Method for coupling two sub-shafts

A method for coupling a first sub-shaft, which has a first fluid-flow machine and a generator connected to a mains supply, to a second sub-shaft, which has a second fluid-flow machine, by means of an overrunning clutch, comprising the steps:

• a) rotating the second sub-shaft with an initial rotational speed which is lower than the rotational speed of the first sub-shaft;
• b) measuring the mains frequency of the mains supply;
• c) measuring a differential angle between the first sub-shaft and the second sub-shaft;
• d) accelerating the second sub-shaft with an acceleration value which is produced by using the mains frequency measured in step b), the differential angle and the initial rotational speed, so that the overrunning clutch couples the two sub-shafts to each other with a previously determined target coupling angle;
• e) measuring a new mains frequency during the accelerations of the second sub-shaft;
• f) in the event that the new mains frequency is different from the mains frequency measured in step b), accelerating the second sub-shaft with a changed acceleration value, which is produced by using the new mains frequency.