The subway is a fast, large-capacity, and powerful rail transit built in the city. The train runs on a fully enclosed line, located in the central city
The lines in urban areas are basically located in underground tunnels, and the lines outside the central city are generally located on viaducts or on the ground. The subway covers various types of services in urban areas.
An urban rail transit system with exclusive underground and above-ground right-of-way, high density and high transportation volume.
A subway station consists of a subway entrance and exit, hall level, station hall equipment level, and platform level. The comprehensive grounding of a subway station refers to the station equipment layer
Ground. The equipment layer is generally located tens of meters underground.
(- )Environmental and material selection requirements for subway projects
1. The installation site of grounding materials has a humid environment, often with water seepage, and the environment is highly corrosive to the materials. Therefore, comprehensive grounding materials for subways need to have excellent corrosion resistance. The corrosion rate of carbon steel is 0.075mm/year; the corrosion rate of copper pipes is <0.005mm/year.
2. There are many electrical equipment in subway stations, including vehicles, signal systems, power supply systems, communication systems, automatic ticket vending and checking systems, and maintenance equipment. Therefore, the comprehensive grounding materials used in subways need to have excellent large current passing capacity--DC (705~870A)
3. The horizontal grounding network of the station comprehensive grounding is buried under the main structure of the station. After completion, it cannot be excavated, renovated and maintained. Therefore, the comprehensive grounding materials used in subways need to have excellent environmental stability--the design service life is 100 years. Therefore, the selection of the main grounding materials for subways is mainly based on copper (copper bars, copper tubes, and copper rods), and the connection between materials is hot-melt welding.
(II) Comprehensive grounding schemes for subways and application material specifications
At present, there are many design schemes for the comprehensive grounding schemes of subways, and valuable experience has been accumulated during the operation process. The following is an analysis of the three main comprehensive grounding schemes for subways:
Advantages of scheme 1: This scheme has the highest safety performance, and the two cables form a primary and backup backup mode for each device. Disadvantages of scheme 2: It consumes a lot of grounding cables, increases the complexity of the routing of grounding cables, and has high construction costs.
Advantages of Option 2: Reduces a large number of connecting cables and has low construction costs. Disadvantages of Option 2: Provides a transmission path for fault current and has the lowest safety performance.
Advantages of Option 2: Low construction cost and high safety performance. This solution has been widely used in engineering.
2. Advantages of grounding lead-out device
① Effectively prevent groundwater seepage. ② Effectively protect against fault current (stray current).
3. Composition of grounding lead-out device
The grounding lead-out wire uses a 50*5 copper bar, a 304 stainless steel non-magnetic steel pipe, and the hollow part is filled with insulating epoxy resin.
4. Technical requirements for grounding lead-out device
① The water stop ring is fully welded on the outer wall of the steel pipe, and the weld height is 26mm. ② All welding is treated with first-level anti-corrosion. ③ The steel pipe is made of non-magnetic stainless steel. ④ The steel pipe is filled with epoxy resin densely, and the water pressure requirement is 20.3MPA. ⑤ The lead-out wire has a reserved length of 400mm from the steel pipe mouth. ⑥ The bow lead and the metal pipe body should be insulated.
5. Water pressure test of grounding lead-out device
According to the requirements of subway construction, grounding lead-out device adopts high-quality raw materials and segmented filling technology, with a water pressure resistance of 20.6MPA, which greatly exceeds the 0.3MPA requirement of subway design.
(III) Subway grounding installation process
[Subway comprehensive grounding construction process]
Surveying and setting out - + trench excavation and drilling - > grounding grid laying - > grounding grid connection - grounding lead-out device connection - > backfilling - + resistance detection.
