How much do you know about the difference between three-phase three-wire and three-phase four-wire meters?

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How much do you know about the difference between three-phase three-wire and three-phase four-wire meters? [Copy link]

Whether we use a three-phase three-wire or three-phase four-wire meter is determined by the user's incoming line and the nature of electricity consumption. Now many people may not understand the difference between them well enough. The following article will tell you about their differences from four aspects.

1. What do three-phase three-wire and three-phase four-wire mean?

Whether to use a three-phase three-wire or three-phase four-wire meter is determined by the user's incoming line and the nature of electricity consumption.

If the user is a pure three-phase electrical appliance, such as a three-phase transformer, a three-phase motor, etc., a three-phase three-wire line can be used. A three-phase three-wire line has only three wires and no neutral line, so only a three-phase three-wire meter can be used.

If the user has both single-phase and three-phase loads, it is a three-phase four-wire or three-phase five-wire (multiple neutral grounding) line, and a three-phase four-wire meter must be used.

The three-phase three-wire line has no adjustment capability and requires the three-phase load to be basically balanced. Therefore, the wiring methods of the three-phase three-wire meter and the three-phase four-wire meter are also different.

① Wiring of three-phase three-wire active meter: The three-phase three-wire active meter (mechanical meter) consists of two driving components, two aluminum disks fixed on a rotating shaft, and has a total of 8 external terminals. ② Wiring of three-phase four-wire active electric meter: Three-phase four-wire active electric meter consists of three driving components, called three-element electric meter. The biggest difference from single-phase and three-phase three-wire electric meter in appearance is that it has 11 terminals. This wiring method is often used in power supply circuits mixed with power and lighting. 2. Differences and application places of three-phase three-wire and three-phase four-wire systems Three-phase four-wire has one more neutral wire than three-phase three-wire. Three-phase three-wire can only provide 380 volt power supply, while three-phase four-wire can provide both 380 volt and 220 volt power supply.

Three-phase three-wire obviously saves money, but when the load is unbalanced, the current cannot be fed back through the zero phase, which is easy to burn things. Three-phase four-wire can solve this problem.

3. The difference between three-phase three-wire and three-phase four-wire motors (power motors)

Three-phase motors are balanced loads, the phase current is equal to the line current, and the vector sum is zero, so there is no need for a neutral wire. The motor with a delta connection has no neutral wire to connect. The star connection can connect the neutral wire at the neutral point, but it is meaningless. It is the same whether it is connected or not.

4、In the low-voltage power supply system, the scope of application and advantages of the three-phase four-wire system and the three-phase three-wire system

The three-phase three-wire power supply system is only suitable for three-phase symmetrical loads(such as three-phase power transformers, three-phase motors, etc.). If the three-phase load is asymmetrical, voltage will appear at the neutral point. The three-phase four-wire power supply system can obtain line voltage and phase voltage, which is more convenient for users. In addition, when the three-phase load is asymmetrical, the neutral line impedance is very small, and the voltage displacement of the neutral point can also be eliminated.

The above is the difference between the three-phase three-wire and three-phase four-wire meters. You can choose to use a three-phase three-wire meter or a three-phase four-wire meter based on the above characteristics.

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Whether we use a three-phase three-wire or three-phase four-wire meter is determined by the user's incoming line and the nature of electricity consumption. Now many people may not know enough about the difference between them. The following article will tell you about their differences from four aspects.

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In actual operation, the principle is that three-phase three-wire is generally used in situations with higher power. Three-phase four-wire is generally used in situations with lower power or for household use.