[Lucien Nunes]

This is a normal rotary converter that produces 110V 50Hz AC from 110V DC.

L= Line, F= (shunt) field, A = Armature.
S1, S2 = secondary i.e. output winding.
Per = periods = cycles = Hz

It would typically have been used for supplying AC-only equipment where the mains or on-site generation was DC, or from a battery bank. I have a number of similar units that were used for this purpose, of various voltages. The nearest modern equivalent would be something like a PV (solar) inverter, powering domestic loads from DC solar cells.

L, D & C did make a lot of battery charging sets, some of which were interesting and now very scarce. Where the mains were DC, a DC-DC rotary was needed. Where AC, options included an induction-start AC-DC rotary, a motor-generator set, or a synchronous rotary commutator which looks similar but doesn't convert the power, only rectifies it. Obviously this unit goes the other way, producing AC from DC. The firm also made general purpose motors, dynamos and alternators.

One other application of these units in the early 1930s that was often 110V DC to 110V AC was to power early cinema sound equipment. 110V DC was often available from the arc supply, and much of the sound equipment was imported from the US and was 110V as standard. However, it was also 60Hz and the rotaries likewise, so this unit was unlilkely to have been for that purpose.

Have you tested the windings / insulation resistance yet? 110V machines are normally pretty robust so hopefully it will all measure OK. If you want to run it from rectified mains, you can start it with a variac on the AC side.