Steam turbines are responsible for 80% of global electricity production and the presence of moisture significantly reduces the turbine efficiency costing 50 million pounds per annum in UK alone. The mechanisms of condensation in steam turbines are, however, not well understood. For example, the usual steady condensation theories, a conglomeration of gas dynamic equations, nucleation rate equation and droplet growth laws, cannot reproduce the characteristics of experimentally measured droplet size spectra. In this paper, therefore, the effects of two unsteady flow phenomena on the homogeneous nucleation of water droplets are investigated : unsteady flow due to supercritical condensation and that due to wake segmentation. Both calculations give rise to characteristics of measured droplet spectra, though the effects of wake segmentation seem to have the dominating influence in a multistage steam turbine. The theory presents a radically different perspective of nucleation in turbines from the generally accepted view and, if correct, will have a major influence on the future development of calculation procedures for non-equilibrium steam flow in turbines.