Analysis of the Influence of Steam Electrification on the Working Processes of a Wet Steam Turbine

Abstract

The effect of steam electrification on the operation of a wet steam turbine, as well as the main processes sensitive to the electrification of the working fluid are considered in the paper. The types of additional losses caused by electrification are indicated. It is noted that these losses are not counted in the currently existing physical and mathematical models, since data on electrification are not taken into account and there is no possibility to make a clear theoretical description of the electrophysical model of a neutral steam even. In this regard, a simplified qualitative physical model of the electrophysical processes that occur during the electrification of the steam flow in the turbine was studied. Based on this, an assumption regarding the properties of the space charge in the steam flow, which is the source of the electric field and determines its intensity and spatial distribution in the flow part, is made. A qualitative analysis of the effect of the space charge field on the physical and thermodynamic properties of the steam flow was carried out with the set assumptions. It is proposed to perceive the process of steam polarization in the space charge field as the main result of its influence, and the dielectric constant of the steam – as the most representative parameter characterizing the thermodynamic state, including with the field influence. The thermodynamic relations of the operation of the dielectric in an electric field are given. The relation between the dielectric constant of steam and the change in the internal energy of the working fluid, its entropy and free energy is shown. It is theoretically substantiated that the influence of the electric field also leads to a change in the isobaric heat capacity and enthalpy. It is concluded that the process of expansion of the wet steam flow of charged steam in the turbine unit can be accompanied by a change in the main thermodynamic parameters of the working fluid, and therefore, its design characteristics can change, including the losses that occur in the process of expansion. On the basis of previously obtained experimental data on real turbines, a numerical assessment of the change in the thermodynamic parameters of the working fluid under the influence of an electric field is carried out. The performed numerical studies unequivocally indicate the need to take into account the phenomena caused by the electrification of the wet steam flow in the low-pressure cylinder in the existing physical and mathematical thermodynamic models of the wet steam expansion process, as well as to clarify the main thermodynamic parameters and calculated characteristics of the flow of electrified wet steam depending on the change in its dielectric constant.