Delta Electronics VFD-VE Series manual Capacity Formulas, 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. 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.

				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 and	Constant torque
		Constant output
	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				●
C.1 Capacity Formulas
Revision August 2008, 03VE, SW V2.04							C-1