Possible Motor Modifications for Australia's Future Submarine

wispywood2344's diagram of a Soryu class submarine. To accommodate more powerful motor(s) changes like a longer section 12 (at the back) would be required. See larger, more readable, image of the diagram at http://blog.livedoor.jp/wispywood2344/others/Soryu_cutaway.svg. 

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Submarine Matters has lately concentrated on diesels for Australia Future Submarine but motors are equally important in submarine generator sets (gensets).

Anonymous has kindly made comments of January 19, 2018 on submarine motors. The comments have been further translated by Pete.

Japan’s proposed submarine design “SEA-J” for the Australian Future Submarine (SEA 1000) competition was to be 92m long. Naval Group of France won the competition in April 2016, but it is still relevant how Japan would have handled the more powerful propulsion solutions for a large Australian submarine. Relevant because Naval Group will need to resolve similar propulsion issues.

SEA-J is 8m longer than Japan's already built Soryu submarine’s 84m. In the cutaway diagram above the main motor section (12) was lengthened by 2m to improve the performance of the main motor. As SEA-J would have been required to transit long distance (perhaps 3,000 km each way) and at high speed, the durability and reliability of the main motor is all the more essential. The motor’s durability could be improved by measures such as adopting a tandem connection of two main motors. This results in longer length.

Neodymium magnets (which experience thermal and electrical environmental degradation) and bearings (which experience wear) are used in a submarine’s Permanent Magnet Synchronous Motor (PMSM). A PMSM uses permanent magnets embedded in a steel rotor to create a constant magnetic field. The stator carries windings connected to an AC supply to produce a rotating magnetic field. To prevent damage, the magnets, made out of Neodymium are kept cool. This is achieved by limiting the rotation speed/load and limiting bearing temperature. 

Japan's current Soryu Mk.I (with LABs and AIP) is equipped with one SMC-8 main motor. This is the first time the Soryu’s motor has been named in English to Pete’s knowledge.) 

The SMC-8 consists of two rotors and three bearings (two journal bearings which support the cylindrical rotating shaft at bow and stern sides, and one thrust bearing in which supports the axial load caused by propulsion at stern side). The SMC-8’s maximum output is 5.9 MW.

The tandem motor consists of two motors (four journal bearings, one thrust bearing). The load at each journal bearing will reduce than single motor (two journal bearings, one thrust bearing) with same output, because weight of rotor per unit journal bearing reduces. Disadvantages of tandem motor are unchanged thrust load, increased size of motor, increased number of vibration sources (increased number of bearings) and so on. A tandem motor may be suitable for large conventional submarine or nuclear submarine.

Regarding motor components, of interest is the RENK Company of Hanover, Germany's “Propulsion Motor Bearings and Thrust Bearings for Naval Application (Submarines)” document (PDF 2MB). In it: 

-  A stern side picture of a PMSM motor is shown at Fig. 3, on page2.

-  Most western submarine builders including Naval Group, TKMS and Navantia (S-80s) use RENK

   products. See page 4 which indicates “Over the last 50 years RENK slide bearings [have]

   equipped...more than 160 submarines.”

By Anonymous and Pete