How does the CVT transmission work

The high-voltage direct current transmission

Where this technology is needed and how it works. High-voltage direct current transmission allows high electrical energy to be transported over long distances with lower losses than with alternating current systems.

At the beginning of electrification there was competition between electricity systems. Direct current or alternating current was the question. Thomas Alva Edison, the inventor of the light bulb, propagated direct current. His competitor Gorge Westinghouse favored alternating current.

The strengths and weaknesses of the systems

Electric current is the movement of electrical charges from the energy producer to the energy consumer. With direct current, this charge current always moves in one direction. With alternating current, the charges move in rhythm with the grid frequency.

The main advantage of AC systems is that the voltage for transmission can be increased or decreased using transformers. This has advantages when it comes to the transmission of electrical energy, since higher voltages generate lower currents for the same amount of energy to be transmitted. As a first approximation, the conduction losses are proportional to the current strength. However, with alternating current transmissions, additional losses occur due to reactive currents, which cause the electric and magnetic alternating field. In addition, there are losses of the so-called skin effect. Because the AC transmission is concentrated on the outer skin of the conductor.

Since the transformation in DC voltage networks was not feasible at the time, but the transmission of electrical energy over greater distances was necessary, AC voltage with network frequencies of 50 or 60 Hertz finally caught on worldwide.

The exchange of energy over great distances

The longer the transmission path for electrical energy, the more important the reactive power losses are in an alternating current system. With the same voltage, direct current transmission has a clear lead over longer distances because of lower transmission losses.

And technical progress has made possible with semiconductors what was still unthinkable at the time of Edison and Westinghouse around 1880: the transformation of direct current sources to a higher voltage level.

The high-voltage direct current transmission (HVDC)

With these technologies, long lines with high transmission capacity and low transmission losses are now being implemented. The pure line losses add up to around 3% per 1000 kilometers of such an HVDC transmission system. In addition, there are the losses when decoupling from an alternating current network and feeding it back into an alternating current network.

A realized example of an HVDC transmission system is a submarine cable connection between Norway and the Netherlands. This connection is 580 kilometers long and causes a total loss of 3.7% of the fed-in energy. A comparable alternating current connection would entail much higher losses and, as a cable connection, could only be implemented with considerable additional effort.

The importance of high voltage direct current transmission

The transmission with very high power and / or over long distances is the strength of the HVDC transmission. It also has the great advantage that it can also be economically implemented as a cable connection. The availability of high-voltage direct current transmissions is a prerequisite for the connection of power generators in North Africa and the Middle East with power consumers in Europe, which is planned under the keyword Desertec.

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