Trains also have a front bow, so why do they always run with a back bow?

Why do you often say "no double bows" beside the tracks? I finally understand after reading it.

With the continuous development and progress of railway traffic, people's travel has become more and more convenient. In the short-distance travel demand, people can solve it by bus or self-driving. In long-distance travel, trains, high-speed trains and airplanes have become the main modes of travel, especially trains and high-speed trains. Passenger flow will surge every holiday. The difference between a train and a high-speed rail is that the train has a price advantage. After all, many people prefer to save a little money and choose to take the train or high-speed rail. People who often take the train know that trains mainly rely on overhead wires to transmit electricity, so they are also called electrified trains. However, some friends will be puzzled, that is, the slogan "No Double Bows" is often written next to the railway tracks, which is inevitably confusing. What does this slogan mean and what is its purpose?

In fact, the "unparalleled bow" is mainly written for insiders. We ordinary passengers basically can't understand it, and it's hard to understand its meaning. Are people forbidden to play with bows and arrows on the tracks? The answer is of course not. This is a slogan that only train drivers can understand. This is a warning sign to remind train drivers to be careful. What does this mean? Let's take a look and finally know the answer.

First, let's explain what a double bow is. Double bow refers to the arm connecting wires on the train or moving roof, and there is a professional name called pantograph. Generally, a train has two identical pantographs, which are distributed at the front and rear of the train. The main function of pantograph is to receive the current on the conductor and convert it into electric energy, so that the train can move forward. Many people may ask, since there are two pantographs, isn't it to raise both of them to make the current more stable and the train more dynamic? In fact, the train can raise two pantographs where the slogan "No Double Bows" appears, but if "No Double Bows" appears, in order to prevent short circuit and trip, only one pantograph must be used, because the wires above the train are actually distributed in sections, and the wires in different areas are supplied by different power supplies. When the train passes through the section, different currents are generated between different wires, which is easy to short-circuit and trip, so in the place where there is no bow.

Of course, wherever the slogan "Don't use double bows" appears, trains can use double bows, so that the current will be more stable and all aspects of performance will be better. Finally, the headmaster thinks that there is no need to be confused when we see the place where double bows are forbidden next to the train in the future. In fact, it is mainly to warn train drivers not to use double bows. Have you finally understood after reading it?

What do you think of this?