Turbine Inlet Valve’s Self-Excited Vibrations Risk the Safe Operation of Hydropower Plants

Abstract

PurposeThe main function of the turbine inlet valve (TIV) in a hydroelectric power plant is to prevent flow of water to the turbine whenever the turbine is not operating. Usually, the valve responsible for this operation is spherical with annular seals to perform the sealing function. Occasionally, when the valve is set into a closed orientation, the annular seal may not execute its sealing function properly though develop periodic oscillations accompanied by periodic leakage flows. These seal vibrations cause pressure fluctuations in the penstock pipeline, which risks the plant’s reliable and safe operation. Therefore, the primary goal of this research is to present a simplified theoretical model, able to clarify the excitation mechanism of the periodic seal vibration and simulate the plant’s transient behavior. Afterwards, develop some recommendations to enhance the stable operation of the (TIV).MethodsThe system governing equations comprises the water hammer equations to model the water flow through the various pipelines, the vibrating seal equation of motion, and the system boundary conditions.ResultsThe dynamic instability of the (TIV) vibrations is more likely to arise at higher input reservoir energy levels and at the first harmonic of the seal oscillation. In addition, modifying the (TIV) by increasing pilot pipeline head losses and reducing its diameter can eliminate the (TIV) vibrations and warrant the plant’s safe operation.ConclusionResults revealed that fluid compressibility and acoustic transmission have a decisive effect on the fluid-dynamic forces acting on the seal and the (TIV) stability. In addition, the origin of the (TIV) vibrations is the valve leakage flow through the service seal.