Rotary closed Rankine cycle engine powered electric generating apparatus including a rotary boiler, power fluid expander and means for condensing the exhaust vapor from the expander. The power fluid expander is rotatably driven at a predetermined speed by pressure fluid generated in the boiler and in turn drives an alternator that is hermetically sealed in a casing rotatable with the boiler and condensing means as a unit. The alternator is rotatably mounted in gas bearings and a portion of the power fluid condensed in said condensing means is utilized to cool the alternator and to provide power fluid vapor at a constant low pressure which is supplied to the gas bearings to lubricate said bearings. In the disclosed embodiments a magnetic-harmonic drive between the alternator and the rotary engine rotatably drives the latter at a predetermined speed substantially slower than the speed of the expander and alternator. In one disclosed embodiment separate primary and secondary condensers are employed for the exhaust vapor condensing means, and in another disclosed embodiment a single condenser is employed.