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<br />usbr/wapa <br /> <br />reporting, as efforts are being made to verifY the accuracy of converting the flowmeter <br />data. <br /> <br />Reasons Wby tbe Scbedule Targets are not Usually Acbieved and Degree of Error <br /> <br />The relationship between water flow through a unit and the amount of power generated is neither <br />constant nor linear. There are several variables that affect the amount of water flowing through <br />the power plant at Glen Canyon: <br /> <br />Western's Prescbedule: In determining generation releases, Western preschedules the <br />power plant using a conversion factor to translate energy (megawatts) to water (cfs). A <br />single conversion factor is used for the entire month based on the power/water ratio from <br />the previous month. lbis method is different from the SCADA report, which reflects the <br />turbine rating curves. By comparison, this measurement differs from the Accusonic <br />flowmeteci by approximately:!: 7%. <br /> <br />Lake elevation: The difference in elevation between the forebay and the tailbay is <br />referred to as the "head". "Head" is affected by lake elevation and the amount of water <br />being released from the generating units. Changes in "head" affect the efficiency of the <br />generatoring units and head may differ over the course of the day and from one month to <br />the next. Western's scheduling office uses the "head" from the previous month in <br />preparing its schedule. Because of this, and the possibility of "head" changing over the <br />day, the generation at Glen Canyon will always result in water releases that differ from <br />anticipated or scheduled release. <br /> <br />Generator efficiency: Generator efficiency is relatively constant while turbine efficiency <br />varies significantly with discharge and head. <br /> <br />Starting or stopping: When a unit is shut down, there is water flow through the turbine <br />even though there are no energy is being generated. A unit shutdown, or one in standby <br />status; waiting to be started. has wicket gate leakage of approximately 50 cfs. Also, when <br />a unit is started or stopped, water is released before an electricity is generated. As an <br />example: in preparation to bring a unit on line to meet Western's schedule, water release <br />begins and "spins" the generator for a 10 minute period to allow the unit to come up to <br />normal operating temperature. This will add about 155 cfs to the total water release <br />during that 10 minute interval. The water released during this period is not "counted" in <br />the quantity of water released in the hour. The water that is "counted" is that water <br />recorded by the SCADA, which is the official measurement for compliance with the <br />ROD. <br /> <br />Number of generators: Both Western and Reclamation have historically used 60 <br /> <br />6 <br />