The relationship between the bending amplitude and bending stress/strain at the mouth of a so-called square-faced clamp for different conductor sizes and different tensile loads : experimental approach.

Abstract

In this research, realistic models were developed using experimental approach and statistical or deterministic analysis in the relationship between bending amplitudes and bending stress (strain) of the overhead line conductor. This was rigidity clamped and subjected to Aeolian vibration (1Hz-150 Hz). The experiments were performed at the Vibration Research and Testing Centre (VRTC) laboratory of the University of KwaZulu-Natal. A shaker connected to the conductor was used to simulate the Aeolian vibration and transducers (accelerometers, thermocouples and strain-gauges) to control the shaker and collect data. For almost half a century, in transmission lines, bending stress which is a key factor in determining the life expectancy prediction of overhead conductor is assessed by using an idealized model the so-called Poffenberger-Swart formula based on cantilever beam theory and many assumptions [2]. Four overhead line ACSR (Aluminum conductor steel-reinforced) conductors i.e. Rabbit (6 Al. /1St.), Pelican (18 Al. /1St.), Tern (45 Al./7St.) and Bersfort(48 Al./7St.) were investigated at three different ranges of tensile load i.e. 20 %, 25%, and 30% Ultimate Tensile Strength (UTS). Bending amplitudes (0.0 1mm -1.2mm) and bending stresses measurements were collected and plotted as bending stress σb versus bending amplitude Yb, curve-fitting with polynomial function of the third order in terms of four parameters (where curve fitting coefficients B0, B1, B2, and B3) provided excellent simulations (predictions) of the experimental data for the conductors. However, it was found that the accuracy of the fit is not improved by the inclusion of higher order terms. Therefore, only four-parameters (for all cases high order than 3 are ambiguous, in spite of the Regression parameter or predictor were R2 ≥ 0.998 but Standard errors were large). It was noticed that the precedent model is the simplest polynomial to be employed for the characterization of all conductors investigated (for all three wires). Other ways to obtain the best curve fittings were explored and discussed such as power model. The experimental results were compared to the Poffenberger-Swart model. In all cases, it was observed that the deviation from the results to the above model is significant for small bending amplitudes and is small for high bending amplitudes and good correlations were observed when associated this with the bending stiffness model developed by Papailiou [17].