The ship electrical motor is the most commonly used device for conversion from electrical to mechanical power on ship and is used for ship electric propulsion, thrusters for propulsion on ship or station keeping, and other on-board loads such as ships winches, pumps on ship, fans, etc.
Typically, 80-90 % of the loads in ship installations will be some electrical motors.
In this chapter, a brief overview of different motors and their applications in ship installations is given and for more detailed description of design, performance, and characteristics, references to other books are made.
The ship electrical motors in use are:
– DC motors on Ship
The DC motor on ship must be fed from a DC supply, and since the power generation and distribution system on ship normally is a three-phase system, this means that a DC motor must be fed from a thyristor rectifier. This gives also a speed control of the motor.
– Asynchronous (induction) motors on Ship
The asynchronous or induction motor on ship is the workhorse of the industry. Its rugged and simple design ensures in most cases a long lifetime with a minimum of breakdown and maintenance. The asynchronous motor is used in any applications, either as a constant speed motor directly connected to the network, or as a variable speed motor fed from a static frequency converter.
– Synchronous motors on Ship
The synchronous machine on ship is normally not used as a motor in ship applications, with exception of large propulsion ship drives, typically > 5 MW directly connected to propeller shaft, or >8- 10 with a gear connection. In power range smaller than this, the asynchronous motor is normally cost-competitive.
The design of a synchronous motor on ship is similar to that of an synchronous generator. It is normally not used without a ship frequency converter supply for variable speed control in ship applications.
– Permanent magnet synchronous motors on Ship
Permanent magnet synchronous motors on ship system are used in industrial drives for some few kW drives, also for direct on-line applications. In recent years, it has been introduced also for large power applications; in several MW ship propulsion drives, firstly in navy applications but now also in podded propulsion applications. The benefit of this design is high efficiency with compact design, making it especially interesting for podded propulsion where the dimensions should be as small as possible, and direct water cooling would eliminate the need for air cooling of the pod motor and simplify the construction and installation work.
– Other motors on Ship
A range of other motors on ship is used in commercial or experimental applications. Few of them have gained a high market share, and especially not in marine applications. It might in future be seen some new concepts for variable speed drives, based on motor designs with higher efficiency, small dimensions, or specially designed for certain applications. They will most likely though be based on the principles described above or derivatives of these.
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