Can anyone tell me what the common railway slogans such as "once stopped", "once stopped" and "closed" mean?

A one-time stop means that the train stops once at a designated location when leaving or entering the station, confirms that the signal is correct, confirms that the line ahead is safe, and then proceeds according to the signal command again.

This is a safe driving system.

Similarly, when a car encounters an intersection or turns, it should slow down and keep a lookout to ensure safety.

Not seen once parked.

"Close" means closing the main circuit breaker.

On the railways, power supply is provided between zones. In order to reduce the loss of long-distance power transmission, a power supply interval is generally 10 kilometers in length.

In other words, there are many power supply points on a railway line, and each power supply point is responsible for supplying power to locomotives within a line range of about 10 kilometers.

Each power supply point provides three channels of 25kV single-phase high-voltage AC power to the railway. The AC power provided by different power supply points cannot be connected together due to different phases. As a result, there will be a non-power zone between adjacent power supply points. This no-electricity area is called a split-phase area, and the train passing through this area is called an over-phase.

In order to protect the locomotive circuit, the main circuit breaker should be disconnected when passing through a no-electricity zone to avoid the impact of the sudden change in the voltage of the contact network on the locomotive circuit.

Therefore, before entering the power-free zone, the main circuit breaker should be closed in advance. Similarly, after entering the next power supply interval at a certain safe distance, the main circuit breaker can be closed and the locomotive circuit reconnected. This "close" sign tells the driver that the main circuit breaker can be closed.

Some power-free zones are very short, shorter than the distance between the front and rear pantographs, so the pantographs must be lowered. Avoid two pantographs and the car body acting together as conductors for two power supply zones.

So, the complete process is roughly like this:

Break - lower the bow - no electricity area - raise the bow - close

The entire area About 180m long.