VFD Variable Frequency Inverter Drives
We usually have a small selection of VFDs or Variable Frequency Drives. These are also known as Adjustable Frequency or Adjustable Speed Drives. They are for use with 3-phase motors. They control the speed of the motor by regenerating AC voltage and current at a different speed or frequency than the incoming power line's 60 cycles. They can typically go down to within about 5 or 10% of rated motor speed and 50 to several hundred % above rated motor speed (use in this later case needs do be done with great care as strange and dangerous things can happen). It must be noted that these are high-power unit that can easily supply deadly amounts of electrical energy. They are only for installation by qualified electricians.
An interesting thing about most VFD's is that they can actually be used as phase converters. This means that you can feed them single phase power and get 3 phase power out of them. The caveat to this is that they usually need to be derated by about half when used this way unless they are modified specifically for this function.
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