Stability Criteria of Reversible Pump Turbines

Abstract

The objective in this Master's Thesis was to verify the stability criteria for a centrifugal pump. Operation of an unstable pump may lead to either exponential or oscillatory unstable behavior of both pressure and volume flow of the water in the conduit system. This is of course unwanted, and fulfilling the stability criteria is desirable. The idea is to test an unstable pump, which was done at the Technical University Berlin (TU) in Germany. Most of the test set-up was already installed, but a new pump and a pressure accumulator was inserted. Unfortunately the experiment was not able to verify the stability criteria systematically, because the set-up was a closed loop without reservoirs; and because the different parameters affecting the stability were difficult to change. The experiment was educational even though the stability criteria were not verified. Different tasks were executed at TU, like installing the pressure accumulator and a pressure sensor, and measuring the pump characteristic. The work with the Master's Thesis also improved the candidate's understanding of the stability criteria and the dynamic behavior of the water in general.A simulation program was made in Matlab, and the aim of the program was to simulate the oscillations of the water in the conduit system. Most of the parameters put into Matlab were measured at TU, except the volume of the air inside the pressure accumulator. This volume affects the frequency of the oscillations a lot, but a good estimation of the volume of the air, made the simulations quite similar to the measured results. In addition to simulating the existing set-up, the simulation program made it easy to vary the parameters affecting the stability criteria. The simulation program was tested this way, and the stability criteria seem to be correct.