Superconducting DC Motors for Marine Propulsion

Electric propulsion power transmission is usually economical only for special vessels. However, superconducting motors with their greatly reduced weights and sizes indicate that this type of propulsion may become more widespread in the future.

The energy crisis of the early 1970s provided impetus for more sufficient energy conservation and for exploiting hitherto untapped resources.

The superconducting dc motor adds a potent new factor to this situation. It offers the best of these options in that it is lighter than the equivalent conventional ac motor and is a dc motor which may be operated from an ac generator via a simple diode-rectifier-convertor. It offers all the advantages of a dc propulsion system, together with high efficiency, and performance characteristics particularly suited to high efficiency propellers; with no practical power limit.

What is a Shaft Generator? Automatic Control of the Shaft Generators

When the order is issued for the main engine to operate at a constant speed corresponding to the correct frequency, and if the load on the distribution network is not in excess of the maximum permissible load on the shaft generator, and if no alarm is operative on the shaft generator, this combination of conditions is indicated on the control panel by the "shaft generator ready" lamp lighting up.

The generator then rotates at the correct speed although without excitation, i. e. it generates no voltage.

If the change-over switch on the control panel is set to the "shaft generator on" position the generator will be excited and will generate a voltage. When about 85% of the normal voltage is attained, control of excitation shaft generator will be taken over by the voltage regulator in the switchgear.