Keywords: Multi-circuit transmission lines on the same tower, Live working, Swing method.

Transcription

1 17 nd International Conference on Electrical and Electronics: Techniques and Applications (EETA 17) ISBN: Research on New Method of Live Working on /5kV Mixed-voltage Four-circuit Transmission Lines on the Same Tower Wen LI 1, Zhi-wei CHENG, De-hua ZOU 1, Jie NIU 1, Zhi-gang WANG 1, Yu YAN 1, Lan-lan LIU 1 and Yue-xiong OU 1 1 State Grid Hunan Electric Power Company Live Working Center, China Loudi Power Supply Branch of State Grid Hunan Electric Power Company, China Keywords: Multi-circuit transmission lines on the same tower, Live working, Swing method. Abstract. Multi-circuit transmission lines on the same tower are widely used in recent years, and maintenance is an important technical means for ensuring safe and stable operation thereof. This paper aimed at the operation characteristics of multi-circuit transmission lines on the same tower, and presented a swing method for getting in the electric field during live working of operating circuit lines, which is applied to actual lines, and the application result show that the method is safe and reliable. The research result of this paper provides strong technical support for maintenance of multi-circuit transmission lines on the same tower. Introduction The technology of multi-circuit transmission lines on the same tower can effectively alleviate the contradiction between shortage of corridor resource of transmission lines and insufficient power transmission capacity so as to reduce power transmission corridors, increase transmission capacity and save land resources[1-4]. The safety distance of the multi-circuit transmission lines on the same tower is too short that it is difficult to carry out live working on operating lines, and untimely defect elimination will affect safe and stable operation of lines[5-6]. Thus, in order to ensure safety of the maintenance workers and smooth operation of line maintenance, it is extremely necessary to make deep research on maintenance mode of lines and safety protection measures of the maintenance workers. Project Overview This paper takes Hunan /5kV Yue-Kun line as the object of research, wherein the mode of the fourth circuit line tangent tower is SSZ1-39, the total height of the tower is 88.m, and the nominal height is 39m. The model of the fourth circuit tension support is SSDJ1-7, the total height of the tower is 76.5m, and the nominal height is 7m. Take the tangent tower for example, its arrangement of wires is shown in Figure 1. and its parameters of guide wires and ground wires are as shown in Table 1. Table 1. /5kV guide and ground parameter table. Model of guide and ground Calculated section (mm) Calculated outer diameter (mm) bundle spacing(mm) Bundle number LGJ-4/ LGJ-3/ OPGW OPGW Note: OPGW is 4-core OPGW compound optical cable and OPGW3 is 48-core OPGW compound optical cable. 13

2 Figure 1. Arrangement of wires. Maintenance Mode of Operating Circuit The live working mode must be used to carry out maintenance operation of normal operating circuits. However, due to compact structure, complex electromagnetic environment and short safety distance of the multi-circuit transmission lines on the same tower, the existing electric field in and out method cannot meet the Safety Code of Electric Power Industry (hereinafter referred to as Safety Code) in terms of safety distance[7]. To solve this problem, this paper presented an improved method for getting in and out the electric field (hereinafter referred to as swing method) based on a flexible ladder, which can be used to effectively solve the problem that live working of /5kV multi-circuit transmission lines on the same tower is difficult to carry out. Working Theory of Swing Method Take live working on the 5kV Yue-Kun I circuit (tangent tower)shown in Figure 1. for example, the operation process and typical operation positions are as shown in Figure. The implementation steps include that the ground potential operator suspends the insulation flexible ladder through the ground wire, the equal potential operator boards the ladder along a crosspiece (position 1), the ground operator moves the flexible ladder to a position (position) in certain distance from the crosspiece in a direction away from the tower along the ground wire, after sufficient complex space is ensured, the equal potential operator climbs down the flexible ladder to a position (position 3) level with the guide wire, the ground operator coordinates with the equal potential operator by controlling a control rope at the end of the flexible ladder to enable the equal potential operator to reach the guide wire (position4) from the outside of the guide wire (out-span), and then the equal potential operator reaches the operation spot (position 5) by moving along the guide wire to carry out maintenance operations of insulator replacement and guide wire repair. 14

3 Figure. The typical position of swing method when in-out Electric Field. Check of Safety Distance and Complex Gap In order to ensure safety of the operator, safety check should be performed on the safety distance and complex gap in the operation method. The front view of typical operation positions is shown in Figure 3. Figure 3. The front view of typical job location. Safety distance of discharge of the guide wire to the tower is taken into consideration during design of line operation, thus it is not dangerous for the operator to move within the cross arm. When the operator moves from position 1 to position, the complex gap is the sum of distance from the operator to the ground wire and distance from the operator to the guide wire (the sum of distance from the operator to cross arm and distance from the operator to guide wire), and the minimum complex gas in this process is 5.4m (namely at position 1); the minimum complex gas in the process when the operator climbs down from position to position 3 is 6.1m (namely at position ); and the body of the operator is about.6m higher than the guide wire at position 4 and 5, and the height of the operator is set at 1.8m during calculation. The Safety Code stipulates that risk of live working of transmission lines should meet R<1. 1-5, thus safety of the proposed method should be checked through further calculation of the risk of live working [8,9]. Risk of live working R can be obtained from formula (1)-(3), and the calculation results are described in Table. R 1 P ( U ) Pd ( U ) du. (1) 15

4 1 1 U U ( U ) e ( av ) P 1. () u 1 U U 5 Pd ( U ) e ( ) du d d. (3) In this formula, P(U) is a probability density function of amplitude of operation overvoltage; Pd (U) is the probability distribution function of breakdown of air gap under the operation overvoltage with the amplitude of U. P(U) and Pd (U) are shown in formula () and (3). σ is standard deviation of operation overvoltage, Uav is average value of operation overvoltage, σd is standard deviation of discharge voltage of air gap, and U5-is 5% discharge voltage of air gap. Table. Safety factor of typical location. Position Minimum safety distance(m) Minimum complex gap (m) Risk R As stipulated, the minimum safety distance and complex gap for live working of 5kV transmission lines should meet 3.4m and 3.9m respectively. By means of analysis of data in Table, the swing method presented in this paper meets requirements of the Safety Code in terms of safety distance, complex gap and risk, thus safety of the swing method presented in this paper is verified. Field Application On November1, 15, Hunan Live Line Working Center, State Grid completed live working on #13 tower of /5kV Yue-Kun line by using the swing method, and the operating process is shown in Figure 4. The equal potential operator was not discomforted at all and risks were not caused through the operating process, thus verifying feasibility of the method presented in this paper. (a)swing method into the electric field (b) Carry out equal potential operation Figure 4. Job site. Conclusion Relied on actual project lines, this paper presented a swing method for getting in and out electric field during live working of mixed-voltage transmission lines on the same tower, which meets requirement of the Safety Code according to safety parameter calculation and check, and safety of the swing method presented in this paper was verified through field application, thus providing reference and technical support for live working of multi-circuit transmission lines on the same tower. 16

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