User Manual of EM760 High-Performance Inverter Chapter 9 Select accessories 9.1 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 ofthe 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 ofenergy 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 Чbraking 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 The recommended power and resistance for the braking resistor ofthe EM760 series inverter are given in the table below. The recommended resistor power is calculated based on the braking rate (10% to 20%). It is for reference only.
If the inverter is used in the case of frequent acceleration/deceleration or continuous braking, the power of the braking resistor needs to be increased. The user can change the value according to the load conditions, but within the specified range. Table 9-1 Selection ofbraking resistors 228 Inverter Model Motor (kW) Resistance (Ω) Resistor Power (W) Wire connected to resistor (mm2) EM760-0R7-3B 0.75 ≥360 ≥200 1 EM760-1R5-3B 1.5 ≥180 ≥400 1.5 EM760-2R2-3B 2.2 ≥180 ≥400 1.5 EM760-4R0-3B 4 ≥90 ≥800 2.5