After riding so many trains, what do the signs prohibiting double bows mean? What should we do?

After riding so many trains, what do the signs prohibiting double bows mean? What should we do?

Electric locomotives have two pantographs, which are divided into "front pantograph" and "rear pantograph". Generally, only one bow is raised during a run (usually the rear bow run). "No double bows" means that the front and rear bows are prohibited from contacting the contact grid at the same time. Because the power grid is powered by sections, using double bows during operation can easily cause a short circuit.

This kind of sign is often seen next to electrified railways. The purpose of prohibiting double bows is to prevent the two-phase electricity of the contact network from short-circuiting when the phases are separated by insulation, causing the substation to trip. Generally, there will be an insulation phase split every 30-50 kilometers. This is because it is necessary to reduce the voltage drop of the catenary and maintain a higher catenary voltage. However, in the catenary section using autotransformer, this distance is longer. Much longer. In fact, even if a single pantograph is used, there is still a situation where the two phases of electricity are short-circuited. When the pantograph is over-phased, if the pantograph is not lowered, an arc will occur when the pantograph is disconnected from one of the phases. The arc in the arc may be stretched and stretched to another phase, which will also cause a short circuit. Therefore, try not to use double bows. Use double bows only when the weather is bad and the contact is not good.

For example, when it snows, even a single bow has to be lowered when passing through the insulation section. Of course, this is more troublesome. Therefore, the current technology is to add a current induction device on the roof of the car. This problem can be solved by automatically opening the circuit breaker when there is no current in the contact network, such as when there is an overphase. When it senses that there is current, it will automatically close the circuit breaker. Of course, this device is only available on relatively new electric locomotives. Only then will there be, for example, SS7 modular locomotives and SS9 modifications. "Double bow prohibited" signs can only be seen on both sides of electrified railways

The bow of an electric locomotive refers to the part where it is connected to the wire, also known as the pantograph. Electric locomotives have two bows, and usually only the rear bow is used (the reason for using the rear bow instead of the front bow is to prevent the friction between the bow and the wires from falling materials that may fall on the locomotive and damage the locomotive); only in rain and snow Only use double bows when there is bad weather and poor contact.

The current used by electrified railways comes from a three-phase generator. In order to prevent the generator from being overloaded, a phase line must be replaced every 30 to 50 kilometers. Near the contact point of the replacement phase line, the train passes by inertia. If the train uses double bows at this time, when the front bow passes the contact point but the rear bow has not passed the contact point, it means that the two phase wires are short-circuited, which must be avoided. Therefore, there will be "No Double Bows" signs near the contact point.