Delta VFD-EL-W Series - Considerations for Special Motors

Appendix C. How to Select the Right AC Motor Drive｜VFD-EL-W
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The choice of the right AC motor drive for the application is very important and has a big influence on the
drive’s lifetime. If the capacity of the AC motor drive is too large, it cannot provide complete protection to
the motor and motor might be damaged. If the capacity of the AC motor drive is too small, it cannot
provide the required performance and the AC motor drive might be damaged due to overloading.
Simply selecting the AC motor drive with the same capacity as the motor cannot completely meet the
application requirements. Therefore, a designer should consider all the conditions, including load types,
load speeds, load characteristics, operation methods, rated output, rated speed, power and the change
in load capacity. The following table lists the factors you need to consider, depending on your
requirements.
Item
Related Specification
Speed and
Torque
Characteristics
Time
Ratings
Overload
Capacity
Starting
Torque
Load type
Friction load and weight load
Liquid (viscous) load
Inertia load
Load with power transmission
●
●
Load speed and
torque
characteristics
Constant torque
Constant output
Decreasing torque
Decreasing output
●
●
Load
characteristics
Constant load
Shock load
Repetitive load
High starting torque
Low starting torque
●
●
●
●
Operation mode
Continuous operation
Short-time operation
Long-time operation at medium/low
speeds
●
●
Rated output
Maximum output current
(instantaneous)
Constant output current (continuous)
●
●
Rated speed
Maximum frequency
Base frequency
●
Power supply
Power supply transformer capacity
or percentage impedance
Voltage fluctuations and unbalance
Number of phases, single phase
protection
Frequency
●
●
Load capacity
change
Mechanical friction, losses in wiring
●
●
Duty cycle modification
●