Diagnosis, Analysis and Retrofit of Machinery Vibration for a Synchronous Condenser Founded on Piles

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Unit 3 of the Soldiers Pond Synchronous Condenser Station experienced unacceptable vibration, with a pronounced resonance around 800–900 RPM (13–15 Hz). Earlier analytical models could not reproduce the measured response because they did not adequately represent the interaction between the machinery, structure, soil, and six cased piles socketed into bedrock.<br /><br />The investigation developed a detailed three-dimensional soil–structure interaction (SSI) finite-element model using SC-SASSI and SC-Pile elements, alongside a lumped-mass model of the machinery. Incorporating the pile system enabled the model to replicate the as-built vibration behavior and provided a basis for evaluating retrofit options.<br /><br />Retrofit analysis considered the site’s constraints, including existing equipment, foundations, utilities, and nearby facilities. Soil improvement showed analytical promise but appeared difficult to implement. Base isolation was deemed unsuitable because of the low resonance frequency. Various foundation-stiffening concepts were also assessed, including slab connections, pile connections, and slab extensions.<br /><br />The case demonstrates that deep foundations can strongly influence a machine foundation’s dynamic response. A realistic SSI model was essential both to explain the measured vibration and to identify potentially feasible retrofits. It also highlights the value—and relative scarcity—of comparing numerical SSI predictions with actual measured responses.

Keywords

Soldiers Pond

synchronous condenser

vibration resonance

soil-structure interaction

SSI model

finite-element analysis

cased piles

foundation retrofit

dynamic response

machine foundation