Direct current

Types of direct current:
Above: as defined, sometimes made clear as "pure direct current";
including: mixed current from rectification, also referred to as "pulsating direct current"

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 .

Circuit symbol direct current

Mark for direct current, international
Indicator for direct current, Anglo-Saxon

The following circuit symbols are used to identify direct current.

Generation, application

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.

literature

• Almost every textbook on electrical engineering