When:
The project began construction in 1993 and was put into use in 1999. The UHVAC transmission system, which is only about 190+240km long, took seven years to complete and was put into use in two stages. After completion it is the world’s largest double circuit three-phase electric power line.
Scope:
The length of the first phase of the project is 190km, starting from the Kashiwazaki-Kariwa nuclear power plant, through the Nishi-Gunma switch to the Higashi-Yamanashi substation, with a design voltage of 1100kV. The second phase of the project is 240km in length, starting from Nishi-Gunma substation and passing through Higashi-Gunma substation to Minami-Iwaki switch, with a design voltage of 1100kV.
Unfortunately, the downlink port usage is not required to reach 1100kV, so the project is currently operating at 500kV voltage. However, if the demand increases and the nuclear power plant resumes operation, it can be operated at 1100kV voltage at any time through a small range of repairs.
Successfulness:
The UHV AC project is a classic case of failure. Since Japan had hoped to deliver power from the Kashiwazaki-Kariwa nuclear power plant to nearby cities through the project, it chose a dual circuit of ultra-high voltage alternating current for transmission. There are many reasons for project failure, which will be analyzed below.
- They miscalculated the electricity use of nearby cities. Most of the cities within 300km of the nuclear power plant are small cities, which already have a lot of traditional energy generation methods. Nuclear power has no absolute advantage for these small traditional power plants. However, the construction cost of ultra-high voltage alternating current is much higher than that of ordinary high voltage network cable. UHVAC is like a double-track high-speed train with too much capacity on the basis of nearby cities where demand is not as high, so it has to run on a single line first to reduce costs.
- Design distance is too short. The distances of 190km and 240km are not advantageous for UHV transmission lines but increase the cost because new conversion stations and conversion equipment need to be built over shorter distances. The line has at least three substations over a short total distance of 400km, adding to losses and equipment costs. Land is also expensive in Japan, pushing up costs further. Unlike China’s State Grid, this is not a public project, but a semi-private one (TEPCO is privately owned but has deep ties to the Japanese government). This results in a higher apportionable cost per use of UHV transmission lines. Such a short distance also fails to take advantage of the two advantages of UHV: small land area and low transmission losses.
- Nuclear power is more expensive than hydro and wind power, and the Kashiwazaki-Kariwa plant has been out of operation since 2011 because of Tepco’s problems at the Fukushima plant. This is a big blow to the already “excess capacity” of ultra-high voltage transmission lines. At the time of its design, Kashiwazaki-Kariwa was the world’s largest nuclear power plant in terms of net fixed power. The electricity produced, if the demand is sufficient, is sufficient to support transmission lines running at 1100kV, even though the relative cost is high. But after 2011, when TEPCO shut down the plant completely for safety checks, the transmission line lost all hope of resuming operation.
- Blind pursuit of advanced design. Dual return UHV transmission lines are relatively more difficult to build and require more lines to carry more power on a smaller footprint. This was a good idea to start with, but it became a problem because there was no need for such a large amount of electricity to be transmitted locally. One drawback of dual-circuit transmission lines is that they are difficult to maintain because they either work near high pressures or need to close both circuits. If there is a failure, both systems will be affected. This has produced higher requirements for maintenance, operation and maintenance. In 2000, Japan was already one of the most expensive countries to work in. Such a combination of plans failed to show the advantages of the project itself. Combined with the existing problems, it led to the complete failure of the project today.
What can we learn from it?
Since this is the world’s largest dual-loop three-phase UHV AC project, and one of the few commercial UHV transmission projects that has failed, there is much to learn from it.
The first is to understand the advantages and disadvantages of UHV and build where needed. The advantage of Supergrid is the combination of UHV grid and smart grid. One of the prerequisites of a smart grid is to build the right voltage lines in the right places to distribute and transport the electricity needed. In the ultra-short distance (less than 500km), it is necessary to consider the advantages and disadvantages between the cost increase brought by the construction of ultra-high voltage substation and the land cost savings of the line. The low loss advantage of UHV can not be reflected at this distance, so the land price has become an important measurement standard.
The second is the use of new technology. We should choose the most appropriate technology instead of the most advanced. At the same time, a large number of existing substations and lines are used to try to adapt to the existing power grid to ensure low cost operation. The purpose of Supergrid is to increase the proportion of clean energy by reducing power loss and electricity price. Therefore, we should reduce the cost link of each project as much as possible, and at the same time, cover more areas to spread the cost.
Finally, reduce project completion time. If the project can be completed in a shorter construction time, it can take advantage of other construction around the grid rather than changing the grid itself as a result of changes in urban planning. The construction time of each line should be limited to about 4 years.