What is the difference between three phase four wire system and three phase five wire system

First, the role is different:

Three-phase four-wire system.

Phase line A, B, C, protect the neutral line PEN, there is a working current on the PEN line, and the PEN should be repeatedly grounded when entering the power building.

It belongs to the TN-C grounding system.

Three-phase five-wire. System: phase wire A, B, C, neutral line N, protective grounding wire.

PE, N wire has a working current passing through, PE line.

There is no current at normal time (there is only a fault current in the event of leakage or short circuit to the ground); The power distribution mode of civil buildings in China adopts TN-S grounding system.

Second, the meaning is different:

The three-phase four-wire system is three sine waves that derive a difference of 120 degrees.

voltage of the live wire, plus a neutral point.

The zero line that is drawn out. Residential electricity is taken from a line of fire and flows back to the generator from the zero line. The three sine waves at the neutral point cancel each other out, and the voltage is 0, so it is called the zero line (n).

The three-phase five-wire system is based on the three-phase four-wire system and adds an additional grounding ground wire (PE), which is connected to the metal surface of the electrical appliance and uses the zero potential of the earth to guide away the leaked electricity.

Note that the "three-phase four-wire" system is one of the classifications of live conductor systems

It has nothing to do with the classification of the grounding system, and care should be taken to avoid the erroneous name of "three-phase five-wire system", and the TN-S system is not "three-phase five-wire system". Any grounding system can be used with any electrical conductor system. For example, a three-phase four-wire live conductor system can use a TN-S grounding system, a TN-C-S or TT grounding system.

All three types of grounding systems end with five wires, all of which can be called "three-phase five-wire systems".

The above content reference: Encyclopedia - three-phase four-wire system.

Today, I learned that there are three forms of three-phase electricity, and many electricians are confused and never understand.

1. The three-phase four-wire system is the phase line A, B, C, to protect the zero line Pen, there is a working rush current on the Pen line, and the Pen should be repeatedly grounded when entering the electricity building; It belongs to the TN-C grounding system.

2. The three-phase five-state judgment line system is phase line A, B, C, neutral line N, protective grounding wire PE, N line has working current through, PE line usually has no current; The power distribution mode of civil buildings in China adopts TN-S grounding system.

3. In the TN-C system, the protection line and the neutral sail elimination line are combined into the PEN line, which has the advantages of simplicity and economy. When a grounding fault occurs, the fault current is large, and the general overcurrent protection electrical appliance can be used to cut off the power supply to ensure safety. At the same time, because the PEN wires are often electrically connected to each other in the same building, when the PEN wire is broken or the phase wire is directly short-circuited to the earth, it will present a fairly high fault voltage to the ground.

4. In the TN-S system, the protective wire is separated from the neutral wire, which has the advantages of TN-C system, because the PE wire does not pass the load current under normal circumstances, and the metal shell of the electrical equipment connected to the PE wire does not have potential, so it is suitable for data processing and power supply of precision electronic equipment, and can also be used in dangerous environments.

At present, most of the power supply systems are three-phase five-wire system and three-phase four-wire system, which is the lack of ground wire.

The three-phase five-wire system includes three phase wires (A, B, C lines) and neutral wires (N lines) of three-phase electricity; and ground wire (PE line).

The neutral line (n-line) is the zero line. When the three-phase load is symmetrical, the sum of the current vectors flowing into the neutral line of the three-phase line is zero, but for a single phase, the current is not zero. When the three-phase load is asymmetrical, the current vector sum of the neutral wire is not zero, which will produce a voltage to the ground.

The three-phase five-wire system is divided into TT grounding mode and TN grounding mode, of which TN is specifically divided into three modes: TN-S, TN-C, TN-C-S.

TT Grounding Method:

The first letter T represents the neutral point grounding of the power supply, and the second T is the grounding of the metal shell of the equipment, which is commonly used in high-voltage systems, and should not be used when there are large-capacity electrical appliances in low-voltage systems.

TN-S Grounding Method:

The letter S stands for N to be separated from PE, the metal shell of the device is connected to PE, and the neutral point of the device is connected to N.

The advantage is that there is no current in the PE, so the potential of the metal housing of the device to ground is zero. It is mainly used for data processing, precision detection, and power supply system of high-rise buildings.

TN-C grounding mode:

The letter C indicates that N is merged with PE to form PEN, which is actually a four-wire power supply system. Both the neutral point and the metal housing of the device are connected to N. Due to the three-phase unbalanced current and harmonic current circulating when n is normal, the metal shell of the equipment has a certain voltage to the ground normally, which is usually used in general power supply places.

TN-C-S Grounding Method:

Part of N is separated from PE, and it is a four-wire and a half-system power supply mode. It should be used in places with poor environment.

When N and PE are separated, they are not allowed to be merged.

China stipulates that the voltage between the phase wires (i.e. line voltage) of civil power supply lines is 380V, and the voltage between the phase line and the ground wire or neutral wire (i.e. phase voltage) is 220VThe entrance line generally adopts a single-phase two-wire system, that is, any one of the three phase lines and a neutral line (as a neutral line).In case of high-power electrical appliances, you need to set the grounding wire by yourself.

Three-phase five-wire system", people usually refer to a certain electrical equipment has five wires leading out. Specifically, the function of the five wires is usually described in the following two ways: the first statement, the five wires are three phase wires, a neutral wire, and a ground wire connected to the equipment housing; In the second statement, five wires refer to three phase wires, a working neutral wire (or system neutral wire), and a protective neutral wire connected to the equipment housing.

Both of these statements have something in common, when the three phases are unbalanced, the neutral line or the working neutral line (system neutral line) flows through the unbalanced load current, while the wires connected to the equipment have no current through. Three-phase power supply, five-wire connection, at first glance, reasonable.

What is the difference between three-phase four-wire and three-phase three-wire?

1. In general practical application, there is only a three-phase four-wire system (not counting the ground wire, counting the ground wire is called a three-phase five-wire system), and the three-phase three-wire system will not be used.

2. In addition to the three live wires of the three-phase four-wire system, the fourth one is called the middle line (and the disadvantage note: there is only a zero line in the single phase, and there is no zero line in the three-phase system), and the middle line plays a role in ensuring that the load phase voltage is unchanged.

3. If the load connected to each of the three-phase circuits is the same, and the sum of the currents flowing through the center line at each moment is zero, remove the center line and use the three-phase three-wire system to supply power. However, this is an ideal situation, and in practice it is impossible for a three-phase load to be perfectly symmetrical in a three-phase circuit with multiple single-phase loads connected to a three-phase circuit. In this case, the midline is particularly important and not optional.

4. If there is no center line in the case of asymmetrical load, the three-phase three-wire power supply of asymmetrical load will be formed. Due to the asymmetry of the load impedance, the phase current is also asymmetrical, and the load phase voltage is naturally not symmetrical. Some phase voltages may exceed the rated voltage of the load, and the load may be damaged (the bulb of the phase is too bright and burned); Some phase voltages may be lower and the load may not work properly (the bulb is dim).

With the light on, the light off and other reasons cause the change of the load impedance of each phase. The phase current and phase voltage all change accordingly, the lights flicker and flicker, and other electrical appliances cannot work properly, or even be damaged. So there must be a center line, that is, a three-phase four-wire system.

1. Three-phase four-wire system: refers to R yellow, S green, T red, N blue or black line or R yellow, S green, T red, rehmannia plus green two-color line.

In the low-voltage distribution network, the transmission line generally adopts a three-phase four-wire system, in which three lines represent A, B, C three phases, and the other is a neutral line N or Pen. In the single-phase transmission line that enters the user, one is called the phase line L, and the other is called the middle line N, and in the three-phase system, when the three-phase is balanced, the neutral line (neutral line) is current-free, so it is called the three-phase four-wire system.

2. Three-phase five-wire system: refers to R yellow, S green, T red, N blue or black, rehmannia and green two-color lines.

3 phase wires, plus a ground wire, and a neutral wire. The most widely used low-voltage transmission mode is the three-phase four-wire system, which adopts three phase wires plus the neutral line for power supply, the neutral line is drawn out and grounded by the neutral point of the transformer, the voltage is 380 220V, and any phase wire plus the neutral line is taken to form a 220V power supply line for general household use.

The differences between three-phase three-wire system and three-phase four-wire system are as follows:

1. The three-phase three-wire system is to use only three phase wires, and the three-phase four-wire system is to use three phase wires plus a neutral wire.

2. The three-phase three-wire system is a connection method of three-phase AC power supply, which leads out 3 wires from the end of the 3 coils, and connects the tail end of the 3 coils together, also called the star wiring, and the commonly used symbol "Y" indicates that the way of leading out the power supply of 3 wires is called the three-phase three-wire system.

3. Three-phase four-wire has one more power neutral wire than three-phase three-wire, three-phase three-wire can only provide 380 volt voltage power supply, three-phase four-wire can provide both 380 volt voltage and 220 volt power supply.

The three-phase powered volt is outlined as follows:

At present, China's production and distribution are three-phase alternating current. Three-phase alternating current has many advantages in the world, such as the use of three-phase alternating current motors, generators energy-saving and material-saving, easy maintenance, in the three-phase circuit, from the end of the three coils of the power supply to draw out three wires for power supply, this power supply method is called three-phase three-wire power supply.

In the star-connected circuit, in addition to three wires from the ends of the three coils of the power supply, one wire is also drawn from the neutral point, and this four-wire power supply method is called three-phase four-wire power supply. <>