Water Column Separation at Turbine Start up Loading

Abstract

According to authors knowledge this is the first case of water column separation that happened, not during load rejection, but during the turbine start and loading to full power output. To control the transient flows in water courses, the wicket gates of turbine are the primary flow regulators. The minimum pressure during transient operations of hydroelectric turbine units may cause a water column separation and the subsequent re-joining creates forces that could damage turbine runners, non-rotating parts, and the whole machine house. This condition occurs when a local pressure drops below the vapour pressure or partial pressure of gases (air). The instant pressure rises from collapse of voids have the potential to crack internal linings of water conductors and connections between steel and concrete, and may damage hydraulic machines, air valves, penstock valves, or gates. The damage may not be evident immediately but would be observed after repetitive transients. All calculations and measurements of transients must be completed for analysis of the water column separation, following existing guidelines, though there is no standards and recommendation on the subject of waterhammer and hydraulic vibrations. This paper presents an approximate analysis of water column separation based on the pressures measured on site.