Though widespread use of DC ultimately lost favor for distribution, it exists today primarily in long-distance high-voltage direct current ( HVDC ) transmission systems.

Some HVDC power transmission systems use the ground as second conductor.

In the mid 1950s, HVDC transmission was developed, and is now an option instead of long-distance high voltage alternating current systems.

A high-voltage, direct current ( HVDC ) electric power transmission system uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current systems.

For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses.

HVDC allows power transmission between unsynchronized AC distribution systems, and can increase system stability by preventing cascading failures from propagating from one part of a wider power transmission grid to another.

While high-voltage direct current ( HVDC ) is increasingly being used to transmit large quantities of electricity over long distances or to connect adjacent asynchronous power systems, the bulk of electricity generation, transmission, distribution and retailing takes place using alternating current.

DC power remains the only practical choice in digital systems and can be more economical to transmit over long distances at very high voltages ( see HVDC ).

High-voltage direct current ( HVDC ) transmission lines are either monopolar or bipolar systems.

The HVDC control and protection systems are also interlocked to prevent operators from operating the link with southbound flow in excess of the difference between the capacity of transmission lines into Haywards and Wellington's minimum regional load.

Like all transmission systems, the HVDC Inter-Island link is not immune to failures.

Pole 2 was commissioned in 1992 with HVDC control systems utilising late 1980s technology.

It was at one time the only application of the technology of high voltage direct current transmission for the supply of transformer stations in a city, and the first HVDC link to be embedded within an AC system, rather than interconnecting two asynchronous systems.

It was also the first HVDC scheme to be equipped with self-tuning harmonic filters and to be controlled with a " Phase Locked Oscillator ", a principle which subsequently became standard on all HVDC systems ..

Apart from the Nelson River Bipole 1 system in Canada, all later-built HVDC systems used thyristor valves.

The former mercury valves were available with ratings to 100 kV in a single unit, simplifying their application in HVDC systems.

Early HVDC systems used mercury-arc valves, but since the mid 1970s, solid state devices such as thyristors are used.

In HVDC systems typically two conductors are carried per line, but rarely only one pole of the system is carried on a set of towers.

High Voltage Direct Current ( HVDC ) was chosen both because this technique allows long transmission lines with little loss compared to other systems ( like AC ), and also allows interchange of the Paraguayan 50 Hz input and the Brazilian 60 Hz input and user grid.

This is the only crossing of an HVDC powerline and a single-phase AC powerline in the world and the only place where all kinds of electric transmission systems, three phase AC powerline, single phase AC powerline and HVDC come close together.

As is the case in all modern HVDC systems, thyristor static inverters are used.

The Eel River Converter Station consists of two separate 12-pulse bidirectional solid-state non-synchronous HVDC ties of 4800 thyristors ( each nominally rated 160 MW ) connecting 230-kV transmission systems of Hydro-Québec and NB Power.

Despite the simplification they can bring to the electronics of an HVDC valve, light triggered thyristors may still require some simple monitoring electronics and have the disadvantage of being available from only very few manufacturers.

Line commutated converters require voltage from the AC network for commutation, but since the late 1990s, voltage sourced converters have started to be used for HVDC.

Two of three thyristor valve stacks used for long distance transmission of power from Manitoba Hydro damsSince modern thyristors can switch power on the scale of megawatts, thyristor valves have become the heart of high-voltage direct current ( HVDC ) conversion either to or from alternating current.

The inter-island transmission system was designed as an HVDC system, despite the cost of the conversion from AC to DC and back, to suit the requirements of a long transmission line and a sea crossing. The link crosses Cook Strait, between the two islands, using submarine power cables laid along the sea floor.

HVDC is more suitable than AC for transmission over long distances, and particularly where cable transmission is required, because it is typically more economic, and has lower energy losses, despite the high costs of the AC / DC conversion process.

Almost all converters used for HVDC are intrinsically able to operate with power conversion in either direction.

In modern systems, high-voltage DC ( HVDC ) " back-to-back " stations are used instead of mechanical equipment to convert between different frequencies and phases of AC power and solid-state thyristor rectifier systems are used for conversion from AC power to DC traction power.

Two 600 kV HVDC lines, each approximately 800 km long, carry both Brazilian and Paraguayan energy to São Paulo where the terminal equipment converts the power to 60 Hz.

Following Transpower's decommissioning of the original Pole 1 equipment, there was no longer any direct connection between the generator 16 kV busbars and the HVDC link, and the limited capacity of the Benmore interconnecting transformers would have constrained the maximum output of the 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 transmission line.

The design and equipment for the Eel River HVDC station was provided by General Electric with its commissioning being completed in 1972.

The equipment was built indigenously by BHEL and APGENCO. This HVDC is used for grid synchronization between central and southern India.

Bipolar HVDC lines at which each pole is operated with the same voltage toward ground are also balanced lines.

* Power cables: Three submarine power cables cross Cook Strait between Oteranga Bay in the North Island and Fighting Bay in the South Island as part of the HVDC Inter-Island, which provides an electricity link between Benmore in the South island and Haywards in the North Island.

The boundary between the two regions contains four back-to-back high-voltage direct-current ( HVDC ) substations which convert the frequency ; these are Shin Shinano, Sakuma Dam, Minami-Fukumitsu, and the Higashi-Shimuzu Frequency Converter.

However only two very short sections exist where a pylon carries as well AC as DC circuits: these are the pylons in the terminal of HVDC Volgograd-Donbass on Volga Hydroelectric Power Station and 2 pylons south of Stenkullen, which carry one circuit of HVDC Konti-Skan and the three-phase AC line Stenkullen-Holmbakullen.

A HVDC back-to-back facility called GKK Etzenricht was installed there from 1991 to 1993, which made the name of the municipality Etzenricht supraregionally popular.

It has 2 Aluminium conductors each with a cross section of 910 mm2, which are installed on wooden poles-perhaps the only HVDC powerline using such poles.

Because the first installation did not meet increasing requirements, it was replaced in 1975 – 1986 by a new HVDC system with a maximum transmission rating of 2, 000 MW between France and Great Britain, for which two new converter stations were built in Sellindge ( UK ) and in Bonningues-lès-Calais ( Les Mandarins station ), near Calais, ( France ).

It is commonly referred to as the Cook Strait cable, which is somewhat of a misnomer, because only a short section of the complete link is in cable, and there are actually three operational HVDC power cables across Cook Strait.

The HVDC Vancouver Island is the name for HVDC interconnection between the Vancouver Island Terminal ( VIT ) near North Cowichan, British Columbia on Vancouver Island at and the Arnott Substation ( ARN ) near Delta, British Columbia at on the Canadian mainland, which went into operation in 1968 and was extended in 1977.

It is connected with Vancouver Island Terminal by a overhead electrode, which is mounted between Vancouver Island Terminal and a point northwest of Maple Bay at on the towers of the main HVDC line.

# GK Dürnrohr, a decommissioned HVDC back-to-back station, which played before 1996 an important role in the transmission system of Europe

In great extent, it was identical with the HVDC back-to-back station in Etzenricht, which was used for coupling the power grids of Bavaria and Czech and built at the same time.

* The largest credible single generation failure, which is currently either Sizewell B nuclear power station ( 1, 260 MW ) or one cable of the HVDC Cross-Channel interconnector ( 1, 000 MW )

In 1902 Hewitt developed the first mercury arc rectifier, which was an efficient way of converting alternating current power to direct current for use in electric railways, industry, and high-voltage direct current ( HVDC ) power transmission.

The first consist of an HVAC double circuit overhead lines running over a distance of 160 km from Bakun Dam to Similajau Static Inverter Plant, situated east of Bintulu and is planned beside the HVDC also the Sarawak state electricity grid which is operated by Sarawak Electricity Supply Corporation.

Thyristor valves are used, which unlike other HVDC schemes are mounted outdoors and not in a hall.

In installing Cross-Skagerrak 3, the old poles Cross-Skagerrak 1 and Cross-Skagerrak 2 were converted to monopolar HVDC schemes, which run with opposite polarity to Cross-Skagerrak 3.

A valve hall is a building which contains the valves of the static inverters of a HVDC plant.

It is notable for its large electrical substation, which is the main switching point for the Wellington region, and the home of the North Island converter station for the HVDC Inter-Island, which links the North and South Island electricity networks together.