This paper investigates the effect of surge tank throttling on governor stability, power control, and hydraulic transients in hydropower plants. The work is intended to be practical, but includes some new research. The practical contributions include a methodology for a combined evaluation of the effects of installing surge tank throttles in hydropower plants, and a demonstration of the throttle effects through a case study. The research contributions include the evaluation of the throttle effect on power control, and a comparison of the throttle effects on power control for governor systems with speed feedback exclusively versus combined speed and power feedback. Field measurements are used to calibrate a numerical model of the case-study hydropower plant. The results from the case study show that the throttle has an insignificant positive impact on governor stability. Power control is improved when a throttle is installed; the overshoot of produced power and the time until steady-state conditions occur are reduced. The throttle has a significant effect on the hydraulic transients, and increases the water hammer and reduces the mass oscillations in the system.

The fundamentals of oscillating flow in a reservoir-pipe-orifice system are revisited in a theoretical study related to acoustic resonance experiments carried out in a large-scale pipeline. Four different types of system excitation are considered: forcing velocity, forcing pressure, linear oscillating resistance and nonlinear oscillating resistance. Analytical solutions are given for the periodic responses to the first three excitations. Analytical and numerical results for the large-scale pipeline are presented and some peculiarities are discussed.

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Acoustic resonance in a two-pipe system is simulated with four different models for the periodic excitation. Analytical solutions are provided in full for the three linear excitations. Exact numerical results are presented for the nonlinear excitation. The influence of a large-diameter supply pipe (instead of a constant-head reservoir) on the system's fundamental frequencies and mode shapes is studied. The peculiar behaviour of wave reflection at an orifice is fully explained.

This paper presents results from an experiment performed to obtain the dynamic characteristics of a reversible pump-turbine model. The characteristics were measured in an open loop system where the turbine initially was run on low rotational speed before the generator was disconnected allowing the turbine to go towards runaway. The measurements show that the turbine experience damped oscillations in pressure, speed and flow rate around runaway corresponding with presented stability criterion in published literature. Results from the experiment is reproduced by means of transient simulations. A one dimensional analytical turbine model for representation of the pump-turbine is used in the calculations. The simulations show that it is possible to reproduce the physics in the measurement by using a simple analytical model for the pump-turbine as long as the inertia of the water masses in the turbine are modeled correctly.