Mains frequency
Due to historical developments, a mains frequency of 50 Hz is used in Europe, Asia, Australia, most of Africa and parts of South America, while a mains frequency of 60 Hz has become established for the public power grids in North America.
The specification of the mains frequency is necessary for the selection of the electric drive. For pumps that are operated with single-phase or three-phase motors without a frequency converter, the synchronous motor speed changes in the same ratio as the frequencies, i.e. from 50 to 60 Hz by a factor of 1.2. In accordance with the affinity laws, this also changes the pump’s performance data.
A frequency converter is often used to adapt the performance data to the operating point. The electrical energy drawn at the mains frequency is converted into a voltage with a different frequency in order to change the motor speed.
2. Model law
3. Model law
Q – flow rate
H – delivery head
P – power consumption
n – speed
The indices relate to the respective speed.
The affinity laws apply exactly to frictionless, incompressible flows. For technical applications, they are to be regarded as an approximate solution.
In general, these affinity laws are independent of how the speed change is technically implemented. Traditionally, multi-speed functions of small and medium size pumps are realized by changing the motor windings configurations to achieve stepped speed variations. Meanwhile, these have been largely replaced by frequency converters.
Slow-running electric drives are very expensive for larger centrifugal pumps, so that reduction gears are used for these cases.
Combustion engines are used for some mobile applications. They are also variable in speed within a specified range. 