A Variable Frequency Drive (VFD), also known as an Adjustable Speed Drive (ASD), converts the fixed supply frequency to a variable frequency, variable voltage output to control the speed of an AC motor. AC drives save energy, reduce mechanical shock, and allow the user to dynamically control the speed, torque, and direction of the motor.
Unlike testing when testing Pumps, Speed Control is typically not needed when testing electric motors. However, a VFD can be applied in the Motor Test lab if the incoming power system cannot tolerate the RVSS voltage reduction during starting, and the in-rush current must be limited to the full load rating of the motor. Using a VFD, the motor acceleration & deceleration is controlled by ramping up frequency, and the voltage at the motor terminals is directly proportional to the frequency supplied by the VFD, and is not dependent on the motor load.
Pump Lab, utilizes a VFD for speed control. The VFD allows for the Pump Lab to test flow rates throughout the pump speed curve. An increasingly common requirement in residential and agricultural groundwater extraction is for a VFD to control pressure during non-peak utilization of the water supply. To test these specific conditions, a VFD will be required.
Additionally, some VFDs include integrated safety features that can be utilized for emergency stop procedures.