A 35kV lightning protection insulator cross arm and its production method

Abstract

A 35kV lightning protection insulator cross arm, comprising a cross arm body and two metal encapsulation parts; the cross arm body is made of fiberglass, the cross arm body is in a rectangular tubular shape, and two holes are evenly distributed along the axial direction on both the front side wall and the rear side wall of the cross arm body. The two metal encapsulation parts are respectively sleeved and fixed at both ends of the cross arm body, and the upper surface of the metal encapsulation part is upturned by a certain angle relative to the upper side wall of the cross arm body. A production method of the 35kV lightning protection insulator cross arm is also provided. The present invention replaces the traditional iron cross arm, uses the cross arm body made of fiberglass to enhance the insulation function of the insulator, and the metal encapsulation parts upturned at both ends meet the upwarping requirements for insulator installation. It has the characteristics of excellent insulation performance, high pollution resistance level, convenient live working, simple construction and maintenance, reduces the operation and maintenance workload of the overhead line, and improves the reliability of the operation of the overhead insulated line.

Description

Technical Field

[0001] The invention belongs to the technical field of fixed buildings, relates to overhead line facilities, and particularly relates to a 35 kV lightning protection insulator cross arm. Background Art

[0002] At present, the insulator cross arms widely used on 35 kV lines are made of iron materials. Due to the conductivity of the iron materials, all the insulators on the iron cross arms will bear the lightning voltage or overvoltage, and insulator flashover accidents are extremely likely to occur. Therefore, the lightning trip rate of 35 kV overhead lines occurs from time to time. With the improvement of power supply reliability, live working is increasing, and the conductivity of the iron cross arm brings difficulties to live working. When carrying out live working, it is necessary to first shield the iron cross arm with insulating covers, which not only increases the workload, but also does not meet the requirements of live working regulations during the installation of the covers. In recent years, with the gradual improvement of the ecological environment, the number of 35 kV overhead line external force damage accidents caused by short circuits between the iron cross arm and the overhead line due to small animals climbing the poles has increased. Due to the ferromagnetic properties of the traditional iron cross arm, there are eddy current losses and hysteresis losses in the overhead line during operation. With the introduction of the national energy conservation and emission reduction policy, new requirements for reducing line losses have also been put forward. Summary of the Invention

[0003] The invention aims at the above problems and provides a 35 kV lightning protection insulator cross arm and its production method, which are used to replace the traditional iron cross arm to strengthen the insulation function of the insulator, and have remarkable effects in reducing the lightning trip rate of the overhead line, reducing external force damage and reducing energy consumption (no iron loss).

[0004] The object of the invention can be achieved by the following technical solutions: A 35 kV lightning protection insulator cross arm includes a cross arm body and two metal encapsulation parts; the cross arm body is made of fiberglass, the cross arm body is in a rectangular tubular shape, and two holes are evenly distributed along the axial direction on the front side wall and the rear side wall of the cross arm body. The two metal encapsulation parts are respectively sleeved and fixed at both ends of the cross arm body, and the upper surface of the metal encapsulation part is tilted upward at a certain angle relative to the upper side wall of the cross arm body.

[0005] Further, the holes are round holes, oval holes or waist-shaped holes.

[0006] Further, the material of the cross arm body is epoxy fiberglass.

[0007] A production method of a 35 kV lightning protection insulator cross arm includes the following steps:

[0008] (1) The glass fiber reinforced material is led out from the rack, gathered into a bundle through a guide plate, and soaked with solvent-free epoxy resin through a glue tank;

[0009] (2) Enter the preforming die, remove the excess glue and form preliminarily;

[0010] (3) Enter the forming mold of rectangular shape. The solvent-free epoxy resin starts to gel inside the forming mold when heated, then cures and bonds with the reinforcing material to form an integral whole, taking on a fixed shape.

[0011] (4) Enter the curing furnace for curing.

[0012] (5) Cool naturally or by forced cooling.

[0013] (6) The traction device continuously pulls and draws it out.

[0014] (7) The cutting device cuts it into a certain length to obtain the crossarm body.

[0015] (8) Metal encapsulation parts are respectively encapsulated at both ends of the crossarm body.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: It replaces the traditional iron crossarm, uses the crossarm body made of fiberglass to enhance the insulation function of the insulator, and the metal encapsulation parts with upturned ends at both ends meet the upturn requirements for insulator installation. Fiberglass has good mechanical strength and excellent insulation performance, making the 35kV lightning protection insulator crossarm have the characteristics of excellent insulation performance, high pollution resistance level, convenient live working, and simple construction and maintenance. It can effectively solve the lightning trip accidents easily caused by insufficient insulation in overhead insulated lines and insulation accidents caused by external force damage, reduce the operation and maintenance workload of overhead lines, and further improve the operation reliability of overhead insulated lines. Description of the Drawings

[0017] Figure 1 It is the front view of the present invention.

[0018] Figure 2 It is the top view of the present invention.

[0019] The component reference numerals in the figures are as follows:

[0020] 1 Crossarm body

[0021] 101 Hole

[0022] 2 Metal encapsulation parts. Detailed Embodiments

[0023] The following describes in detail the specific embodiments of the present invention with reference to the accompanying drawings, so that those skilled in the art can more clearly understand how to practice the present invention. Although the present invention is described in conjunction with its preferred specific embodiments, these embodiments are only illustrative and do not limit the scope of the present invention.

[0024] See Figure 1 and Figure 2, A 35kV lightning protection insulator cross arm, comprising a cross arm body 1 and two metal encapsulation parts 2; the cross arm body 1 is made of fiberglass, the cross arm body 1 is in a rectangular tubular shape, and two holes 101 are uniformly distributed along the axial direction on both the front side wall and the rear side wall of the cross arm body 1. The holes 101 are round holes, oval holes or waist-shaped holes, and the holes 101 are used to connect the hoop bolts and then install the hoop; the two metal encapsulation parts 2 are respectively sleeved and fixed at both ends of the cross arm body 1, and can be fixed by interference fit or bolt connection. The upper surface of the metal encapsulation part 2 is upturned by a certain angle relative to the upper side wall of the cross arm body 1. This structure not only facilitates the connection between the metal encapsulation part 2 and the insulator and meets the upward deflection requirement for insulator installation, but also can improve the end strength of the cross arm.

[0025] Among them, the material of the cross arm body 1 is specifically epoxy fiberglass.

[0026] Fiberglass is a glass fiber reinforced plastic (also known as fiberglass) made of glass fibers and synthetic resins, and is a type of engineering structural material that has been widely used. Compared with traditional steel and aluminum alloy materials, it has unique advantages such as high specific strength and specific stiffness, strong designability, good fatigue resistance, corrosion resistance, and special electromagnetic properties, and has been widely used in the fields of architecture, ships, transportation, electricity, sports equipment, and aerospace.

[0027] The advantages of using fiberglass for the cross arm body of the 35kV lightning protection insulator cross arm are as follows: (1) The cross arm has good insulation performance and good lightning overvoltage withstand performance. The power frequency withstand voltage reaches about 300kV per meter. When lightning strikes, due to the insulation effect of the cross arm, the insulator is not likely to flash over, thereby reducing the lightning trip rate. (2) Under the same specifications and dimensions, its weight is 1 / 5 of that of the traditional iron cross arm. Under the same strength and stiffness requirements, fiberglass materials can greatly reduce the structural mass, facilitate construction and installation, and are conducive to improving the safety of live working; (3) Compared with the iron fuse cross arm, the fiberglass fuse cross arm can greatly reduce external force damage accidents, the power supply reliability will be gradually improved, and its economic benefits will be greatly enhanced; (4) It has good flexibility and thus has strong impact resistance; (5) It has no eddy current loss and hysteresis loss, and can reduce line loss; (6) The overall cost during its comprehensive service life is much lower than that of the iron cross arm.

[0028] The production process of the cross arm body is a continuous automated process, and its specific steps are as follows:

[0029] (1) The glass fiber reinforcing material is led out from the rack, gathered into a bundle through the guide plate, and soaked with solvent-free epoxy resin through the glue tank;

[0030] (2) Enter the preforming die, remove the excess glue and be preliminarily formed;

[0031] (3) Enter into the rectangular-shaped forming die. The solvent-free epoxy resin starts to gel inside the forming die upon heating, then cures and bonds with the reinforcing material to form an integral whole, taking on a fixed shape.

[0032] (4) Enter the curing furnace for curing.

[0033] (5) Undergo natural or forced cooling.

[0034] (6) The traction device continuously pulls out by drawing.

[0035] (7) The cutting device cuts it into a certain length to obtain the crossarm body.

[0036] Finally, a metal encapsulation part is respectively encapsulated at both ends of the crossarm body to obtain the 35kV lightning protection insulator crossarm product.

[0037] The following is the performance parameters, mechanical and electrical strength calculation, and crossarm bending strength calculation of this 35kV lightning protection insulator crossarm.

[0038] I. The performance parameters of this 35kV lightning protection insulator crossarm are shown in the following table:

[0039]

[0040] The specification dimensions of the 35kV lightning protection insulator crossarm are generally 1200mm × 70mm × 50mm, and the insulation distance on both sides of the hoop is 400mm, that is, the distance from each hole to the adjacent end of the crossarm is 400mm.

[0041] It can be seen from the table that the crossarm has good dielectric strength and mechanical strength; has strong impact resistance ability; has excellent insulation performance, which can win more space for live working and provides material conditions for live working (calculated based on live working once every 5 years on average, for a 400kVA capacity, each time the power outage is reduced by 4 hours, and at 0.63 yuan per kWh, the increased electricity sales revenue can be 2016 yuan). The probability of being damaged by lightning strikes is greatly reduced, the losses caused by lightning strike damage are greatly reduced, and the line discharge distance can be increased to have a lightning protection effect.

[0042] The iron crossarm has ferromagnetic loss, and the power loss caused by iron loss within a 10-year operation cycle is at least 2000 kWh. While this crossarm is made of non-ferromagnetic material, without eddy current loss and hysteresis loss, it can reduce line loss.

[0043] II. Mechanical and electrical strength calculation of this 35kV lightning protection insulator crossarm

[0044] 1) Line insulation level and arc building rate

[0045] When lightning strikes an insulator, the flashover of the insulator depends on the overvoltage value and the line insulation level. The probability of arc generation depends on multiple parameters: the rated line voltage U2, the flashover path L, the moment of lightning strike, the magnitude of the lightning current, and line parameters, etc. Among these parameters, it mainly depends on the average gradient of the operating voltage along the flashover path.

[0046] E = U2 / (√3·L)

[0047] where, U2 ---- rated line voltage, V

[0048] L ---- flashover length, m

[0049] The arc building rate decreases as E decreases. Through data analysis of the arc spark discharge process, it is concluded that when E ≤ 6 - 10 kV / m, the arc building rate is zero.

[0050] Currently, for the existing 35 kV lines in Shanghai, according to the typical design regulations, the flashover length L1 of the insulator is 0.46 m. Then, the average gradient E1 of the operating voltage of the insulator along the flashover path at this time is:

[0051] E1 = U2 / (√3·L) = 35 / (√3·0.46) = 43.93 kV / m

[0052] At this time, the arc building rate η1 after the lightning flashover of the line is:

[0053] η1 = (4.5E 0.75 - 14)×10 -2 = (4.5×43.93 0.75 - 14)×10 -2 = 62.8%

[0054] When the 35 kV lightning protection insulator crossarm replaces the original iron crossarm, the line-to-ground flashover length L is the sum of the original insulator flashover length L1 and the insulated part L2 of the fiberglass insulation crossarm:

[0055] L = L1 + L2 m

[0056] where, L1 ---- original insulator flashover length, m

[0057] L2 ---- insulated part of the fiberglass insulation crossarm, m

[0058] Currently, for the existing 35 kV lines in Shanghai, according to the typical design regulations, the original insulator flashover length L1 is 0.46 m, and the insulated part L2 of the 35 kV lightning protection insulator crossarm that plays the role of extending the flashover length is 0.4 m. Therefore

[0059] L = L1 + L2 = 0.46 + 0.4 = 0.86 m

[0060] E = U2 / (√3·L) = 35 / (√3·0.86) = 23.5 kV / m

[0061] At this time, the arc - building rate η after lightning flashover of the line is as follows:

[0062] η1=(4.5E 0.75 - 14)×10 -2 =(4.5×23.5 0.75 - 14)×10 -2 = 34%

[0063] It can be seen from this that when the 35 - kV lightning - protection insulator cross - arm replaces the original iron cross - arm, the probability of power - frequency follow - current arc - building after lightning flashover of the line insulators is almost reduced by half, and correspondingly, the lightning - strike tripping rate is also almost reduced by half. Therefore, the lightning - protection effect of the 35 - kV fiberglass lightning - protection insulator cross - arm is remarkable.

[0064] III. Bending strength calculation of the 35 - kV lightning - protection insulator cross - arm

[0065] The bending strength F of the 35 - kV lightning - protection insulator cross - arm can be obtained from the following formula:

[0066] F = M / Lw N

[0067] Where, M----Maximum bending moment, N·m

[0068] Lw----Longest bending moment, m

[0069] Here, the longest bending moment is the sum of the original insulator structure length and the cantilever length of the 35 - kV lightning - protection insulator cross - arm, and its value is 0.9 m here.

[0070] M = W·σ N·m

[0071] W----Bending modulus, m3

[0072] σ----Maximum bending stress, Mpa

[0073] For a rectangular fiberglass lightning - protection insulator cross - arm, the bending modulus W can be calculated from the following formula:

[0074] W=(bh 3 - b1h1 3 ) / 6h m 3

[0075] b-----Rectangular width, m

[0076] b1----Inner - hole width of the rectangle, m

[0077] h-----Rectangular height, m

[0078] h1----Inner - hole height of the rectangle, m

[0079] So W = (bh 3 - b1h1 3 ) / 6h = (0.05×0.073 - 0.034×0.543) / (6×0.07) = 2.81×10 -5 m

[0080] M = Wσ = 2.81×10 -5 ×600×10 6 = 16860 N·m

[0081] F = M / Lw = 16860 / 0.9 = 18733 N

[0082] The above calculation is based on the entire cross - arm as a cantilever beam for bending strength calculation. In actual situation, the hoop bolts pass through the center of the cross - arm. Therefore, the main force - bearing point of the cross - arm is located at the mid - point of the rectangular cross - arm. So, taking half of the F value obtained from the above calculation as the bending strength of the 35 kV lightning protection insulator cross - arm is a slightly conservative estimate.

[0083] F / 2 = 18733 / 2 = 9367 > 5000 N

[0084] Since the rated bending strength of the 35 kV cross - arm insulator is 5000 N, and the bending strength of the 35 kV lightning protection insulator cross - arm is 9700 N, which is much greater than 5000 N, it fully meets the strength requirements.

[0085] It should be noted that for the present invention which has been fully described, there can be various transformation and modification implementation schemes, and it is not limited to the specific embodiments of the above - mentioned implementation manners. The above embodiments are only for the illustration of the present invention, rather than a limitation to the present invention. In short, the protection scope of the present invention should include those transformations, substitutions and modifications that are obvious to those of ordinary skill in the art.

Claims

1. A 35kV lightning protection insulator cross arm, characterized in that, It includes a cross arm body and two metal encapsulation parts; the cross arm body is made of fiberglass, the cross arm body is rectangular tubular, and two holes are evenly distributed along the axial direction on the front side wall and the rear side wall of the cross arm body. The two metal encapsulation parts are respectively sleeved and fixed at both ends of the cross arm body, and the upper surface of the metal encapsulation part is tilted upward at a certain angle relative to the upper side wall of the cross arm body; the holes are round holes, oval holes or waist-shaped holes; the material of the cross arm body is epoxy fiberglass.

2. A production method of a 35kV lightning protection insulator cross arm, characterized in that, It includes the following steps: (1) The glass fiber reinforced material is led out from the rack, gathered into a bundle through the guide plate, passed through the glue tank, and soaked with solvent-free epoxy resin; (2) Enter the preforming die, remove the excess glue and preliminarily form; (3) Enter the forming die with a rectangular shape. The solvent-free epoxy resin starts to gel in the forming die, then cures and bonds with the reinforcing material to form an integral body, forming a fixed shape; (4) Enter the curing furnace for curing; (5) Cool naturally or forcibly; (6) The traction device continuously pulls out by drawing; (7) The cutting device cuts it into a certain length to obtain the cross arm body; (8) A metal encapsulation part is respectively encapsulated at both ends of the cross arm body. The metal encapsulation parts are respectively sleeved and fixed at both ends of the cross arm body, and the upper surface of the metal encapsulation part is tilted upward at a certain angle relative to the upper side wall of the cross arm body.

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