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Application of overhead insulated conductors in distribution networks

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Application of overhead insulated conductors in distribution networks

作者: Release Date: 2018-07-21 Author: Click:

As an important part of power fragmentation, the distribution network is responsible for the normal and safe distribution of electrical energy to users. With the increase of power demand, the lines are increasingly dense, and overhead wires are the main. Bare wires are relatively rare, but as the power distribution network becomes more and more complex, lightning strikes or short circuits can easily occur, hindering the operation of power distribution tasks and even causing serious safety accidents. For this reason, a layer of insulation is wrapped in the outer layer of the overhead wire, that is, the insulated wire, which is quite common in the future.

1 overhead insulated wire and its disadvantages

There are two types of transmission and distribution lines: overhead lines and cables. The outer layer of ordinary overhead bare conductors is covered with an insulating sheath, which is an overhead insulated conductor, which is an important way for future distribution network lines. It is suitable for densely populated areas, severely contaminated by salt fog, lush trees, and narrow corridors. Compared with cables, overhead insulated wires do not need to be excavated, so erection is easier, construction is faster, and investment is relatively low. Compared with overhead bare conductors, overhead insulated conductors have better insulation functions and safer power distribution. The insulation layer is not easy to be oxidized, which can extend its service life. The interval between lines has been increased, which is beneficial to the same The improvement of the number of pole circuit loops has greatly reduced the rate of short-circuits between phases; the high voltage can deepen the load center, which is conducive to the improvement of voltage quality; the improvement of the safety function has extended its maintenance cycle, and it can reduce the line corridor; it has a higher machine Strength and good resistance to corrosion.

2 Specifications and use of overhead insulated conductors

According to the information, there are two types of insulation layers wrapped on the outer surface of the wire: light polyethylene and cross-linked polyethylene. The latter is more disadvantageous in terms of insulation function. According to the thickness of the insulation layer, it can be divided into two types: thin insulation, When erected, there should not be too much or too long contact with the trees; the second is thick insulation, which can have long contact with the trees.

Scope of application

(1) Bare conductors are prone to lightning and are short-circuited in lightning-prone areas. Insulated conductors can provide good insulation due to the insulation layer, reduce line lightning, and increase the incidence of accidents. Corresponding shutdowns have also increased significantly.

(2) Cities with more trees are also paying attention to environmental protection while setting up lines, so the number of trees is increasing. When these bare conductors are erected in the center, they will conflict with greening and environmental protection, and overhead insulated conductors can alleviate this contradiction. While improving Ping An Power Distribution, it is also more favorable to the city appearance and environment.

(3) Salt fog area Salt fog is very corrosive, which will weaken the tensile strength of the bare wire, cause it to break and short circuit. Insulated wires can have better corrosion resistance and delay the aging of the line.

(4) In the old urban area, the insulated wire can accept a voltage of 15KV, and it should maintain a distance of at most 0.75m from the building to the extent or vertical. Therefore, the use of 10KV overhead insulated conductors instead of high-voltage branch lines and indirect feeding into the load center can extend the power supply radius of the high-voltage grid, which is very suitable for the reconstruction of old urban areas.

3 Practical use of overhead insulated conductors in distribution networks

The distribution network of a city is mainly responsible for the power transmission and distribution tasks in the eastern part of the city. Some of the lines are bare overhead conductors. In the daily power distribution operation, it is easy to be affected by the external environment. Especially during thunderstorm weather, the line is extremely vulnerable to lightning strikes, which can cause large-scale power outages and make power distribution tasks fail to complete normally. With the increase of population, the power consumption is getting larger and larger. For this reason, relevant departments have stopped introspecting and updating the lines and replaced them with overhead insulated wires.

Preliminary task

When stopping the erection planning and design, the urban planning should be taken as the foundation, as far as possible to coordinate with it; the use of aluminum alloy core, the minimum cross section of the main branch and branch lines are identified as 240mm2, 70mm2; considering the poor heat dissipation of the insulated conductors, Relatively weak, so choose a larger wire, use the stress of 40N / mm; the gap is 42.5m, the degree of display is selected, the phase spacing is set to 0.8m; the tensile length is controlled within 1Km; the wire and equipment The insulation cover is installed at the joint, which has good insulation and tightness; a power failure task contact point is provided on the conductor of the branch point which can reverse power transmission.

Data selection

On the basis of the national rules, select suitable insulated conductors based on the distribution voltage and configure the relevant information completely; the project uses a compact erection method, so the suspension rods are used for the linear rods, and the insulated conductors are Insulation rods and endurance tension clamps.

Detailed construction

The erection tasks are carried out under normal weather, and the construction should be stopped as much as possible in the dry season or in humid weather. The insulation function of the insulated wire is very important, which indirectly affects the safe fluctuation of power distribution. Before and after construction, the insulation resistance should be stopped and tested to ensure that the insulation layer is not damaged. Do not prolong the insulated wire during the laying process. If the damage level of the insulation layer exceeds 10% of its own, it must be repaired or replaced immediately. When the insulated wires are connected, stop the winding scene, and you can continue the pipe connection, and the connection must not stop within the span; if the situation is special, within a span, each conductor must not exceed one socket. At most, the joint should be separated from the fixed point of the wire by 0.5m. If the specifications and data are different, the insulated wire must not be connected within the span. After the connection, it is necessary to stop the insulation treatment in time, stop the sealing of the ends and the connectors, and prevent the exposure of the wires and connectors.

If the fiber core is damaged, the damaged cross-sectional area is less than 17% of the conductive part, and the wire can be repaired. The length of the applied wire should be longer than the damaged part, and the winding length of each end exceeds the damaged part by up to 100mm. 6%, and the damage depth is within 1/3 of the diameter of the single-stranded wire. A single-stranded wire of the same metal is used to wound around the damage, and the winding length exceeds 30mm at each end of the damage.

4 Lightning protection measures for overhead insulated conductors

Although overhead insulated wires have many disadvantages, there are still some shortcomings in practice. It is very rare that the lines are disconnected after being struck by lightning. Overvoltage includes two types: direct lightning strike and induced lightning overvoltage. The latter is a secondary cause of problems with insulated wires. After being struck by lightning, the insulation layer will be moved by the arc to form a barrier, so that the speed of the arc movement is slowed down, and the power frequency arc is concentrated at the damage point of the insulation layer. Once the insulation layer is damaged, it is easy to present phase-to-phase short circuit. For this reason, it is necessary to do a lightning protection task. A line lightning arrester can be installed to release the lightning current to the sky to increase the damage to the insulated conductors; a lightning protection device is installed; a adjustable maintenance gap is installed; a 10KV line overvoltage maintenance device is installed to avoid The basic method of a lightning strike disconnection is to cut off the power frequency freewheel in time. In order to improve the reliability of the overvoltage maintainer, a structure with an external series gap and a lightning arrester can be used, and a group of base pole towers must be installed.

Overhead lines are the basic equipment for power distribution, and they serve as the transmission and distribution of electrical energy, which is of great significance. However, affected by many factors, overhead lines are easily corroded and damaged, resulting in reduced functionality. The overhead insulated wire has strong corrosion resistance, which is conducive to the safe distribution of electrical energy. Considering that the insulated wire is greatly affected by lightning, it is necessary to do a lightning protection task when setting up.


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Keywords: overhead insulated conductor

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