Method for controlling coupling of shafts between a first machine and a second machine using rotation speeds and angles

A method for controlling coupling between a gas turbine and a steam turbine in a combined cycle power plant, the gas turbine including a first rotating shaft having a first shaft indicia and the steam turbine including a second rotating shaft having a second shaft indicia, the method comprising:

• monitoring a rotational speed and rotational angle of the first shaft;
• controlling rotation of the second shaft comprising:
• determining a first positional phase angle of the first rotating shaft,
• determining a second positional phase angle of the second rotating shaft,
• determining a relative phase angle between the first positional phase angle and the second positional phase angle,
• controlling the rotational speed of the first shaft constantly at a synchronous speed,
• accelerating the second shaft to a predetermined rotational speed relative to the synchronous speed of the first shaft,
• reducing the acceleration of the second shaft when a rotational speed of the second shaft is approaching the synchronous speed so that the second positional phase angle is slowly changing,
• waiting until the second positional phase angle is at a predetermined relative phase angle to the first positional phase angle, and
• coupling the first and second shafts at the same time when the second shaft is brought to the predetermined rotational speed and the second positional phase angle is at the predetermined relative phase angle,
• wherein a position of the first shaft indicia at each rotation of the first shaft is sensed by a first once per revolution sensor to determine the first positional phase angle of the first shaft and a position of the second shaft indicia at each rotation of the second shaft is sensed by a second once per revolution sensor to determine the second positional phase angle of the second shaft.