Several decades ago, electricity production sources could be a few tens of kilometers or a maximum of a few hundred kilometers away from the big places of consumption, and the electricity transmission lines operated almost exclusively with alternating current, because it was considered that the option with direct current would generate higher losses, especially when converting large power values into alternating current. However, direct current line projects occasionally existed even back then. But later, closer to our times, more and more renewable energy projects began to appear, which increasingly changed the way transmission lines are built until now, when all the projects of strong, longer-distance lines , are increasingly dominated by HVDC technology of high voltage direct current, or voltage if we were to decipher the abbreviation. Today we are talking about such a grandiose project which was built exactly 10 years ago and which showed the whole world more than any other the viability of the technology, pushing it to develop even more. It is about the Rio Madeira electric overhead transmission line in Brazil, which has a huge length of 2,375 km.
From the start we will say that today it is no longer the longest HVDC line in the world, but 10 years ago it had that title, and it kept it until 2019. And it was also the line that made a huge leap of distance achieving things that seemed impossible until then, namely to transport electricity of a huge power, over a distance of 2,375 km, with minimal transmission losses.
Initially, in our world, photovoltaic and wind parks were not very far from the places of consumption either. Even offshore wind farms were built close to the shore, precisely so that they could be easily connected to the grid, in addition to the ease of fixing wind turbines to foundations on the seabed. Later, however, the technology of wind turbines advanced a lot and they can be installed much further in the seas and oceans, hundreds of kilometers from the shore, making use of much more prolific winds and giving a higher capacity factor. And that makes the transmission lines much larger, having to face the greater losses generated by laying them on the bottom of the sea. The HVDC lines were the ones that brought the solution to the minimum losses for maritime wind farms, especially since in the meantime, direct to alternating current transformation stations, mounted on the shore, were also invented, which reduce the losses to a minimum. And these developments were driven especially by the Rio Madeira line, which we are talking about today.
So what is Rio Madeira and what makes its engineering fascinating? It is an overhead electricity transmission line, which can transmit 7.1 GW of power, or 7.1 MW, over a distance of 2,375 km. And the power of 7.1 GW is equal to the entire daytime consumption of Romania! And all this power goes through just a few wires!
The Rio Madeira direct current line arose from the need to transmit the electricity generated from two adjacent hydroelectric plants on the Madeira River in northwestern Brazil, in the area of the Amazon forests, to its southeast, where the big cities are concentrated. The two hydro plants, Sant Antonio and Jirau, are located about 100 km apart, and produce 3,150 MW and 3,750 MW of power respectively, adding up to 6.9 GW of total power, so the overhead line was designed for 7.1 GW power, to have a power reserve.
Of course, there was at that time a dilemma whether the direct current option was the right one, but the answer became obvious very quickly, because Brazil already had shorter HVDC lines in operation that indicated 30-50% lower losses than direct current lines alternative back then. Therefore, the engineers had already come to the idea that lines longer than 600-800 km should be built only with direct current, even if they are more expensive in the transformer stations. The difference between the lost current is huge and makes those investments quickly recovered.
The engineers designed the Rio Madeira line in a curious way. The electricity is initially transmitted from the hydropower plants by alternating current to the end where the HVDC line begins, in Puerto Velho. There are two direct current transformation stations, and further two HVDC lines of 2,375 km length, each of 3,150 MW power, at 600 kV, reach close to the Sao Paolo region, to Araraquara, where there are two more DC stations. transformation from direct current to alternating current, and that alternating current is already distributed to the city of Sao Paolo and the entire region through the usual lines. This configuration of HVDC lines can be called bipolar stations.
The transformer stations use 12-pulse converters, this formula allowing the configuration of correct wavelengths, excluding possible deviations with a smaller number of pulses. Simply put, we could compare the balance of a V12 engine, which is naturally self-balancing from two 6-cylinder blocks. In the case of these transformers, at the end a much more precise, balanced and consistent electric current is obtained in the desired parameters.
We can see that 2 x 3,150 MW make 6,300 MW, while the total power of the system, mentioned above, is 7,100 MW, and the hydro plants produce 6,900 MW. The truth is that near Puerto Velho there are still two back-to-back HVDC stations, which transmit 800 MW of power locally, in the region of northwestern Brazil.
Then Brazil decided to divide the construction contract of this record length overhead line between two leading companies in the world, and they were also among the few specialized in HVDC lines at the time, which could ensure minimal transmission losses. The American company General Electric, through its Grid Solutions division, which today became part of the GE Vernova company, built the HVDC transformer stations for one of the two 3,150 MW lines that make up the project. They also delivered the lavas with thyristors for transformers, as well as other additional equipment.
And the Swedish-Swiss company ABB received the contract for the transformation stations of the second line and for the two back-to-back stations totaling 800 MW. ABB is, in fact, the first company in the world to build HVDC lines and it had also built lines in Brazil earlier, so it already had an impeccable reputation. By the way, later ABB formed a new company together with Hitachi, focused on high-power transformers and related equipment, a company that then became Hitachi Energy and was bought by Hitachi in full from ABB, and with that Hitachi Energy became the entity which inherited all the experience and technologies, and innovated even further in increasing efficiency.
At that time, the losses allowed by the new HVDC line over a distance of 2,375 km at a maximum of 7%, which was exceptionally good. For comparison, a similar power and voltage line, but made in a direct current system, at such a distance would generate losses of about 17%, up to 19%! So, there is a difference of at least 10% of avoided losses due to the fact that the transmission is direct current, and at 6,300 MW of power transmitted through those lines, even if we estimate a real flow of 6,000 MW, that means 600 MWh of electricity saved by to transmission losses per hour! Per day, this means about 14 GWh, and per year we have about 5 TWh that are not wasted! Even at a minimum price of 5 cents per kWh, this means avoiding losses of 250 million dollars annually in this case. Relative to the total cost of this line, just over 1 billion dollars, the difference of choosing HVDC instead of AC is quickly recovered, especially since HVDC lines require even less steel, thanks to thinner cables, and therefore have an impact smaller. And with the decades-long lifespan of hydropower plants and these transmission lines, opting for HVDC pays off many times during operation, especially with such a 2,375 km line.
And all these characteristics and differences have led to the increasing popularity of HVDC projects in solar and wind energy, as the differences in loss are even more pronounced in underwater cables. This HVDC line in Brazil, however, which marked the world record for length at its time, was the one that absolutely clearly demonstrated the parameters of this technology and its advantages and boosted all the galloping development from there.