User Manual of A90 Series Inverter
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Chapter 11 Optional Accessories
11.1 Braking Resistor
If the speed of the controlled motor drops too fast or the motor load shakes too fast
during the inverter operation, its electromotive force will charge the internal capacitor
reversely via the inverter, resulting in the voltage boost at two ends of the power module.
This is likely to cause damage to the inverter. The internal control of the inverter will
suppress this based on the load. If the braking performance does not meet the customer
requirements, an external braking resistor is needed to release energy in a timely manner.
Due to the external braking resistor of energy consumption braking type, the energy will be
completely dissipated to the power braking resistor. Hence, the power and resistance of the
braking resistor must be selected reasonably and effectively.
The power of the braking resistor can be calculated by the following formula:
Resistor power Pb = inverter power P × braking frequency D
D - Braking frequency. This is an estimated value, depending on the load conditions.
Under normal circumstances, D is as follows:
D=10% under ordinary loads
D=5% for occasional braking loads
D = 10% to 15% for elevators
D = 5% to 20% for centrifuges
D = 10% to 20% for oilfield kowtow machines
D = 50% to 60% for unwinding and winding. It should be calculated based on the
system design indicators.
D = 50% to 60% for lifting equipment with a lowering height over 100m
