Reconstruction of Nizhne-Svirskaya HPP hydroturbines using propeller blade runners with variable rotation speed

Abstract

Reconstruction of axial-flow hydroturbines through installation of variable speed propeller blade runners is considered. Using daily information about water head, capacity, and suction height of Nizhne-Svirskaya HPP units, topograms of hydro equipment operating conditions were created. For obtaining a regular pattern of unit capacity usage in power grid, those topograms were redesigned into histograms of relative duration of normalized capacity. Using aforementioned histograms enabled to substantiate the possibility of application of propeller blade runners for HPP reconstruction. The most dangerous unit operating conditions were identified in terms of cavitation. The upper limit for turbine cavitation coefficient was established. Methodologies were presented and a choice was made from several blade angles using analysis of efficiency levels, maximum normalized capacity, and turbine cavitation coefficient. Based on empirical dependencies, approximate losses in water parts induced by differences in geometry of old and reconstructed turbines were considered. With specifics of the propeller blade runner and losses in elements of the turbine water part taken into account, an estimated model hill chart of a hydroturbine with a new blade runner was created. This was used to plot an estimated prototype hill chart of the reconstructed hydroturbine operating with variable rotation speed. Three main operating zones are highlighted on the prototype hill chart. Simultaneously with achieving higher values of capacity compared to those of a Kaplan turbine, the operating range has been widened compared to traditional propeller turbines with a constant speed.