# Study on the Method and Tool for Replacing 500 kV "V" Insulator Strings with Power

Abstract: This article introduces the method of designing the insulation rods and bottle holders with a new type of foam-filled insulation tube, and using special clamps to make the insulator string into a whole under the support of the bottle holder. The entire series cannot be replaced with a live one. The article calculates, designs and checks the stress of each part of the jig, and all reach the required range.

Keywords: live operation; “V” shaped insulator string; insulation rod; bottle holder; replacement of insulator string 1 The proposal of the problem As the 500 kV line matures, in order to reduce the steel tower steel index, reduce the cost, and reduce the phase deviation, At present, a large number of "V" shaped insulator string structures are used in 500 kV transmission lines. Because the "V" shaped insulator string has a certain angle, when the wire is lifted, the insulator string is affected by its own gravity to make the whole string of bows incapable of being separated from the upper and lower hanging points. Maintenance work brings certain difficulties. In order to solve this problem, the North China Electric Power Research Institute successfully developed a method and tool for replacing 500 kV "V" shaped insulator strings with power. 2 Design ideas The new foam-filled insulation tube is used to design the insulation rod and bottle holder, and the special clamp is designed. The "V" shaped insulator string is integrated under the support of the bottle holder, so that the upper and lower hanging points can be picked smoothly Take off. On the basis of this solution, as long as the problem of clamping at both ends is solved, other problems can be solved smoothly. "V" shaped insulator string installation structure is shown in Figure 1.

Figure 1 Schematic diagram of "V" shaped insulator string installation structure

3 Mechanical calculation of “V” shaped insulator string clamp 3.1 Known conditions Wire size LGJ-400 ／ 50 Calculated cross section S = 467.2 mm2 Horizontal pitch L = 400 m Vertical pitch Lch = 600 m Wind speed v = 10 m / s 3. 2 Load calculation According to the above conditions, check the load table of the wire to get: unit specific gravity g1 = 3.55 × 10-3 kg / (m · mm2) 的 unit specific gravity of 4 wires g4 = 0.412 × 10-3 kg / (m · mm2 ) Comprehensive specific load Single wire load T1 = SLg6 = 467.2 × 600 × 3.573 × 10-3 = 1 001.7 (kg) 4 wire loads T4 = 4007 kg 004 (kg) "V" shaped insulator strings have an included angle of 90 ° and a slope of 1.4. The oblique load of each string of insulator is T1 / 2/2 = 1.4 T1 / 2/2 = 2 805 (kg). When the safety factor K = 3.0, the destructive force of the fixture TB = 3T1 / 2/2 = 3 × 2 805 = 8 415 (kg). The tie rods are double rods, so the damage force of each insulated tie rod TLB = TB / 2 = 4 208 (kg) Factory test K = 2.5 Factory test load fixture load TK = 7 013 kg Tie rod load TL = 3 507 kg 3.3 card With the strength check 3.3.1, the structure of the rear card is shown in Figure 2.

Figure 2 Schematic diagram of the rear card

(1) Section selection. Bending moment Mn = P (La) / 4 = 4 208 × (430-130) / 4 = 63 100 (kg · mm) Area of ​​section Wm = 2bh2 / 6 = 2 × 30 × 592/6 = 34 810 (m2 ) (Including lower bolts) Mm / Wm = 91 500/34 810 = 2.63 (kg / mm2) ≤40 kg / mm2 (allowable stress value of material), so the cross section selection is safe and reliable, with a certain margin. (2) Cut the end hole. Cross-sectional area of ​​end hole Sd = 2 (ad) b = 2 × (60-18.5) × 22 = 1 826 (mm2) KP / Sd = 0.8 × 8 415/1 826 = 3.7 (kg / mm2) ≤20 kg / In the formula of mm2 (end-hole shear stress allowable value), the safety factor K = 0.8 and the shear force P = 8 415. (3) Squeeze the end hole. Sd = 2db = 2 × 18.5 × 22 = 814 (mm2) KP / Sd = 8 415 × 1.0 / 814 = 10.34 (kg / mm2) ≤40kg / mm2 (allowable value of end hole extrusion stress) Conclusion: The safety of the rear card The degree is large, but considering the material properties and the dispersion of the process, the cross-sectional size is not reduced for the time being. 3.3.2 Front Card (Separate Report Card) 示意图 The schematic diagram of the front card structure is shown in Figure 3.

Figure 3 Schematic diagram of the front card structure

(1) Bending strength. Bending moment Ma = P (L-δ-2b) / 4 = 8 415 × (430-22-2 × 22) / 4 = 8 415 × 364/4 = 765 765 (kg · mm) Area Wa = bh2 / 6 = 22 × 802/6 = 23 467 (mm2) Ma / Wa = 765 765/23 467 = 32≤40 kg / mm2 (allowable value of bending strength) (2) Shear holes. S = 2 (ad) b = 2 × (40-18) × 20 = 880 (mm2) P / S = 8 415/880 = 9.56 (kg / mm2) ≤20 kg / mm2 ) (3) The bolt is stretched. T = P (Ld) / 8H = 8 415 (430-22) / (8 × 143) = 3 001 (kg) S = πd2 / 4 = π × 162/4 = 201 (mm2) Therefore, K1T / S = 1.2 × 3 001/201 = 17.92 (kg / mm2) ≤ 60kg / mm2 (allowable value of bolt tensile stress) (4) End hole shearing. S = 2 (ad) b = 2 × (80-2 × 12) × 10 = 1 120 (mm2) P / S = 8 415/1 120 = 7.5 (kg / mm2) ≤20kg / mm2 (end hole shear Allowable stress) (5) Extrusion of the end hole. S = 4ab = 4 × 12 × 10 = 480 (mm2) P / S = 8 415/480 = 17.53 (kg / mm2) ≤ 40kg / mm2 (allowable value of end hole extrusion stress) Conclusion: There is a certain selection of the section of the separation card Degree. 3.3.3 Bolt connection strength check of insulation rod 杆 The pipe is 32 × 4 round pipe, and the holes are double holes. (1) Tensile strength. S = π / 4 × (D2-d2) -d1 (Dd) = π / 4 × (322-242) -12 × (32-24) = 276.5 (mm2) In the formula, D is the outer diameter of the draw tube, mm; d is the inner diameter of the draw tube, mm. P / 2S = 8 415 / (2 × 276.5) = 15.2 (kg / mm2) ≤60kg / mm2 (allowable value of tensile strength), so the margin of tensile strength is large. (2) Shear strength. S = 2 (Dd) t = 2 × (32-24) × 80 = 1 280 (mm2) P / S = 8 415/1 280 = 6.57 (kg / mm2) ≤10kg / mm2 (allowable value of shear strength) Where t is the height of the connection. (3) Squeeze strength. S = 2 × (Dd) d1 = 2 × (32-24) × 12 = 192 (mm2) P / S = 8 415/192 = 43.8 (kg / mm2) ≤70 kg / mm2 (permissible value of compression strength) Through calculation, design and check the stress of each part of the jig, all reach the required range. The design of the insulating rod uses the 32 foam-filled insulating rod produced by Shaanxi Qinchuan Electric Power Equipment Industry Co., Ltd., its tensile strength and insulation performance can fully meet the design requirements, and no verification is performed here. 4 Conclusions The 500 kV “V” shaped insulator string live replacement tool has met the design requirements through design, test, trial operation, and further modification and processing. The site was performed on the Shanxi 500 kV Lincheng Line 156 tower in December 2004. The actual line trial has fully met the requirements for on-site use. See Figure 4 for actual site operation. And in January 2005 in Taiyuan, Shanxi Province, it passed the technical review of the national technical experts on live working. The experts agreed that this project filled the domestic gap and reached the domestic leading level.

Figure 4 Field operation of replacing 500 kV “V” shaped insulator strings with power