Method of operating a turbine engine after flame off

1. A method of decelerating a turbine rotor of a turbine engine, wherein at least one electric motor is engaged with the turbine rotor, wherein a braking system is engaged with the at least one electric motor so as to use the at least one electric motor to apply a negative torque on the turbine rotor; the method, comprising:

after flame off, dissipating kinetic energy available in the turbine engine after the flame off by using the at least one electric motor to apply the negative torque on the turbine rotor; and

varying the negative torque on the turbine rotor.

2. The method according to claim 1 , wherein the electric motor is an electric generator, the electric generator provided for supplying a grid with power during normal operation of the turbine engine, the method comprising:

using the braking system for transforming the kinetic energy into electric energy by the electric generator.

3. The method according to claim 1 , wherein the braking system is provided by a starting system for run-up of the turbine rotor to firing speed.

4. The method according to claim 1 , comprising:

varying the negative torque applied on the turbine rotor during the deceleration of the turbine rotor in dependence of at least one key parameter selected from the group consisting of: rotation speed of the turbine rotor, vibrational loading on elements or groups of elements connected to or including the turbine engine, condition of the braking system, in particular its temperature, or a condition of the electric motor.

5. The method according to claim 4 , comprising:

using the rotation speed of the turbine rotor as said key parameter; wherein at least one critical rotation-speed range is provided within a total rotation speed range of the turbine rotor after flame off, in which at least one critical rotation-speed range vibrational loads occur due to excitation of resonance frequencies of the elements or groups of elements connected to or being part of the turbine engine; and

using the braking system to increase the negative torque to the turbine rotor applied from a first level to a second level if the rotation speed of the turbine rotor lies within the critical rotation-speed range.

6. The method according to claim 5 , wherein two or more critical rotation-speed ranges are provided in the total rotation speed range of the turbine rotor, the method comprising:

applying the negative torque to the turbine rotor at least temporarily during deceleration of the turbine rotor through the critical rotation-speed range, so that the braking system is used in peak-loading operation; and

applying the negative torque to the turbine rotor after said peak-loading operation and during deceleration through a rotation speed range that is not a critical rotation-speed range, at a loading below its peak loading.

7. The method according to claim 6 , wherein the two or more critical rotation-speed ranges are not overlapping one another.

8. The method according to claim 6 , wherein the two or more critical rotation-speed ranges are at least partly overlapping one another.

9. The method according to claim 2 , comprising:

feeding the electric energy into the high-voltage grid while a generator output meets requirements of a high-voltage grid in-feed.

10. The method according to claim 2 , comprising:

feeding the electric energy into a medium-voltage grid while a generator output meets requirements of a medium-voltage grid in-feed.

11. The method according to claim 2 , comprising:

feeding the electric energy into an external load bank, into a battery element, and/or into at least one auxiliary power consumer of the turbine engine, so as to dissipate at least part of the electric energy; and

dissipating the electric energy by recharging the battery element and/or by at least partly covering an auxiliary power demand by the at least one auxiliary power consumer, respectively.

12. The method according to claim 11 , wherein the at least one auxiliary power consumer of the turbine engine is selected from the group consisting of lube oil pumps, enclosure ventilation, cooling water pumps, due point heaters, trace heaters, and the like.

13. The method according to claim 1 , wherein the turbine engine is a single shaft gas turbine engine and the kinetic energy stored in the rotating turbine shaft is dissipated.

14. Use of a method according to claim 1 during shut down of an industrial gas turbine engine or another turbine engine.

15. The method according to claim 1 , wherein the turbine engine is a steam turbine and the kinetic energy stored in the rotating turbine shaft is dissipated.