July 19, 1979
TO: H. V. AIKEN, Chief of Hydrologic Review, Regulatory Division 19
FROM: L. S. HENNESSEY, Hydrologist, Regulatory Division
RE: Diversion from Little Manatee River, Florida Power, and Light Company
As a result of the July 16 meeting at Florida Power and Light, Manatee Plant,
staff concludes that Florida Power and Light are within the flow diversion rate
limitations of their agreement. Following is an explanation of the problems
surrounding the automated computer system and the monthly diversions report.
Line glitches (false electronic signals) caused by brief surges of electrical
Result: The erroneous electronic signals are interpreted by the computer
into letters and numbers. A faulty report results with numbers incorrectly
describing the pumpage.
Solution: Devices have been added to reduce the computer systems sensitivity
to minor power surges. However, surges can still occur. If one does occur
resulting in a faulty reading, an alarm is triggered, and the system automati-
cally takes a second reading. Any corrections would be made within 3 to 6
seconds of the first (incorrect) reading.
Turbulent flow and noise interference at flow meter in pipe between river and
Result: The interference caused the meter to register non-existent flow.
Solution: The problem has been solved by the installation of a check valve
and pressure switch.
Automated system operation of pump. The computer system automatically selects
pumps for operation based on the pump capacity necessary to achieve the allowable
diversion rate. If more than one pump is needed, the program assigns the same
allowable diversion rate to each pump operating.
Result: For a short time interval the computer senses each well pumping in-
dependently toward the allowable diversion rate. This proceeds until the
total flow equals or surpasses the allowed rate. An alarm is triggered if
the flow rate exceeds the allowable diversion. Within 3 seconds the "over
diversion" situation is corrected by valve adjustment to reduce flow. If
after the adjustment the total flow is under the allowed diversion rate, the
valves will again open slightly. The result is that the actual diversion
rate is "chasing" the allowed diversion rate (see diagram). Noticeable over
and under diversions can occur for a period of 2 to 3 minutes. As a result,
the maximum pumped, though only an instantaneous reading, is recorded with-
out an reference to the duration of that pumping rate.
July 19, 1979 --
H. V. AIKEN
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