Variable Frequency Drives
When large AC motors are being used, an efficient way of cutting down the energy cost on these motors is to vary the frequency, or speed of operation, of the motor. This is the purpose of a variable frequency drive (VFD). Motors that do not vary their frequency are forced to operate at their maximum frequency at all times, even when this much power is not needed. Having the ability to change the frequency, for times when less power is needed, and still being able to achieve the full power of the motor can improve efficiency, energy savings, and optimize the motor-driven process. The energy savings from a VFD can be dramatic, with common energy savings of fifty percent or more. Another advantage of using VFD’s is their ability to extend the speed range of a motor by being able to have adjustable frequencies up to 120 Hertz rather than the normal maximum of 60 Hertz. However, operation of motors at speeds above their rated operating speeds must be checked and approved by the manufacturer. Most drives are often programmable and allow the operator to select the conditions that are most suitable for their particular application. Common applications for VFD’s include pumps, fans, mixers, blenders, air handlers and conveyor systems.
A more specific application of variable frequency drives are their use for dairy farmers in milking cows. These types of farms could use variable frequency vacuum pumps, because the VFD matches the pump speed to the actual air in the system. The efficiencies of this system could approach 100 percent. The variable speed drive will modulate both the speed and energy consumption of the motor in order to match the actual vacuum capacity that is needed. The energy savings vary from case to case but test cases concluded that the energy savings were over fifty percent. VFD's designed for dairy milking are as reliable as regular vacuum drives and research has shown that they do not increase milking time or have any adverse impacts on the health of the cows.
Small Variable Frequency Drive (above)