If a turbine rotor is left to not be rotated while an operation of a steam turbine or the like is stopped at a high temperature, a temperature difference inside a turbine casing occurs according to a decrease in a temperature of steam or gas inside the turbine. Due to this temperature difference, thermal distortion may occur in the turbine rotor or bending may occur in the turbine rotor due to its own weight of the turbine rotor.
Accordingly, in order to avoid the occurrence of the bending in the turbine rotor used in the steam turbine or the like, it is necessary to perform turning which rotates the turbine rotor at a lower speed during a predetermined time when the operation of the steam turbine or the like is stopped or before the steam turbine starts. In order to perform this turning, a turning apparatus which rotates a turbine rotor by power of an electric motor is widely used.
In the turning apparatus, when the turbine rotor starts a normal rotation, an excessive load is applied to the turning apparatus. In order to prevent the turning apparatus from being damaged by the load, a mechanism which removes a pinion gear to protect the turning apparatus is provided. Meanwhile, during the turning of the steam turbine or the like, the turbine rotor may reversely rotate due to occurrence of a backflow or the like of a compressor process gas. In this case, the pinion gear cannot be removed, an excessive load is applied to the turning apparatus, and thus, the turning apparatus may be damaged.
In order to avoid damage of a turning apparatus, for example, PTL 1 discloses an apparatus which includes a one-way clutch for automatically releasing a turning apparatus from a turbine rotor in a case where a rotating speed of the turbine rotor exceeds a rotating speed of the turning apparatus and a one-way clutch (a reverse rotation prevention device) for preventing (restraining) a reverse rotation of the turning apparatus.