On the electrical side, the electrical side of the problem

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 principles of protection are 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, and 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 to promote the rapid action of the protection device on the line with the help of the zero connection line, so that when the equipment hits the shell after the insulation is damaged to form a single-phase metal short circuit. 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.

The TT system is usually suitable for rural public low-voltage power grids, and the system belongs to the grounding protection mode in protective grounding; TN system (TN system can be divided into TN-C, TN-C-S, TN-S three-kind) is mainly suitable for urban public low-voltage power network and special low-voltage power network 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, three-phase four-wire 380 220V power distribution, which supplies power to lighting loads and power loads at the same time.

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.

Therefore, AB is right, the neutral point is directly grounded in the system, the grounding current is of course very large, and the TT system is very small in the grounding due to the impedance grounding, and the two are not contradictory.

Both are right, the two protection methods said, in relay protection, one uses quick breaking, and the other is delay protection.

Summary. In circuit design, the magnetic coil is energized to generate a magnetic field, and when the coil to be held is close to the magnetic field, it will be attracted by the magnetic field and approach, and it will remain in this state after reaching dynamic equilibrium. When the coil is de-energized, it relies on the elastic force of the spring to maintain the position of the coil.

This kind of circuit switch that is controlled by electromagnetic principles is called a relay. The purpose of the relay with two p is to control the two contacts separately. For example, when the current reaches a certain value, the contact will be turned on, the normally open contact will be closed, and the normally closed contact will be disconnected; When the current decreases to a certain value, the contact is opened, the normally open contact is closed, and the normally closed contact is opened.

In this way, when the coil is energized, the relay will have a state of being turned on, and the normally open contact is closed; When the coil is de-energized, the relay will have a state of disconnection, and the normally closed contact will be disconnected. Therefore, the purpose of the relay connecting two p is to control the two contacts separately, so that they can be in the state of power on and off at the same time, so as to realize the role of switch.

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An electrical problem is a problem that involves an electrical circuit or electronic slip device. Electrical faults can be caused by a variety of causes, including environmental factors, aging equipment, overloads, and short circuits. We hope you find the above helpful. Thank you!

Why can't this be connected to the PLC signal point, I skip the relay and directly contact the X point, what are the causes of the PLC can light up normally.

Dear, please output in the form of text, I can better answer for you, ** is only one-sided, can not fully answer for you.

Why do relays need to connect two P24V, pro, in the circuit design, the electromagnetic coil is energized to generate a magnetic field, when the coil to be held is close to the magnetic field, it will be attracted by the magnetic field and approach, and it will remain in this state after reaching dynamic equilibrium. When the coil is de-energized, it relies on the elastic force of the spring to maintain the position of the coil. This kind of circuit switch that is controlled by electromagnetic principles is called a relay.

The purpose of the relay with two p is to control the two contacts separately. For example, when the current reaches a certain value, the contact will be turned on, the normally open contact will be closed, and the normally closed contact will be disconnected; When the current decreases to a certain value, the contact is opened, the normally open contact is closed, and the normally closed contact is opened. In this way, when the coil is energized, the relay infiltration will have a state of on, and the normally open contact will be closed; When the coil is de-energized, the relay will have a state of disconnection, and the normally closed contact will be disconnected.

Therefore, the purpose of connecting the two P's of the relay is to control the two contacts of the nuclear world respectively, so that they can be in the state of power-on and power-off at the same time, so as to realize the role of switch.

Knowledge of phase wire, neutral wire, and grounding wire.

For household electricity, the standard single-phase user has three wires, phase wire, neutral wire and ground wire, neutral wire and phase wire of the same cross-section, and the grounding wire is square millimeter, double color. The protection of household electricity is completed by the wiring of the socket plug, and the wiring principle of the plug and socket is: the left zero and the right phase are grounded.

It is the plug-in connection between the shell and the plug of the household appliance, the plug-in connection between the grounding wire and the socket from the outside, and the reliable connection between the shell of the household appliance and the earth to realize the safety protection of electricity.

Ground and neutral wires cannot be mixed:

1. The neutral wire of the neutral line and the transformer is directly connected, and the live wire directly forms a loop, without voltage drop loss;

2. The grounding resistance of the neutral line and the neutral wire is very high, the grounding resistance of the transformer below 100kva cannot be higher than 10 ohms, and the grounding resistance of the transformer above 100kva cannot be higher than 4 ohms;

3. The grounding wire is connected with the neutral line and the neutral wire at the transformer, and it will be independent in the future, and the grounding will be repeated to the distribution box, but the grounding resistance is only 30 ohms or less.

4. The cross-sectional area of the neutral wire and the live wire are the same, and the same current should be passed, while the ground wire is generally a square millimeter, and a larger current cannot be passed, so the grounding wire cannot be used as the neutral line;

5. Users who do not have a grounding wire, household appliances are not grounded, and they can't get the grounding wire by themselves (if they are unqualified, the harm is greater), and they can't use the zero wire as the grounding wire (when the three-phase current is unbalanced, the zero line is live, and the shell of the household appliance is also pointed, and the shell of the household appliance is directly connected to the thermal power when the zero line is broken, which is more dangerous.) ), which will affect the normal operation of the power system.

6. Users who do not have a grounding wire can install a leakage protector to protect.

If the neutral wire is removed and replaced with a ground wire, then the current path will not pass through the neutral wire and become a loop, which is not possible. Reason - the existing household switchboard or the place where the home is installed with leakage-proof contact air switch, the principle of the air switch is to detect whether the current in the same group of live wire and the zero line is equal, if not, it means that there is leakage in the circuit (if the person is electrocuted to the ground, or the electrocution to other circuits is equivalent to leakage), the air switch will automatically trip, but if the person is invalid for the electric shock between the live wire and the zero line of this group, so you can not use this socket at all, as long as you plug in the electrical equipment, The current will be left over the ground wire and the switch will trip.

The zero line forms a loop with the live wire, and the other point of the live wire is connected to the terrain and does not form a loop, and the electrical appliances cannot work normally.

This is not allowed. Reason - the existing household switchboard or the place where the home is installed with leakage-proof contact air switch, the principle of the air switch is to detect whether the current in the same group of live wire and the zero line is equal, if not, it means that there is leakage in the circuit (if the person is electrocuted to the ground, or the electrocution to other circuits is equivalent to leakage), the air switch will automatically trip, but if the person is invalid for the electric shock between the live wire and the zero line of this group, so you can not use this socket at all, as long as you plug in the electrical equipment, The current will be left over the ground wire and the switch will trip.

If you are not afraid of electric shock, you can do this, and the zero wire and the ground wire must be distinguished!! The neutral line is connected to the load is the live line voltage.

Appliances work properly, but they are not safe.

In this way, the grounding safety can be relied on, and all components are connected separately with the grounding copper bar, which is not affected by other wiring.

First of all, the wiring should be identified in strict accordance with the process, and the line should be divided into two steps: non-hail wheel energized line and energized line.

Step 1. There is no power to check the line.

Put the circuit breaker, fuse, switch, etc. in the breaking position, and do not plug the components with sockets into the socket first (ensure that the judgment of the line is not affected by these devices);

Then check the conduction of all wires with a multimeter against the wiring table.

Step 2. Power on the line.

Install all components with sockets on the source scramble, and then connect to the power supply;

First of all, check whether the power supply of the strong current part is normal, check each power supply branch in order (close the circuit breaker fuse and other components in turn), do not close all the circuit breaker fuses before powering on, so as to reduce the loss caused by wiring errors, and also facilitate the judgment of the cause of the failure;

Then, the relevant operating elements are operated to check the operation and output signals of the corresponding components.

The specification requires that the ground wire of each electrical control cabinet is strictly forbidden to be connected in series with the dust, and the lead wire must be connected with the ground wire in order to be reliable; The wiring of all components in the more complex electrical control cabinet is the line number, and the line should be checked according to the drawing line number compared to the component wiring number in the electrical control cabinet during maintenance.

Each grounding wire is connected to the grounding bronze medal separately to be more reliable; After placing and connecting the wire, it is required to be marked

After the motor is energized, it is called the start of the motor from stationary to reaching the rated speed! The motor turns when it is energized, hehe.

The contactor is actually a relay with a relatively large contact capacity, which is just given a name. It is a switch that replaces human labor with electromagnetic force. It is composed of a contact group and an electromagnet, when the core coil of the electromagnet is energized, the moving core drives the moving contact movement of the switch, so that the static contact of the switch is closed or opened, and it is as simple as that.

Hehe, you understand this explanation?

Oh, if it's too basic, you still have to read the book yourself, and if it's not easy to look up the book, ask others.

Judging from the wiring diagram, the main circuit does not seem to be the wiring of S-D, please check carefully, about the problem of LZ, or check the relevant books, I believe it can be solved.

Symmetrical three-phase circuit power expression:

p=√3uicosφ

where you and i are line voltage and line current, respectively. cos is the power factor of the load.

In this question, the star load line voltage is 220V, the line voltage is 380V, the current is 220 22=10A, cos = Cos60°=, and the power expression is substituted:

p = load impedance is 22 60 °, which means that the load impedance is 22 and the radial angle (power factor angle) is 60 degrees.