Fast transition from pump to turbine mode of operation

The reversible pump turbine (RPT) is a suitable machine to control fluctuations in the energy market. The usage of RPTs for this purpose will increase the number of operational mode changes of the machine. In order to reduce the response time of the machine, fast transitions between the modes of operation are necessary. Therefore, increased knowledge of how the machine operates during these fast transitions is needed. This includes the investigation of the transient characteristics for the whole operating range of the machine. This paper presents experimental results from a fast transition from pump to turbine mode. The flow rate is measured by the use of a modified pressure time method. The resulting transient characteristics are compared with steady state characteristics. Experiments have been preformed on a model scale reversible pump turbine in the Waterpower Laboratory at the Norwegian University of Science and Technology (NTNU). The results show that the pressure pulsations are highest at low discharge in both pump and turbine mode of operation and at runaway speed in turbine. Oscillations at runaway speed is reduced with lower opening degree on the guide vanes. The results also show a difference between the steady state and transient characteristics in the pump mode due to the inertia of the water masses.