Direct current

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Definition and Characteristics of Direct Current
Direct current (DC) is the one-directional flow of electric charge.
– It can flow through conductors, semiconductors, insulators, or even through a vacuum.
– DC flows in a constant direction, distinguishing it from alternating current (AC).
– DC can be converted from AC using a rectifier or converted into AC using an inverter.
– High-voltage DC is used for transmitting large amounts of power.

Historical Development of Direct Current
– Italian physicist Alessandro Volta produced the first DC in 1800 with his Voltaic pile.
– French physicist André-Marie Ampère proposed that current flows from positive to negative.
– Hippolyte Pixii built the first dynamo electric generator in 1832, producing alternating current.
– Pixii later added a commutator to generate DC using the dynamo.
– Power stations generating DC were established in the late 1870s and early 1880s.

Applications of Direct Current
– DC is used for charging batteries and powering electronic systems and motors.
– Large quantities of DC are used in smelting and electrochemical processes.
– Some railways, especially in urban areas, utilize DC for power distribution.
– High-voltage DC is employed for transmitting power from remote generation sites.
– DC is used in third rail power systems, where AC is converted to DC at substations.

Types of Direct Current
– DC refers to power systems with only one electrical polarity of voltage or current.
– It can also refer to the constant, zero-frequency, or slowly varying mean value of voltage or current.
– DC voltages can vary in time, as seen in the raw output of a rectifier or telephone line.
– Some forms of DC have almost no variations in voltage but may still have variations in output power and current.
– DC circuits consist of constant voltage sources, constant current sources, and resistors.

Specific Applications of Direct Current
– Automotive: Most automotive applications use DC, such as batteries for engine starting, lighting, ignition systems, climate controls, and infotainment systems.
– Telecommunication: Telephone exchange communication equipment uses standard −48V DC power supply. Telephones connect to a twisted pair of wires and use a bias tee to separate AC and DC components.
– High-voltage power transmission: High-voltage direct current (HVDC) systems use DC for bulk transmission of electrical power. HVDC systems may be less expensive and have lower electrical losses for long-distance transmission.
– Low voltage power transmission: Low voltage direct current (LVDC) transmission was developed by Thomas Edison but failed due to resistance on power lines. LVDC transmission was ultimately replaced by AC transmission.
– Other: Fuel cells produce only DC, light aircraft electrical systems are typically 12V or 24V DC, DC is used in solar panels for electricity generation, and DC bias is a phenomenon in electronics. Source:  https://en.wikipedia.org/wiki/Direct_current

Direct current (Wikipedia)

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 even through a vacuum as in electron or ion beams. The electric current flows in a constant direction, distinguishing it from alternating current (AC). A term formerly used for this type of current was galvanic current.

Direct current (DC) (red line). The vertical axis shows current or voltage and the horizontal 't' axis measures time and shows the zero value.

The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.

Direct current may be converted from an alternating current supply by use of a rectifier, which contains electronic elements (usually) or electromechanical elements (historically) that allow current to flow only in one direction. Direct current may be converted into alternating current via an inverter.

Direct current has many uses, from the charging of batteries to large power supplies for electronic systems, motors, and more. Very large quantities of electrical energy provided via direct-current are used in smelting of aluminum and other electrochemical processes. It is also used for some railways, especially in urban areas. High-voltage direct current is used to transmit large amounts of power from remote generation sites or to interconnect alternating current power grids.

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