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.