SELECTED PROBLEMS IN CALCULATION PROCEDURES FOR THE GIBSON DISCHARGE MEASUREMENT METHOD

The pressure-time (Gibson) method belongs to the primary methods of discharge measurement through hydraulic machinery. The method consists in determining the flow rate by the integration of recorded time course of pressure difference variations between two cross-sections of the hydropower plant penstock. The paper presents two selected problems related to calculation procedure of discharge measurement by means of Gibson method. The first one is connected to the calculation of hydraulic losses in a penstock measurement section while determining flow rate by means of Gibson method. The modification of procedures usually utilized to calculate these losses was proposed and the experimental results that verify its importance, basically in case of applying Gibson method for flow rate measurement in investigated hydraulic machinery under the pump regime, were presented. Second problem regards the estimation of upper integration limit of pressure gradient time-course recorded when using considered measurement method. To determine this limit, the free oscillations characteristic of recorded pressure difference occuring after shutting-off the liquid flow in a pipeline was applied. Two methods of eliminating the effect of these fluctuations on determined volumetric flow rate value were presented. They differ from the testing procedure described by the International Standard IEC 41.