Direct current

An electric current will be referred to as a direct current, the strength and the direction does not change. In electrical engineering, but also mixed flow with a predominant DC component is referred to as direct current, when the fluctuations of the current for the intended effects are negligible or if the fluctuations are caused by load variations. Then, the arithmetic mean of the current is considered to be direct current.

The English name is direct current with the abbreviation DC, which is used synonymously for DC voltage (see AC for alternating current).

In colloquial language often takes place confusion and equating between DC voltage and the DC voltages caused by direct currents.

Generation

DC is preferably obtained from chemical elements, such as electrochemical cells, batteries and fuel cells, and also of special electrical generators which are based on the unipolar induction.

A inserted at higher current consumption of electrical generator always generates AC voltage. In order to receive direct current therefrom, were used earlier, a commutator. Since the commutator to cause harmful interference, and his abrasive contacts wear out, it is now replaced by generators such as the alternator rectifier.

Importance

Technical significance of the DC and Others in electronics, electroplating, and partly in the railway power supply.

Virtually all electronic circuits ( for example, computers ) must be operated with DC voltage / DC current. If electronic devices are not from batteries or accumulators but of power supplies are energized, the DC supplies a rectifier in the power supply. As an indicator for DC is standing next to switching characters.

Solar cells can also produce only DC. If photovoltaic systems to initiate the electrical energy produced by them into the public grid, an inverter must be switched between.

Must electrical energy can be transmitted over long distances, is used for historical reasons, alternating current, because this can easily transform to very high voltages. Only in recent years have the necessary power devices available to use DC on particularly long stretches in so-called HVDC lines, in contrast to the alternating current in the electrical conductor has no current displacement and thus lossless at the same voltage in an equally long line as AC transfers. For required at power stations for grid feed-in rectifier equipment and at the other end of the transmission line to the consumer large scale, high- voltage inverters that convert the information transmitted in 2 ( 1) line ropes DC into three-phase alternating current with the usual frequency (eg 50 Hz in Europe ). For large transformer and switchgear they are connected in suitable buildings with high investment costs and currently still the alternating current transmission is the preferred and most economical solution for the energy transfer in supply routes over several 1000 km.

History

Originally had direct current power plants with relatively low " voltage sockets " for the consumer, produced 110 or 220 volts. With more connected consumers, the total amperage added to very high values ​​. Then thick and expensive cable would be needed to bridge larger distances to keep the transmission losses within limits. In contrast to direct current to alternating current can be easily transformed to high voltage and the current to be transmitted intensity decreases, the electrical energy generated can be transported relatively low loss over long distances. Thus the triumph of alternating current power grids began.

Can only since about 1980 ( three-phase ) AC high voltage is rectified and then converted back to AC. Since DC power is again increasingly used for transport over long distances, since in this case the losses are even lower, see high voltage direct current transmission.

Conversion of AC to DC

The supplied mains transformers and AC generators AC voltages / AC currents can be converted by the rectifier. The result is electrical voltage, although not in amount, but does not vary in sign.

Parallel connection of a sufficiently large smoothing capacitor or in series switching a smoothing coil, the alternating component of the voltage can be reduced, so that all that remains is a small ripple. The larger the capacitance of the capacitor or the inductance of the coil, the smaller the peak-to- valley value of the superimposed alternating voltage. The power delivered to a load current related can now be considered as direct current. In particular, when used in communication technology systems, only a very small ripple is allowed so as not to interfere with the sensitive electronics. In audio engineering, a hum is heard when there is inadequate smoothing.