Path 27

Path 27, also called the Intermountain or the Southern Transmission System (STS), is a high-voltage direct current (HVDC) electrical transmission line running from the Intermountain Power Plant near Delta, Utah, to the Adelanto Converter Station at Adelanto, California, in the Southwestern United States. It was installed by Asea, a company based in Sweden, and commercialized in July 1986. The system is designed to carry power generated at the power plant in Utah to areas throughout Southern California. It is owned and operated by the Intermountain Power Agency, a cooperative consisting of six Los Angeles-area cities, the largest member being the Los Angeles Department of Water and Power (LADWP), and 29 smaller Utah municipalities. Path 27 consists of an overhead power line long, and is capable of transferring up to 2,400 megawatts (MW) of power at ±500 kilovolts (kV), higher than the power plant's operational output of 1,900 MW. The resulting maximum current is 4,800 amperes. Given its length, a direct current (DC) is preferred to the more common alternating current (AC) as it allows the electrical energy to travel farther with minimal loss to resistance and requires no intermediate stations. It is bipolar, meaning that it has two conductors of opposite polarity (in place of three conductors for AC lines).…

Path 27, also called the Intermountain or the Southern Transmission System (STS), is a high-voltage direct current (HVDC) electrical transmission line running from the Intermountain Power Plant near Delta, Utah, to the Adelanto Converter Station at Adelanto, California, in the Southwestern United States. It was installed by Asea, a company based in Sweden, and commercialized in July 1986. The system is designed to carry power generated at the power plant in Utah to areas throughout Southern California. It is owned and operated by the Intermountain Power Agency, a cooperative consisting of six Los Angeles-area cities, the largest member being the Los Angeles Department of Water and Power (LADWP), and 29 smaller Utah municipalities. Path 27 consists of an overhead power line long, and is capable of transferring up to 2,400 megawatts (MW) of power at ±500 kilovolts (kV), higher than the power plant's operational output of 1,900 MW. The resulting maximum current is 4,800 amperes. Given its length, a direct current (DC) is preferred to the more common alternating current (AC) as it allows the electrical energy to travel farther with minimal loss to resistance and requires no intermediate stations. It is bipolar, meaning that it has two conductors of opposite polarity (in place of three conductors for AC lines). Both conductors for the entire length are three cables bundled together; this is done to reduce the effects of EM interference and enhance the power line's performance. At each end of the line is a converter station that changes AC to DC on one side and back again on the other. Each terminus also features a dedicated ground which is connected by an electrode line to a grounding site away from the converters to provide ample earth return; this helps protect the main line and equipment from faults, and allows the system to operate at partial capacity when one conductor is out of service. Sections of Path 27 are paralleled by other AC transmission lines, including some of 500 kV. The powerline is also visible from the Interstate 15 which it passes over multiple times. The HVDC line's converter stations will be replaced as part of a project to repurpose the Intermountain Power Plant as a hydrogen-burning facility. The stations are expected to go online by June 2026. HVDC exhibits significant potential such that the converter's onsite grounding devices are not enough to withstand alone, and a return current would otherwise cause issues at the electrical facility including rapid metal corrosion, so the grounding nodes are set at remote locations. On Path 27, the IPP converter's grounding point is situated about southwest of the valves (here), while the Adelanto converter's lies about to the northeast (here) on the edge of a playa known as Coyote Lake. These spots were chosen in part for high conductivity within the earthen minerals. Each node covers an area of approximately . At each grounding point is an array of buried conductive rods that form an electrode, marking the actual transition point into the earth for the current. Within the electrodes for Path 27 are sixty rods arranged in a circular rim about in diameter and spaced evenly for the best result. Each rod is placed vertically to reach subterranean layers with the least resistivity possible: IPP's electrode rods are deep, and Adelanto's extend downward. The rods are individually encased in a perforated-metal tube, or a "well", to retard corrosion. The wells are filled with petroleum coke to enhance the current's connectivity into the soil. Additionally, the coke regulates heat that the rod naturally emits when a current is induced; this is to mitigate the electrode's impact on the surrounding environment. A series of jumper cables radiating from the center of the circle feed the return current into the rods. At the center is a small structure perched on the surface called a terminal house, which is also equipped with a transmitter that helps technicians monitor the electrode's performance. The circular "deep-well" setup of Path 27's electrodes is a variation of the "ring-style" electrode found on other HVDC projects such as the Nelson River Transmission System in Canada. The converters are linked to the electrodes by a pair of conductive cables, each measuring in thickness, to enable physical contact with the earth. These are the electrode lines, arteries for the return current. More precisely, the electrode line carries the current to the terminal house which then injects it through the electrode. Starting at both termini, the electrode line runs atop Path 27's main pylons in lieu of shield wires before branching off along a standalone set of steel utility poles. Steel poles have been selected for their resiliency in the hot, arid locales. The electrode line for the IPP converter has a total length of , and the Adelanto's extends . Uniquely, Adelanto's electrode line travels underground for its final approximately till the grounding site. The electrodes and electrode lines are distinct from the metallic return, which would involve an extra third conductor along the span of Path 27—the former HVDC Vancouver Island being an example. Such method would likely be infeasible for its scope and magnitude. ==Route== Following the regular power flow, Path 27 begins at the Intermountain Power Plant in Utah and heads briefly west before curving southward, passing over the US 50/US 6 duplex west of Hinkley. The DC line ventures through legions of dry basins and high mountains in the state due southwest; all the while crossing Utah Routes 21, 56, and 18; before reaching Nevada about north of Arizona's northwestern corner, simultaneously entering the Mojave Desert. Inside Nevada, Path 27 traverses the Mormon Mesa, bypassing Glendale and crossing the Muddy River. It bisects the Moapa River Indigenous Reservation lands before crossing Interstate 15 near Crystal. Across Las Vegas Valley, the line meets with NV 564 while riding through the Frenchman Mountain, straddles the River Mountains outside Henderson, and crosses Interstate 11 at Railroad Pass before heading into Eldorado Valley. Upon traversing the McCullough Range, it descends into Ivanpah Valley, missing Primm in its north and crossing Interstate 15 again. Shortly thereafter, it enters California. Path 27 cuts across isolated, oft-rugged tracts of the High Desert while also encountering CA 127 north of Baker. Now in the Inland Empire, the line proceeds through Victor Valley where it crosses Interstate 15 once more near Yermo, as well as old US 66 and Interstate 40 between Daggett and Newberry Springs. It then encounters CA 247 south of Barstow. Around Bell Mountain, Path 27 meets with Interstate 15 one last time, and then old US 66 a second instance and US 395 near Oro Grande before reaching Adelanto, where the line arrives at its final destination of the Adelanto Converter Station. Numerous AC transmission lines parallel Path 27 throughout its course. A 345 kV circuit runs beside the DC line interlinking the IPP and a wind farm near Milford. A second 345 kV circuit leading to the Harry Allen Generating Station joins Path 27 near Cedar City. North of Mesquite, both are joined by a 500 kV line connecting the decommissioned Navajo Generating Station; the three travel somewhat within eyeshot of Interstate 15 until a solar park near Crystal. An assortment of 500 kV transmission corridors then follow Path 27 through Las Vegas Valley toward another collection of solar farms outside Boulder City. From Ivanpah Valley onward, two more 500 kV circuits and a third of 287 kV accompany Path 27 across the desert—these three constitute WECC Path 46. By Victorville, Path 27 splits from the three AC routes but is once again shadowed by others of various voltages before culminating in Adelanto. Stringing multiple circuits on the same right-of-way is often favored, as it consumes less land per mile. ==Further reading== Debroy, Rupam ==External links== Map of Path 27's course, including overhead electrode lines, locations of converters and grounding points, Google Maps Intermountain HVDC transmission system, The ABB Group Transmission Accuracy in Western Electricity Coordinating Council; Path 27's usage value listed The Intermountain Power Project (IPP) HVDC Schema The Intermountain Power Project (IPP) HVDC Pictures

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