Electric propulsion systems, electric drive systems

The concept of electric propulsion is over 100 years old with battery-powered vessels recorded in Russia and Germany around 1870. In 1893, one of the first electric boats ELECTRICITY carried passengers on the River Thames in England. The most famous was the 1936 built trans-Atlantic liner NORMANDIE which used electric propulsion via four 29MW synchronous motors, each powered by a dedicated turbo-generator and driving one of the four propellers.

This type of propulsion system consists of prime movers (diesels, gas turbines or steam turbines), AC generators, power conditioners (cyclo-conventers, pulse-width-modulated inverters, load-commutated inverters), DC or AC propulsion motors. The term “DC propulsion system” implies that a propulsion system includes a power conditioner to convert AC to DC, such that a DC motor can be used. An “AC propulsion system” consists of a different type of power conditioner and an AC motor.

The electrical connection between a generator and the propulsion motor provides a freedom of arrangement not offered by a mechanical system.

The ability to separate the engine and the propeller, flexibility of multi-power operation and the ability to combine auxiliary propulsion are the performance and economic factors that have made electric drive a popular choice for modern cruise ships.

Electric propulsion systems are used for the following applications:

- Vessels requiring a high degree of manoeuvrability (ferries, icebreakers, tugs, cablelayers),

- Vessels requiring large amounts of special-purpose power (self-unloaders, dredges,

drill ships),

- Vessels with large hotel loads,

- Vessels using non-reversing, high-speed, and multiple prime movers.

Benefits of the electric propulsion include:

- Better space utilisation permitting to carry more cargo

- Less machinery space required.

- More efficient use of fuel resulting in reduced fuel consumption at variable operational

speeds.

- Improved manoeuvrability with azimuth or podded propulsors installed.

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