6.10.6
Calculating the energy saving for fluid flow machines
Overview
Fluid flow machines, which mechanically control the flow rate using valves or throttle flaps,
operate with a constant speed corresponding to the line frequency.
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Figure 6-106
Flow control with pump and throttle connected to a 50 Hz line supply
The lower the flow rate, the poorer the efficiency of the fluid flow machine (pump). The fluid flow
machine (pump) has the poorest efficiency when the throttle or valve is completely closed.
Further, undesirable effects can occur, for example the formation of vapor bubbles in liquids
(cavitation) or the temperature of the medium being pumped can increase.
The converter controls the flow rate by appropriately varying the speed of the fluid flow
machine. By controlling the flow rate, the fluid flow machine operates at the optimum efficiency
for each flow rate. This situation means that in the partial load range less electric power is
required than when controlling the flow rate using valves and throttles.
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Figure 6-107
Flow control with pump and converter
Function description
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The converter calculates the en‐
ergy saving from the flow charac‐
teristic associated with a me‐
chanical flow control and the
measured electric power that is
drawn.
The calculation is suitable for
centrifugal pumps, fans, radial
and axial compressors, for in‐
stance.
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Advanced commissioning
6.10 Energy saving
SINAMICS G120X converter
Operating Instructions, 06/2019, FW V1.01, A5E44751209B AC
453
