Dancing a 700 meter long ultra-high voltage AAAC Cable that is thick at the mouth of the bowl and runs 3 kilometers underground, what are you doing? How many people will that take? How fierce is that? How hard is it to control?
On May 27, with a series of questions, the author came to the venue area of the 14th National Games in the northeast of Xi’an, Shaanxi Province, walked into the cable construction site of 330kV Jingxuan line I and II project of Shaanxi power transmission and Transformation Engineering Co., Ltd., and explored how to lay the longest 330kV UHV cable in China.
700 meter long cable “Jiaolong”
The 14th National Games is located in the northeast of Xi’an, and the ancient city ushers in the National Games for the first time. The relocation and landing of 330kV overhead transmission line in the northeast of Xi’an provides reliable power guarantee for the main stadium and surrounding area of Xi’an Olympic Sports Center. At the same time, by optimizing the 330kV line design and replacing the overhead line with the ground ABC Cable, the 330kV overhead line will be eliminated in the key areas of the National Games, creating a new sky landscape and showing the new style and features of the Millennium “charming ancient city” New weather.
The relocation and landing project of 330kV overhead transmission line in Northeast Xi’an involves 7 relocation and 2 new lines, 2 21km cable pipe corridors, 2 cable terminal stations and 100 km 330kV EHV cable lines, with a total investment of 8.274 billion yuan. After the completion of the project, it will be the largest 330kV and above UHV cable project in China.
The cable part of 330kV Jingxuan I and II line project is the longest and largest 330kV cable line in China. The first stage laying construction task is along the cable pipe gallery of Xingwei Road, with a total length of 6.3 km for single phase and 37 km for all cables. It is divided into nine sections, each section is 700 meters long, and each section contains six 700 meters long cables.
Green concept behind
There are 30 air vents in the underground high-voltage pipe gallery of Xingwei section, and 8 shafts for high-voltage cable laying. According to the conventional operation, each section of cable can enter the pipe gallery from the ground by selecting the nearest shaft, so as to minimize the cable transmission path. However, the actual construction scheme did not follow the conventional operation. Only two shafts were selected to enter the 9 sections of cables, and 6 of them need the whole cable to enter the pipe gallery and continue to transmit underground. After entering from shaft 24, the section with the longest transmission distance still needs to travel 3 kilometers underground, and it takes 6 hours to be in place.
Why choose this unconventional scheme of underground transmission?
“Mainly to make way for greening.” Wang Hailong, manager of Shaanxi power transmission and transformation construction project, said. High pressure pipe gallery in Xingwei section is mainly constructed by large-scale excavation except for shield construction in some sections. After the backfill treatment of the pipe gallery construction, the ground surface is planned as urban road and green belt according to the unified planning of the venue area of the 14th National Games“ Road construction, green belt planting, all need time, we occupy the site, we have to drag green back. At present, most of the greening of Xingwei road has been in good order.
Behind the posture is strength
Following Wang Hailong into the underground high-voltage pipe gallery, he saw the sparse construction workers along the cable line, and was puzzled: “can such a few people dance the 700 meter cable?”
“Let’s call four or two thousand catties.” Wang Hailong squatted down, pointed to the roller under the cable and said, “this is the frequency conversion guide wheel, the main power of underground horizontal transmission of the cable.” A total of 900 electric frequency conversion rollers are arranged along the laying line, with a spacing of 5 meters, and a non powered roller support is arranged between the two. 900 variable frequency rollers are controlled by intelligent control box to start and stop synchronously. Although each variable-frequency roller intelligently generates a torque of 70kg, if 900 wheels rotate at the same time, the 700m “dragon” will move steadily along the passage at the speed of 6m per minute. In addition to the need for two people at the front end of the cable to lift the cable end to the next roller, the remaining 30 workers just need to watch the roller run well.
What should we do if there is any abnormality? There’s no cell phone in the tunnel. Moreover, the channel is too long and there are many turns, so the transmission distance of walkie talkie is greatly reduced.
“We have two call systems.” Wang Hailong said. They are equipped with 30 walkie talkies with coaxial cable signal relay. Another 50 walkie talkies are equipped with wireless chain relay. The two systems operate independently, which can realize the information synchronization of the whole cable laying line without delay, and ensure that the system can be shut down at the first time in case of abnormality.
“The pipe gallery is a limited space. In order to prevent accidents, we have gas masks every other section.” They did what they should have thought under special conditions.
“At the most spectacular time, there were three 700 meter long pipes running underground. The pipe gallery could not see the end at a glance, and the scene of more than 40 people dancing the 700 meter” dragon “could not be fully seen.” Wang Hailong added. Behind the grand scene is the courage, responsibility and courage of Shaanxi power transmission and transformation to seize the new challenges, explore new fields, start new engines, stimulate new power, help the new development of Shaanxi power grid, and serve the economic take-off of Shaanxi.