High-voltage direct current

Long distance HVDC lines carrying hydroelectricity from Canada's Nelson River to this converter station where it is converted to AC for use in southern Manitoba's grid
Schematic diagram of a Thury HVDC transmission system
HVDC in 1971: this 150 kV mercury-arc valve converted AC hydropower voltage for transmission to distant cities from Manitoba Hydro generators.
Pylons of the Baltic Cable HVDC in Sweden
Three-phase high voltage transmission lines use alternating currents to distribute power over long distances between electric generation plants and consumers. The lines in the picture are located in eastern Utah.
A twelve-pulse bridge rectifier
Thyristor valve stacks for Pole 2 of the HVDC Inter-Island between the North and South Islands of New Zealand. The man at the bottom gives scale to the size of the valves.
A single-phase, three-winding converter transformer. The long valve-winding bushings, which project through the wall of the valve hall, are shown on the left. The line-winding bushing projects vertically upwards at center-right
Block diagram of a monopole system with earth return
Block diagram of a bipolar system that also has an earth return
A block diagram of a bipolar HVDC transmission system, between two stations designated A and B. AC – represents an alternating current network CON – represents a converter valve, either rectifier or inverter, TR represents a power transformer, DCTL is the direct-current transmission line conductor, DCL is a direct-current filter inductor, BS represents a bypass switch, and PM represent power factor correction and harmonic filter networks required at both ends of the link. The DC transmission line may be very short in a back-to-back link, or extend hundreds of miles (km) overhead, underground or underwater. One conductor of the DC line may be replaced by connections to earth ground.
Two HVDC lines cross near Wing, North Dakota.

Electrical superhighway) uses direct current (DC) for the transmission of electrical power, in contrast with the more common alternating current (AC) systems.

- High-voltage direct current

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Direct current

One-directional flow of electric charge.

Direct current (DC) (red line). The vertical axis shows current or voltage and the horizontal 't' axis measures time and shows the zero value.
Brush Electric Company's central power plant with dynamos generating direct current to power arc lamps for public lighting in New York. Beginning operation in December 1880 at 133 West Twenty-Fifth Street, the high voltages it operated at allowed it to power a 2 mi long circuit.
Types of direct current
This symbol which can be represented with Unicode character (⎓) is found on many electronic devices that either require or produce direct current.

High-voltage direct current is used to transmit large amounts of power from remote generation sites or to interconnect alternating current power grids.


Conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry.

The Solar Settlement, a sustainable housing community project in Freiburg, Germany.
Photovoltaic SUDI shade is an autonomous and mobile station in France that provides energy for electric cars using solar energy.
Solar panels on the International Space Station
Solar cells generate electricity directly from sunlight.
Photovoltaic power potential map estimates, how many kWh of electricity can be produced from a 1 kWp free-standing c-Si modules, optimally inclined towards the Equator. The resulting long-term average (daily or yearly) is calculated based on the time-series weather data of at least recent 10 years.
Price per watt history for conventional (c-Si) solar cells since 1977.
Worldwide growth of photovoltaics on a semi-log plot since 1992
Best Research-Cell Efficiencies
Grids with high penetration of renewable energy sources generally need more flexible generation rather than baseload generation
This chart illustrates the effect of clouds on solar energy production.
AWM Munich ETFE Cushions-Photovoltaics.

The use of PV as a main source requires energy storage systems or global distribution by high-voltage direct current power lines causing additional costs, and also has a number of other specific disadvantages such as unstable power generation and the requirement for power companies to compensate for too much solar power in the supply mix by having more reliable conventional power supplies in order to regulate demand peaks and potential undersupply.

Alternating current

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 (green curve). The horizontal axis measures time (it also represents zero voltage/current) ; the vertical, current or voltage.
A schematic representation of long distance electric power transmission. From left to right: G=generator, U=step up transformer, V=voltage at beginning of transmission line, Pt=power entering transmission line, I=current in wires, R=total resistance in wires, Pw=power lost in transmission line, Pe=power reaching the end of the transmission line,  D=step down transformer, C=consumers.
Three-phase high-voltage transmission lines use alternating currents to distribute power over long distances between electric generation plants and consumers. The lines in the picture are located in eastern Utah.
A sine wave, over one cycle (360°). The dashed line represents the root mean square (RMS) value at about 0.707.
The Hungarian "ZBD" Team (Károly Zipernowsky, Ottó Bláthy, Miksa Déri), inventors of the first high efficiency, closed-core shunt connection transformer
The prototype of the ZBD transformer on display at the Széchenyi István Memorial Exhibition, Nagycenk in Hungary
Westinghouse Early AC System 1887
(US patent 373035)

High-voltage direct-current (HVDC) electric power transmission systems have become more viable as technology has provided efficient means of changing the voltage of DC power.


Solid-state semiconductor device with four layers of alternating P- and N-type materials.

Layer diagram of thyristor.
V – I characteristics.
A bank of six 2000 A thyristors (white disks arranged in a row at top, and seen edge-on)
Waveforms in a rectified multiple thyristor circuit controlling an AC current.
Red trace: load (output) voltage
Blue trace: trigger voltage.
Valve hall containing thyristor valve stacks used for long-distance transmission of power from Manitoba Hydro dams
Electronic symbol for light-activated SCR (LASCR)

Because thyristors can control a relatively large amount of power and voltage with a small device, they find wide application in control of electric power, ranging from light dimmers and electric motor speed control to high-voltage direct-current power transmission.

Power electronics

Application of electronics to the control and conversion of electric power.

An HVDC thyristor valve tower 16.8 m tall in a hall at Baltic Cable AB in Sweden
A battery charger is an example of a piece of power electronics.
A PCs power supply is an example of a piece of power electronics, whether inside or outside of the cabinet.
Figure 8: The AC input for an ASD
FIGURE 9: Single-phase half-bridge voltage source inverter
FIGURE 3: Single-phase voltage source full-bridge inverter
FIGURE 4: Carrier and modulating signals for the bipolar pulsewidth modulation technique
FIGURE 10: Three-level neutral-clamped inverter
FIGURE 6: Three-phase square-wave operation a) Switch state S1 b) Switch state S3 c) S1 output d) S3 output
FIGURE 7: Three-phase current source inverter
Figure 8: Synchronized-pulse-width-modulation waveforms for a three-phase current source inverter a) Carrier and modulating Ssgnals b) S1 state c) S3 state d) Output current
Figure 9: Space-vector representation in current source inverters
Output voltage of a full-wave rectifier with controlled thyristors

Uno Lamm developed a mercury valve with grading electrodes making them suitable for high voltage direct current power transmission.

Electric power transmission

Bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation.

Five-hundred kilovolt (500 kV) Three-phase electric power Transmission Lines at Grand Coulee Dam; four circuits are shown; two additional circuits are obscured by trees on the far right; the entire 7079 MW nameplate generation capacity of the dam is accommodated by these six circuits.
Diagram of an electric power system; transmission system is in blue
Five-hundred kilovolt (500 kV) three-phase transmission tower in Washington State, line is "Bundled" 3-ways
Three abreast Electrical Pylons in Webster, Texas
New York City streets in 1890. Besides telegraph lines, multiple electric lines were required for each class of device requiring different voltages
Working for Westinghouse, William Stanley Jr. spent his time recovering from illness in Great Barrington installing what is considered the world's first practical AC transformer system.
Westinghouse alternating current polyphase generators on display at the 1893 World's Fair in Chicago, part of their "Tesla Poly-phase System". Such polyphase innovations revolutionized transmission
A transmission substation decreases the voltage of incoming electricity, allowing it to connect from long-distance high voltage transmission, to local lower voltage distribution. It also reroutes power to other transmission lines that serve local markets. This is the PacifiCorp Hale Substation, Orem, Utah, USA
The synchronous grids of Europe
A high-power electrical transmission tower, 230 kV, double-circuit, also double-bundled
A 115 kV subtransmission line in the Philippines, along with 20 kV distribution lines and a street light, all mounted in a wood subtransmission pole
115 kV H-frame transmission tower
Electrical grid without a transformer.
Electrical grid with a transformer.
"Black box" model for transmission line
Voltage on sending and receiving ends for lossless line
High voltage pylons carrying additional optical fibre cable in Kenya

Transmission lines mostly use high-voltage AC (alternating current), but an important class of transmission line uses high voltage direct current.

Ground (electricity)

Reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the Earth.

A typical earthing electrode (left of gray pipe), consisting of a conductive rod driven into the ground, at a home in Australia. Most electrical codes specify that the insulation on protective earthing conductors must be a distinctive color (or color combination) not used for any other purpose.
Metal water pipe used as grounding electrode
Busbars are used for ground conductors in high-current circuits.
3 ply static dissipative vinyl grounding mat shown at macro scale

Some high-voltage direct-current (HVDC) power transmission systems use the ground as second conductor.

Mercury-arc valve

Type of electrical rectifier used for converting high-voltage or high-current alternating current (AC) into direct current (DC).

Mercury rectifier on display in the Beromünster AM transmitter in Switzerland, before being decommissioned. Three-phase full-wave rectifier with six anodes.
One of the first mercury arc bulbs built by Cooper Hewitt
Glass-bulb mercury-arc rectifier from the 1940s
A glass-envelope mercury-arc rectifier valve
Mercury arc valves of ASEA design, with four anode columns in parallel, in the HVDC Inter-Island scheme in New Zealand.
A 150-kilovolt, 1800 amp mercury-arc valve at Manitoba Hydro's Radisson converter station, August 2003
An experimental mercury arc amplifier for use on long-distance telephone circuits. It was never commercially used after the development of the audion tube.

Invented in 1902 by Peter Cooper Hewitt, mercury-arc rectifiers were used to provide power for industrial motors, electric railways, streetcars, and electric locomotives, as well as for radio transmitters and for high-voltage direct current (HVDC) power transmission.

Wind power

Mostly the use of wind turbines to generate electricity.

Wind farm in Xinjiang, China
Electricity production by source
Global map of wind speed at 100 m above surface level.
Roscoe Wind Farm in West Texas
Distribution of wind speed (red) and energy (blue) for all of 2002 at the Lee Ranch facility in Colorado. The histogram shows measured data, while the curve is the Rayleigh model distribution for the same average wind speed.
The world's second full-scale floating wind turbine (and first to be installed without the use of heavy-lift vessels), WindFloat, operating at rated capacity (2 MW) approximately 5 km offshore of Póvoa de Varzim, Portugal
Wind energy generation by region over time
Wind generation by country
Share of electricity production from wind, 2020
Wind turbines are typically installed in windy locations. In the image, wind power generators in Spain, near an Osborne bull.
Seasonal cycle of capacity factors for wind and photovoltaics in Europe under idealized assumptions. The figure illustrates the balancing effects of wind and solar energy at the seasonal scale (Kaspar et al., 2019).
Onshore wind cost per kilowatt-hour between 1983 and 2017
A turbine blade convoy passing through Edenfield in the U.K. (2008). Even longer 2-piece blades are now manufactured, and then assembled on-site to reduce difficulties in transportation.
A small Quietrevolution QR5 Gorlov type vertical axis wind turbine on the roof of Colston Hall in Bristol, England. Measuring 3 m in diameter and 5 m high, it has a nameplate rating of 6.5 kW.
Livestock grazing near a wind turbine.
Part of the Seto Hill Windfarm in Japan.
Wind turbines such as these, in Cumbria, England, have been opposed for a number of reasons, including aesthetics, by some sectors of the population.
A panoramic view of the United Kingdom's Whitelee Wind Farm with Lochgoin Reservoir in the foreground.
Charles F. Brush's windmill of 1888, used for generating electric power.

Intermittency and the non-dispatchable nature of wind energy production can raise costs for regulation, incremental operating reserve, and (at high penetration levels) could require an increase in the already existing energy demand management, load shedding, storage solutions, or system interconnection with HVDC cables.

Power outage

Loss of the electrical power network supply to an end user.

Vehicle lights provided the only illumination during the 2009 Ecuador electricity crisis
Transient fault
Tree limbs creating a short circuit in power lines during a storm. This typically results in a power outage in the area supplied by these lines
Comparison of duration of power outages (SAIDI value), in 2014.

Others advocate greater use of electronically controlled high-voltage direct current (HVDC) firebreaks to prevent disturbances from cascading across AC lines in a wide area grid.