Direct current
Direct current is the constant flow of
electrons from low to high potential. This is typically in a conductor such as a wire, but can also be through
semiconductors,
insulators, or even through a
vacuum as in
electron or ion beams. In direct current, the electric charges flow in the same direction, distinguishing it from
alternating current . A term formerly used for
direct current was Galvanic current.
The first commercial
electric power transmission used direct current.
Encyclopedia
Direct current is the constant flow of
electrons from low to high potential. This is typically in a conductor such as a wire, but can also be through
semiconductors,
insulators, or even through a
vacuum as in
electron or ion beams. In direct current, the electric charges flow in the same direction, distinguishing it from
alternating current . A term formerly used for
direct current was
Galvanic current.
The first commercial
electric power transmission used direct current.
Because alternating current is much more convenient than direct current for electric power distribution and transmission, today nearly all electric power transmission uses alternating current.
See War of Currents.
Various definitions
Within
Electrical Engineering, the term DC is a synonym for constant. For example, the voltage across a DC
voltage source is constant as is the current through a DC
current source. The DC solution of an electric circuit is the solution where all voltages and currents are constant. It can be shown that any voltage or current waveform can be decomposed into a sum of a DC component and a time-varying component. The DC component is defined to be the average value of the voltage or current over all time. The average value of the time-varying component is zero.
Although DC stands for "Direct
Current", DC sometimes refers to "constant polarity." With this definition, DC voltages can vary in time, such as the raw output of a rectifier or the fluctuating voice signal on a telephone line.
Some forms of DC have almost no variations in
voltage, but may still have variations in output
power and current.
Applications
Direct current installations usually have different types of sockets,
switches, and fixtures, mostly due to the low voltages used, from those suitable for alternating current. It is usually important with a direct current appliance not to reverse polarity unless the device has a
diode bridge to correct for this.
High voltage direct current is used for long-distance point-to-point power transmission and for submarine cables, with voltages from a few kilovolts to approximately one megavolt.
DC is commonly found in many low-
voltage applications, especially where these are powered by batteries, which can produce only DC, or
solar power systems, since
solar cells can produce only DC. Most automotive applications use DC, although the
alternator is an AC device which uses a
rectifier to produce DC. Most
electronic circuits require a DC
power supply. Applications using
fuel cells also produce only DC.
Most
telephones connect to a
twisted pair of wires, and internally separate the AC component of the voltage between the two wires from the DC component of the voltage between the two wires .
Telephone exchange communication equipment, such as
DSLAM, uses standard -48V DC power supply. The negative polarity is achieved by grounding the positive terminal of power supply system and the battery bank. This is done to prevent
electrolysis depositions.
See also
External links
- "?". Edison's Miracle of Light, .
