Determination of dynamic loads caused by aeolian vibration on composite insulator : experimental approach.

Abstract

High voltage insulators have to fulfil high reliability criteria by being one of the main components for the operational safety and operating efficiency of the transmission system of electrical power. Various advantages and the attractive price of composite insulators have made them the most frequently used insulators in the power industry and have generally proven to be extremely reliable. Nevertheless, there are certain variable loads which occur on the overhead conductor in the field, such as mechanical loads caused by wind-induced vibrations, so-called Aeolian vibration, which might affect the insulators. It should be noted, that standardized tests of composite insulators are providing information only on their static mechanical strength This thesis describes the experimental investigation of a realistic model to determine the dynamic mechanical loads of the overhead line conductor undergoing Aeolian vibrations. In addition, the dynamic behaviour of the composite insulator was investigated. The tests were performed using a test span in an indoor laboratory. The test procedures used are the swept sine and the steady frequency tests. A shaker connected to a single conductor has simulated Aeolian vibration. Two types of ACSR (Aluminium Conductor Steel-Reinforced) conductor (Tern 45Al. /7St. and Pelican 18Al. /1St.) were tested on two different types of support configurations (suspension and line post), placed at mid-span at four different ranges of static tensile loads (15- 30% Ultimate Tensile Strength – UTS with 5% of increment). For both types of support configurations, the suspension clamp was blocked or articulated in order to know the influence of the oscillation motions on vibrational loads of the vibrating conductors. The measurements were done using the bending amplitude range of 0.1 to 1.0 mm on the conductor at 89 mm away from the last point of contact between the suspension clamp and the conductor. In accordance with the stick-slip bending model of overhead conductors, which predicts a certain degree of non-linearity at low vibration amplitudes, the results obtained were statistically analysed by graphing the vibrational loads versus the bending amplitude. It was found that the magnitude of dynamic mechanical loads on a composite insulator caused by Aeolian vibration is relatively low (10% less) compared to its mechanical strength and can thus most probably not induce fatigue failures on the insulator.