The video Swadian Hardcore found is for a similar, but perhaps not identical sleeping car. I think that it's a training film.
At 6:30 the announcer mentions sleeping compartments, room for service personnel, and the provodnitsa's compartment. The one two-person compartment must be that room for service.
At 11:40 you see the big circle Swadian was wondering about. It is the heating system, which can use either electric heat or coal. At 16:47 you see the samovar. It also is dual fuel.
The announcer has a classic Soviet style of delivery. Even, clear tones, good enunciation, which makes it easier for people for whom Russian is a second language.