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

[AM-DXer@xxxxxxxxx (Patrick Griffith, N0NNK / WPE9HVW)]

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.

//////

The Pacific DC Intertie consists of: 
1. The Celilo Converter Station which converts three phase 60 Hz AC at
235 to 525 kV to 500 kV DC. The grounding system at Celilo consists of
1,067 cast iron anodes buried in a two foot trench of petroleum coke,
which behaves as an electrode, arranged in a ring of 3,255 meters (2.02
mi) circumference at Rice Flats (near Rice, Oregon), which is 10.6 km
(6.5 mi) SSE of Celilo. It is connected to the converter station by two
aerial cables. 

2. A 1,362 kilometer (841 mile) overhead transmission line consisting of
two uninsulated conductors containing a steel wire core for strength.
The wires have a capacity of 2 gigawatts in bipolar mode and 1.55
gigawatts in earth return mode. 

3. The Sylmar Converter Station which converts DC to AC (a process also
called inverting) and phase-synchronized with the L.A. power grid. The
Sylmar grounding system is 24 silicon-iron alloy electrodes submerged in
the Pacific Ocean suspended in concrete enclosures about one meter above
the ocean floor. The grounding array is in Santa Monica Bay 48 km (30
mi) from the converter station.

Patrick Griffith, Westminster CO
Broadcast Technician
NRC Broadcasting - Denver
http://community.webtv.net/N0NNK/
http://community.webtv.net/AM-DXer/

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