The objective of the present work is to evaluate the performance of a hydraulic turbine by means of the measurement of flow using the Gibson method based on recording pressure–time rise in one section of the penstock and relate it to the pressure in the upper reservoir to which the penstock is connected. Volumetric flow is determined by integration of the time function of a differential pressure (between the section and the inlet to the penstock). Flow measurement was possible this way because the influence of penstock inlet was negligible as far as an error of the measurement is concerned. The paper presents the results obtained with this method for the case of a 170 MW hydraulic turbine. The length of the penstock was 300 m. Previous experience and a standard IEC-41-1991 were the criteria adopted and applied. An efficient and fast acquisition system including a 16 bit card was used. The flow rate was calculated using a computer program developed and tested on several cases. The results obtained with the Gibson method were used for calibration of the on-line flow measuring system based on the Winter-Kennedy principles. This last method is used for continuous monitoring of the turbine flow rate. Having calculated the flow rate and output power the efficiency is calculated for any operating conditions. A curve showing the best operating conditions based on the highest efficiency is presented and discussed. Flow simulation allowed having an estimation of a flow recirculation region size.

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