Shaft generator systems with frequency converters supply a three-phase current of constant voltage and frequency to the mains at variable main engine speeds. The useful speed range of the shaft generator can be defined from the ship’s operational requirements. For example, it is possible to select a shaft generator speed range of 60% to 100% of the main engine speed with a constant system output.
All shaft generator systems have one thing in common: The active power required for the mains is generated by the main engine. However, the shaft generator can be arranged and driven by the main engine in various configurations.
The shaft generator is installed in the shaft line between the low-speed main diesel engine and the propeller. This configuration has a large air gap between the stator and the rotor, and without additional bearings has proven very successful as the most frequently used configuration. It is particularly simple and sturdy and requires little maintenance. Contrary to other arrangements, torsional vibration problems relating to the design and operation are not anticipated with this configuration.
The shaft generator is operated via a power take-off by a reduction gear which is arranged between the medium-speed main diesel engine and the propeller. This is the usual and appropriate configuration for medium-speed main diesel engines.
The shaft generator is operated via a tunnel gear unit installed in the shaft line between the low-speed main diesel engine and the propeller.