Factors and Measures to Be Considered in Overhead Insulated Wires
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With the improvement of living standards, people on the power quality, especially for the reliability of a higher demand. Improve the power capacity of the corridor area to reduce the area of the corridor of the corridor, in order to save the line investment; application of new technologies to improve the reliability of equipment to adapt to the new changes in the development of power systems, power planning and design is facing a new topic.
1 path with rod type
Urban limited corridors rarely use separate loops, while double or multiple loops on both sides of the center line require equal half corridor width. Therefore, the overhead line selection along the road, river canal, green belt set up, by road, green side of the semi-corridor can be free to use, but also easy to agree with the views of the urban planning department. In some cases, the use of unilateral three-phase vertical arrangement of the rod, although only set up a line, but compared with the cable line, the benefits are very impressive.
Narrow path corridors, to promote the emergence of steel pipe, it is technically able to meet the requirements of transmission lines, such as price and angle steel tower, its application will be more extensive. Steel pipe rod is not only beautiful shape, fast installation, covers an area of ?? province, in line with the modern urban environment on the overhead line of high demand, but also with the city terrain is relatively flat, the width of the corridor is small, line construction is not convenient and so on. Since the 1990s, the domestic steel pipe rod manufacturers continue to emerge, the material from the thin-walled centrifugal concrete pipe rod to the pure steel pipe rod, the appearance from the conical to the polygon, the connection from the welding, flange connection to the plug, Hot galvanized, the manufacturing process is also increasingly reliable to the quality, beautiful, convenient direction. Recently, by the Northeast Electric Power Design Institute editor of the "transmission line steel pipe design technical requirements (draft)" has been delivered as a power industry standard discussion. In the future, the steel pipe rod will become the main rod type of the city's overhead transmission line.
The SDJ3-79 Overhead Transmission Line Design Technical Regulations stipulate that the minimum horizontal distance from the outer edge of the tower to the edge of the roadbed is 5-6 m in the restricted area, but it is practically difficult to implement because the line centerline is often arranged on the road Green belt, and even the edge of the sidewalk, and the edge of the fast lane distance of less than 5m. To this end, in the corner of the steel legs or steel pipe on the side of the fast lane buried pipe pier (diameter 0.1m, high 1m), to reduce the damage caused by car collision.
2 Insulation wire safety factor
According to the "overhead insulated distribution line design technical specification" design wind speed 25m / s, the design safety factor of the wire should not be less than 3, the city network in the low-voltage line spacing is generally not more than 50m. Taking into account the use of large wire cross-section in the city network, the wire safety factor is very important for the economic cost of the project, the safety of operation and maintenance and the disconnection caused by stress concentration.
3 Insulated wire lightning protection
The 20th century, the early 60s, insulated wire in France, Japan, Australia and other countries began to use, has more than 40 years of experience. According to the relevant information, Japan in the early 90s of the last century has been replaced by overhead wire twisted all insulated wire, line lightning strikes increased. Lightning flashover occurs between two or three phases, the frequency current is often concentrated in the insulation of the breakdown point, so that the insulation conductor in the circuit breaker before the trip. Overhead insulated wire in the event of vibration and lightning susceptible to damage, the damage occurred in the pole part of the pole on the fixed line, from the poles 200-500mm. City network insulation line lightning protection, the general use of the installation of lightning arrester method, according to domestic information, that in the minefield, each should be installed every 360m arrester.
The famous Japanese lightning protection experts Yokoyama Mao that every interval of every 200m installed lightning arrester. The choice of resistance to gold, the occurrence of disconnection has a certain impact. Insulated wire resistant sheet gold with stripping clip and no peeling clip two. Jiujiang Power Supply Bureau is mainly used in Hongdu production of wedge self-locking stripping clip. The first reason to use this clip is to consider the issue of wire breakage caused by lightning protection and stress concentration. Not peeled off the clip, the resistance of the mouth for the hard plastic two wedge-shaped splint, the edge of the insulation at the edge of the wire, due to the resulting grip to the insulation layer creep damage, coupled with its structure has a parallel sharp angle will produce induction Overvoltage, causing lightning strikes. When the wire near the ground or the trees are struck by lightning when the counterattack voltage will be counterattack on the wire, do not peel the wire clip and the wire is insulated, insulated wire to withstand high residual pressure and break the wire, peeled off the clip to bear the residual pressure It is by the tension with a clip itself to bear, in the straight line with the installation of the interval with the lightning arrester or install the long flash lightning arrester is the same reason. This is the second reason. The third reason is that we have been tested on the stripping of the tension-resistant clip and do not peel the tension clamp, insulation 240mm2 without steel wire wire, and gradually increase the tension, stripping resistance-resistant clip has no cramps, Until the tensile force of more than 3.5t, the wire is destroyed; and not stripping resistant wire clip, pull up to 1.7t, the insulating skin and aluminum core separation, cramping phenomenon. This shows that the stripping resistance to the line clamp for Zhang, when the traction force in the case, always maintain a tight state, than the non-peeling of the tension clamp is much better. In the operation, due to the tightening of the actual force when the tight line, when the use of non-peeling clip, caused by the insulation creep, prone to disconnection.
The contradiction between overhead lines and corridors is the inevitable development of the city. In the design of urban overhead lines, the range of consideration and the complicated situation of the scene are different from the overhead lines of the past. Planning, designers to meet the reliability requirements of the conditions, to find ways to control the overhead range of action, full restrictions on the width of the corridor to dig the potential of the corridor.
 Lin Jian. Design of urban overhead transmission lines [J]. Fujian Electric Power and Electrician, 1999, (02).
 Miao Shengzhi. On the design requirements and material quality of overhead lines [J]. Rural Electric Power, 1995, (08).
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