The Diagnosis of Foundations of 220-500 kv Electrical Transmission Line Supports

Abstract

This thesis explores a vibration-based diagnostic method for assessing foundation condition in 220-500 kV overhead electric transmission towers. Research evaluates model for the mass-spring-damper system for a transmission tower and its foundation, with realistic values for its mechanical properties obtained from literature studies, coupled with information from the Aghsu 220kV Corridor. Simulation studies are conducted dynamically, with soil properties being varied for different forces, simulating operational forces like wind excitation. Outputs simulated for transient response to these forces include displacement, velocity, and acceleration, processed with filtering algorithms, Fast Fourier Transforms, spectral analysis, and features extracted for diagnostic indicators like frequency deviations, damping ratios, and acceleration magnitude levels, in combination forming a diagnostic foundation to ascertain differences between a healthy foundation from a deteriorated foundation.Simulation results are validated with model predictions based on operational expectations, along with published values from international studies. The simulation results for natural frequency (≈2-12 Hz) and damping coefficients (0.03-0.08) for modelled soil-structure interaction dynamics match published values from observed practices in the energy sector. It has now been validated from simulation analysis that vibration diagnostics have proved to be an efficient, non-destructive technique for condition analysis to monitor Azerbaijan’s 220-500 kV high-voltage transmission network. The thesis explores a vibration diagnostic technique to analyze the condition of foundations for 220-500 kV overhead electrical transmission towers. Conventional visual analysis, adopted in Azerbaijan’s energy power network, explored on-site defects, such as deviations in overhead wires, gaps in support foundations, with no information regarding changes in soil resistance for support foundations. By overcoming these defects, researchers developed simulation-based analysis on mathematical models for dynamic soil-structure interaction principles to explore early indicators for loss, degradation, and damage to electrical support foundations. Starting with creating simplified mass-spring-damper models for the transmission tower, along with its foundation, based on real-world, realistic model parameters extracted from literature, in addition to simulation analogues for the Aghsu 220 kV route, dynamic simulations with varying soil properties for different levels of stiffness, damping, and forces are employed for simulating operational forces such as wind-borne vibrations. Along with simulation results on displacement, velocity, and acceleration, post-processing is performed on these parameters for filtering, spectral analysis based on Fast Fourier Transforms, and indications such as natural frequency deviations, damping ratios, and Root Mean Square acceleration indicators. Outputs from the model are validated by comparison with analytical results and published values in international studies. The match between model results for natural frequency ranging between 2-12 Hz, with damping coefficients between 0.03-0.08, is accurate enough to validate model performance in simulating real-life dynamic performance for transmissions in real foundations. These results validate the utilization of vibration analysis for diagnosing real foundations, particularly for identifying loss in foundation stiffness, which will not be detected during conventional analysis. Concluding, this method is an efficient, non-destructive, and scalable process for testing Azerbaijan's high-voltage power transmissions, with applications for incorporating automated analysis via machine learning algorithms in its evaluation method.