A giant underground cable tunnel is deeply buried near Zhongxiao-Fuxing MRT Station! Wen-Sheng Tseng, Deputy Minister of the Ministry of Economic Affairs and Acting Chairman of Taipower, inspected the Da'an Substation today (Sept. 7). This is not only the first underground ultra-high voltage substation in downtown Taipei, but also the first substation in Taiwan that has an integrated structure with a commercial hotel. In terms of excavation depth, advancing speed, and sharp curvature, building the Da'an Substation is no easier than building an MRT line. The 10-year-long construction of the "Songhu-Da'an" transmission line will soon be completed in September. However, tunnel penetration is only the first step, which will serve as the pre-construction for the pipeline project of the future Songhu Substation. Wen-Sheng Tseng said that after the completion of the Da'an Substation in 2025, it will become a power supply hub in the core region of Taipei City. Scientific data has proven that the electromagnetic waves of the Substation are close to that of the environmental background values. Wen-Sheng Tseng emphasized that through the efforts of Taipower and the actual performance of substations in various areas, it is hoped that substations will no longer be NIMBY (Not In My Back Yard) facilities, and that the Songhu Substation, which is indispensable to the Taipei Eastern District, can be promoted as soon as possible.
Unit length, transformer capacity, and degree of undergroundization are all higher than those of Japan and South Korea
The Da'an Substation is comprised of a hotel aboveground and substation facilities as well as two 345kV transmission lines underground. The transmission lines are the "Songhu-Da'an" line leading to Neihu, with a length of 4,634 m and a hole diameter of 4.6 m, and the "Shenmei-Da'an" line that connects the common pipeline from Xinyi Road leading to Shenkeng, with a length of 966 m and a hole diameter of 5.5 m. The total cost of the two was about NT$3.6 billion.
Wen-Sheng Tseng, Acting Chairman of Taipower, mentioned that Taiwan is densely populated. Compared with the grid construction of the neighboring Japan and South Korea, the length of transmission lines per unit area is higher than that of Japan and South Korea, and the transformer capacity is higher than that of Japan and South Korea. Even the level of undergroundization is higher than that of Japan and South Korea. In particular, the construction operations for underground projects are complex and extremely difficult. Every meter of advancement is full of challenges. Taipower staff often feel that "implementing grid construction is really difficult, and every meter of advancement is hard work."
No easier than a MRT station in terms of excavation depth, advancing speed, and sharp curvature
Han-Hsi Chang, Director of the Northern Region Construction Office of Taipower's Department of Transmission Line and Substation Construction, pointed out that carrying out the electrical grid project is no easier than carrying out an MRT construction project. In terms of excavation depth, the excavation depth of 31 m exceeds that of Taipei 101 (22.95 m). In terms of the speed of advancement, the overhead line can be completed at an average speed of 30 m per day. However, the underground shield tunneling can only advance up to 5 m per day. If hard rock is encountered, the advancing speed may be reduced to 2-3 m per day. The construction speed of shield tunnel is only one tenth of that of overhead line; however, its cost is 8 times more than that of the overhead line. As to the number of sharp curves, the "Shenmei-Da'an Line" turns east from Fuxing South Road into Ren'ai Road, and then goes south along Da'an Road. There are three "sharp curves" on such a short path, making the construction extremely difficult.
Additionally, by law, the MRT and THSR tunnels can go under houses. Cable tunnels, however, can only be constructed beneath roads. Taking the "Songhu-Da'an Line" as an example, the underground tunnel has a diameter of 4.6 m. Its path encounters the continuous walls of the Zhongxiao-Dunhua MRT Station, the foundation piles of the Wenhu Line, the continuous walls of the Taiwan Railway and Taiwan High Speed Rail (THSR), and the foundation piles of the Keelung River embankment; therefore, it can only pass them from below. For this reason, the average depth of the tunnel is 45 m, with the deepest portion reaching 55 m, making it the deepest underground tunnel in the Taipei metropolitan area.
Drilling into the ground for 50 meters. The ground freezing method and the operation environment create challenges for workers
At the same time, the operating environment is also a big challenge. Just drilling and climbing the stairs down to a 50-meter-deep tunnel is quite exhausting. Not to mention the working space is limited and the air quality is not great. In addition, the project uses the "ground freezing method." In this method, freezing pipes are buried in the ground to keep the underground soil at a temperature of about -10 degrees celsius; this means that workers have to carry out their tasks in an environment with a temperature below 0 degrees celsius.
Taipower hopes that the public can understand that the closer the substation is to the core region of electricity use, the more stable and safer the power supply will be. For this reason, the substation should no longer be regarded as a NIMBY facility. The completion of each substation can form a network with nearby substations that support each other, providing stable and reliable power for everyone, and speed up the pace of urban development.
Spokesperson: Professional Chief Engineer, Chin-Chung Wu
Tel: (02) 2366-6271 / 0910-192-766
Email: u850899@taipower.com.tw
Contact Person: Director of the Northern Region Construction Office, Han-Hsi Chang
Tel: (02) 2322-9950 / 0939-309-161
Email: u906444@taipower.com.tw