My presentation provides theoretical determination and experimental validation of the interaction between Thyristor Variable Frequency Drive (TVFD) and turbine generator units in Oil&Gas plant. The voltage oscillations caused by torsional and speed oscillation of a turbine generator unit become disturbances for the power electronics devices. They react injecting back into the grid current disturbances, that finally excite the air gap torque through the electric generator. This phenomenon, called Sub-Synchronous Torsional Interactions (SSTIs), can lead to blackouts of the plant or damage of the equipment. An integrated electrical and mechanical simulation model allows to emulate the behavior of the overall Oil&Gas plan, to evaluate torsional stability in particular configurations as the start-up of the moto-compressor train.