On the eve of the Spring Festival in 2024, a rainy and snowy weather hit the southeastern region of China. Freezing rain and snow in some places have "increased" the annual Spring Festival transportation. High-speed trains, which are known to be punctual in people's minds, have also been widely delayed or even stopped running. But while some netizens were waiting anxiously on the high-speed train, they saw the "green car" speeding around them against the snow. Why are the seemingly more advanced high-speed rails inferior to the “old-timers” green cars?
Source: News screenshot
How does heavy snow affect high-speed rail?
On February 4, Wuhan Railway Bureau’s Weibo issued an announcement explaining the reasons for widespread delays in high-speed trains in freezing, rainy and snowy weather, which mainly include three points: poor conductivity due to icing on the catenary, inflexible switching due to icing on the switches, and reduced speed of trains on snow-covered lines.
Among them, the factor of snow on the line is very easy to understand. Let’s focus on the other two points: icing on the turnouts and icing on the catenary.
Source: Weibo screenshot
Icy on turnouts
When high-speed rail trains change routes, they need to change their routes through switch structures just like ordinary trains. Snow and ice in the switch will affect the normal operation of the switch.
Railway switch structure, image source: Wikipedia
Although some high-speed railways have turnout snow-melting devices, the turnout structure may still fail in the event of extreme snowfall.
For example, the "Baolan-Lanzhou High-speed Railway" opened in 2017 had three turnout failures in its first winter due to snow and ice on the turnouts, affecting the normal operation of the trains.
The sudden heavy snowfall not long ago also had an impact on the turnout structure. In response, the railway department immediately dispatched special personnel to handle the snow and ice removal work on the turnouts, and they were on duty 24 hours a day.
Source: Weibo screenshot
Thanks to the hard work of railway workers, the problem of icy track switches was quickly resolved. But high-speed rail still faces another more difficult problem - icing on the catenary.
Contact network icing
Usually when we talk about high-speed rail, the image of a bullet train comes to mind. But the "inconspicuous" wires above the high-speed rail are also an important part of the high-speed rail.
Unlike traditional trains, the power source of high-speed trains is not traditional diesel but electricity. This electricity comes from the high-voltage lines above the high-speed rail cars. The network composed of these high-voltage lines is called "catenary" or "overhead catenary".
High-speed rail can draw electricity through a structure called a pantograph, which is connected to high-voltage lines. The pantograph takes the high-voltage electricity into the car, and after voltage reduction, it is used to drive the high-speed rail.
The pantograph above the high-speed rail carriage, picture taken from the documentary "China High-Speed Rail"
But if ice appears on the wire, the contact between the bow head and the wire will be affected. The "lightning effect" that some people see when high-speed trains are running all the way is caused by the ice between the bow head and the wires.
Arc on pantograph, picture source: Reference 2
In addition, ice on the wires may also make the wires heavier and shake more. It also affects the power supply of high-speed trains. In order to obtain current as stably as possible, high-speed trains can only reduce their running speed. In severe cases, they can only stop and wait temporarily.
To solve this problem, the method is very simple and crude, which is to remove the ice. Although engineers are developing automated de-icing equipment. But at this stage, the fastest and most direct method for this large-scale contact network ice coating is manual removal.
Use an ice pole to remove ice, picture source: news screenshot
Under the influence of these factors, high-speed rail trains have to run at reduced speeds, which leads to a reduction in the utilization rate of high-speed rail EMU vehicles. As a result, there were a lot of delays and outages.
What exactly does "passenger green truck" mean?
When the high-speed train stopped on the road, many netizens took pictures of the "green car" whizzing by next to it. So why are green cars not afraid of heavy snow?
First of all, let me explain that the green train we often refer to is actually the common name for trains with green bodies. Moreover, what we call green cars today is very different from what we called green cars more than ten years ago.
More than ten years ago, the green cars we often referred to were "old green cars." These green cars refer to some very early railway passenger cars, such as Type 22 buses or some Type 25B buses.
The typical feature of these "old green cars" is that they are slow, and most of the "old green cars" do not have air conditioning. In hot summers, people often have to open the windows to get some air.
Type 22 bus, picture source, Wikipedia
More than ten years ago, if you took a train starting with K (fast), Z (direct), or T (express), you might see some orange or blue painted bodies.
The configurations of these "orange cars" and "blue cars" are often better than those of "old green cars". They are basically equipped with air conditioning, and they often run faster than "old green cars".
Orange-painted 25G and blue-painted 25K buses, picture source: Wikipedia
But starting in 2014, the railway department decided to use dark green as the unified color for ordinary speed trains (non-high-speed EMU trains), and began to repaint the color of the train body that year. The previous orange and blue painted trains have gradually become "new green trains".
Therefore, do not equate the "new green trains" and "old green trains" on the railways today. The speed and comfort of "new green cars" may not be as good as high-speed rail, but they are still much more comfortable than the early "old green cars".
Although the number and capacity of "green trucks" are far less than before, and the name "green trucks" sounds like "abandoned by the times", "green trucks" have not abandoned the times. They can still be seen on railway lines across the country, and for areas that have not yet opened high-speed rail, "green trains" are still important.
At the same time, during this year's Spring Festival travel season, at a critical moment when high-speed rail operations were delayed in large areas, "green trucks" were also shuttled through the heavy snow, transporting tourists eager to return home one by one.
Why can green cars "move forward in the snow"?
To be sure, green trains will of course be affected by icy turnouts and snow on lines, but because of its relatively slow speed and the overnight repairs by railway workers, these problems have little impact on the running of green trains.
In addition, green cars have different types of power sources. Some green cars are purely electric driven like high-speed rail.Some green cars are powered by internal combustion engines, while others are powered by steam engines.
Dongfeng 11 diesel locomotive, picture source: Wikipedia
Therefore, the "icing on the catenary" that has the most serious impact on high-speed train EMUs has almost no impact on the "green trains" driven by internal combustion engines and steam engines. This is why the scene of high-speed trains parked on the roadside waiting while green trains whizz by.
References
[1] ZhouH, DuanF, LiuZ, et al. Study on electric spark discharge between pantograph and catenary in electrified railway [J]. IET Electrical Systems in Transport, 2022, 12 (2): 128-142.
[2] Ding Shanfeng, Man Kaiquan, Wang Tingting. Impact of ice and snow weather on high-speed railway switching equipment and countermeasures [J]. Railway Communication and Signal Engineering Technology, 2020.
[3] People's Daily Online: The railway department's restoration of "green trains" red trains and blue trains will become history
http://finance.people.com.cn/n/2014/1017/c1004-25857015.html
Planning and production
This article is a work of Popular Science China-Starry Sky Project
Produced by Science Popularization Department of China Association for Science and Technology
Producer｜China Science and Technology Press Co., Ltd., Beijing Zhongke Galaxy Culture Media Co., Ltd.
Planning丨Lin Lin
Author丨Xiaowei popular science creator
Review丨Lu Fang, master's tutor at the School of Transportation, Beijing Jiaotong University, deputy secretary-general of the Expert Academic Committee of the China Urban Rail Transit Association
Editor丨Lin Lin
Editor in charge: Luo Mu