Delta Electronics VFD-S Appendix C How to Select the Right AC Motor Drive, Related Specification

Appendix C How to Select the Right AC Motor Drive

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.

			Related Specification
	Item	Speed and		Time	Overload	Starting
		torque
				ratings	capacity	torque
		characteristics
	Friction load and weight load
Load type	Liquid (viscous) load	●				●
	Inertia load
	Load with power transmission
Load speed	Constant torque
	Constant output
and torque		●		●
	Decreasing torque
characteristics
	Decreasing output
	Constant load
Load	Shock load
	Repetitive load	●		●	●	●
characteristics
	High starting torque
	Low starting torque
Continuous operation, Short-time operation				●	●
Long-time operation at medium/low speeds
Maximum output current (instantaneous)		●			●
Constant output current (continuous)
Maximum frequency, Base frequency		●
Power supply transformer capacity or
percentage impedance
Voltage fluctuations and unbalance					●	●
Number of phases, single phase protection
Frequency
Mechanical friction, losses in wiring					●	●
Duty cycle modification				●
Revision August 2008, SE09, SW V2.61						C-1