| The power transmission tower is crushed, pulled and twisted to be broken by the excessive weight of ice or other physical factors. The cross arms bear more forces and is easily damaged, so, when the forces exceed the limited, it will be crushed, broken, flexed and affects the safety running of the transmission line. Consequently, the deformation monitoring of power transmission tower is needed. If the FBG strain sensors are installed on the surface of the cross arms, they can measure the deflections of main beams under the foreign force.In this article, study on theory and experiment for the surveying of main beams deflections is held. Based on the structure and operational principle of the cross arm, a duckbill-type model is developed. The two ways of welding and bolts are applied to reinforce the joints between cross arms and brackets. The main contents are as follows:(1) Under the stress of loading, main beams are distorted, and the linear strain which cause the wavelength shift of fiber Bragg gratings mounted on the surfaces of main beams appeared. By the way, the sensor model is built.(2) Besides finishing the material selection and size design, the related parameters are computed in this article. When the measuring points are respectively located at the position of 1/2 length of four main beams, the relations between the wavelength shift of fiber Bragg gratings and the forces are: G=-5.1019Δλ1+1.1358Δλ2-5.0658Δλ3+1.1285Δλ4 FT=3.7513Δλ1+3.5504Δλ2+3.7247Δλ3+3.5275Δλ4。(3) The comparative calculation of measurement results is hold in this article. The yield strength of angle arms is 215～235 N/mm2 and the related wavelength-shift is 1251～1368 pm. The long-term allowable strain of Fiber gratings is 3000με, so, the wavelength-shift of 3600 pm can be measured, and it meets the survey claims.(4)The loading experiments of welded model show that the sensitivity of the four Fiber Bragg gratings are:6 pm/kg,2 pm/kg, pm/3 pm/kg,2 kg/pm. |
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