What is the harm of the three phase four wire system interrupting zero

Mainly depending on the load situation, if you use a single-phase 220V load and the three-phase load is balanced, there is no big problem, if you do not balance, there will be phase current imbalance, if you use a 380V three-phase load, there is no big problem.

As a result, the neutral point is shifted, and the potential of the neutral line is increased, and when the ground touch wire reaches a certain value, it will cause the risk of electric shock accidents.

In the three-phase four-wire power supply system, if the neutral line is not well grounded or the ground terminal is broken, the consequence is that the potential of the neutral line is not equal to 0 when the three-phase load is unbalanced, that is, the neutral point is offset.

The specific zero line potential is related to the three-phase load unbalance, the more unbalanced, the greater the neutral point offset, and the higher the potential of the neutral line. After the neutral potential is offset, the phase voltage of the three phases is generally not 220V. Some phases may exceed 220V, while others may be below 220V.

If the neutral point offset is too large, the phase voltage of the three phases may be burned out, and the phase voltage of the three phases may not work. When the potential of the neutral wire is raised, the ground touch wire will cause a risk of electric shock when it reaches a certain value.

Summary. In the three-phase four-wire low-voltage power supply system, the function of the neutral line is to ensure that the potential of the neutral line is zero when the three-phase load is asymmetrical, so as to eliminate the change of neutral potential and keep the voltage of each phase symmetrical, that is, the phase voltage of each phase load is always equal to the phase voltage of the power supply, and has nothing to do with the load change. If there is a phase open circuit in the three phases, it will only affect the phase, and the voltage of the remaining two phases remains unchanged, and the electrical equipment connected to the two phases can still work normally. Some phase voltages are too low, and electrical equipment cannot be used normally.

In the three-phase four-wire low-voltage power supply system, the function of the neutral line is to ensure that the potential of the neutral line is zero when the three-phase load is asymmetrical, so as to eliminate the neutral point electric dislike bit change, so that the phase voltage of each phase load is always equal to the phase voltage of the power supply, and has nothing to do with the load change. If there is a phase open circuit in the three phases, it will only affect the current phase, and the voltage of the remaining two phases remains unchanged, and the electrical equipment connected to the two phases can still work normally, once the zero line in the three-phase four-wire system is broken for some reason, in the case of asymmetry of the three-phase load, the neutral point displacement will be generated, resulting in the three-phase voltage imbalance, and some phase voltages are too high, which may burn the electrical equipment; Some phase voltages are too low, and electrical equipment cannot be dismantled and used normally.

Hope it helps!

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. Additional Information:

Difference between three-phase four-wire system and three-phase five-wire system:

1. The number of lines is different

The three-phase five-wire system is R yellow, S green, T red, N blue or black, rehmannia and green two-color lines; The three-phase four-wire system is R yellow, S green, T red, rehmannia and green two-color wire.

2. The system is different.

Three-phase four-wire phase line A, B, C, protection zero line Pen, there is a working current on the PEN line, and the PEN should be repeatedly grounded when entering the electricity building, which belongs to the TN-C grounding system.

Three-phase five-wire phase line A, B, C, neutral line N, protective grounding wire PE, N line has working current through, PE line usually has no current (only in the case of leakage or short circuit to the ground, there is fault current); The power distribution mode of civil buildings in China adopts TN-S grounding system.

Three-phase four-wire power supply, three-phase load is not necessarily balanced, three-phase unbalanced current is returned to the power supply through the neutral line, so four-core cable must be used. Otherwise, unbalanced currents (zero-sequence currents) will be generated, causing problems such as heating of the bushing. If it is a three-phase three-wire power supply, this problem will not occur.

Summary. 1.The reasonable selection of the wire is that the branch neutral line should be able to withstand the off-circuit impulse current of the power supply for a certain period of time and the maximum unbalanced current for a long time, as well as sufficient mechanical strength.

2.The line joint should be standardized and qualified: connect the branch zero line from the trunk zero line, the joint must be connected by a wire crimping plate or a wire clamp, the connecting wire head should have enough length, and more than two wire chucks should be used.

Repeated grounding measures should be taken at the end of the zero line and every ICM along the line: once the zero trunk joint is damaged or part of the zero trunk circuit is broken due to external strength, after the secondary breakpoint, the unbalanced current of the three-phase power supply will flow back to the neutral point of the transformer through the repeated grounding at the unfinished end, so the three-phase power supply voltage caused by the three-phase load imbalance should be abnormal. To sum up, as long as you do each of the above tasks carefully and avoid some of the problems raised above, the zero line disconnection can be completely avoided.

How to solve the situation of burning out electrical appliances after the zero line of the three-phase four-wire system is broken.

1.The reasonable selection of the wire is that the branch neutral line should be able to withstand the off-circuit impulse current of the power supply for a certain period of time and the maximum unbalanced current for a long time, as well as sufficient mechanical strength. 2.

The line joint should be standardized and qualified: connect the branch zero line from the trunk zero line, the joint must be connected by a wire crimping plate or a wire clamp, the connecting wire head should have enough length, and more than two wire chucks should be used. Repeated grounding measures are taken at the end of the zero line and every ikm along the line

Once the zero trunk joint is damaged or part of the zero trunk is broken due to external strength, after the secondary breakpoint, the three-phase power supply unbalanced current will flow back to the neutral point of the transformer through the repeated grounding at the first end, so the three-phase power supply voltage caused by the three-phase load imbalance should be abnormal. To sum up, as long as you do each of the above tasks carefully and avoid some of the problems raised above, the zero line disconnection can be completely avoided.

1. There are four wires without skin on the pole, and when the wind blows, the four wires keep shaking, and the zero wire is merged into the live wire, and the two wires become a live wire with a very low voltage, and this live wire is adding a normal live wire next to it. 2. This situation is called stranded wire, and there are two kinds of stranded wire, one is that the lamp is very bright, that is, as mentioned above, the zero wire and the live wire are together. There is also a light cannon that is not very bright (just a little red wire), which is two lines of fire together.

3. In order not to burn out the electrical appliances at home, it is necessary to make the circuit into the back of this situation, the main method is: the four wires should be arranged on the edge of the zero line (generally the zero line is on the side), that is, the sequence zero, fire, fire, fire, or fire, fire, fire, zero. Anyway, the neutral line can't be in the middle, so you only need to use the live wire next to the neutral line for your household electricity.

The neutral line in the three-phase four-wire system is without electricity, and the neutral line in the single-phase electricity in household is electric. The power supply of three-phase four-wire power supply has only three live wires and one neutral wire, this neutral wire is the integration of the neutral line and the ground wire, and this neutral wire is drawn out by the secondary neutral point of the transformer, and the secondary neutral point is connected with the zero potential of the earth, and the three live wires form a loop; So under normal circumstances, the zero line of the three-phase four-wire system is without electricity.

The single-phase electricity commonly used in the home is a circuit composed of a live wire and a neutral wire, and the third is a ground wire, which is a protective wire to prevent electric shock; The zero line in this circuit is called the working zero line, and the working zero line is live, but we can't measure it when measuring with an electrical measuring instrument, the reason is that one end of the zero line is drawn from the neutral point of the power supply, and the potential difference to the ground is zero.

An over- and under-voltage protector can be installed, and the over-voltage and under-voltage automatically disconnect the circuit to protect the equipment.