Direct current or alternating current for long distances?
I always thought that alternating current was only needed because only with alternating current can you increase the voltage and decrease the current using transformers (and not with direct current).
And because a lot of energy is lost in the form of heat (-> current) over long distances, alternating current is needed for this.
But now I just watched a video from studyflix where it was explained as alternating current at the beginning, saying exactly the same thing, but at the end it was explained as direct current, saying the opposite…
that direct current would be needed for long distances, as it would save more energy than alternating current.
Now I'm totally confused..
I would be pleased to receive clarification,
LG Mayu
https://studyflix.de/elektrotechnik/gleichstrom-wechselstrom-5004?topic_id=20
(3 votes)
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This is a very complex issue in itself. In fact, in a complex network with meherer producers, the matter can be regulated with direct current more severely than with alternating current.
a very intressant YouTube video approaches this issue.
50 Hz – How to avoid a blackout – YouTube
But come back to the core of the question! In power transmission, we have to deal with two different losses. the resistance-related losses, and the inductive losses that arise because it needs energy to repolate each time.
The conversion of alternating current into leakage current, but also the direct current to alternating current does not work without loss.
the high voltage (or is called high-performance) current transmission is a comparatively new discipline. About 50 years ago, the first HGÜ route went into operation in Great Britain.
It is therefore simply necessary to calculate whether what is saved from inductive losses is more than what is generated from losses for the conversion. It’s not easy, but it’s not rocket science.
There are two further problems, one of which has already been solved, the route that led to Londo was unidirectional. In the meantime, however, an inverter can also be converted in such a way that it becomes the rectifier (controlled rectification) so modern HGÜ lines can also be operated in both directions. In view of the increasing decentralization of our power supply, it is inevitable!
and thus we come to the next problem: similar to the case of a transformer (iron losses / copper losses) the efficiency of the same or Inverters with increasing or decreasing load. the point from which the effort for HGÜ is worth walking.
Lg, Anna
https://de.wikipedia.org/wiki/high voltage DC %C3%9C Transfer
In fact, the first HGÜ experimental plant stood in Germany at the end of the 1930s.
On the “transmitter side” it consisted of a large alternating current motor which drives several superimposed “stacked” and mutually insulated direct current generators via non-conductive belts. As a result of the series connection of the generators, a large dc voltage can then be generated without danger of breakdowns.
On the other hand, of course, reversed, i.e. several DC motors which drive an AC generator via a belt.
After the Second World War, the Russians disassembled it and then developed it further in the Soviet Union and used it for the first time in regular operation (Commercially it cannot be said:P )
With modern high voltage, high power semiconductor components, you can build a direct current network very well and actually save some energy. So HGÜ becomes more and more interesting.
The disadvantage is, of course, the active equipment that requires a lot of maintenance and costs. In addition, a repair in case of a defect takes a very long time.
Trafos are passive and in the case of large criminals one can say that the practically never break – within the expected life of course.
The biggest problem with HGÜ is no longer the conversion AC ←→DC but galvanic corrosion. The direct current lines “gamme” hundreds of times faster than if alternating current on it. In order to cure this, one has to repolate polarity several times a day – and then the repolate is generated so that one is then dependent on alternative lines, then HGÜ is best always to build pairs.
mechanical converter I actually know from several sources
It’s a heart changer. Nowadays usually electronically. 200V is the usual international industrial tension. Most large CNC machines run on 200V, either with internal transformer or on a separate network.
It’s rare. The most extreme power comes from own generators in power plants. These are mainly hydropower and coal power plants. Since there are hardly any hydroelectric power plants in Germany, the railway is driven, although the “CO2 Neutral” is on top of it, mainly on coal. The “thumps” then the black stream against green on the power exchange.
This is a wardLeonard–Former – or also briefly Leonardsatz or Leonardumformer.
AC motors cannot be regulated well and have very little torque at low rpm. That is why (or before there were electronic frequency converters) many large motors have preceded a Leonardset. The trick is that you can easily control the power of the DC generator via the exciter voltage. For this purpose, for example, the speed or other of the load is converted into a mechanical tensile force which then draws a potentiometer. The potentiometer in turn controls the excitation voltage of the generator. Since the excitation power is only a fraction of the power of the system, it is possible to obtain relatively small resistances which then also only heat a very small portion of the total power.
While a (small) mercury rectifier cannot be regulated – or only with a gigantic adjusting folio, the leon set can be controlled or regulated very easily.
While a rectifier can be used in an elevator or in an escalator, and the power/speed can then be made via the rotor winding of a DC motor, stronger machines such as cable tracks then need a leon set because both generator and motor can be controlled in this case and thus comes together to a controllable power for control/control.
The losses in alternating current transmissions are caused by the alternating magnetic field, with direct current there is no reason why there are lower losses.
https://www.bfs.de/DE/themes/emf/netzausbau/basiswissen/hgue/hgue_node.html
In the alternating current there are additional capacitive and inductive losses which depend on the frequency. In the case of direct current, the frequency 0 is thus present only the purely ohmic losses.
In order to transform a voltage with a transformer up or down, however, an alternating voltage is required and no polarity has to be observed in the alternating current, which makes much easier.
Alternating current has been used historically for two reasons:
The transmission of direct current is more effective because the same voltage is transmitted throughout. During the alternating current, nothing is transmitted at the zero passages.
In the past, direct current could not be transformed, or do not end with reasonable effort. Today you can.
The pure direct line has always been more effective with direct current. As far as I know not only because of the magnetic fields by alternating current, but also because each line is also a capacitor and therefore flows completely unnecessary and generate heat.
The DC transport over long distances without transformers Economicbecause the inductive and capacitive losses of the alternating current do not occur here.
With a high density of transformers on the track, the direct current naturally proves to be disadvantageous because of the required deformations.
The transmission itself is more efficient but the periphery is more complicated and expensive.
https://de.m.wikipedia.org/wiki/high voltage DC %C3%9C Transfer