Method for securing the operation of a turbomachine

A method of making safe operation of a rotary assembly of a turbomachine, which rotary assembly includes a turbine that is caused to rotate by expansion of a drive fluid that is to flow through the turbine, and a rotary machine that is driven mechanically in rotation by the turbine to move a driven fluid that is to flow through the rotary machine, wherein an event of the rotary assembly exceeding a predetermined threshold speed is anticipated by repetitively performing a prediction cycle comprising:

• measuring following magnitudes during a predetermined time interval:
• a real speed of rotation of the rotary assembly at a given observation instant of the time interval;
• at least one fluid/turbine interaction parameter that is representative of the interaction between the turbine and the drive fluid;
• and
• at least one fluid/rotary machine interaction parameter that is representative of interaction between the rotary machine and the driven fluid;
• estimating driving torque applied by the turbine to the rotary assembly, based on the real speed of rotation and the at least one fluid/turbine interaction parameter;
• estimating, independently of estimating the driving torque, resisting torque applied by the rotary machine to the rotary assembly, based on the real speed of rotation and the at least one fluid/rotary machine interaction parameter;
• preparing a representative value that is representative of the difference between the driving torque and the resisting torque;
• calculating a predicted speed of rotation for the rotary assembly at a prediction instant later than the observation instant based on the real speed of rotation, the representative value, and the time difference between the prediction instant and the observation instant;
• and
• determining that a first condition is satisfied if the predicted speed of rotation exceeds the predetermined threshold speed;
• and
• wherein an action is taken on an operation of the turbomachine to limit an extent to which the speed of the rotary assembly exceeds the threshold speed in the event that, during the prediction cycle, it is determined that at least the first condition is satisfied.