Feedback unit suppliers remind you: What peripherals do frequency converters have? What is the purpose of each?
(1) The power transformer T is used to convert the power voltage to the voltage level required by the general frequency converter. The input current of the frequency converter contains a certain amount of high harmonic, so that the power factor on the power side is reduced. If the operating efficiency of the frequency converter is considered, the capacity of the transformer is often calculated as follows:
T—Power transformer QF—Power side circuit breaker KM1—Power side electromagnetic contactor FIL—Radio noise filter UL1—Power side AC resistor R—Brake resistor KM2—Motor side electromagnetic contactor KM3—Contactor for working frequency grid switching UL2—Motor side AC resistor
Among them, when there is an input AC resistor UL1, the power factor of the frequency converter is 0.8 to 0.85; When there is no input AC resistor UL1, the power factor of the inverter is 0.6 ~ 0.8. The efficiency of the inverter can be 0.95, the output power of the inverter should be the total power of the connected motor.
(2) Power side circuit breaker QF is used to interrupt the power circuit, and automatically cut off the power when there is a current or short circuit accident, in order to prevent the accident from expanding. If grounding protection is required, leakage protection circuit breaker can also be used.
(3) The electromagnetic contactor KM1 is used to interrupt the power supply, cut off the power supply when the inverter protection function works. For power recovery after a power outage, it can prevent automatic re-insertion to protect the safety of the equipment and personal safety.
(4) Radio noise filter FIL is used to limit the frequency converter due to high harmonic interference with the outside world, can be used as appropriate.
(5) AC resistor UL1 is used to suppress the harmonic current on the input side of the inverter to improve the power factor. The selection and rejection of the matching situation of the power transformer and the capacity of the inverter and the degree of distortion allowed by the grid voltage. In general, it is better to use.
(6) AC resistor UL2 is used to improve the waveform of the output current of the frequency converter and reduce the noise of the electric motor.
(7) Brake resistance R is used to absorb the regenerative electric energy of the motor regenerative brake (also known as feedback brake), which can shorten the free parking time of large inertial load. In addition, regenerative braking can be achieved when the bit load is discharged.
(8) The electromagnetic contactor KM2 and KM3 are used for switching operation between the inverter and the power grid. In this way, KM2 is essential, and the interlocking between it and KM3 can prevent the output of the inverter from being connected to the power grid.