Propulsion system

Abstract

An arrangement is disclosed for supplying propulsion power to a contra rotating propellers (CRP) propulsion system in a marine vessel, which arrangement can include a first propeller driven by a rotating power unit, and a second propeller driven by an AC motor. The second propeller can be rotated in an opposite direction relative to the first propeller, wherein an AC generator is driven by the rotating power unit and the AC generator is electrically connected to the AC motor. The rotation speed of the second propeller is between for example 95% and 150% of the rotation speed of the first propeller. The AC motor and the AC generator have the same electrical frequency. The pole number of the AC generator is from for example 2 to 40 and the pole number of the AC motor is from for example 2 to 40.

1 . An arrangement for supplying propulsion power to a contra rotating propellers (CRP) propulsion system in a marine vessel, which arrangement comprises:
 a rotating power unit for driving a first propeller;   an AC motor for driving a second propeller, whereby the second propeller is configured for rotation in an opposite direction relative to rotation of the first propeller; and   an AC generator configured to be driven by the rotating power unit, the AC generator being electrically connected to the AC motor, wherein a rotation speed of the second propeller will be between 95% and 150% of a rotation speed of the first propeller, wherein the AC motor and the AC generator have the same electrical frequency, and wherein a pole number of the AC generator is from 2 to 40, and a pole number of the AC motor is from 2 to 40 so that a ratio of the pole numbers of the AC motor and the AC generator is from 0.05 to 20.   
     
     
         2 . An arrangement according to  claim 1 , wherein a diameter of the second propeller is smaller than a diameter of first propeller. 
     
     
         3 . An arrangement according to  claim 1 , wherein a distance between the first propeller and the second propeller is less than twice a diameter of the first propeller. 
     
     
         4 . An arrangement according to  claim 1 , wherein a power proportion of the first propeller and the second propeller ranges between 50:50 and 80:20. 
     
     
         5 . An arrangement according to  claim 1 , wherein the AC motor is supplied by a second electrical power source which is electrically connected in parallel to the AC generator. 
     
     
         6 . An arrangement according to  claim 1 , wherein the AC generator supplies electric power to a second electrical consumer which is electrically connected to the AC generator. 
     
     
         7 . An arrangement according to  claim 5 , wherein the second power source comprises:
 a frequency converter, the second power source being electrically connected via a switch to the AC motor.   
     
     
         8 . An arrangement according to  claim 5 , wherein the second power source is switchable to the AC motor and/or the AC generator when changing power distribution between the first propeller and the second propeller. 
     
     
         9 . An arrangement according to  claim 5 , wherein an electrical power connection between the AC motor and the AC generator comprises:
 a line breaker, the AC generator and the second power source being configured to be alternatively switchable to the AC motor when maneuvering a vessel.   
     
     
         10 . An arrangement according to  claim 1 , wherein the AC motor and/or the AC generator have one or more independent windings. 
     
     
         11 . An arrangement according to  claim 1 , wherein the AC generator comprises:
 one or more separate generators.   
     
     
         12 . An arrangement according to  claim 1 , comprising:
 one or more mechanical gears between the first propeller and the rotating power unit driving the first propeller.   
     
     
         13 . An arrangement according to  claim 1 , comprising:
 one or more mechanical gears between the AC generator and the rotating power unit driving the AC generator; and/or a gear unit arranged between the second propeller and the AC motor.   
     
     
         14 . An arrangement according to  claim 1 , wherein the second propeller is of an azimuth type. 
     
     
         15 . An arrangement according to  claim 1 , in combination with a marine vessel comprising:
 first and second propellers.