The Synchronous Condenser Unit 3 (SC3), in charge of adjusting the electric power between the
hydroelectric generating facility and the transmission grid, experienced undesirable vibration levels
during its initial stages of operation. The source of the high vibration levels is attributed to the resonant
dynamic interaction between the condenser, its foundation, and the supporting soil media. The
undesirable vibration was detected in SC3, and similar patterns are likely to occur for units 1 and 2 once
they begin operation.

A Synchronous Condenser is a rotatory machine operating at a stationary frequency. The foundation of
SC3 consists of a massive reinforced concrete block supported on steel casing piles with reinforced
concrete infill.

The goals of this project are: (1) diagnose the problem, (2) identify feasible retrofit solutions, and (3)
perform engineering analysis of the proposed retrofit solution. The work is divided accordingly in three
stages and accomplished using rigorous Soil Structure Interaction (SSI) analysis.

A detailed three‐dimensional (3D) Finite Element SSI Model is developed to accurately represent the
interaction between forces, structure, soil, and foundation. The model is analyzed using the proprietary
computer software SC‐SASSI, including the recently implemented SC‐Pile elements.

A number of possible solutions are evaluated with the objectives of: (1) reducing vibration amplitudes,
(2) shifting away the system frequency from the operation frequency, which are both achieved by
increasing the system stiffness, and therefore minimizing potential resonance conditions; and (3)
minimizing the disruption of the surrounding critical equipment already installed.

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