POWER-GRID RESILIENCE Hardening the Grid: Research Team Focuses on Quake Proofing Transformer Bushings
During an earthquake, the place where a large, high-voltage power transformer is most vulnerable is its bushings – hollow electrical insulators that safely guide current between a transformer’s internal windings and external power lines.
Keeping the nation’s lights on is no small job. The grid we take for granted involves large, expensive equipment, most notably power transformers. If one goes down, it can take more than a year to replace and at massive costs. In heavily populated, seismically active areas like California or the Pacific Northwest, time is not a luxury.
During an earthquake, the place where a large, high-voltage power transformer is most vulnerable is its bushings – hollow electrical insulators that safely guide current between a transformer’s internal windings and external power lines. They are most often made of porcelain due to its ability to isolate the conducting material, usually copper or aluminum, and keep high-voltage current from leaking or sparking and causing explosions.
Bushings are bolted onto a transformer’s turrets, which extend up from the main tank (see Figure 1). These connections are what a team of researchers at the Idaho National Laboratory (INL) has focused on. The team’s goal is to develop a mechanically simple, adjustable isolator, known as a decoupler, that can be mounted at the base of a bushing and tuned to prevent resonant frequencies in the bushing and the turret from matching (which results in amplified mechanical stress on the porcelain bushing).
“Resonant frequencies are the lynchpin,” said Bjorn Vaagensmith, the principal investigator on the project and 2025 Presidential Early Career Award for Scientists and Engineers recipient.
Resonance Explained
All objects have a resonant frequency, which occurs when input vibrations are maximally amplified in an object. When a sound wave shatters a wine glass or a mirror, that is resonant frequency at work. In the history of civil engineering, perhaps the best-known example is the collapse of the Tacoma Narrows Bridge in 1940. Wind speed and direction combined with the bridge’s design and materials to create a resonant frequency that caused its deck to oscillate wildly. This earned the newly built bridge the nickname “Galloping Gertie” – before it broke into pieces and dropped into Puget Sound after four months.
