Appendix C How to Select the Right AC Motor Drive_VFD-B Series
C-4 Revision 10/2005, BE13, SW V4.08
C.2 General Precaution
Selection Note
1. When the AC Motor Drive is connected directly to a large-capacity power transformer (600kVA or
above) or when a phase lead capacitor is switched, excess peak currents may occur in the power
input circuit and the converter section may be damaged. To avoid this, use an AC input reactor
(optional) before AC Motor Drive mains input to reduce the current and improve the input power
efficiency.
2. When a special motor is used or more than one motor is driven in parallel with a single AC Motor
Drive, select the AC Motor Drive current
t1.25x(Sum of the motor rated currents).
3. The starting and accel./decel. characteristics of a motor are limited by the rated current and the
overload protection of the AC Motor Drive. Compared to running the motor D.O.L. (Direct On-Line), a
lower starting torque output with AC Motor Drive can be expected. If higher starting torque is required
(such as for elevators, mixers, tooling machines, etc.) use an AC Motor Drive of higher capacity or
increase the capacities for both the motor and the AC Motor Drive.
4. When an error occurs on the drive, a protective circuit will be activated and the AC Motor Drive output
is turned off. Then the motor will coast to stop. For an emergency stop, an external mechanical brake
is needed to quickly stop the motor.
Parameter Settings Note
1. The AC Motor Drive can be driven at an output frequency up to 400Hz (less for some models) with
the digital keypad. Setting errors may create a dangerous situation. For safety, the use of the upper
limit frequency function is strongly recommended.
2. High DC braking operating voltages and long operation time (at low frequencies) may cause
overheating of the motor. In that case, forced external motor cooling is recommended.
3. Motor accel./decel. time is determined by motor rated torque, load torque, and load inertia.
4. If the stall prevention function is activated, the accel./decel. time is automatically extended to a length
that the AC Motor Drive can handle. If the motor needs to decelerate within a certain time with high
load inertia that can’t be handled by the AC Motor Drive in the required time, either use an external
braking resistor and/or brake unit, depending on the model, (to shorten deceleration time only) or
increase the capacity for both the motor and the AC Motor Drive.
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