FRA (or SFRA) injects a low-voltage swept-frequency signal into windings and measures the response, creating a fingerprint of the mechanical and electrical network. Changes in the signature over time can indicate winding displacement, core movement, clamping loosening, or lead deformation caused by faults, transport shocks, or short-circuits. It is extremely sensitive to mechanical changes and is widely used after shipping, fault events, or major short-circuit incidents to verify internal mechanical integrity without de-tanking.