The open circuit of the braking resistance of the frequency converter will affect the braking of the driven mechanical load of the frequency converter. Because the braking resistor is open, the electric energy loaded at both ends of the braking resistor cannot be released, which is equivalent to no braking function.
Braking resistor, commonly known as braking resistor of frequency converter, is also briefly introduced here. What is the function of the braking resistance of the frequency converter? When the motor driven by the frequency converter is stopped, the driven motor cannot stop rotating in time due to inertia. At this time, the motor is equivalent to a generator, and the electric energy generated by the generator will be applied to the module inside the frequency converter, which will cause damage or damage to the module of the frequency converter. The braking resistance is used to consume this part of electric energy.
★ under normal conditions, if the output power of the frequency converter is below 7.5kVA, the braking resistance is installed inside the frequency converter (built-in); For frequency converters with power greater than 7.5kVA, the braking resistance is basically external. For example, the braking resistance of hundreds of watts of delta frequency converter also needs to be external.
The braking resistance of the frequency converter shall be selected according to the output power, braking time and braking times. Including the resistance value of braking resistance and the power of braking resistance; For example, the external braking resistance of 5.5kva frequency converter is required to be ≥ 22 Ω, but the power of the braking resistance is 800W (W), so the high-power resistance has a large volume, and it will produce a lot of heat energy when working, so it cannot be directly connected next to the frequency converter. When installing it, its heating capacity shall be fully considered and away from the frequency converter.
If it is a 55kva frequency converter, the power of its braking resistance is 5.5kW × 2 is composed of two resistors in series, so its power is 11kw, and the resistance value of braking resistor is recommended to be ≥ 5 Ω × 2。 It also needs to use professional axial flow fan for forced heat dissipation, and the connecting wires at both ends are temperature resistant wires.
See the following figure for the functions of the main circuit wiring terminal of three-phase frequency converter.
Generally, Pb and (+) are the terminals for external braking resistance. There is no difference between positive and negative poles for connecting the braking resistance. The cross-sectional area of the conductor is sufficient, and the conductor can be connected above two points between them. In addition, for the braking resistance, enter the function code to set the DC braking time, shutdown DC braking waiting time.
★ generally, the open circuit of the braking resistor is caused by the small power of the selected braking resistor and the poor heat dissipation of the braking resistor.
When the braking resistance is braking, almost all the regenerative energy of the motor is consumed on the braking resistance. Here, a calculation formula is recommended: U × U / r = Pb, u is the voltage of stable braking of the system (the U value is different for different systems, and 700V is generally taken for 380VAC system), and Pb is the power of braking resistor.
Editor in charge: yyx