The subway runs tens of meters deep underground. According to common sense, it seems that it has no chance of lightning from the sky. Even if it is struck by lightning, it is only limited to the "light rail" part that is exposed above the ground. How to choose a lightning arrester monitor? In fact, the underground equipment of the subway is also threatened by lightning. As the backbone of public transportation, the consequences of lightning damage to the subway are very serious, and lightning protection is indispensable for it.
Above and below ground: inextricably linked
Today, many "subways" are not actually underground, they run on viaducts. According to statistics, the above-ground part accounts for about 1/5 of the total mileage of Beijing subway. These parts are located at high altitudes, and light poles, antennas on viaducts, running trains, etc. are undoubtedly easy targets for lightning strikes.
In addition to the elevated lines that the public is familiar with, many components of the subway system are located above ground and are subject to the same threat from lightning strikes as ordinary buildings. For example, the subway operation control center is responsible for the operation and dispatch of the entire city's subway. This is a building on the ground. The subway's depot (a place where trains are prepared, inspected, and maintained), parking lots, and offices of subway company staff are also located above ground. Due to their use, these buildings are often located in relatively open areas, so special attention needs to be paid to lightning protection.
In addition, since the entire subway line is interconnected, underground stations close to the elevated portion will also be threatened by lightning conducted from the ground. Pure underground stations will also be threatened by lightning strikes because there are many connections between the ground and the underground. First of all, the entrances and exits of underground subway stations and cooling towers are built on the surface. In addition, there are some GPS antennas, wireless communication antennas, etc. connected to the underground. Once a lightning disaster occurs, it can easily be transmitted to the underground.
Even so, it is not easy for people to imagine how lightning penetrates deep into the ground to "make waves." To explain this problem clearly, we need to invite the main character of thunder and lightning to threaten the subway system-the lightning sensor.
Thunder and lightning induction: the killer of "beating cattle across mountains"
Lightning induction is caused by the huge impact lightning current producing a rapidly changing strong magnetic field in the surrounding space during lightning discharge. It can propagate along circuits or through electromagnetic fields in space. If the electromagnetic energy caused by lightning induction is not released into the ground in time, discharge sparks may occur, causing fires, explosions or electric shock accidents. The favorite prey of lightning induction is all kinds of electronic equipment, and the subway is a system with very dense electronic equipment.
Let’s see what electronic devices are in the subway! The first is the signaling system, which shoulders the important tasks of subway operation control and operating status monitoring, and can be called the "brain" of the subway; the communication system, which is responsible for transmitting various information, such as broadcasts, clocks, monitoring, and mobile networks used by passengers; the environmental control system, which mainly includes air conditioning and heating, etc., to regulate the environment of the station carriages; in addition, there are screen door control, automatic ticketing machines, and passenger information systems. How to buy European cable joints? These complex electronic devices are the key to maintaining the smooth and safe operation of the subway. They are interconnected with each other. Once they are attacked by lightning induction, the consequences will be disastrous.
In addition, the subway relies on electricity to operate, and its power supply system is also vulnerable to lightning induction. In the past, subways mostly used contact rails (also known as "third rails") to feed power (meaning to supply power to a circuit). The power supply rails were located underneath the trains, so the risk of lightning strikes was low. The subways constructed in recent years have adopted catenary feeds with higher voltages and more sufficient power. The transmission lines are located above the trains, and the probability of being struck by lightning has also increased accordingly, adding greater pressure to subway lightning protection work.
Subway lightning protection: long way to go
The lightning protection measures for subways are roughly similar to those for buildings on the ground. There are all kinds of lightning protection technical measures and means such as lightning protection belts, lightning protection nets, lightning rods, down conductors, grounding bodies, voltage equalizing rings, equal potentials, and surge protectors (commonly known as lightning arresters). In order to deal with the "big enemy" lightning induction, many circuits in the subway system are installed in metal shielding trenches. It is similar to the troughs commonly used in offices to place telephone lines and network cables. Its metal material can effectively isolate the damage caused by lightning induction. What are the PT cable joint manufacturers? Nowadays, as subway construction projects are launched in various places, subway lightning protection still has a long way to go.
(Source: China Meteorological Science Network. This article is only for academic exchange and not for any commercial use! The copyright belongs to the original author. If there is any infringement, please contact this site to delete it)
