As a direct current one is electric current indicated, the instantaneous values of the current strength in time do not change. Its course over time is shown in a line diagram as a straight line parallel to the time axis - as shown in the adjacent figure in the upper part. In electrotechnical applications, a fluctuating mixed current due to a superimposed residual ripple is also referred to as direct current if the strength changes over time, but not its sign and the fluctuations are insignificant for the intended effect. In this case, the strength of the direct current is considered to be the equivalent of the current strength.
The course of the current over time is the characteristic of a source of electrical energy , usually a voltage source ; then direct current arises from direct voltage . The relationship between the strength of the direct current and the direct voltage at an ohmic resistor is described using Ohm's law . Fluctuations in the strength of the current as a result of fluctuations in load are not detrimental to the term direct current.
The English name is direct current with the abbreviation DC , which is also used synonymously for direct voltage (just like AC for alternating current / alternating voltage ).
The historical development of the first power grids in North America is shown under power war .
The following circuit symbols are used to identify direct current.
Direct current is generated to a considerable extent from alternating current by rectifiers . In many cases, the AC component that occurs during rectification must be reduced by smoothing capacitors or smoothing chokes . There are also various electrical energy sources that supply direct current to a connected load, such as solar cells , electrochemical accumulators , batteries and direct current generators . Conversely, alternating current can be generated from direct current with the help of an inverter .
Direct current is widely used in the household sector, e.g. B. in computers, audio and video equipment. However, there is no direct current from the socket. Rather, each device is supplied individually from a power supply unit , possibly with intermediate storage in an accumulator.
In the industrial sector, direct current z. B. used for electrolysis and electroplating . These applications require direct current, since alternating current would not run the desired electrochemical processes . Furthermore, direct current is sometimes used as traction current .
In the case of electrical energy transmission, alternating current has significant advantages over direct current. With the control of converter stations , high-voltage direct current transmission is becoming increasingly important.
- Almost every textbook on electrical engineering
- ↑ Wilfried Weißgerber: Electrical engineering for engineers 1: DC technology and electromagnetic field. , Springer Vieweg, 9th edition, 2013, p. 12.
- ^ Marlene Marinescu, Nicolae Marinescu: Electrical engineering for study and practice. Springer Vieweg, 2016, p. 4.
- ↑ a b DIN 5483-1: Time-dependent quantities - naming the time-dependency , 1983.
- ↑ IEC 60617-2: 1996; German version: DIN EN 60 617-2: 1997: Graphic symbols for circuit diagrams, Part 2: Symbol elements, labels and other circuit symbols for general applications .
- ↑ IEC 60417: 2002 DB: Graphical symbols for use on equipment . Link to symbol 5031 . At least DIN EN 60417 (IEC 60417) has been withdrawn.