth as
>the ground return. They said they don't like use the ground return mode
>unless they have to because it increases the corrosion on underground
>pipelines and effects other underground utilities. NO KIDDING! You guys
>on the Pacific coast had better check the current on your ground rods!
>The following contains a description of the grounding system used at
>each end of the line for the ground return mode which I thought would be
>of interest to you folks.
>

Patrick,

Just down my line of interest. Studying bulk power systems is a hobby of
mine.

Went under the Pacific DC Intertie four times on way to/coming back from
VOA Delano. Fascinating.

One reason for DC is that the AC system at one end doesn't have to be
synchronized with the AC system at the other end (both being 60 Hz, in
this case). Although they WILL be synchronized 99% of the time, a big
fault may disrupt the AC ties along the west coast for a while. Until
they can get the two or three systems resynchronized, power cannot be
interchanged between (for example) Puget Sound Power and Los Angeles
Water and Power Department.

A bunch of systems are interconnected via DC ties for exactly this
reason. Experimentally, East and Midwest North America has been synch-
ronized with West North America, but the tie line was too low capacity
and just the synchronizing current flow was near its capacity. DC ties
make that synchronization unnecessary.

There is a widely used low-voltage (11 kV) single-wire, earth-return
system in Australia. There is/was a small extension of a cooperative
out here in NC that had no ground return, but in both cases corrosion
isn't a problem.

Ground return DC systems are widely used in Europe to interconnect
islands.

Ya got me charged up!

73 de Charlie


Charles A Taylor, WD4INP
Greenville, North Carolina 


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