| Transmission line(tower) as the aorta of electric power system industry is of great importance, so that researching the internal force of the structure and ensuring its safe, reliable and stability are major jobs which are related to national economy and people’s livelihood. Considering the structure’s practical shape、loads and deformation of the iron tower are complexible, using the simple idealized models to analysis and check the structure of iron tower is difficult and the result does not meet the actual situation. This article has researched the stress testing method of one transmission company’s SJ331A-18 double circuit steel tower and 2B-GJ31-18 single circuit steel tower, and analyzed the dynamic stress of the SJ331A-18 type tower under various load conditions.Research results and conclusions of this paper are as follows:1. Suitable and safe loading procedure and method have been determined according to "Overhead line tower structure load test"DL/T899-2012. Combining the actual operation of the tower, this article has determined 4 kinds of experimental condition which meet the fact:Normal working condition, the condition of 15mm simulation icing load, breakage and failure. Acoording to the statistic which is from the antecedent experiment, this research accomplished the calculation of the loads for every working condition.2. According to the test of waterproof and moistureproof of the strain gauge, the protective layer of paraffin wax mixture will be lost under the condition of high temperature and exposure to sun, then the protection of strain gages won’t be avalible. However, if anti-corrosion paint is used to protect strain gauge, under the simulation condition of more than 30 days’ high temperature and invasion of water tide, insulation resistance value is still more than 500MΩ. Moreover, the strain gauge will not meet the problem of zero drift and the use of anti-corrosion paint is more convenient than paraffin wax mixture.3. According to the test of the measurement efficacy of strain gauge and repeatability of load step, the results reval that the maximum difference between the measurement results and the theoretical results is 4.4%, the maximum difference is 4.3% when loaded repeatedly if strain gauge is protected by anti-corrosion paint, even under the condition of high temperature and invasion of water tide within 30 days, so that the result meets the request of outdoor’s long time stress test.4. Stress test of transmission tower was done. The height of the transmission tower tested is respectively 36.6m,27.5m and the span between the towers is 73.32m. The towers have been arranged 96 strain measuring points and hung 48 simulate load pulls. In Guangxi, such a large scale synchronous and real-time monitoring is the first case. During the test, the problem of strain gauge’s long-term protection is solved by using anti-corrosion paint; the problem that synchronous and real-time monitoring of the pull load is solved by connecting strain gauge with self-tension meter; the problem about power frequency, static electricity and geoelectric interference is eliminated by adapting group test, reducing the wire length and arranging the lines reasonably.5. The results from the measurement of the towers reveal that, in normal conditions, the maximum compression stress of double circuit tower is 179.1MPa which appears in the second layer of material on the lower cross arm and is much less than the designed value 310MPa. The stress of this place is still the maximum when the stress is reached as much as 75% under the condition of icing. It is compressive stress about 290.33MPa, which is more than the allowable calculation value of stability 275.199MPa. The facts above show that the main material below the second layer cross arm of the tower is the weak part of the whole structure, so that we should take some measures to strengthen it in the process of designing and maintaining. |
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