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SAINT PETERSBURG WILL RECEIVE ELECTRICITY TROUGH THE WORLD’S LONGEST SUPERCONDUCTOR LINE

It’s hard to believe, but it’s true: in the nearest future, a significant part of the electric power in St. Petersburg will be transmitted almost without loss through the world's biggest direct current high-temperature superconducting cable line (HTS CL). Rosseti FGC UES has performed large-scale testing on the full length of this cable line at its research and development center (R&D center of FGC UES, Rosseti Group).

The solution is the company's own design. It will be deployed in Saint Petersburg power system in 2021. The amount of investment is 3.5 bn rubles.

The main advantage of HTS is transmission of higher power at medium voltage due to the greater value of current. An alternative for a megacity, such as Saint Petersburg, is installation of conventional cable lines. But a conventional cable of comparable dimensions and voltage is physically unable to transmit the necessary power, therefore, several lines would need to be laid, which is a more complex task, often unfeasible with the adequate resources in an urban infrastructure.

Here, it seems, we have to choose what is more important: providing the northern capital of Russia with electricity at a new technological level, or preserving its cultural and historical heritage, which has been recognised as a treasury of world. Or ... we don’ t have to? The answer is we can do both at the same time.

Nikolay Voropay, member of the Global Energy Prize International Award Committee, scientific adviser of Melentiev Energy Systems Institute Siberian Branch of RAS, corresponding member of RAS, sees several advantages of the new technology, and one of them is zero energy loss. Moreover, in terms of practical application in St. Petersburg, underground cable laying of high power is extremely important. The scientist said in the interview with the Global Energy Association: “In big cities high voltage overhead power lines can be observed for the so-called deep input of electricity into the power consumption center. This requires land allocation under the power transmission lines.  It is very hard to find extra spots it in the center of St. Petersburg, where a lot of architectural and historical objects exist.”

According to experts this technology is especially efficient in building circular schemes and power bridges, and to release power from big generation facilities (nuclear, hydro power plants, etc.). As for megacities, the HTS CL will enable more flexibility in the urban planning owing to accumulation of power as districts are developed without installing additional electricity networks.

For example, the withdrawal of electricity from a thermal power plant or the transfer of high power between large supply centers under normal conditions involves the construction of many power lines, and additional space for them. Just imagine how many power transmission towers will be pinned near the stations! Also, the installation of a high voltage class cable is in some cases restricted by urban planning regulations. Furthermore, the lower voltage class is generally more preferable for a city in terms of the right of way, as well as ecology and safety. The HTS CL is able to replace this infrastructure by building only one line with minimal impact on the environment.

In 2021, the HTS CL will link two existing substations of Saint Petersburg: 330 kV Tsentralnaya and 220 kV RP-9. They are located downtown (near Ligovsky avenue), where areas are deficient for new power engineering projects, with the growing demand for electricity and high requirements to the reliable delivery of power. The line is designed to transmit 50 MW of power at the medium voltage of 20 kV.

There are HTS CL specimens up to 1 km long in other countries (USA, European Union, Japan, South Korea, and China). The most indicative project is AmpaCity in Essen, Germany. The line length is 1 km. Its designed transmission capacity is 40 MVA. The line has an open single-loop system, which requires replenishment with liquid nitrogen every one to two weeks. The St. Petersburg line connects two substations in the city center. The Russian HTS line in the longest one in the world – the line itself is 2.5 kilometers. In addition, its cryogenic system is closed and has a total length of 5 kilometers, which also makes it unique. Now only Russia has got solutions to develop and create closed-loop automated cryogenic management system.

According to specialists, this is the basic and pilot project to justify promising projects of upgrading the energy supply systems of megacities, which are currently being discussed and developed in many countries around the world.

But there are some problems. The main ones are the extremely expensive cryogenic cooling system, and technological limitations to ensure uniform cooling of the cable line by pumping refrigerant over long distances. According to Nikolay Voropai, to make this cable hundreds of kilometers long is, unfortunately, an impossible task for now. The scientist believes:“The problem of high costs will be resolved, and technical solutions will be found eventually.” 

With this new technology the end users will  receive electricity in the required amount with the required reliability. Nikolay Voropai also highlights another advantage of the new system, the so-called warm superconductivity, cooling not to absolute 0 K, but only to the boiling point of liquid nitrogen.

Another expert, Liye  Xiao (China) the Global Energy Prize International Award Committee member,  Director of Applied Superconductivity Laboratory, CAS, also points out that cryogenic system should be kept at liquid nitrogen (LN) temperature 77, 4 K.   But, if the operation temperature of superconductor would be raised up to 200 K or even room temperature 300 K , the HTS power cable would be more competitive. “Currently, there is no such kind of superconductor for power application, hopefully this kind of superconductor would appear in the future”.

The HTS CL is based on the superconductive material, Bi2223/Ag (distinct for high content of silver), the resistance of which vanishes at certain temperatures 65-80 K. Two-circuit cooling system is needed to ensure the necessary temperature conditions. The first circuit contains gaseous helium that cools down the liquid nitrogen circulating in the second circuit over the whole length of the line. With current flowing through the HTS CL, no heat is emitted, the magnetic field is localized, and the energy losses are virtually absent.

The Rosseti FGC UES project is inter-sectoral. Beside the application in electricity networks, HTS CL may be implemented in all energy-intensive sectors. Scaling of the technologies will assist the growth of energy efficiency of the economy.

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