Study on the dynamic characteristics and the flange joint damping model of hollow composite insulators

Composite insulators are widely used in high voltage projects in seismic areas due to their high strength and light weight. However, the composite insulator shows nonlinearity under seismic loads and lacks an accurate mechanical model to describe the dynamic behaviors, introducing difficulties in seismic design. This study performs dynamic tests on a 500 kV hollow composite insulator under various loading amplitudes and frequencies to investigate the mechanical behavior of the specimen. Based on the test data, a flange joint model (FJM) is established for the tested tube-flange system by combining a linear viscous component and a Bouc-Wen-type hysteretic component. The model is calibrated and evaluated using the equivalent damping ratios identified from the dynamic tests. Then seismic analysis is conducted to investigate the influence of the proposed model on the seismic responses. The test data shows that the equivalent damping ratio of the specimen increases with the loading frequency, while increases then decreases with the loading amplitude. The proposed FJM can reproduce the test damping ratios of the specimen under various loading amplitudes and frequencies. The FJM generates larger seismic responses than the popular Rayleigh damping model, especially the low frequency responses. Therefore, the FJM provides a practical way to incorporate the experimentally identified amplitude- and frequency-dependent damping behavior into the seismic analysis of this type of post composite equipment.