Facilities: Pumps and Fans - Energy Conversion and Management - page 168

Fig. 10.8 Pump curves at different shaft speeds
shaft speed by means of variable-speed drives (hydraulic or electromechanical
coupling to regulate the shaft speed at constant electric motor speed, electrical
variable-speed drives to regulate the motor speed and so the shaft speed).
In large pump systems, drivers like steam engines or turbines, gas turbines, and
diesel engines can also be applied (see Chap. 9 ) .
Figure 10.8 shows a typical example of flow regulation obtained by varying the
pump speed until the curve of the pump crosses the curve of the load at the desired
working point.
Great precision is not generally necessary; note that the bottom speed limit does
not usually go below 40-50 % of the design speed.
Comparison of dissipative with non-dissipative methods underlines
the following energy-saving advantages of the latter:
• Reduction of energy consumption at constant energy delivered to
the load
• Reduction of the power demanded from the electric line due to the
reduction of the shaft power
The commonest electrical drives are d.c. motors with a.c./d.c. converters and
a.c. motors with inverters; the latter can also be applied to existing motors and are
suggested for hazardous environmental conditions (see Sect. 7.4 ).