Three-phase (AC) alternating current is an advanced version of AC. Three-phase power is a sophisticated version of AC. Here are three times 230V AC summarized. They have the same frequency (50Hz) and share the neutral conductor. This works because the three phases are offset by one third in time to each other. So the neutral conductor can have the same diameter as the three phases respectively. Between neutral and a phase are 230V and between the phases about 400V.