Delta Electronics VFD-S Manual De Usuario

 

Revision August 2008, SE09, SW V2.61

 

C-1

 

The choice of the right AC motor drive for the application is very important and has great influence 

on its lifetime and the performance. If the capacity of AC motor drive is too large, it cannot offer 

complete protection to the motor and it may be damaged. If the capacity of AC motor drive is too 

small, it cannot offer the required performance and the AC motor drive may be damaged due to 

overloading. 

 

But by simply selecting the AC motor drive of the same capacity as the motor, user application 

requirements cannot always be fully met. 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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