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It is a bipolar overhead power line 488 miles (785 km) long, and can transfer a maximum power of 2,400 megawatts at ±500 kV. The part of the line that travels through the Mojave Desert is followed by many other AC 500 kV lines and Interstate 15.
The Pacific DC Intertie is the other HVDC line serving Los Angeles. This HVDC line is owned and operated by the Los Angeles Department of Water and Power (LADWP). HVDC lines such as the Intermountain line and the Pacific DC Intertie can be distinguished by having two transmission wires, rather than the three necessary for transmission of three phase AC power.
ABB Group, a Swiss-Swedish multinational corporation headquartered in Zürich, Switzerland, was the primary entity commissioned for this turnkey project in the mid-1980s. ABB also had responsibility for the converter stations, which were commissioned in April 1986.
In 2008, ABB received the order for an additional upgrade. This upgrade included delivery of the MACH2 control and protection system along with additional AC filters and cooling systems. This upgrade has allowed the link to reach a transmission capacity of 2400 MW (2.4 GW).
From the south, the Intermountain DC circuit starts at the Adelanto substation and static inverter plant. The line heads east for a short distance, until two 500 kV circuits and one 287 kV tower line (all carrying LADWP Path 46 power) meet the DC line from the Victorville substation, which the DC line bypasses. Heading together, the four lines head generally northeast, paralleling Interstate 15 and crossing the highway at two places. An additional line, called Path 64, but part of Path 46, parallels the Interstate 15 and the four lines until the California-Nevada border.
The DC line follows three 500 kV lines and the 287 kV line into Eldorado Valley. There the AC lines terminate at McCullough, Marketplace, and Mead substations. Then two 500 kV lines from McCullough and Mead substations join it to head further north. They cross U.S. Route 95 in Henderson with one 500 kV line on double-circuit towers. These lines run east of Las Vegas Valley. Just short of crossing I-15, one 500 kV line splits off for the Harry Allen substation. One 500 kV line comes back from Harry Allen substation and joins the other 500 kV line at Crystal substation. Another 345 kV line runs parallel to head into Utah.
The three lines run northeast together somewhat north of I-15, until about 10 miles northwest of Mesquite, where the 500 kV (Path 21) line abruptly turns east, spanning the Virgin River to head to the Najavo plant. The DC line continues north-northeast as the line crosses high mountains and large desert basins until it turns east in west-central Utah and terminates at the Intermountain substation.
Electrodes and Electrode Lines
The electrode line from Adelanto Static Inverter Station is carried for 84.5 kilometres on the shield wire positions of the pylons. South of Coyote Lake atthe electrode line branches on steel tube poles northward and ends at . The electrode line from Delta Static Inverter Station is carried for 44 kilometres on the shield wire positions of the pylons. At the electrode line branches westward to the grounding electrode situated at . Both electrode lines consist of two 908 mm2 Falcon conductors, mounted on ANSI Class 52-5 porcelain insulators. Each electrode consists of 60 deep walls with depth of 87 metres in Delta and 60 metres in Coyote Lake covering an area of approximately 0.65 km2.
- Intermountain HVDC transmission system, The ABB Group