Delta Electronics VFD-VE Series User Manual

 

Revision August 2008, 03VE, SW V2.04 

C-1 

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. 

 

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 

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Load speed and 
torque 
characteristics 

Constant torque 
Constant output 
Decreasing torque 
Decreasing output 

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Load 
characteristics 

Constant load 
Shock load 
Repetitive load 
High starting torque 
Low starting torque 

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Continuous operation, Short-time operation
Long-time operation at medium/low speeds

 

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Maximum output current (instantaneous) 
Constant output current (continuous) 

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Maximum frequency, Base frequency 

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Power supply transformer capacity or 
percentage impedance 
Voltage fluctuations and unbalance 
Number of phases, single phase protection
Frequency 

 

 

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Mechanical friction, losses in wiring 

 

 

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Duty cycle modification 

 

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