These are similar to the ones that I operated for several years as a DC substation operator in NYC. The main differences were that we did not use pony motors, although the NYC transit system did. In addition, when we synchronized the rotary converters we used a ac voltmeter and a set of lights, when the vm read near zero decreasing or the lights were dimming to out we closed a spring loaded oil emersed motor driven circuit breaker.
The exact operation as so eloquently stated by Alan is better then I can remember, as I left the DC system in 1969-1970, and do not have any of my reference material left.
You did an excellent job in describing the operation of the rotary converter
