What is the protection zero connection and what is the function of the protection zero connection?

Protective grounding. It is a grounding to prevent the metal shell of electrical installations, the frame of power distribution devices and line towers from being electrified and endangering the safety of people and equipment, and it is a measure to grounding the metal shell of electrical equipment. It can prevent strong current from passing through the human body when the metal shell is energized in the case of insulation damage or accidents, so as to ensure personal safety.

The so-called protective grounding is to be insulating material that will not be charged under normal circumstances.

It is a protective wiring method that reliably connects the metal part of the electrical appliance (i.e., the metal structural part insulated from the live part) that may be charged after damage or under other circumstances with a wire and the grounding body. Grounding protection is generally used in the power supply system where the neutral point of the distribution transformer is not directly grounded (three-phase three-wire system), so as to ensure that the voltage to the ground generated when the electrical equipment leaks due to insulation damage does not exceed the safety range.

Protection zero. It is an electrical safety measure that reliably connects the metal shell of electrical equipment with the neutral line of the power grid to protect personal safety.

Grounding protection and zero protection, collectively referred to as protective grounding, is an important technical measure taken to prevent personal electric shock accidents and ensure the normal operation of electrical equipment. The differences between these two types of protection are mainly manifested in three aspects:

First, the principle of protection is different. The basic principle of grounding protection is to limit the leakage current of the leakage equipment to the ground, so that it does not exceed a certain safety range, once it exceeds a certain setting value, the protector can automatically cut off the power supply; The principle of zero connection protection is to use the short-circuit current when the equipment hits the shell to form a single-phase metal short circuit after the insulation is damaged.

Prompt the protective device on the line to act quickly.

Second, the scope of application is different. According to the load distribution, load density and load nature and other related factors, the "Rural Low-voltage Power Technical Regulations" divides the use scope of the operation system of the above two power networks. Protective Grounding System (TT System.

It is usually suitable for rural public low-voltage power grids, and the system belongs to the grounding protection mode in protective grounding; Protective Zero System (TN System.

It can also be divided into three kinds: TN-C, TN-C-S, TN-S) is mainly suitable for urban public low-voltage power networks and special low-voltage power networks for power customers such as factories and mining enterprises, and the system belongs to the zero protection mode in the protective grounding. At present, China's current low-voltage public distribution network usually adopts TT or TN-C system, and implements single-phase and three-phase mixed power supply modes. That is, the three-phase four-wire system.

380 220V power distribution, both to the lighting load and to the power load.

Third, the line structure is different. The grounding protection system only has a phase wire and a neutral wire, and the three-phase power load can not need a neutral wire, as long as the equipment is well grounded, and the neutral wire in the system shall not be grounded except for the neutral point of the power supply; The zeroing protection system requires that no matter what the situation, the existence of the protection neutral must be ensured, and if necessary, the protection neutral and the zero protection line can be erected separately, and the protection neutral in the system must have multiple repeated grounding.

1) The so-called "zero connection protection" is to connect the metal structural parts insulated from the live part of the electrical equipment with wires and the zero line of the distribution system under normal circumstances. Zero connection protection is generally used in a system where the neutral point of the transformer is directly grounded with fuses and protection devices. This kind of three-phase four-wire system neutral point direct grounding power supply method is commonly used in our daily life.

After the electrical equipment adopts the "zero connection protection", when the insulation of the electrical equipment is damaged or the phase wire hits the shell, because the metal shell of the electrical equipment has been directly connected to the zero line in the low-voltage power grid, the fault current passes through the zero wire and the zero line of the distribution transformer to form a closed loop, and the shell fault becomes a single-phase short circuit, because the impedance of the metal wire is small, the short-circuit current increases instantaneously, which is enough to make the protection device or fuse act quickly (fuse) and cut off the power supply of the leakage equipment, even if the human body touches the shell of the electrical equipment ( Framework) will also not be electrocuted.

2) It is important to adopt the wiring method of zero protection in the neutral point direct grounding system. At present, in China's urban and rural areas, there are three main ways to install zero connection protection:

1) Three-phase four-wire power distribution mode. The advantage of this installation is that it saves money and does not need to set up a special zero protection line. After splitting the working zero wire from the entrance line, one of the wires is used as zero protection, and then connected to the grounding electrode of the socket or the shell of the electrical equipment.

It must be noted that fuses and switches are not allowed to be installed on the neutral line. Because, once the fuse body is blown or the neutral line is broken, the phase voltage will be transmitted to the metal shell through the electrical appliance, which not only does not play a protective role, but has the risk of electric shock.

2) Three-phase five-wire system or single-phase three-wire system power distribution mode. In this way, the protection neutral line is led out from the neutral point of the distribution transformer, laid separately, and separated from the grounding protection line. The long line should also add a repeat grounding device and communicate with the protection zero line.

Although the one-time investment is relatively large, the security is very high.

3) At the entrance point of the three-phase four-wire distribution line, it is changed to the three-phase five-wire system. This method is safer than the three-phase four-wire power distribution method. The installation method is to separate the working zero line and the protection zero line into the house, and install a duplicate grounding body on the protection zero line (some users do not do the grounding body in order to save money).

In fact, this method plays the dual role of working the zero line and protecting the zero line, and the disadvantage is that the zero trunk line must ensure that it has good conductivity and conductive continuity, and cannot be a series branch line. Otherwise, if the zero trunk line is broken, its repeated grounding becomes protective grounding, and the electrical equipment behind the line is still unsafe if other safety protection measures are not taken.

The protection of zero connection is to make the equipment leakage form a single-phase short circuit with the help of the zero connection line, promote the action of the protection device on the line, and cut off the power supply of the faulty equipment. In addition, in the case of a protected zero-connected grid, the protective neutral and repeated grounding also limit the voltage to ground when the equipment leaks. The protection zero connection is only suitable for low-voltage power grids where the neutral point is directly grounded.

The protection of the zero line is also the ground wire, that is, when one of the wires touches the object, so that the leakage protection switch can trip in time without injuring people, the so-called protection zero line.

The function of the protective zero connection is to reliably connect the metal shell of the electrical equipment with the zero line of the power grid to protect personal safety.

It is an electrical safety measure that connects the metal shell of electrical equipment with the neutral line of the power grid to protect personal safety. In the zero-connected power grid with a voltage of less than 1000 volts, if the electrical equipment is energized due to insulation damage or accidents, a single-phase short circuit of the phase wire to the neutral wire is formed.

The protective device (automatic switch or fuse) on the line acts quickly to cut off the power supply, so that the metal part of the equipment does not have a dangerous voltage for a long time, which ensures personal safety. In the multiphase AC power system, the neutral point of the winding connected by the star is directly grounded so that it is equal to the earth, that is, the zero potential.

Advantages of Protecting Zero:

If the electrical equipment is protected by means of protection zero, the short-circuit current (the current that breaks down the insulation of the electrical shell) is generally greater than.

As long as the action current of the protection device is selected and set scientifically and reasonably. If the single-phase short circuit is caused by insulation breakdown, and the short circuit current is relatively large.

In this case, the power supply can be quickly cut off by the protective device, thus avoiding the risk of electric shock to a certain extent.

To sum up, in the grounded power grid, compared with the protective grounding mode, the protective zeroing mode has more advantages in avoiding the risk of electrification and injury to the shell of electrical equipment.

The above content reference:Encyclopedia - Protection Zero.

If the insulation damage of the electrical equipment makes the shell live, because the resistance of the neutral line is very small, the short-circuit current is very large, which will make the protection switch action in the circuit or disconnect the protective fuse in the circuit and cut off the power supply, so that the shell is not charged at this time and avoid the danger of electric shock.

The three-phase four-wire system suitable for direct grounding at the neutral point is to connect the exposed conductive part of the electrical equipment that is usually not charged with the neutral wire of the power supply (the wire has a good electrical connection directly with the ground), and the protective zero connection must have at least two repeated grounding. The key to the effectiveness of the protection zero connection lies in whether the short-circuit protection device of the line can act sensitively and quickly cut off the power supply after the "shell" fault occurs.

In the same system, it is not possible to mix protective ground and protective zero. If combined, when one device fails, all zero-connected devices will have dangerous voltages in their housings.

Protectiveconnecttoneutral is an electrical safety measure that reliably connects the metal shell of electrical equipment with the neutral line of the power grid to protect personal safety. In the power grid, if the protection is carried out by neutral grounding, in this case, it is difficult to ensure that the human body is not harmed by electric shock due to the excessive current of the single relative to the ground.

If the electrical equipment is protected by means of protection zero, the short-circuit current (the current that breaks down the insulation of the electrical shell) is generally greater than that, as long as the action current of the protection device is scientifically and reasonably selected. If the single-phase short-air circuit is caused by insulation breakdown, and the short-circuit current is relatively large, in this case, the power supply can be quickly cut off by the protection device, so as to avoid the risk of electric shock to a certain extent.