Design, Modeling, Vibration Analysis & Control of Pole-Mounted Electric Transformer During Seismic Events

Unstable inverted pendulum-type structures (like ATC towers, overhead water tanks, and pole-mounted electric transformers) are most vulnerable to seismic activity. When designed poorly, these structures further add to the damage caused by earthquakes. However, their functionality during and after an earthquake is what is most desired. In this study, the vibration analysis of an electric transformer of a mass of 250 kg mounted on a pole of 15 m in height was conducted using the time history analysis method. The pole was designed from the response spectrum analysis of a typical earthquake so that its maximum bending stress does not exceed the yield strength of the material. After selecting basic system parameters (mass, stiffness, and damping constant), the pole-mounted transformer was modeled as an SDOF system that resembles a cantilever beam with load at one end. To enhance the accuracy of results, the system was further modeled as a 2 DOF system and its response was checked against 09 types of forcing functions. Since the exact forcing function of earthquakes cannot be estimated from an accelerogram, a combination of different forcing functions was used to predict the behavior of the system. Output response parameters included relative displacement of the transformer, maximum shear, maximum bending moment, and maximum bending stress of the pole. The response parameters obtained from the dynamic analysis of the SDOF and 2 DOF systems produced impermissible vibrations according to international standards on nomographs. Modification in design was also proposed at the end to curb these vibrations. After applying vibration isolation, the system’s response was brought under control, and the pole can now withstand seismic loads without damaging the structure considerably.