What Is The Difference Between Three-phase Four-wire And Three-phase Three-wire Static Voltage Stabilizers?

Q: What is the difference between the Static Voltage Stabilizer of the three-phase four-wire system and the three-phase three-wire system?

A: In general, only the three-phase four-wire system is used in practical applications (excluding the ground wire, which is called the three-phase five-wire system), and the three-phase three-wire system will not be used.

In addition to the three live wires, the third wire of the three-phase four-wire system is called the neutral wire (note: only the single-phase has a neutral wire, not the three-phase), and the neutral wire plays a role in ensuring that the load phase voltage remains constant.

If the loads connected to each of the three-phase circuits are the same, and the sum of the currents flowing through the neutral wire at each moment is zero, it is possible to remove the neutral wire and use the three-phase three-wire system for power supply. But this is an ideal situation. In fact, the three-phase load formed by connecting multiple single-phase loads to the three-phase circuit cannot be completely symmetrical. In this case, the neutral wire is particularly important and is not dispensable.

If there is no neutral wire when the load is asymmetrical, a three-phase three-wire power supply with an asymmetrical load is formed. Due to the asymmetry of load impedance, the phase current is also asymmetric, and the load phase voltage is naturally asymmetric. Some phase voltages may exceed the rated voltage of the load, and the load may be damaged (the bulb of this phase is too bright and burns out); some phase voltages may be lower, and the load cannot work normally (the bulb is dim). As the lights are turned on and off, the load impedance of each phase changes. The phase current and phase voltage change accordingly, the lights flicker, and other electrical appliances cannot work normally or even get damaged. Therefore, there must be a neutral line, that is, a three-phase four-wire system.