Why are some sections of Shenzhen Metro Line 6 powered by three rails and some sections by catenary?

Actually, I'm not lazy to update. As a subway power supply worker, I am really busy at ordinary times. What are you up to? Equipment maintenance, revision and audit of technical manual, daily management of work area, follow-up of new line construction, daily safety operation related work, and recently various guarantees. It is really a big head. But it doesn't matter, take a break from your busy schedule and update your answers quickly, otherwise you will really be forgotten.

I took a general look at everyone's answers and it was really good. I answered your answers from a technical point of view, with pictures and texts, which should be easy to understand. I won't talk about it from a technical point of view, just from our maintenance point of view.

As the power supplier, the third rail and catenary are very important, because it is the most direct way to directly affect the operation of electric buses. What do you mean, the electric bus runs in the tunnel, and the third rail and catenary supply power to the electric bus. There is only one way, and there is no other way. Once the third rail or catenary fails, the electric bus will have no electricity and can't walk, which is a very serious accident for the operating unit! Determined to end this.

Let's talk about the third track first. The third track is divided into an upper power receiving mode and a lower power receiving mode. In fact, it means that the contact surface between the power shoe and the third rail of the electric bus is above or below the third rail. If the contact surface between the power shoe and the third rail is above the third rail, it is called power receiving, and vice versa. These two maintenance methods are also different. Generally, it is better to receive electricity at the lower part, because if the third track of the ground line receives electricity at the upper part in winter, it will be affected by rain and snow. Especially in the northern area, there is more ice and snow, and there will be ice and snow accumulation on the upper contact surface, which will affect the operation. Therefore, there will be a protective cover above the third rail where the upper power is received. This kind of protective sleeve is exposed to the wind, the sun and the rain every day. The material of protective cover is generally plastic fiber products or glass fiber products, which need to be replaced regularly, which brings workload to daily maintenance.

The distance between the third rail and the ground and rail surface is generally low, generally 15-20 cm. Because of the short distance, the voltage of the third rail is generally not high. The power supply voltage of the standard design third rail is DC750V, and the actual value is about 825V V V. The voltage limit directly affects the power of electric buses. The top speed of the third track electric bus is generally less than 80 km/h, and it is generally less than 50 km/h when driving. Some people say that every station of the subway is not far away, so it doesn't need such a fast speed. This is not right. Why? We must first understand the subway power supply system.

Let me briefly talk about the power supply system of the subway. The electricity used by electric buses is direct current, which can't generate electricity directly and needs rectification. Each station has a substation, which supplies power for the * * * station, and DC power supplies power for the electric bus. Yes, every station. These substations are divided into three types: traction step-down hybrid substation, step-down substation and follow-up substation (not mentioned here). Traction step-down hybrid substation means that this substation has both DC system power supply equipment of electric bus and step-down system power supply equipment of station power, while step-down substation only has step-down system power supply equipment of station power. The construction and installation of these devices need a lot of money, so it is necessary to set the location and distance of the substation reasonably, that is, the distance of the station. More traction step-down hybrid substations will cost more money, and the voltage level of the third rail is lower, so a traction step-down hybrid substation cannot support electric buses to run a long distance (generally, the power supply distance of 750v voltage level is about 2 kilometers). It can be said that the voltage level of the third rail directly limits the number of traction step-down hybrid substations, and the more traction step-down hybrid substations are set, the more investment will be.

Let's talk about the maintenance of the third track. The material of the third track is usually steel-aluminum composite. This material is lighter, harder, more wear-resistant and more conductive than steel. It is more suitable for the third rail which needs wear resistance and good conductivity. Moreover, the general maintenance of this material is also very convenient, and daily inspection can meet it. The manufacturer claims that this third rail is maintenance-free for 25 years, and the general operating practice is to overhaul it once every 10, which can be said to be better. However, this kind of material has a disadvantage that the synthesis process is difficult. It is said that there are steel-aluminum composite materials in China now, but the quality is not as good as that of foreign countries, and the three-track material is more expensive.

Furthermore, as mentioned above, the third rail is close to the ground rail surface, which is prone to short circuit. On one occasion, a piece of flat steel on the inner wall of the tunnel fell and overlapped on the third rail due to the vibration of passing vehicles, which caused the third rail to be permanently short-circuited, and the electric bus was cut off, resulting in the bus lying in the interval, which led to the suspension of the interval for 2 hours and the evacuation of passengers. This is a very serious event for the operating unit.

Summarize the third track: 1, which is easy to maintain. 2. The way of receiving electricity will be affected by the weather. 3. The low voltage level of the third rail affects the number of traction step-down hybrid substations, resulting in an increase in construction and operation investment. 4. The material of the third rail is expensive and the synthesis process is difficult.

First of all, OCS, OCS technology, has been introduced, absorbed and developed vigorously in China since it was invented by the Japanese. Now the technology is mature and widely used. Most of the high-speed rail, track laying, subway and light rail are in use, and the new subway line is also based on catenary, which shows that catenary has a great application space.

Catenary is divided into rigid catenary and flexible catenary, which will not be introduced here.

First of all, let's talk about the voltage level of catenary. Because the catenary is installed at the top of the tunnel and the contact wire is made of copper-silver alloy, its conductivity is far superior to that of steel-aluminum composite material. Its voltage level is generally DC 1500V (the voltage level of railway catenary is AC27.5kv). With the increase of voltage, the power of electric bus will increase, the transportation capacity will be enhanced, and the number of traction step-down hybrid substations with longer power supply distance (generally 1500V) is less than that of the third rail.

The maintenance of catenary is complicated. Rigid catenary and flexible catenary have more parts and greater flexibility. Daily maintenance mainly includes the fastening of parts and bolts, the measurement and calibration of lead height and pull-out value of contact wire, the wear detection of contact wire (the wear resistance of contact wire made of copper-silver alloy is lower than that of steel-aluminum composite material), the adjustment of the relationship between contact wire and track (the contact wire is greatly influenced by track, so the contact wire should be adjusted), and the maintenance of flexible contact wire is more complicated (the contact wire is usually replaced within six years), and there are really too many adjustments. From the perspective of manpower allocation, the daily manpower maintenance of the third rail is very little, while the overhead contact line needs at least five people for an ordinary patrol operation, and there are more operators for fastening test, which greatly increases the labor cost.

Then why contact the Internet on a large scale? Because the catenary is relatively safe, with large capacity, high speed and high reliability. In terms of safety, if someone falls into the tunnel at the same time, the height of the catenary is generally 4050mm from the track surface, which is 4 meters, and the third track is at your feet. People are in danger of getting an electric shock at any time, so catenary does not exist. In terms of transportation capacity, due to the improvement of voltage, electric buses can use more powerful traction motors, which are more powerful and faster. The catenary is usually at the top of the tunnel. If the daily maintenance is in place, there are few things around that can affect the operation of catenary (compared with flat steel, the third rail is permanently short-circuited), and the reliability is high. But there are exceptions, that is, catenary is afraid of water leakage at the top of the tunnel, especially directly above it. This is also the key construction point of catenary during the construction of new line.

It should also be noted that catenary is also easily affected by the weather, especially the ground lines, such as windy weather, rain and snow weather, foreign body overlap and so on. The proportion of this kind of thing is higher than that of the third track.

To sum up the catenary: 1, the maintenance is cumbersome (but it can provide a large number of jobs in China). 2. It is more susceptible to the weather. 3. The voltage level is very high. 4. The number of traction step-down hybrid substations is small. 5. Compared with people, it is safer and more reliable.

At present, catenary system is widely used in developed metro cities such as Shanghai, Guangzhou and Shenzhen, but at present, only Line 6 of Beijing Metro adopts catenary system for power supply, and the rest are the third track. Relatively speaking, the maintenance of the third rail is indeed much smaller than that of the catenary system, which may be the reason why most of the Beijing subways adopt the third rail.

Both the catenary and the third track have their unique characteristics and suitable places. As long as it is adapted to local conditions, it will play a great role.

What I said is quite complicated, and there are still some things I haven't said. I hope I can help you.