Slotless-armature DC drives for surface warship propulsion

A slotless armature with multiplex connection can operate with higher coil voltage and current than a conventional armature before the commutation limits are reached and so can achieve higher power ratings. DC motors may thus be designed for powers of tens of MW, suitable for direct-drive ship propulsion. The field system may use conventional wound poles, permanent magnets or superconducting coils for excitation. Slotless-armature designs using alternative types of field system are compared with a conventional slotted design for lOMW, 150 rev/min rating. The slotless-armature superconducting-field design offers the lightest and most compact overall arrangement and the best full-load efficiency. However, permanentmagnet excitation offers a much simpler solution, is the cheapest to build and gives better part-load efficiency. A more detailed design for a 15MW, 200 rev/min permanent-magnet ship propulsion machine is presented.