1. Under normal circumstances, the neutral line of the three-phase four-wire system has no electricity.
The neutral line of the three-phase four-wire system has no electricity. . Single-phase household The neutral electricity wire is live. The three-phase, four-wire power supply has only three live wires and one neutral wire. This neutral wire is the combination of the neutral wire and the ground wire. This neutral wire is derived from the secondary neutral point of the transformer, and from the neutral wire. the secondary neutral point is connected to the secondary neutral point of the transformer. The ground is connected to zero potential and the three live wires form a loop, so under normal circumstances the neutral wire of the three-phase four-wire system has no potential. electricity.
Single-phase electricity commonly used in the home is a circuit consisting of a live wire and a neutral wire. There is also a third thread, which is a thread of twanders, which is a protective wire to avoid. electrical shock ; in this circuit we call the neutral line the working neutral line. The working neutral line is live, but we cannot measure it when using electrical measuring instruments. The reason is that one end of the neutral line is drawn from the. neutral point of the power supply and has an earth potential. The difference is zero.
2. Why is the neutral wire loaded?
1. We all know that there are three main types of wires, one is live wire, one is neutral wire, and the other is ground wire. In the circuit, since there is no voltage between the neutral line and the wire, it means there is no electricity. But if the neutral line is charged, it is because there is a break point in the neutral line. Voltage appears in this part of the circuit before disconnection, which will cause the neutral line to charge.
2.This may be due to poor contact in a certain section of the neutral line and a voltage problem. Once the contact is poor, the resistance will increase and the voltage will increase. With voltage, there will be current.
3. Another situation is that the neutral line is aging and long-term overload will cause damage, so it is very likely to cause electrification problems.
3. The neutral line is electrified in real life
1. There is an electrical leak from the electrical equipment on the line, but the protection device does not work, making the neutral line electrified. . Perform maintenance during a power outage, find leaking equipment to repair, and find out why the protective device is not working.
2. One phase on the line is grounded and the main protection device of the electrical network is not protected, leaving the neutral lineelectrified. After a power outage, first use a megger to measure the line to see if there is poor insulation in the line. When measuring, pay attention to disconnecting the instruments from the line.
3. The neutral line is broken and there is a leak in the electrical equipment behind the break or significant single-phase load operation, making the neutral line electrified. After a power outage, test if the neutral line is broken, and if it is broken, find it and repair it.
4. In the neutral power grid, some electrical equipment adopts protective grounding and leaks electricity, making the neutral line electrified. Distinguish whether the system is a zero-connected system or a grounded system, or whether repeated grounding is carried out in the zero-connected system. Then install the ground wire correctly.
5. In the neutral electrical network, there existse single-phase electrical equipment which adopts "one fire and one earth", that is, there is no functional neutral line, so the neutral line is loaded. When installing N wire, do not use PE wire as N wire.
6. The insulation resistance of some electrical equipment in the power grid was damaged and caused electricity leakage, making the neutral line electrified. Check equipment whose insulation resistance does not meet specified requirements. Make repairs.
7. The working ground connection on the low voltage side of the transformer has poor contact and high resistance. When the unbalanced current of the three-phase load exceeds the allowable range, the neutral line is electrified. . Bad contact is hard to find.
It must be inspected annually or as required. Don't be lazy and inspect it according to regulations.
8. The high voltage changes to low voltage, making the neutral line electrified. It's hard to find and sometimes big problems can arise. The hardest to deal with is the one that is dangerous for people. Be sure to operate in accordance with operating procedures.
9. The high voltage adopts two-wire, one-ground working mode. When the ground body is too close to the low voltage working ground or repeated ground body, the voltage drops to high voltage. -The high voltage working ground will affect the low voltage side working ground, causing the neutral line to be charged. Find the cause and proceed with installation according to the corresponding procedures.
10 The induction of the magnetic field causes the neutral line to charge.
11. Electrostatic induction causes the neutral line to charge.
12. Due to the voltage division effect of insulation resistance and earth capacitancee, the shell of the electrical equipment can be charged.
IV. Methods for dealing with live neutral lines
In order to ensure the safe use of electricity, when adopting zero connection protection measures in an earthed power network, a complete system zero connection must be in place. The complete protective zero connection system must meet the following safety requirements:
1. The earthing device in working order must be in good condition and comply with regulations.
2. The zero connection network and the repeated zero connection device must be intact and meet the specified requirements.
3. The single-phase short-circuit current must meet the action requirements of the protection device on the line.
4. The protection device is correctly selected and adjusted, and the action is sensitive and reliable.
What type of community needs a roompower distribution system
Do you want to know why network transformers cause packet loss? Possible reasons are:
1. The opening speed of the web page is extremely slow and sometimes some contents of the web page or the entire page cannot be displayed.
2. The transmission of data packets cannot be completed 100%. For various reasons, there will always be some loss.
3. The network is blocked while requesting data.
It is known that there is no live neutral wire at the output end of a single-phase generator or single-phase transformer. Grounding method must be used. on the ground.
At present, electrical distribution rooms in newly built communities are often located on the first floor or basement of the building. When installed on the first floor of a building, it conjust make sure that it is not located directly under toilets, bathrooms or other places where water often accumulates.
When the community electrical distribution room is located in the basement of a building
It should be noted that the elevation of the ground in the electrical distribution room is higher than the exterior ground level
p>
High
10 cm
to prevent exterior water from s infiltrate the electrical distribution room.
2.2.
When the community electrical distribution room is set up in the basement of the building, To facilitate the transport of equipment
or to set up the material in advance. Avoid having to dismantle and widen the electrical room door that was built before you can move the equipment to the end.
3.
Coordination reservation for civil construction
3.1.
During the construction process of the saThe distribution room, the foundations of the equipment of the distribution room is often affected. Failing to pay enough attention to them, such as transformers, generators and other equipment, directly placing the equipment on the ground without design drawings. During long-term operation of the equipment, due to its own vibration and other reasons, the ground will sink
or the ground will not be leveled, causing irregular vibration of the equipment.
p>This will greatly affect the performance of the equipment life.
3.2.
During the construction of the electrical distribution room, no incoming cable conduit was reserved or no spare conduit was embedded during construction . The pipes must be drilled manually after the power plant. is built. This not only increases the construction workload, but also makes the parts newement drilled areas subject to water infiltration.
4.
Power distribution room grounding system
4.1.
Grounding Ground of power distribution room equipment can be shared with lightning protection grounding system. The grounding body is
called common grounding
p>
, but the grounding resistance should not be greater than
1Ω
< p> at this time. The so-called common grounding refers to the sharing of grounding devices (horizontal and vertical underground grounding bodies), but the grounding sourceis< /p>
"< /p >
Common ground but not common lines
”
It is best not to share the ground bar, but it can be reconnected in the earth network
for protection Use the earth wire alone
4.2.
If earthing the equipment in the talk roomelectrical distribution is separated from the lightning protection earthing system,
the distance between the two earthing systems
It must not be less than < /p>
20m
The neutral wire of electrical equipment cannot be directly grounded, because you cannot guarantee that the live and neutral wires have no been exchanged during the feeding process. Electrical devices used to switch live and neutral wires can operate normally. However, if someone swaps the live and neutral wires after the neutral wire of the electrical appliance is grounded, the live wire will be grounded.