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How do you perform simple savings and payback calculations?

To perform a useful payback calculation, application-specific data must be gathered from the installation. The load profile under all conditions must be measured or estimated.  As each motor application is unique, only a costing exercise will reveal the potential savings of installing a VSD in a system.
For a simplified example of a payback calculation, see Example of a VSD payback calculation. Note that participation in the ACA scheme further reduces the payback period.
Should you be concerned about harmonics?
All VSDs produce harmonics from pulsed current being drawn from the supply. Harmonics are multiples of the 50Hz supply frequency which become superimposed on the supply system. Harmonics can cause problems such as equipment and capacitor overheating, voltage distortion and equipment malfunction. However, the use of filters, sometimes available as part of a VSD, helps to minimise the effects of harmonics.