Advanced seismic resilience of composite insulators for High Voltage substations

This paper reviews the seismic design principles, terminology, and qualification requirements applicable to composite insulators and presents five representative application cases covering voltage levels from 196 kV to 1000 kV. The investigated configurations include bus support structures, composite-housed oil-filled bushings, disconnect switch supports, a high-voltage AC capacitive voltage transformer, and the interconnection circuit of an ultra-high-voltage surge arrester and instrument transformer.

For each case, detailed numerical seismic models were developed and correlated with full-scale shaketable testing performed in accordance with IEEE Std 693 [1] and relevant national seismic design codes. Both sine-beat and time-history excitations were applied at high-performance qualification levels. Key response parameters—including natural frequencies, dynamic displacements, strains, stresses, and damping ratios—were measured and compared with analytical predictions.

The results demonstrate close agreement between calculated and measured responses, confirming the validity and robustness of the modelling approach. In all cases, composite insulators met or exceeded seismic acceptance criteria, exhibiting no structural damage, stable dynamic behaviour, and significant safety margins relative to specified mechanical load limits and material damage thresholds. The influence of critical design parameters such as fibre winding angle, wall thickness, internal pressure, and top mass was clearly identified, enabling optimisation for combined pressure and cantilever loading conditions.

A comparative assessment with porcelain insulators highlights the superior seismic resilience of composite solutions. Their higher bending strength, increased damping ratio, and substantially reduced mass led to lower inertial forces, improved energy dissipation, and non-brittle failure modes. These findings are consistent with field observations following major earthquakes, where composite insulators remained operational while porcelain units suffered extensive damage.

Based on extensive shake-table testing and continuous model validation, reliable mechanical and dynamic property data can now be provided to utilities and equipment manufacturers. The validated analytical tools presented in this paper support seismic qualification, system-level simulations, and cost-effective design optimisation, contributing to enhanced substation reliability in seismically active regions.