The conductor wire of a single-phase generator is actually no different from the live wire and the neutral wire. However, if one end of the coil is grounded, the voltage of the conductor wire at the ground end is equal. always zero, that's why it's called the neutral wire. If the stator coil ground terminals are reversed, the live and neutral wires are reversed. The same goes for three-phase generators. In order to save material, the three ground terminals are combined to form a common neutral line, saving 2 wires.
PS: In fact, the neutral line voltage is not always zero. When the switch is closed, current flows in the neutral line. Due to the resistance of the wire itself, there is residual tension.
Nobel said it very well and exhaustively.
In the picture above, whatever wire you connect to ground is the neutral wire. The chainThe remaining part is the live wire. Remove only the live wire, pass it very far and connect it to your voltage (current) meter. The other terminal of the meter is grounded, which is the neutral wire. This is essentially how power plants provide electricity. But it's actually much more complicated than that. This is actually three-phase electricity. Three live wires are transmitted. The voltage between one wire and the neutral wire is 220, and the voltage between two wires is 380. This is the actual process, of course, I haven't taken into account the voltage increase and decrease during the transmission.
Also, you mentioned the pen testing issue. According to my explanation above, testing electricity with a test pen involves forming a circuit between the wire to be tested, the test pen, the human body and the ground. If this wire is the live wire, there will be current in the middle and the test pen will light uphas. If this wire is the neutral wire, that is, the ground wire, if you reconnect it, there will be no current. between.
As there is a large resistance in the middle of the test pen, people will not be electrocuted during the electrical test. If the test pen is a light bulb and the resistance is not large, it will electrocute people. . This is why people can be electrocuted if the switch is not connected to the live wire and disconnected.