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Discharge Estimation Techniques for
Hydraulic Efficiency Testing

Pamela Hans, 1997

Field performance testing of hydraulic turbines is used to define the head-power- discharge relationship for a turbine/generator; this relationship is used to identify the peak operating point for a turbine. Of the variables used to determine this relationship, discharge is the most difficult to measure accurately in real time and is most susceptible to measurement error. The velocity-area method of discharge measurement is favored by many hydroelectric utilities as it is well-suited to application at low head plants.

Velocity data collected during field performance tests were used to compare discharge estimates numerically computed using various distributions of metering points. This analysis suggests that an accurate estimate of discharge may be obtained by establishing the arrangement of measurement points based on the true intake velocity profile, rather than on an idealized velocity distribution.

Laboratory testing was undertaken to investigate the results of the numerical analysis. Seven arrangements of velocity points were used to compute discharge through a model of a turbine intake. The accuracy of a discharge estimate was evaluated by comparison to a reference discharge. The results of the laboratory testing are comparable to the numerical analysis and indicate that an accurate discharge estimate may be obtained using a numerical integration strategy.

An observed relationship between the horizontal velocity profile and unit discharge prompted analysis of a Reduced Data Set (RDS) method of estimating discharge. Field data was used to investigate the statistical relationship between discharge and horizontal velocity profile at three locations within the vertical traverse. The analysis was used to evaluate the reliability of a discharge estimate made based on the relationship between the two variables. The results of this analysis suggest that the relationship between horizontal velocity profile and discharge is strongest in proximity to 0.11 D (from top and bottom of the intake).

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