Since 90 times, along with the progress of society industrialization level and national economy strength, our country put forward a development strategy of urbanization to establish. Because the original power lines inhibit the urban development and affect the urbanization construction. In recent years, Zhengzhou City has increased the continuous expansion and transformation of the urban journey, which begged for the original journey of the power equipment to change or cable people. From 2001 to 2004, Zhengzhou invested a total of 269.52 million yuan for the renovation of the old urban area connected overhead lines, and Zhengdong New District invested a total of 180 million yuan for the installation of connected cable network. These data indicate that there will be more and more cable networks in the future, and the animosity between land use issues and urban environmental planning will become increasingly prominent. Especially in the transformation of the old city, the narrow streets and alleyways can not provide satisfactory land for the establishment of switches, and the 10kV outdoor ring network cabinet and cable branch box, which occupy small air space and are easy to move, can play the function of branch, segment and liaison in the distribution node, and have been widely used.
1. Characteristics of ring network cabinet and cable branch box
(1)10kV outdoor ring network cabinet refers to SF: multiple circuit ring network power supply unit with insulation and SF arc extinguishing, referred to as ring network cabinet. Each ring network cabinet is composed of 3~6 switches and a common box. The wiring methods are varied, which can satisfy the needs of different distribution networks. Switch selection of three-phase linkage SF6 load switch or circuit breaker, its rated current is 630A, short-time withstand current up to 20kA(3s). Because of this special arrangement structure, the ring cabinet has the following characteristics: the load switch adopts the pneumatic structure, the arc extinguishing time is short, and the service life is long; The ground switch has an observation window with an obvious visible disconnect point; Outdoor, fully insulated, fully sealed structure, can accustome to any harsh environment; Small size and compact structure, small area, simple equipment, maintenance-free; No matter the load switch, circuit breaker, grounding switch, are three-phase linkage structure, effectively avoid the equipment phase work, easy to operate, safe and reliable; With electric and manual operation organization, distribution automation can be completed with FTU.
(2)10kV outdoor cable branch box is suitable for outdoor cable multi-branch connection. The cabinet body is made of stainless steel plate, which is used for safety and stability. Live body is fully sealed insulation structure, without insulation interval, reliable guarantee of personal safety; The main circuit current grade is 630A, branch current grade is 200A. The cable branch box is fully insulated, fully sealed, corrosion-resistant, maintenance-free, safe and reliable, small size, compact structure, simple equipment, convenient, flexible and so on. Due to the small size and advanced technical objectives of the ring network cabinet and cable branch box, they can play the effect of the traditional switch, and then reduce the land area and the length of the outgoing cable, and reduce the overall cost and maintenance costs, so they are widely used in the reconstruction of the old city line, the new development park and the residential district.
2. Cable ring network structure composed of ring network cabinet and cable branch box
2.1 Power Distribution network structure
The cable ring network structure formed by 10kV ring network cabinet is shown in Figure 1, and the structure of traditional switch is shown in Figure 2. The power distribution transformer set up on the overhead line pole has a small capacity (315kVA and below) and a large number of units. After the man-ground cable network is changed, it is bound by space and cannot choose all the boxes with the same capacity.
(1) Ring network cabinet with transformer (Figure 1 Central network Cabinet 2)
(2) Routing of ring network cabinet to terminal box (Figure 1 Central Network Cabinet 5)
Transformer capacity is generally 400~630kVA
2.2 Comparison analysis between the cable ring network structure composed of ring network cabinet and cable branch box and the traditional switch station
(1) As can be seen from Figure 1 and Figure 2, the normal method of the two power supplies supplies 3 ring network cabinets, and the number of outlet routes can reach 6~24 times, which is equivalent to two traditional switch stations (the outlet of one traditional switch is about 12 times). Two power supplies constitute a "hand in hand" ring network without satisfactory switch by the transfer load function, and the outgoing line into slack distribution, to each branch or the user of the cable length is greatly shortened.
(2) The cable method composed of the ring network cabinet is flexible, which can be connected to the ring network cabinet at any time according to the development needs of users, and can be flexibly connected to the power supply, satisfying the needs of multi-power chaotic distribution network in special areas. And the traditional switch by the establishment of planning binding, not easy to expand.
(3) As shown in FIG. 1 and FIG. 2, each section of the ring network cabinet controls 1-4 lines, and the probability of power failure is small; Switch station each section control 7 road, power outage probability; Together, due to the slack distribution of the ring network cabinet, the power failure area is small when the defect is found quickly, and the maintenance time is short, so the number of households is small when the power failure, and then the power supply reliability is greatly improved.
(4) The air volume of a traditional switch is about 84m2, which is impossible to supply such a large center during the reconstruction of the old city; Each ring network cabinet only accounts for about 3m2, and the cable branch box only accounts for about 1m2, and the ring network cabinet and branch box are more convenient for distribution and implementation because of the slack equipment.
(5) 1.2 million yuan is needed to set up a traditional switch with two power sources and two female modules; While one ring network cabinet is about 200,000 yuan, and one cable branch box is only 30,000 yuan, so the selection of ring network cabinet and cable branch box can greatly reduce the project cost.
(6) Urban line transformation should fully consider the elements of urban scene, such as cabinet type, color selection, etc. Ring network cabinet, branch box because of the appearance of various types, very beautiful, easy to integrate with the surrounding environment. To sum up the above six points, the selection of ring network cabinet and cable branch box in the man-ground transformation of power grid is the choice of aspiration.
2.3 Equipment Selection
(1) The equipment selection should consider the harmony of economy and reliability. For example, in 1999, when Zhengzhou was just connected to the overhead line man-land transformation, due to the immature technology of domestic ring network cabinet, all imported equipment was selected, and the total cost per kilometer man-land was up to about 6 million yuan. Because the current domestic ring network cabinet technology used to be sophisticated, it is recommended to choose domestic ring network cabinet, other relatively compact, small capacity of 10kV private households, can choose cable branch box for its power supply, so that the total cost of each kilometer of people and land is about 3.5 million yuan, can greatly save the investment.
(2) According to the land use situation and the number of users, it is appropriate to choose 3-6 routes of the ring network cabinet.
(3) Consider cooperating with distribution automation, choosing load switches instead of circuit breakers; Ring network cabinets with electric operating organization or PT should be equipped with distribution automation monitoring units or reserved ports.
3, the use of careful matters
(1) As the node of the cable line, the ring network cabinet has flexible wiring and easy operation. And the cable branch box can not be directly operated on each connection, only as the cable branch, so the branch box can not be used for the backbone network.
(2) Reserved loop for future development of users. Reserve the number of outgoing cables in the ring network cabinet and cable branch box. The new ring cabinet can also be connected by trunk cable II. Reserved loop must be sealed with insulation cap before operation.
(3) In the section that has not completed the distribution automation, a short-circuit defect indicator should be installed on the cable side to find the speed of the short-circuit defect section.
(4) The ring cabinet with explosion-proof holes should not be installed on the street to avoid injuring pedestrians in the event of an incident.
(5) When operating the ring cabinet, it is necessary to carefully check all kinds of indicating signals. For the pressure switch, it is found that the pressure lacks to obstruct the operation.
4. Summary
On the premise of reliable operation and economic consideration, it is suggested to choose domestic equipment in the man-ground transformation or new cable network project of urban overhead line. 10kV outdoor ring network cabinet, such as HXGN6 type SF. Ring Cabinet, HXGW--12/630 series SF. Ring network cabinet; The box can be pre-loaded, such as :YBMW- 12/0.4 series box; Cable branch box recommended to use silicone rubber as the main material cable joint flood prevention type, such as :DFW-12 series, there is a special break begged can choose with SF. Load switch broken cable branch box.
