Appendix B How To Select Ac Motor Drive - Delta Electronics VFD-DD Series User Manual

The choice of the right AC motor drive for the application is very important and has great influence on its
lifetime. If the capacity of AC motor drive is too large, it cannot offer complete protection to the motor
and motor maybe damaged. If the capacity of AC motor drive is too small, it cannot offer the required
performance and the AC motor drive maybe damaged due to overloading.
But by simply selecting the AC motor drive of the same capacity as the motor, user application
requirements cannot be met completely. Therefore, a designer should consider all the conditions,
including load type, load speed, load characteristic, operation method, rated output, rated speed, power
and the change of load capacity. The following table lists the factors you need to consider, depending
on your requirements.
Friction load and weight load
Liquid (viscous) load
Load type
Inertia load
Load with power transmission
Constant torque
Load speed
Constant output
and torque
Decreasing torque
characteristics
Decreasing output
Constant load
Shock load
Load
Repetitive load
characteristics
High starting torque
Low starting torque
Continuous operation,
Operation Short-time operation
Method Long-time operation at medium/low
speeds
Maximum output current
(instantaneous)
Rated Output
Constant output current
(continuous)
Maximum frequency,
Rated Speed
Base frequency
Power supply transformer capacity
Percentage impedance
Voltage fluctuations and unbalance
Input Power
Number of phases, single phase
protection
Frequency
Mechanical friction, losses in wiring
Load Capacity
Changes
Duty cycle modification
How to Select AC Motor Drive
Item
Appendix B How to Select AC Motor Drive |DD Series
Related Specification
Speed and
Time
torque
ratings
characteristics
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B-1
Appendix B
Overload
capacity
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Starting
torque
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