Path 27, also called the Intermountain or the Southern Transmission System (STS),
is a
high-voltage direct current
A high-voltage direct current (HVDC) electric power transmission system (also called a power superhighway or an electrical superhighway) uses direct current (DC) for electric power transmission, in contrast with the more common alternating curre ...
(HVDC)
electrical transmission
Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines that facilitate this movement form a ''transmission network''. This is d ...
line running from the
coal-fired
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is formed when dea ...
Intermountain Power Plant
Intermountain Power Plant is a large coal-fired power plant at Delta, Utah, US. It has an installed capacity of 1,900 MW, is owned by the Intermountain Power Agency, and is operated by the Los Angeles Department of Water and Power.
The p ...
near
Delta, Utah to the
Adelanto Converter Station at
Adelanto, California, in the
Southwestern United States. It was installed by the
ABB Group
ABB Ltd. is a Swedish- Swiss multinational corporation headquartered in Zürich, Switzerland. The company was formed in 1988 when Sweden's Allmänna Svenska Elektriska Aktiebolaget (ASEA) and Switzerland's Brown, Boveri & Cie merged to crea ...
, a company based in
Switzerland, and commercialized in July 1986. The system is designed to carry power generated at the
power plant
A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the electricity generation, generation of electric power. Power stations are generally connected to an el ...
in Utah to areas throughout
Southern California
Southern California (commonly shortened to SoCal) is a geographic and cultural region that generally comprises the southern portion of the U.S. state of California. It includes the Los Angeles metropolitan area, the second most populous urban a ...
. It is owned and operated by the
Intermountain Power Agency
The Intermountain Power Agency, located in Utah, is a power generating cooperative of 23 municipalities in Utah and 6 in California. It owns the Intermountain Power Plant near Delta, Utah, one of the largest coal-fired power plants in the Un ...
, a cooperative consisting of six
Los Angeles
Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the List of municipalities in California, largest city in the U.S. state, state of California and the List of United States cities by population, sec ...
-area cities, the largest member being the
Los Angeles Department of Water and Power
The Los Angeles Department of Water and Power (LADWP) is the largest municipal utility in the United States with 8,100 megawatts of electric generating capacity (2021-2022) and delivering an average of 435 million gallons of water per day to more ...
(LADWP), and 29 smaller Utah municipalities.
Path 27 consists of an
overhead power line
An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy across large distances. It consists of one or more uninsulated electrical cables (commonly multiples of three for three-p ...
long, and is capable of transferring up to 2,400
megawatts
The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wat ...
(MW) of power at ±500
kilovolts (kV), higher than the power plant's operational capacity of 1,900 MW. The resulting maximum current is 4,800
amperes
The ampere (, ; symbol: A), often shortened to amp,SI supports only the use of symbols and deprecates the use of abbreviations for units. is the unit of electric current in the International System of Units (SI). One ampere is equal to elect ...
. Given its length, a
direct current
Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or eve ...
(DC) is preferred to the more common
alternating current
Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...
(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
Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electros ...
and enhance conductance. At each end of the line is a
converter station
An HVDC converter station (or simply converter station) is a specialised type of substation which forms the terminal equipment for a high-voltage direct current (HVDC) transmission line.Arrillaga, Jos; High Voltage Direct Current Transmission, se ...
that changes
AC to DC on one side and
back again Back Again may refer to: Albums
* Back Again! (Milira album), ''Back Again!'' (Milira album), 1992
* Back Again (Disciple album), ''Back Again'' (Disciple album), 2003, or the title track
* Back Again! (Mr. Cheeks album), ''Back Again!'' (Mr. Cheeks ...
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.
Sections of Path 27 are paralleled by many other AC transmission lines, including some of 500 kV. The line is also viewable from
Interstate 15
Interstate 15 (I-15) is a major Interstate Highway in the western United States, running through Southern California and the Intermountain West. I-15 begins near the Mexican border in San Diego County and stretches north to Alberta, Cana ...
which it crosses several times on its trek.
Overview
Background
High voltages are typically needed to convey large quantities of
electrical power
Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. Standard prefixes apply to watts as with other SI units: thousands, millions and billions o ...
over a vast distance, while also minimizing the amount of energy lost to
resistance in the
conductive cables as a byproduct from a high
current
Currents, Current or The Current may refer to:
Science and technology
* Current (fluid), the flow of a liquid or a gas
** Air current, a flow of air
** Ocean current, a current in the ocean
*** Rip current, a kind of water current
** Current (stre ...
; that is, raising the
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...
lowers the amperage for the circuit, according to
Ohm's law. Whereas
high-voltage transmission routes commonly use a
three-phase alternating current
Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...
(AC) to move electricity in a to-and-fro fashion,
high-voltage direct current
A high-voltage direct current (HVDC) electric power transmission system (also called a power superhighway or an electrical superhighway) uses direct current (DC) for electric power transmission, in contrast with the more common alternating curre ...
(HVDC) lines, such as Path 27, carry power in only one direction. A
direct current
Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or eve ...
(DC) also incurs less loss of energy than AC over the same distance; in other words, DC can sustain power much further than AC,
which may require intermediate stations, or "taps," along the route. Another disadvantage for AC is that power tends to flow on the outer layer of the conductor, a phenomenon called the "
skin effect." DC avoids this problem; it allows power to penetrate the entire thickness of the conductor for optimal capacity. Finally, DC circuitry has been chosen for Path 27 because the cost of transmitting power over its distance is lower than with AC,
which is best economically suited for shorter stretches. HVDC is also cheaper because it utilizes fewer than three conductors, translating to less materials and subsequently allaying the cost of infrastructure and equipment used.
ABB Group
ABB Ltd. is a Swedish- Swiss multinational corporation headquartered in Zürich, Switzerland. The company was formed in 1988 when Sweden's Allmänna Svenska Elektriska Aktiebolaget (ASEA) and Switzerland's Brown, Boveri & Cie merged to crea ...
, a multinational electrical supplier based in
Switzerland that was also a chief contributor for Path 27, manages the framework and supplies for the power line.
The number in "Path 27" is assigned by the
Western Electricity Coordinating Council
The Western Electricity Coordinating Council (WECC) promotes Bulk Electric System (BES) reliability for the entire Western Interconnection system. WECC is the Regional Entity responsible for compliance monitoring and enforcement. In addition, WE ...
(WECC), which oversees the electrical transmission grid across the
American West, to distinguish this line from the other
critical transmission routes.
Path 27 is owned and operated by an inter-municipality cooperative known as the
Intermountain Power Agency
The Intermountain Power Agency, located in Utah, is a power generating cooperative of 23 municipalities in Utah and 6 in California. It owns the Intermountain Power Plant near Delta, Utah, one of the largest coal-fired power plants in the Un ...
(IPA), thus lending it the alternative name Intermountain. The IPA's roster includes 29 Utah municipalities—amidst them two suburbs of
Salt Lake City
Salt Lake City (often shortened to Salt Lake and abbreviated as SLC) is the capital and most populous city of Utah, United States. It is the seat of Salt Lake County, the most populous county in Utah. With a population of 200,133 in 2020, th ...
, and
Logan as the northernmost participant—and six
Southern California
Southern California (commonly shortened to SoCal) is a geographic and cultural region that generally comprises the southern portion of the U.S. state of California. It includes the Los Angeles metropolitan area, the second most populous urban a ...
cities.
The cooperative was founded around this mission:
Among its objectives is funneling excess energy to communities in Southern California; Path 27 was built to fulfill that purpose. The largest SoCal client by population on the list is the
Los Angeles Department of Water and Power
The Los Angeles Department of Water and Power (LADWP) is the largest municipal utility in the United States with 8,100 megawatts of electric generating capacity (2021-2022) and delivering an average of 435 million gallons of water per day to more ...
(LADWP), the preeminent utility provider for
Los Angeles
Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the List of municipalities in California, largest city in the U.S. state, state of California and the List of United States cities by population, sec ...
, which also receives the greatest share of power through the
plan
A plan is typically any diagram or list of steps with details of timing and resources, used to achieve an objective to do something. It is commonly understood as a temporal set of intended actions through which one expects to achieve a goal.
...
ahead of
Anaheim,
Riverside,
Pasadena
Pasadena ( ) is a city in Los Angeles County, California, northeast of downtown Los Angeles. It is the most populous city and the primary cultural center of the San Gabriel Valley. Old Pasadena is the city's original commercial district.
...
,
Burbank, and
Glendale Glendale is the anglicised version of the Gaelic Gleann Dail, which means ''valley of fertile, low-lying arable land''.
It may refer to:
Places Australia
* Glendale, New South Wales
** Stockland Glendale, a shopping centre
*Glendale, Queensland, ...
(as shown in the table below). Altogether, these members acquire the biggest proportion of energy under the IPA.
History
The earliest concept of Path 27 likely originated in 1973, coinciding with an
energy crisis of that decade plaguing the U.S. During that year, after the
U.S. Bureau of Reclamation warned of a forthcoming energy shortage, representatives for the Utah-based Intermountain Consumer Power Association (ICPA) convened with Southern California localities in a quest for newer power sources and for investors. The IPA established in June 1977.
A crucial step for Path 27 came with the Intermountain Power Project (IPP), which emerged in 1974 as a program for financing the construction of a
coal-fired generator, though it was not until 1977 that Utah's legislatures formally endorsed IPA's implementation of the project.
Caineville
Caineville is an unincorporated community in central Wayne County, Utah, United States.
Description
The community is located east of Capitol Reef National Park and west of Hanksville, along the Fremont River and Utah State Route 24. The set ...
in
Wayne County, UT, was one of several locations suggested for the power plant, prior to settling upon the site north of
Delta
Delta commonly refers to:
* Delta (letter) (Δ or δ), a letter of the Greek alphabet
* River delta, at a river mouth
* D ( NATO phonetic alphabet: "Delta")
* Delta Air Lines, US
* Delta variant of SARS-CoV-2 that causes COVID-19
Delta may also ...
in
Millard County
Millard County ( ) is a county in the U.S. state of Utah. As of the 2010 United States Census, the population was 12,503. Its county seat is Fillmore, and the largest city is Delta.
History
The Utah Territory legislature created the county o ...
, or west of
Lynndyl as stated in the sanction. After clearing environmental checks, the generator broke ground on October 9, 1981, with
$300 million in initial funds. The original plan called for four
thermal units, 750 MW aside, but it had decreased to two due to concerns over precipitous power demand. The generator's first unit was erected in 1983. The first batch of
coal
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is formed when ...
was delivered by train on July 2, 1985, and the first unit came online later that year. The second unit was actuated on June 13, 1987, bringing the plant to its fullest capacity of 1,500 MW.
It would be bolstered to its present-day 1,900-MW productivity in 1989,
hence rendering the electrical generator the largest in Utah.
However, Path 27 fully materialized when the transmission line's construction commenced on May 1, 1984, and took slightly more than sixteen months to complete.
Various American contractors were commissioned for certain aspects and segments of the line; for instance, one entity from
Georgia
Georgia most commonly refers to:
* Georgia (country), a country in the Caucasus region of Eurasia
* Georgia (U.S. state), a state in the Southeast United States
Georgia may also refer to:
Places
Historical states and entities
* Related to the ...
built worth from
Adelanto, California to
Moapa, Nevada
Moapa is an unincorporated town and census-designated place (CDP) in Clark County, Nevada, United States. The population was 1,025 at the 2010 census. It is the largest town in Clark County by land area. Both the second and the third tallest st ...
, and another from
Mississippi
Mississippi () is a state in the Southeastern region of the United States, bordered to the north by Tennessee; to the east by Alabama; to the south by the Gulf of Mexico; to the southwest by Louisiana; and to the northwest by Arkansas. Miss ...
took on the remaining till Delta;
but perhaps the most notable obligation for this turnkey project rested upon
ABB Group
ABB Ltd. is a Swedish- Swiss multinational corporation headquartered in Zürich, Switzerland. The company was formed in 1988 when Sweden's Allmänna Svenska Elektriska Aktiebolaget (ASEA) and Switzerland's Brown, Boveri & Cie merged to crea ...
, who imported the conductive cables and pieces for the steel-lattice support pylons to be assembled on the spot. One phase entailed the emplacement of the pylons' cement
foundations, which are in average depth per pylon and vary in shape based on the tower's height and weight. Newspapers reported that rocky, jagged terrain often posed challenges and had likely necessitated copious excavation and even
dynamiting. In all, six hundred workers were deployed for the labor.
The line achieved revenue service in July 1986
after the ignition of the power plant's first coal-burning unit, even though a document by LADWP attests that it might have been energized as early as December 1985. Depending on official tallies and news accounts, the total cost was $5.5 billion.
Finally yet equally integral for Path 27 are two converter stations (''
see below''), which were inaugurated along with the transmission main, and are vital for its functionality. IPP's converter was installed in conjunction with the power generator, while the second converter in Adelanto and a tangent
switchyard began rising on May 26, 1985, and finished in June 1986
in time to receive freshly-borne energy from borders over. LADWP supervised the construction of the combined facility and tasked ABB Group with the responsibility of the accouterments.
Since its inception, Path 27 saw upgrades and refinements around the latter turn of the century—the IPP's latest proliferation included. At the behest of LADWP and
Southern California Edison
Southern California Edison (or SCE Corp), the largest subsidiary of Edison International, is the primary electricity supply company for much of Southern California. It provides 15 million people with electricity across a service territory of ap ...
, ABB Group and
Hitachi Energy
Hitachi Energy Ltd is a global technology company headquartered in Zurich, Switzerland. The company provides sustainable energy solutions to buildings, utilities, industries, and infrastructure sectors. The company’s portfolio includes high-v ...
modernized the transmission line in 2008 and 2011, respectively, with improved control and protection technology alongside supplemental
filters
Filter, filtering or filters may refer to:
Science and technology
Computing
* Filter (higher-order function), in functional programming
* Filter (software), a computer program to process a data stream
* Filter (video), a software component tha ...
and
cooling systems at each terminal.
This helped raise the power line's capacity to its modern-day level of 2,400 MW.
Installation
Transmission
The primary component of Path 27 is the
transmission line
In electrical engineering, a transmission line is a specialized cable or other structure designed to conduct electromagnetic waves in a contained manner. The term applies when the conductors are long enough that the wave nature of the transmi ...
itself, which travels a length of entirely
aboveground through southwestern
Utah
Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...
,
southern Nevada
Southern Nevada (SNV) is a region and the southern portion of the U.S. state of Nevada which includes the Las Vegas Valley. It also includes the areas in and around Pahrump and Pioche. Tonopah and Hawthorne are sometimes also referred to as part ...
, and southern
California
California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
. It exerts ±500 kV and is rated for 2,400 MW, giving it a maximum current rating of 4,800 amperes; by comparison, the
Intermountain Power Plant
Intermountain Power Plant is a large coal-fired power plant at Delta, Utah, US. It has an installed capacity of 1,900 MW, is owned by the Intermountain Power Agency, and is operated by the Los Angeles Department of Water and Power.
The p ...
(IPP) generates up to 1,900 MW, thus adding to the line's
fault tolerance
Fault tolerance is the property that enables a system to continue operating properly in the event of the failure of one or more faults within some of its components. If its operating quality decreases at all, the decrease is proportional to the ...
. As opposed to three phases, Path 27 has two
poles
Poles,, ; singular masculine: ''Polak'', singular feminine: ''Polka'' or Polish people, are a West Slavic nation and ethnic group, who share a common history, culture, the Polish language and are identified with the country of Poland in C ...
; one positive (
cathode
A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in wh ...
) and another negative (
anode
An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic ...
);
making this a
bipolar configuration. On most HVDC systems, power can be sent in either direction; Path 27 transports electricity from Utah to California under normal circumstances.
Any conductive material engenders
electromagnetic radiation
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) li ...
whenever electricity flows through it. A single cable carrying such high voltage would produce particularly strong
radiation in the form of a
corona discharge
A corona discharge is an electrical discharge caused by the ionization of a fluid such as air surrounding a conductor (material), conductor carrying a high voltage. It represents a local region where the air (or other fluid) has undergone e ...
that can deprive electrical energy and cause
EM interference
Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electros ...
on radio and communication devices. For this reason, Path 27's conductors comprise of three cables fastened together, or are
triple-bundled. This not only reduces the detrimental effects of discharge, it also provides more surface area for power to flow, thereby improving transmission efficiency.
Two
shield wires are mounted above the main conductors and shared by the same support pylons. These wires guard the power line against lightning strikes.
Converters
Both sides of Path 27 feature a
converter station
An HVDC converter station (or simply converter station) is a specialised type of substation which forms the terminal equipment for a high-voltage direct current (HVDC) transmission line.Arrillaga, Jos; High Voltage Direct Current Transmission, se ...
, which bridges electrical power between AC and DC circuitry and are ubiquitous to HVDC projects worldwide. The converters are located at the IPP station north of
Delta, UT, and the
Adelanto Converter Station in
Adelanto, CA, north of
San Bernardino
San Bernardino (; Spanish for "Saint Bernardino") is a city and county seat of San Bernardino County, California, United States. Located in the Inland Empire region of Southern California, the city had a population of 222,101 in the 2020 cen ...
.
The heart of the conversion process transpires in clusters of
electronic valves that procedurally modify the flow of electricity similar to
switches
In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
. The type of valves on Path 27 is
thyristor
A thyristor () is a solid-state semiconductor device with four layers of alternating P- and N-type materials used for high-power applications. It acts exclusively as a bistable switch (or a latch), conducting when the gate receives a current ...
, technology popular in HVDC since the late 1960s.
The valve configuration is identical for both converters: 24 stacks about in height of 24 valves apiece (or three "
quadruple-valves"),
singly containing 144 thyristors, organized into twelve modules.
As a matter of redundancy, the valves at both terminals are grouped two by six; should one be disabled, the other can pick up the slack above its designated capacity for a limited duration.
The entire assemblage is housed in a hangar-like enclosure called a
valve hall
A valve hall is a building which contains the valves of the static inverters of a high-voltage direct current plant. The valves consist of thyristors, or at older plants, mercury arc rectifiers. Mercury arc rectifiers are usually supported by ...
that protects it from the weather and airborne dust. The valves are affixed on tall insulators that separate them from the interior walls, floor, and ceiling; done to hinder
induction
Induction, Inducible or Inductive may refer to:
Biology and medicine
* Labor induction (birth/pregnancy)
* Induction chemotherapy, in medicine
* Induced stem cells, stem cells derived from somatic, reproductive, pluripotent or other cell t ...
and
premature grounding, as well as aid
cooling
Cooling is removal of heat, usually resulting in a lower temperature and/or phase change. Temperature lowering achieved by any other means may also be called cooling.ASHRAE Terminology, https://www.ashrae.org/technical-resources/free-resources/as ...
. Path 27's valve halls are also fortified against earthquakes.
As the IPP converter is adjacent to the
power plant
A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the electricity generation, generation of electric power. Power stations are generally connected to an el ...
, electricity is generally fed into the HVDC line from this terminus. Ingress for power to the system is preceded by a row of
transformers
''Transformers'' is a media franchise produced by American toy company Hasbro and Japanese toy company Tomy, Takara Tomy. It primarily follows the Autobots and the Decepticons, two alien robot factions at war that can transform into other forms ...
that step up the voltage level to 500 . Next, it infiltrates the valve hall through enormous
bushings that protect the building from damage caused by
arcing
An electric arc, or arc discharge, is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma; the plasma may produce visible light. An ...
. Inside the hall, the valves pipe the electrical flow from AC to DC in a complex process called
''rectification''. On the DC circuitry back outside sits a
sequence of filters and reactors that reciprocally serve to cushion the facility from disturbances as a result of
power surges.
The electricity is then sent on its way down Path 27.
The Adelanto Converter Station demarks the receiving end of the HVDC line and has relatively the same layout, but the conversion mechanism is reversed. Beyond another set of reactors and filters, the inpouring power enters the valve hall to be carried over to AC circuitry anew—this is ''
inversion
Inversion or inversions may refer to:
Arts
* , a French gay magazine (1924/1925)
* ''Inversion'' (artwork), a 2005 temporary sculpture in Houston, Texas
* Inversion (music), a term with various meanings in music theory and musical set theory
* ...
'', and it blocks vagrant power on the AC conduit from reaching the valves to enforce unidirectional movement. The electricity advances through a second tier of transformers before disemboguing onto diverging AC lines to be dispersed across the vicinity.
Ideally, Path 27 can work in the opposite direction, with the Adelanto terminal becoming a rectifier, and the IPP an inverter, although this seldom happens out of practicality.
Grounding system
Like any HVDC scheme, Path 27 needs to be
grounded at both ends in order to operate with respect to the earth.
Grounding provides the electrical current a common
path back into the earth, which serves as a neutral point for the circuit.
Even with safeguards and a high fault tolerance, failures on the line can and do occur, thence grounding becomes a workaround for continued reliability of the system. If one pole develops a
fault, its current is diverted via the ground return to complete the circuit.
This de-energizes the problem conductor, while the second pole remains active;
in technical terms, grounding allows the power line to function as a
monopole instead of a bipole.
However, it halves the line's overall capacity.
A pole may also be taken offline by the same means for maintenance, ensuring the safety of work crews. This contingency precludes the need to shut down the whole HVDC system and interrupt the power source, yet it is temporary, as the earth return on a bipolar system is not intended for prolonged use.
HVDC exhibits significant
potential
Potential generally refers to a currently unrealized ability. The term is used in a wide variety of fields, from physics to the social sciences to indicate things that are in a state where they are able to change in ways ranging from the simple r ...
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
Conductivity may refer to:
*Electrical conductivity, a measure of a material's ability to conduct an electric current
**Conductivity (electrolytic), the electrical conductivity of an electrolyte in solution
** Ionic conductivity (solid state), ele ...
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
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials d ...
, marking the actual transition into the earth for the current. Within the electrodes are 60 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
Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
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
Petroleum coke, abbreviated coke or petcoke, is a final carbon-rich solid material that derives from oil refining, and is one type of the group of fuels referred to as cokes. Petcoke is the coke that, in particular, derives from a final cracki ...
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
Jumper cables are electric cables to connect two rail or road vehicles.
Rail
Jumper cables are between the locomotive, the railroad cars and the cab car or the driving van trailer on push-pull trains for multiple-unit train control and the tr ...
radiating from the center of the circle feed the return current into the rods. At the center on the surface perches a small structure called a
terminal house,
which is also equipped with a transmitter that helps technicians monitor the electrode's performance.
The "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
Thickness may refer to:
* Thickness (graph theory)
* Thickness (geology), the distance across a layer of rock
* Thickness (meteorology), the difference in height between two atmospheric pressure levels
* Thickness planer a woodworking machine
...
, 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
A utility pole is a column or post typically made out of wood used to support overhead power lines and various other public utilities, such as electrical cable, fiber optic cable, and related equipment such as transformers and street lights. It c ...
. 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
neutral wire, which would involve an extra third conductor along the span of Path 27—the former
HVDC Vancouver Island
HVDC Vancouver Island is a de-energized high-voltage direct current interconnection between Arnott Substation (ARN) in Delta, British Columbia at on the Canadian mainland, and the Vancouver Island Terminal (VIT) in Duncan, British Columbia on Va ...
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
Intermountain Power Plant is a large coal-fired power plant at Delta, Utah, US. It has an installed capacity of 1,900 MW, is owned by the Intermountain Power Agency, and is operated by the Los Angeles Department of Water and Power.
The p ...
in Utah and heads briefly west before curving southward, passing over the
U.S. 50
U.S. Route 50 or U.S. Highway 50 (US 50) is a major east–west route of the U.S. Highway system, stretching from Interstate 80 (I-80) in West Sacramento, California, to Maryland Route 528 (MD 528) in Ocean City, Maryland, on the Atlantic ...
/
U.S. 6
U.S. Route 6 (US 6), also called the Grand Army of the Republic Highway, honoring the American Civil War Grand Army of the Republic, veterans association, is a main route of the U.S. Highway system. While it currently runs east-northeast fr ...
duplex west of
Hinkley. The DC line ventures though 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
Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...
's northwestern corner, simultaneously entering the
Mojave Desert
The Mojave Desert ( ; mov, Hayikwiir Mat'aar; es, Desierto de Mojave) is a desert in the rain shadow of the Sierra Nevada mountains in the Southwestern United States. It is named for the indigenous Mojave people. It is located primarily ...
.
Inside Nevada, Path 27 traverses the
Mormon Mesa
Mormon Mesa is a mesa between the Virgin River and the Muddy River in Clark County, southern Nevada.
In the south above the confluence of the Muddy and Virgin Rivers, it rises to a height of 1893 feet (577 meters). It extends northward to the f ...
, bypassing
Glendale Glendale is the anglicised version of the Gaelic Gleann Dail, which means ''valley of fertile, low-lying arable land''.
It may refer to:
Places Australia
* Glendale, New South Wales
** Stockland Glendale, a shopping centre
*Glendale, Queensland, ...
and crossing the
Muddy River. It bisects the
Moapa River Indigenous Reservation lands before crossing
Interstate 15
Interstate 15 (I-15) is a major Interstate Highway in the western United States, running through Southern California and the Intermountain West. I-15 begins near the Mexican border in San Diego County and stretches north to Alberta, Cana ...
near
Crystal
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...
. Across
Las Vegas Valley
The Las Vegas Valley is a major metropolitan area in the southern part of the U.S. state of Nevada, and the second largest in the Southwestern United States. The state's largest urban agglomeration, the Las Vegas Metropolitan Statistical Area i ...
, the line meets with
NV 564 while riding through the
Frenchman Mountain
Frenchman Mountain is a mountain located east of Las Vegas, Nevada. Made up of rocks similar to those found on the bottom of the Grand Canyon, Frenchman Mountain formed when faulting elevated and tilted the rocks followed by erosion, giving i ...
, straddles the
River Mountains bypassing
Henderson Henderson may refer to:
People
*Henderson (surname), description of the surname, and a list of people with the surname
*Clan Henderson, a Scottish clan
Places Argentina
*Henderson, Buenos Aires
Australia
*Henderson, Western Australia
Canada
* H ...
, and crosses
Interstate 11
Interstate 11 (I-11) is an Interstate Highway that currently runs for on a predominantly northwest–southeast alignment in the US state of Nevada, running concurrently with US Route 93 (US 93) between the Arizona state line ...
at
Railroad Pass before heading into
Eldorado Valley. Upon traversing the
McCullough Range
The mountains in the McCullough Range lie mostly above the city of Henderson in the U.S. state of Nevada. The range has two distinct areas with the northern portion being primarily volcanic in origin, while the southern part of the range is prim ...
, it descends into
Ivanpah Valley
The Ivanpah Valley is in southeastern California and southern Nevada in the United States. The valley is between the New York Mountains and the Ivanpah Mountains in San Bernardino County on the California side, and in Clark County on the Nevada ...
, 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
The Victor Valley is a valley in the Mojave Desert and subregion of the Inland Empire, in San Bernardino County in Southern California.
It is located east of the Mojave's Antelope Valley, north of the Cajon Pass and the San Bernardino Valley, ...
where it crosses
Interstate 15
Interstate 15 (I-15) is a major Interstate Highway in the western United States, running through Southern California and the Intermountain West. I-15 begins near the Mexican border in San Diego County and stretches north to Alberta, Cana ...
once more near
Yermo, as well as
old U.S. 66 and
Interstate 40
Interstate 40 (I-40) is a major east–west Interstate Highway running through the south-central portion of the United States. At a length of , it is the third-longest Interstate Highway in the country, after I-90 and I-80. From west to ea ...
between
Daggett and
Newberry Springs
Newberry Springs is an unincorporated community in the western Mojave Desert of Southern California, located at the foot of the Newberry Mountains in San Bernardino County, California, United States.
Newberry Spring is a spring that in the 19t ...
. It then encounters
CA 247 south of
Barstow. Around
Bell Mountain, Path 27 meets with Interstate 15 one last time, and then old U.S. 66 a second instance and
U.S. 395 near
Oro Grande before reaching
Adelanto
Adelanto (Spanish for "Advance") is a city in San Bernardino County, California, United States. It is approximately northwest of Victorville in the Victor Valley area of the Mojave Desert, in the northern region of the Inland Empire.Lint ...
, 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
The Harry Allen Generating Station is a natural gas fired combined cycle power plant located in Clark County, Nevada about 30 miles north of Las Vegas. Electricity is generated by two GE Frame 7EA combustion turbines, two GE Frame 7FA+e combustio ...
joins Path 27 near
Cedar City
Cedar City is the largest city in Iron County, Utah, United States. It is located south of Salt Lake City, and north of Las Vegas on Interstate 15. It is the home of Southern Utah University, the Utah Shakespeare Festival, the Utah Summer Gam ...
. North of
Mesquite
Mesquite is a common name for several plants in the genus '' Prosopis'', which contains over 40 species of small leguminous trees. They are native to dry areas in the Americas.
They have extremely long roots to seek water from very far under gr ...
, both are joined by a 500-kV line connecting the decommissioned
Navajo Generating Station
Navajo Generating Station was a 2.25-gigawatt (2,250 MW), coal-fired power plant located on the Navajo Nation, near Page, Arizona, United States. This plant provided electrical power to customers in Arizona, Nevada, and California. It also provi ...
; the three travel somewhat within eyeshot of Interstate 15 until a
solar park
A photovoltaic power station, also known as a solar park, solar farm, or solar power plant, is a large-scale grid-connected photovoltaic power system (PV system) designed for the supply of merchant power. They are different from most building- ...
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
Boulder City is a city in Clark County, Nevada, United States. It is approximately southeast of Las Vegas. As of the 2020 United States Census, 2020 census, the population of Boulder City was 14,885. The city took its name from Boulder Canyon ( ...
. 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
Path 46, also called West of Colorado River, Arizona-California West-of-the-River Path (WOR), is a set of fourteen high voltage (500 kV & 230 kV) alternating-current transmission lines that are located in southeast California and Nevada up to the ...
. By
Victorville
Victorville is a city in Victor Valley in San Bernardino County, California. Its population as of the 2020 census was 134,810.
History
In 1858, Aaron G. Lane came to what is now known as Victorville and founded a waystation called "Lane's Cro ...
, 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 not unusual, as it consumes less land per mile.
Future
The coal-firing powerhouses at the site are to be retired by 2027;
this adheres to LADWP's wishes for reducing its dependence on fossil fuels in favor of
greener energy.
The plant will be replaced with a
gas-powered facility specially tailored for
harvesting hydrogen by 2025,
and paired with a
solar farm on a nearby parcel.
The sources will beget 840 MW and 300 MW at peak, respectively, or 1,140 MW when combined, still lower than Path 27's maximal capacity. Neither is anticipated to alter the power line's structure.
References
Notes
Citations
*
External links
Map of Path 27's course including overhead electrode lines, locations of converters and grounding points,
Google Maps
Google Maps is a web mapping platform and consumer application offered by Google. It offers satellite imagery, aerial photography, street maps, 360° interactive panoramic views of streets ( Street View), real-time traffic conditions, and rou ...
Intermountain HVDC transmission system The ABB Group
* https://web.archive.org/web/20050526185217/http://www.transmission.bpa.gov/cigresc14/Compendium/IPP.htm
* https://web.archive.org/web/20050426153127/http://www.transmission.bpa.gov/cigresc14/Compendium/Ipp+Pictures.pdf
See also
*
Pacific DC Intertie
The Pacific DC Intertie (also called Path 65) is an electric power transmission line that transmits electricity from the Pacific Northwest to the Los Angeles area using high voltage direct current (HVDC). The line capacity is 3.1 gigawatts, whi ...
- a similar HVDC system running through the Western U.S.
*
List of HVDC projects
This is a list of notable high-voltage direct-current power transmission projects.
HVDC projects for long-distance transmission have two (or rarely, more) converter stations and a transmission line interconnecting them. Generally overhead line ...
{{Energy resource facilities in Nevada
Western Interconnection
Energy infrastructure in California
Energy infrastructure in Nevada
Energy infrastructure in Utah
HVDC transmission lines