What is the difference between zero sequence protection and grounding protection?

First, the nature is different.

1. Zero-sequence protection.

is in large short-circuit currents.

When a ground fault occurs in the grounding system, there is zero sequence current, zero sequence voltage, and zero sequence power. These electrical quantities are used to form a protective ground.

Relay protection devices for short circuits are collectively referred to.

2. Grounding protection: It will not be charged under normal circumstances, but in the insulating material.

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, and the grounding body is reliably connected with the wire.

Second, the amount of electrical used is different.

1. Zero-sequence protection: Zero-sequence protection uses the zero-sequence current component generated when the ground fault occurs.

2. Grounding protection: Grounding distance protection is to use the ratio of short-circuit voltage and current, that is, the change of measurement impedance to distinguish the fault of the system from the normal operation state.

Grounding protection uses the ratio of short-circuit voltage to current, that is, the change in measured impedance, to distinguish the fault of the system from the normal operating state. Zero-sequence protection utilizes the zero-sequence current generated in the event of a ground fault. When the three-phase current is balanced, there is no zero-sequence current, and when it is unbalanced, a zero-sequence current is generated.

The sensitivity of the ground distance protection is higher than that of the zero sequence current protection (as you can see, the distance protection uses two electrical quantities in the event of a short circuit, which is naturally more sensitive than a single current protection). Therefore, in terms of protection, the general distance protection is used as the main protection, and the current protection is used as a backup protection, that is, when the first road fails, the first distance protection action is taken, and the zero sequence protection is used as a backup possible action.

The difference between protective grounding and protective zeroing is as follows:

1. The line structure is different.

If protective grounding measures are taken, there can be no working zero line in the power grid, and only a protective grounding line can be set; If protective zero connection measures are taken, a working zero line must be set up, and the working zero line must be used for zero connection protection. The protective neutral wire should not be connected to the switch and fuse, and when the fuse and other interrupting appliances are installed on the working neutral line, the protective grounding wire or neutral wire must also be installed.

2. The scope of application is different.

Protective grounding is suitable for high and low voltage power grids that are generally not grounded, and also suitable for low-voltage power grids that have taken other safety measures (such as installing leakage protectors); The protection zero connection is only suitable for low-voltage power grids where the neutral point is directly grounded.

3. The principle of protection is different.

Protective grounding is to limit the voltage to the ground after the leakage of the equipment so that it does not exceed the safe range. In high-voltage systems, in addition to limiting the voltage to ground, protective grounding also has the effect of promoting the operation of the grid protection device in some cases.

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.

Precautions for protecting zero

1) In the electrical system of the protection zero connection. The neutral line plays a vital role. Once the neutral line is disconnected, the electrical equipment connected to a section of the line behind the broken line is equivalent to no protection zero and protective grounding, if there is leakage of the electrical equipment shell behind the zero line break, it does not constitute a short circuit circuit, and the melt is blown off.

Not only is the housing of the equipment equipped with voltage, but the housing of all equipment behind the disconnection has a voltage to ground close to the power supply phase voltage, and the risk of electric shock will be expanded.

2) In the three-phase four-wire distribution system where the neutral point is not grounded, it is not allowed to use protection to zero, but only to use protection grounding. If any phase in the system is grounded, the whole system is still running as usual, but if the ground and the grounding wire are equipotential, the voltage drop of the electrical equipment shell connected to the neutral line is equal to the voltage value of the phase wire connected to the neutral point from the grounding point to the neutral point, which is very dangerous.

1. The principle is different.

Protective grounding is the grounding carried out to prevent the metal shell of the electrical installation, the frame of the power distribution device and the line tower from being charged to endanger the safety of people and equipment.

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.

2. 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 protection zero connection requires that no matter what the situation, the existence of the protection neutral wire must be ensured, and if necessary, the protection neutral wire and the zero protection line can be erected separately, and the protection neutral wire in the system must have multiple repeated grounding.

3. The scope of application is different

Household appliances do not use grounding protection, when a part of the insulation is damaged or a certain phase wire touches the shell, the shell of the household appliance will be electrified, and the human body will have the risk of electric shock if it touches the insulation damaged electrical equipment shell (frame).

The protection zero connection is suitable for the equipment leakage with the help of the zero connection line to form a single-phase short circuit, promote the action of the protection device on the line, and cut off the power supply of the faulty equipment.

Reference Encyclopedia - Protecting Zero"> Encyclopedia - Protection Zero.

Reference Encyclopedia - Protective Grounding"> Encyclopedia - Protective Grounding.

Protective grounding: the conductor part or shell of electrical equipment is reliably connected with the earth with a metal wire or conductor of sufficient capacity, when the human body touches the live shell, the human body is equivalent to a parallel branch of the grounding resistance, because the human body resistance is much greater than the grounding resistance, so the current through the human body will be very small, avoiding the personal electric shock accident.

Protective zero connection: Under normal circumstances, the metal part of the electrical equipment that is not charged is well connected with the neutral wire with metal or conductor. When a phase insulation is damaged and the phase wire of the power supply touches the shell, and the shell and conductor part of the electrical equipment are electrified, because the shell and the conductor part take the zero connection measure, the phase wire and the neutral wire constitute a loop.

Due to the large single-phase short-circuit current, the fuse of the line protection is blown out. As a result, the equipment is disconnected from the power supply, avoiding the possibility of personal electric shock injury.

The principle is different: protective grounding is to limit the voltage to the ground after the leakage of the equipment so that it does not exceed the safe range. The protection 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.

The scope of application is different: protective grounding is suitable for ungrounded high and low voltage power grids. Protective zeroing is suitable for low-voltage power grids where the neutral point is directly grounded.

The line structure is different: protective grounding measures are taken, and there can be no working zero line in the power grid, only a protective grounding line. To protect the zero connection measures, it is necessary to set up a working zero line.

1. The principle is different: protective grounding is to limit the voltage to the ground after the leakage of the equipment, so that it does not exceed the safety range. In the high-voltage system, in addition to limiting the voltage to the ground, the protective grounding also has the effect of promoting the action of the power grid protection device.

The protection 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 a protected zero-connected grid, the protective neutral and repeated grounding also limit the voltage to ground when the equipment leaks.

2. The scope of application is different: protective grounding is applicable to the high and low voltage power grid that is not grounded, and it is also suitable for the low voltage power grid that takes other safety measures (such as installing leakage protectors). The protection zero connection is only suitable for low-voltage power grids where the neutral point is directly grounded.

3. The line structure is different: take protective grounding measures, and there can be no working zero line in the power grid, and only a protective grounding line is set. To take protective zero connection measures, it is necessary to set up a working zero line and use the working zero line for zero connection protection.

The protective neutral wire should not be connected to the switch and fuse, and when the fuse and other breaking appliances are installed on the working neutral line, the protective grounding wire or neutral wire must be installed separately.

The difference between protective grounding and protective zeroing is as follows:

1. The definitions are different.

Protective zero connection: connect the metal parts of the electrical equipment that are not charged to the neutral wire.

Protective Grounding: Connecting the metal shell of electrical equipment with wires and/or grounding conductors and earth.

2. The principle of protection is different.

Protection zero: After the electrical equipment leaks, a single-phase short circuit will be formed with the neutral line, which will cause the protection equipment on the voltage network to trip and cut off the power supply.

Protective grounding: It refers to limiting the voltage to the ground after the electrical equipment leaks electricity to keep it within a safe range. In some cases, it will also cause the circuit breaker to act and cut off the power supply.

3. The scope of application is different

Protective zero: suitable for use in low-voltage power grids with direct grounding.

Protective grounding: It is used in high- and low-voltage power grids that are not directly grounded, or low-voltage power grids that are installed with safety measures such as leakage protection.

4. The line structure is different.

Protective zero: There must be a working neutral line, because it uses the neutral line as a protective measure.

Protective grounding: There can be no working neutral line, and the ground wire should be grounded.

What to pay attention to when protecting the zero

1. When the voltage network is connected to zero, we need to pay attention to the fact that the zero line of the electrical protection equipment should be connected in parallel, and cannot be connected in series. If the electrical equipment and the neutral line are connected in series, then once the neutral line is disconnected, the electrical equipment behind the neutral wire disconnection will not be protected to zero. When doing zero protection, the zero line should be installed firmly and reliably, and the terminal bolts should be tightened.

2. In the non-grounded power distribution system, it can not be connected to zero with protection, but only with grounding protection, otherwise there will be potential safety hazards. In the zero system, it can also be done with work grounding or repeated grounding. For example, we can follow the zero line and repeatedly connect the zero line to the ground, which can reduce the low voltage to the ground and reduce the risk of electric shock.