V/F Control 75kw 3 Phase VFD VSD Variable Speed Drive Frequency Converter

V/F Control 75kw 3 Phases VSD Variable Speed Drive VSD Frequency Converter

How to size a VFD/VSD?

• Load Type for Variable Frequency Drives

Does your Variable Frequency Drive application require a variable torque or constant torque drive?

If the equipment being driven is centrifugal, such as a fan or pump, then a variable torque drive will be more appropriate.

One primary VFD Benefit and usually the primary motivation for installing Variable Frequency Drives for centrifugal applications is energy savings, and variable torque drives offer the greatest energy savings.

For example, a fan needs less torque when running at 50% speed than it does when running at full speed. Variable torque operation allows the motor to apply only the torque needed, which results in reduced energy consumption. Conveyors, positive displacement pumps, punch presses, extruders, and other similar types of applications require a constant level of torque at all speeds. In which case, constant torque variable frequency drives would be more appropriate for the job.

A constant torque drive should have an overload current capacity of 150% or more for one minute. Variable torque variable frequency drives need only an overload current capacity of 120% for one minute since centrifugal applications rarely exceed the rated current. When buying a VFD for a system needing tight process control, then you may need to look into purchasing a sensorless vector, or flux vector Variable Frequency Drive, which allows a high level of accuracy in controlling speed, torque, and positioning.

• Motor Information

The following motor information will be needed to select the proper variable frequency drive:

• Full Load Amp Rating: Using a motor's horsepower is an inaccurate way to size variable frequency drives.
• Voltage Rating
• Speed Range: Generally speaking, a motor should not be run at any less than 20% its specified maximum speed allowed. If it is run at a speed less than this without auxiliary motor cooling, the motor will overheat. Auxiliary motor cooling should be used if the motor must be operated at slow speeds.
• Multiple Motors: To size a variable frequency drive that will control more than one motor, add together the full-load amp ratings of each of the motors. All motors controlled by a single driver must have an equal voltage rating.

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